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Microplastic and soil protists: A call for research
Abstract
Microplastic is an emerging contaminant of concern in soils globally, probably gradually increasing in soil due to slow degradation. Few studies on microplastic effects on soil biota are available, and no study in a microplastic contamination context has specifically addressed soil protists. Soil protists, a phylogenetically and functionally diverse group of eukaryotic, unicellular soil organisms, are major consumers of bacteria in soils and are potentially important vehicles for the delivery of microplastics into the soil food chain. Here we build a case for focusing research on soil protists by drawing on data from previous, older studies of phagocytosis in protist taxa, which have long made use of polystyrene latex beads (microspheres). Various soil-borne taxa, including ciliates, flagellates and amoebae take up microplastic beads in the size range of a few micrometers. This included filter feeders as well as amoebae which engulf their prey. Discrimination in microplastic particle uptake depended on species, physiological state as well as particle size. Based on the results of the studies we review here, there is now a need to study microplastic effects in a pollution ecology context: this means considering a broad range of particle types under realistic conditions in the soil, and exploring longer-term effects on soil protist communities and functions.
... Large volumes of plastics in the form of plastic bags, sheets, fishing nets, tires, and bottles are fragmented into smaller particles called secondary microplastics (Rillig and Bonkowski, 2018). Fragmentation can be dependent on environmental factors like sunlight and temperature. ...
... In some places with limited water suppliee water is utilised for irrigation (Blasing and Amelung, 2018). Also, from the atmosphere, tiny microplastic particles get deposited on the soil which later reaches the soil through leaching (Rillig and Bonkowski, 2018;Dris et al., 2016). Microplastics can be transported and accumulated in the soil by street runoff and flooding where waste is brought close to the road by flooding and street drainage system (Blasing and Amelung, 2018), and also by abrasion of tyres (He et al., 2018). ...
... Boots et al. (2019) in their study found that Lolium perennes root growth slowed down following exposure to LDPE microplastics. Plastic particles contain relatively high amounts of inert carbon molecules which give them non-soluble nature resulting in immobilisation of pathogens due tohigh C: N ratio (Rillig and Bonkowski, 2018). Qi et al. (2018) in their study first investigated that how the buildup of recyclable plastic residues in the environment impacted a range of plant performance metrics, comparable to how biodegradable polymers affected the results i.e. leaf area. ...
The inflated demand for plastic products has led to tremendous rise in plastic debris in different environmental matrices, thereby resulting in plastic pollution. This affects plants, animals, and even humans, as microplastics can enter the food chain and cause several health implications. Microplastics are the small plastic particles (size below 5 mm) that are largely debated nowadays owing to their environmental risk assessment. Their potential to interact with other toxic contaminants, their tendency to be ingested or taken up by living organisms and their longevity is a serious threat to our environment. However, despite wealth of recent information, still there is a gap, particularly in eco-toxicology studies, fate, prevalence and feasible solutions to cope up with the menace of microplastics pollution. This review unravels the environmental fate and behaviour of microplastics as well as their global distribution in the marine and terrestrial environment. Furthermore, we aim to contribute to the international debate on the microplastics global paradigm. We briefly suggest sustainable solutions and recommendations to achieve future research goals on microplastics. Our review reveals some of the newest biological (green algae and modified sponges) and physical (nano-particles and membrane treatment) remediation solutions to eradicate microplastics from different types of environment. This review presents a critical evaluation of the state of knowledge of micro-plastics and suggested some recommendations which can help in identifying some important key questions for future research.
... They are incorporated into soil aggregates in consort with minerals and organic matter. Microplastics can be disguised as part of soil carbon storage independent of photosynthesis and net primary production (Rillig and Bonkowski 2018). Due to its resistance to decomposition, microplastic carbon tends to accumulate in the soil and eventually be immobilized by microbes after a long time span, which may somehow contribute to the carbon cycle and affect SOM turnover (Chen et al. 2022d;Liu et al. 2017). ...
... Many previous records have shown the microbial mineralization of microplastic carbon based on direct and indirect evidence, such as changes in surface roughness and functional groups, the diminishment of particle size, the loss of plastic weight, and the colonization of biofilms (McCormick et al. 2014;Yang et al. 2018). In the soil environment, the degradation of microplastics was proven to be very slow (Rillig and Bonkowski 2018). For example, only 0.1 to 0.4% weight loss was observed for PE after 800 days of burial in soil (Albertsson 1980). ...
Soil, as a primary repository of plastic debris, faces an escalating influx of microplastics. Microplastics have the potential to decrease soil bulk density and pH, as well as alter soil pore structure and aggregation. These changes in soil physico-chemical properties subsequently lead to habitat degradation for microbes and environmental shifts that impact plant growth. Masquerading as soil carbon storage, microplastics can distort assessments of the soil carbon pool by introducing plastic-carbon and associated leachates, influencing soil organic matter (SOM) turnover through priming effects (e.g., dilution, substrate switching, and co-metabolisms). Additionally, microplastics can influence the distribution of soil carbon in particulate and mineral-associated organic matter, consequently affecting the accumulation and stability of soil carbon. Furthermore, microplastics can also influence the chemodiversity of dissolved organic matter (DOM) in soils by increasing DOM aromaticity and molecular weight while deepening its humification degree. The changes observed in soil DOM may be attributed to inputs from microplastic-derived DOM along with organo-organic and organo-mineral interactions coupled with microbial degradation processes. Acting as an inert source of carbon, microplastics create a distinct ecological niche for microbial growth and contribute to necromass formation pathways. Conventional micro-plastics can reduce microbial necromass carbon contribution to the stable pool of soil carbon, whereas bio-microplastics tend to increase it. Furthermore, microplastics exert a wide range of effects on plant performance through both internal and external factors, influencing seed germination, vegetative and reproductive growth, as well as inducing ecotoxicity and genotoxicity. These impacts may arise from alterations in the growth environment or the uptake of microplastics by plants. Future research should aim to elucidate the impact of microplastics on microbial necromass accumulation and carbon storage within mineral-associated fractions, while also paying closer attention to rhizosphere dynamics such as the microbial stabilization and mineral protection for rhizodeposits within soils. Highlights • Microplastics (MPs) have either positive or negative effects on SOM mineralization. • MPs affect soil carbon distribution in particulate and mineral-associated fraction. • MPs increase the aromaticity, molecular weight and humification degree of soil DOM. • Conventional MPs can reduce microbial necromass, whereas bio-MPs cannot. • MPs influence plant performance through both internal and external factors.
... Biological processes contributed to the horizontal and vertical redistribution of MPs in the soil. In these processes, MPs can be ingested and selectively discharged by soil protists, such as earthworms and collembola [53,54]. The pore structure of soil and disturbance of soil organisms such as earthworms help MPs to migrate deep underground and even reach the groundwater layer [53,55]. ...
... When the abundance of MPs is high, the growth and reproduction of other soil organisms, such as earthworms, is greatly affected [117]. MPs can accumulate in the body of earthworms, affecting the immune system and reproduction of earthworms, thus decreasing soil fertility and inhibiting crop growth [53,54]. MPs could also be brought downward by earthworms and pose a great risk to the groundwater [53,118,119]. ...
The risks brought by microplastics (MPs) to agricultural soil structure and crop growth in the agricultural system are the focus of global debate. MPs enter the soil through various routes, such as through the use of agricultural mulch and atmospheric deposition. Here, we review the research on MP pollution in the soil during the last 30 years. This review focuses on (i) the sources, types, and distribution characteristics of MPs in agricultural soils; (ii) the migration and transformation of MPs and their interactions with microorganisms, organic matter, and contaminants in agricultural soils; and (iii) the effects of environmental factors on the composition and structure of MPs in agricultural soils. This review also proposes key directions for the future research and management of MPs in the agricultural soil. We aim to provide a theoretical basis for the fine management of agricultural farmland.
... Although MNPs contain C in molecular structure, it is unclear whether they provide the same ecological functions as SOM (Xiao et al., 2022). MNPs function differently with soil microorganisms, indicating a unique C source pathway (Rillig and Bonkowski, 2018). Escalation of MNPs in soils reduces soil bulk density and moisture permeability, deteriorates soil porosity and water-holding capacity, and obliterates the structural integrity and stability of the soil (de Souza Machado et al., 2018. ...
... Carbon sequestration, water purification, organic waste recycling, and water and nutrient provision for human-required crops and plants are just a few of the many functions that rely on soil biodiversity (Helmberger et al., 2019). Soil biota, biodiversity, and ecological processes are increasingly being examined in relation to MNPs (Rillig and Bonkowski, 2018). MNPs present in the soil cause harmful effects from alternations in the physical properties, lower fertility and disturb the microorganisms resulting changes in soil quality and nutrient cycles (Xu et al., 2019). ...
The ecological impacts of micro(nano)plastics (MNPs) have attracted attention worldwide because of their global occurrence, persistence, and environmental risks. Increasing evidence shows that MNPs can affect soil nutrient cycling, but the latest advances on this topic have not systematically reviewed. Here, we aim to present the state of knowledge about the effects of MNPs on soil nutrient cycling, particularly of C, N, and P. Using the latest data, the present review mainly focuses on three aspects, including (1) the effects and underlying mechanisms of MNPs on soil nutrient cycling, particularly of C, N and P, (2) the factors influencing the effects of MNPs on soil nutrient cycling, and (3) the knowledge gaps and future directions. We conclude that MNPs can alter soil nutrient cycling via mediating soil nutrient availability, soil enzyme activities, functional microbial communities, and their potential ecological functions. Furthermore, the effects of MNPs vary with MNPs characteristics (i.e., polymeric type, size, dosage, and shape), chemical additives, soil physicochemical conditions, and soil biota. Considering the complexity of MNP-soil interactions, multi-scale experiments using environmental relevant MNPs are required to shed light on the effects of MNPs on soil nutrients. By learning how MNPs influence soil nutrients cycles, this review can guide policy and management decisions to safeguard soil health and ensure sustainable agriculture and land use practices.
... The amount of MPs entering agricultural lands through biocomposting, plastic mulching and other methods is estimated to exceed the total amount of MPs in the oceans (Nizzetto et al., (2016b)). Because the degradation rate of MPs is lower than their rate of input into environmental systems, MPs gradually accumulate in soils (Rillig and Bonkowski, 2018). Therefore, the impact of MPs on ecosystem function and health increases over time. ...
... These MPs are very small and microscopic in size range, ubiquitous in nature and due to their bio-availability; these MPs have already been accepted as proven contaminants with numerous ill effects on the ecosystems (Scheurer and Bigalke, 2018). In aquatic systems, MPs have been investigated in depth and many reports proved the deleterious effects on a range of biological communities (Rillig and Bonkowski, 2018). ...
... MP is found in almost all imaginable matrices, including marine ecosystems (Andrady, 2011), stormwater retention ponds (Liu et al., 2019a;Liu et al., 2019b;Rasmussen et al., 2024), air (Dris et al., 2015), road dust (Rasmussen et al., 2023), agricultural soils (Zubris and Richards, 2005), and remote arctic regions (Kanhai et al., 2020;Kelly et al., 2020). Even though there is a high diversity in the investigated areas, the most wellresearched area is the aquatic environment, leaving the knowledge about MP in soil limited (Rillig and Bonkowski, 2018;Zhou et al., 2020;Nizzetto et al., 2016b). ...
... On the other hand, since soil organic matter content is measured by determining the amount of oxidant (acidic dichromate) consumed (Section 2.3.2), aged PS, as an organic material, may also consume oxidants [42,72] (pathway 2 for increase). For the brown soil, cinnamon soil and red soil with relatively low organic matter content, the pathway 2 could be dominant, thus their organic matter content showed a net increase. ...
Whether coexisting microplastics (MPs) affect the ecological and health risks of cadmium (Cd) in soils is a cutting-edge scientific issue. In this study, four typical Chinese soils were prepared as artificially Cd-contaminated soils with/without aged polystyrene (PS). TCLP and in vitro PBET model were used to deteremine the leachability (ecological risk) and oral bioaccessibility (human health risk) of soil Cd. The mechanisms by which MPs influence soil Cd were discussed from direct and indirect perspectives. Results showed that there was no significant difference in the leachability of soil Cd with/without aged PS. Additionally, aged PS led to a significant decrease in the bioaccessibility of soil Cd in gastric phase, but not in small intestinal phase. The increase in surface roughness and the new characteristic peaks (e.g., Si-O-Si) of aged PS directly accounted for the change in Cd bioaccessibility. The change in organic matter content indirectly accounted for the exceptionalincrease in Cd bioaccessibility of black soil with aged PS in small intestinal phase. Furthermore, the changes in cation exchange capacity and Cd mobility factor caused by aged PS explained the change in Cd leachability. These results contribute to a deeper understanding about environmental and public health in complicated emerging scenarios.
... Furthermore, MP particles can enter the human body through the food chain, potentially causing adverse health impacts (De-la-Torre et al. 2023a;Wu et al. 2021). Instances of MP occurrence have been reported in various food sources, including chicken meat (Huang et al. 2020), pig lung tissue , terrestrial edible snails (Panebianco et al. 2019), the intestinal tracts of ducks (Susanti et al. 2021), the gastrointestinal tracts of birds (Zhao et al. 2016), earthworms (Lahive et al. 2022;Rillig and Bonkowski 2018), and among other animals (Abelouah et al. 2023;Saldaña-Serrano et al. 2022). Moreover, plastic pieces have been found in the digestive systems (rumen and reticulum) of sheep and cow (Abebe and Nuru 2011;Mekuanint et al. 2017;Ngoshe 2012;Omidi et al. 2012;Otsyina et al. 2018). ...
Plastic contamination is widely recognized as a major environmental concern due to the entry of small plastic particles into the food chain, thereby posing potential hazards to human health. However, the current understanding of microplastic (MP; < 5 mm) particles in livestock, which serve as an important food source, is limited. This study aims to investigate the concentration and characteristics of MPs in edible tissues of cow and sheep, namely liver, meat, and tripe, obtained from butcher shops in five areas of Bushehr port, Iran. The mean concentration of MPs in different tissues of cow and sheep were 0.14 and 0.13 items/g, respectively. Among the examined tissues, cow meat exhibited the highest concentration of MPs, with a concentration of 0.19 items/g. Nylon and fiber were identified as the predominant polymer types and shapes of MPs found in cow and sheep tissues, respectively. Furthermore, no statistically significant difference was observed in MP concentration across different tissues of cow and sheep. Significantly, this study highlights the elevated hazards associated with exposure to MPs through the consumption of edible cow and sheep tissues, particularly for children who consume meat. The results underscore the potential transfer of MPs from the environment to livestock bodies through their food, contamination during meat processing, and subsequent health hazards for consumers.
... Microplastics can also introduce pollutants and toxic additives into the soil environment, which can negatively impact the health of organisms and disrupt biodiversity in soil ecosystems [9][10][11]. Smaller microplastic particles in the soil can be ingested by some protists [12] and earthworms, causing intestinal damage and affecting their growth [13,14]. Moreover, these microplastics can potentially enter higher trophic levels through the food chain [2]. ...
The increasing concern over microplastic pollution has led to a growing number of studies and reports on microplastic contamination in soil. However, currently, there is no convenient and efficient method for detecting microplastics in soil. Therefore, we propose the use of hyperspectral imaging technology as a detection method and employ supervised classification algorithms for direct and effective identification and classification of microplastic pollutants in soil. In this study, experiments were conducted based on a hyperspectral imaging system with a wavelength range of 400-1000 nm. Three supervised classification algorithms, namely Support Vector Machine (SVM), Mahalanobis Distance (MD), and Maximum Likelihood (ML), were utilized to identify microplastics in the hyperspectral images. White and black polyethylene (PE) microplastic particles in the particle size range of 1-5 mm were extracted from the soil for analysis. The results indicate that SVM is the most suitable algorithm for detecting white PE microplastics in soil, with an average identification accuracy of 84% for white PE microplastic particles with particle sizes ranging from 1-5 mm.
... An example includes the production of degradable plastics instead of hard-to-degrade plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS). Most degradable plastics are produced in the early stage of plastics production by adding functional monomers with light energy sorption capabilities or photosensitizers with chromophores to stimulate their photodegradability (Cai et al. 2018;Rillig and Bonkowski 2018). Plastic removal refers to the decontamination of MPs already present in the environment through physical, chemical, and biological techniques, including incineration, landfills, ozonation, microbial degradation, and enzymatic remediation (Canopoli et al. 2020;Ganesh et al. 2019). ...
This study investigated the photodegradation of microplastics (MPs) by α-Fe2O3/g-C3N4. The effects of α-Fe2O3/g-C3N4 on MPs' surface were investigated through various techniques. With the addition of α-Fe2O3/g-C3N4 and under visible light irradiation, cracks and folds were observed on the MP films and particles. Compared to the treatment without photocatalyst addition, the mass loss of MPs increased with irradiation time when α-Fe2O3/g-C3N4 was added. Specifically, polystyrene films and particles in water showed 9.94% and 7.81% increased mass loss, respectively. The degradation of MPs using α-Fe2O3/g-C3N4 demonstrated the behavior consistent with the pseudo-first-order kinetic model. The presence of α-Fe2O3/g-C3N4 led to an increase in surface oxygen-containing functional groups and crystallinity while decreasing the average molecular weight of MPs. After 30 days of irradiation, the characteristic tensile bands of MPs with α-Fe2O3/g-C3N4 significantly increased, and the detection of carboxyl bands indicated the formation of carboxylic acid, ketones, and lactones as degradation products.
... For example, PBDEs were detected in Puffinus tenuirostris (Bakir et al., 2014) and mono-2-ethylhexyl phthalate was found in Cetorhinus maximus (Fossi et al., 2017). Many of these additives may be mutagenic and carcinogenic, and may also adversely affect animal reproduction (Mathieu-Denoncourt et al., 2015;Rillig and Bonkowski, 2018). Toxic microbes may also adhere to plastics and act as disease vectors in the marine ecosystem (Osborn and Stojkovic, 2014;Harrison et al., 2018b). ...
... Owing to their manufacturing origin and environmental degradation, MPs may occur in many shapes and sizes [30][31][32][33], and these different physical characteristics may have different effects on soil properties [34,35] and invertebrates [36]. For example, smallersized MPs are easier to ingest [37] and are supposedly more toxic to soil fauna [38,39], whereas fibers are supposedly more toxic to invertebrates than beads (under specific experimental conditions) [40]. Despite these results, previous studies have mainly explored the ecotoxicological effects of MP characteristics on organisms, and little is known about the effects on transport (review in [41]). ...
We investigated the impact of shape (beads, fibers and films) and size (0.5 and 1.0 mm; diameter or length) of polypropylene microplastics (MPs) on MP transport by a springtail species, Folsomia candida in dishes. The percentages of transported beads, fibers and films were 9.10%, 3.18% and 4.10%, respectively. For 1.0 mm MPs, the number of MPs transported was significantly higher for beads than for fibers and films, whereas, for 0.5 mm MPs, the number was significantly higher for fibers than for the other MP types. Additionally, the number of MPs transported was higher for small fibers than for large fibers, whereas it was higher for large beads than for small beads. These results indicate that the effects of F. candida on MP migration depend on MP shape and size. Our results highlight the importance of considering the physical characteristics of MPs while elucidating the interaction between soil fauna and MPs.
... This variability contributes to processes like flotation and sedimentation that influence the fate of microplastics (Hinata et al., 2023;Long et al., 2015). Further investigation is necessary to fully understand this phenomenon as the residence time of microplastics greatly influences their remobilization process and subsequent exposure (Rillig and Bonkowski, 2018;Waldschläger and Schüttrumpf, 2019), to organisms residing in mangroves ecosystem -habitats which support diverse marine organisms and play crucial ecological roles (Jiao et al., 2022;Li et al., 2020c;Luo et al., 2021). Moreover, a reduction in bulk density and decreased porosity within sediments similar to fine sediment infiltration processes results in the infiltration of microplastics (Ballent et al., 2013;Dong et al., 2022;Horton et al., 2017). ...
Mangrove environments have been well recognized as marine litter traps. However, it is unclear whether mangrove sediments sink microplastics more effectively than other marine sediments due to active sedimentation. Furthermore, microplastics archives in mangrove sediments may provide quantitative data on the impact of human activities on environmental pollution throughout history. Microplastic abundance varied markedly between high and low anthropogenic activities. Both mangrove and adjacent mudflats sediments act as microplastic sequesters, despite having similar microplastic abundances and depth profiles. The decreasing trend of microplastics was observed until the sediment layers dated to the first-time plastic was manufactured in Indonesia, in the early 1950s, but microplastics remained present beneath those layers, indicating the downward movements. This discovery highlighted the significance of mangrove sediments as microplastic sinks. More research is needed to understand the mechanisms of microplastic deposition in sediments, as well as their fate and potential impact on mangrove sediment dwellers.
... Exposure to MPs also shifts the soil microbial community structure, function, and activity (Bogati & Walczak, 2022;Rillig & Bonkowski, 2018). Increased microbial biomass and decreased soil biodiversity occur when MPs provide a growth habitat for certain microorganisms . ...
... An example includes the production of degradable plastics instead of hard-to-degrade plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS). Most degradable plastics are produced in the early stage of plastics production by adding functional monomers with light energy sorption capabilities or photosensitizers with chromophores to stimulate their photodegradability under light conditions (Cai et al., 2018;Rillig et al., 2018). Plastic removal refers to the decontamination of MPs already present in the environment through physical, chemical, and biological techniques, including incineration, land lls, ozonation, microbial degradation, and enzymatic remediation (Canopoli et al., 2020;Ganesh et al., 2019). ...
This study investigated the photodegradation of microplastics (MPs) by α-Fe 2 O 3 / g -C 3 N 4 . The effects of α-Fe 2 O 3 / g -C 3 N 4 on MPs' surface were investigated through various techniques. With the addition of α-Fe 2 O 3 / g -C 3 N 4 and under visible light irradiation, cracks and folds were observed on the MP films and particles. Compared to the treatment without photocatalyst addition, the mass loss of MPs increased with irradiation time when α-Fe 2 O 3 / g -C 3 N 4 was added. Specifically, polystyrene films and particles in water showed 9.94% and 7.81% increased mass loss, respectively. The degradation of MPs using α-Fe 2 O 3 / g -C 3 N 4 demonstrated the behavior consistent with the pseudo-first-order kinetic model. The presence of α-Fe 2 O 3 / g -C 3 N 4 led to an increase in surface oxygen-containing functional groups and crystallinity while decreasing the average molecular weight of MPs. After 30 days of irradiation, the characteristic tensile bands of MPs with α-Fe 2 O 3 / g -C 3 N 4 significantly increased, and the detection of carboxyl bands indicated the formation of carboxylic acid, ketones, and lactones as degradation products.
... The impact of microplastics on aquatic and soil organism has been well reported. In the open literature, the investigations by Egbeocha et al., 19 Wright et al., 20 Guzzetti et al., 21 Rillig and Bonkowski, 62 and Guo et al. 63 are a few of the available studies that reviewed the impact of microplastics on soil and aquatic organisms. Meanwhile, Prata et al. 86 explored the impact of airborne microplastics on humans. ...
Plastic pollution and climate change are two major environmental focuses. Having the forming potential due to ambient plastic pollution, the environmental fate of microplastics shall be inevitably impacted by global warming. This manuscript discusses the destiny of environmental microplastics and characterizes their fate considering the framework of the planetary boundary. The major routes for microplastic discharge include the release of microplastic stored in the ice into the sea when the ice melts as a result of global temperature increase, flushing of the plastic/microplastic debris from the shorelines into the adjacent water bodies as a result of increased rainfall, redistribution of the microplastics away from the source of plastic debris as a result of increased wind, and accumulation of microplastics in the soil as a result of drought. A perspective on the impact of climate change and microplastic pollution on aquatic and soil organisms was discussed as well.
... Predatory protists (e.g., Cercozoa) may alter the composition of their prey community, typically promoting functions related to (plant-) pathogen suppression . Furthermore, the diverse functional roles of predatory protists are also associated with the cycling of nutrients such as carbon, nitrogen, phosphorous, and silicon Rillig and Bonkowski 2018). ...
On the Qinghai-Tibet Plateau, the restoration of natural grasslands is an urgent task, but finding the appropriate green restoration approach still faces many challenges. In this study, experimental plots were set up in a degraded alpine meadow with different fertilization treatments, i.e., chemical fertilizer (F), microbial fertilizer (M) (i.e., Rhizobium indicum strain JKLM 13E), and unfertilized (CK). Grass yields, soil properties, and the rhizospheric and bulk soil microbial communities (including both prokaryotes and eukaryotes) were measured to evaluate grassland productivity and soil sustainability. Both microbial and chemical fertilizers could significantly increase grassland biomass, as well as the biotic interactions of the inorganic nitrogen-related prokaryotic communities. We evaluated the biomass and productivity of the aboveground vegetation in response to the fertilization treatments. Our results demonstrated that both chemical and microbial fertilizers significantly increased the yield of grassland vegetation, with the effect of chemical fertilizer treatment being the most prominent (P <0.05). Moreover, chemical fertilizer mainly increased the concentration of NO3⁻-N by reshaping the bulk soil microbial community, while microbial fertilizer mainly increased the concentration of NH4⁺-N by reshaping the rhizospheric microbial community. Both the chemical and microbial fertilizers could significantly increase the predation of Cercozoa to the inorganic nitrogen-related prokaryotic community, thus improving the soil resistance to pathogenic bacteria. In conclusion, our results suggest that microbial fertilizer treatment shows potential as an alternative or complementary approach to chemical fertilizer, potentially reducing the environmental impact associated with chemical fertilizers. While the chemical fertilizer treatment demonstrated higher biomass production in our experiment, further investigations combining the two types of fertilization may provide insights into the synergistic effects and potential for optimizing grassland restoration strategies.
Graphical Abstract
... In the case of nematodes, bacterivorous nematodes with large mouth cavities are more vulnerable to microplastic ingestion than fungivorous nematodes, which often have a stylet used to puncture fungal hyphae (Fueser et al., 2019). More detailed nematode and protist responses to microplastic pollution and traits underlying this variation remain unknown (Rillig & Bonkowski, 2018). While the impacts of GCDs on individual microbiome predator taxa may be explained by traits, the traits best explaining community-level microbiome predator responses to distinct GCDs remain unknown. ...
Microbiome predators shape the soil microbiome and thereby soil functions. However, this knowledge has been obtained from small-scale observations in fundamental rather than applied settings and has focused on a few species under ambient conditions. Therefore, there are several unaddressed questions on soil microbiome predators: (1) What is the role of microbiome predators in soil functioning? (2) How does global change affect microbiome predators and their functions? (3) How can microbiome predators be applied in agriculture? We show that there is sufficient evidence for the vital role of microbiome predators in soils and stress that global changes impact their functions, something that urgently needs to be addressed to better understand soil functioning as a whole. We are convinced that there is a potential for the application of microbiome predators in agricultural settings, as they may help to sustainably increase plant growth. Therefore, we plea for more applied research on microbiome predators.
... The aquatic ecosystems and surface waters are subject to pollution due to the nature of pervasive microplastics and contamination with discarded plastic materials (Thompson et al. 2004;Browne et al. 2011). The presence of microplastic is widespread in the open ocean, soil, and freshwater (Faure et al. 2015;McCormick et al. 2016;Rillig and Bonkowski 2018). Microplastic pollution is becoming a major environmental problem across the globe and poses a threat to the ecosystem, human health, and food safety (Parvin et al. 2021). ...
Microplastics (MPs) are pervasive in aquatic environments, but inland waterbodies (rivers and floodplains) have received much less attention. The present study assesses the incidence of MPs in the gastrointestinal tracts of five commercially important edible fish species-two column feeders (n = 30) and three benthivores (n = 45) from upstream, midstream, and downstream of the Old Brahmaputra river in north-central Bangladesh. MPs were detected in 58.93% of fish, with the highest level in freshwater eel, Mastacembelus armatus (10.31 ± 0.75/fish). Fibers (49.03%) and pellets (28.02%) were the most frequent MPs. Nearly 72% MPs were smaller than 1 mm, and 50.97% were black. FTIR analysis showed 59% polyethelene (PE), followed by polyamide (40%) and unidentified (1%). MP ingestion was linked to fish size and weight, and a high incidence was recorded in the downstream river. Two omnivorous benthic fish ingest more MPs than others. The results corroborate the presence of MPs in the inland river and fish fauna and augment our understanding of heterogeneous MP uptake by fish.
... Because all soil phagotrophic protist species are transferable, they are ideal indicator species because potential harmful particles may be observed within. Despite their potential and abundance in soils, little is known about protist ecology and their involvement in soil micro-organisms' communities (Rillig & Bonkowski, 2018). It is unclear if phagotrophic protists can break down MP. ...
Microplastics (MPs) with slow degradation rates carry toxins and pathogens from surroundings, accumulate and pollute the environment. They bio‐accumulate on humans and other lifeforms leading to health concerns, including inflammatory lesions, oxidative stress and increased cancer risk, thus requiring immediate remediation actions. This review summarizes, categorizes and analyses recent findings on MP source, transit and environmental toxicity and explores their microbe‐mediated breakdown. Various micro‐organisms such as fungi, bacteria, algae and protists interact with and build biofilm on MP surfaces and alter their surface morphology for their degradation. Pure strains and microbial consortia have been successfully able to degrade MPs. Extracellular enzymes are produced by these micro‐organisms that convert the complex recalcitrant polymeric structure of MP to simpler forms. Further, knowledge of factors associated with MP degradation along with the development of genetic tools enhances the rate of microbial degradation with consortium having an advantage over single bacterium‐mediated MP transformation, which has been discussed.
... These MPs have a deleterious effect on soil, the organisms that live in it, and the plants that grow in it (see Fig. 1). Additionally, as chemicals were required to make MPs, they may be harmful to soil-dwelling microorganisms [25]. Furthermore, MPs have been shown to reduce microbial population in the soil [26]. ...
Plastic, in all its forms, always harms the environment, humans, and other living organisms. The coronavirus situation exacerbates the use of plastic products more than at any other time, of which surgical masks contribute to plastic pollution the most. These masks spread to terrestrial and aquatic environments, where they break down into even more noxious microplastics. These microplastics enter the human food chain through water and fish, causing severe damage to the lungs, kidneys, and intestines and even causing death. In this paper, a jute nose holder mask was prepared as an alternative to typical masks to reduce plastic pollution. The jute nose holder was produced with a modified jute flyer-spinning frame machine, where jute was used as the sheath and metal wire was applied as the core component. The nose holder was later coated with starch-based natural gum. Then, the non-woven fabric of 75 grams per square meter (GSM), and the jute nose holder were used to produce the alternative, environmentally friendly mask, which might reduce the 773 tons of plastic waste generated daily from the nose holder of the mask. This alternative mask was then distributed to 900 people for a survey to find out their opinion. From the results of the survey, it is seen that 82.6% of people felt no problem in the nose when they put on the given mask. 85.6% considered the mask more comfortable than the traditional mask, and it was rated above average by 79.8% of the surveyors. So, this study suggests that the given mask can be a sustainable alternative to traditional masks.
... The adsorption and subsequent desorption behaviors of pollutants on MPs may change the occurrence form, transport, and bioavailability of pollutants in the environment and influence the ecosystem positively or negatively [5,67]. MPs can be ingested by kinds of aquatic organisms (e.g., zooplankton, mollusks, and fish) [24,51] and terrestrial organisms (e.g., earthworms, nematodes, ciliates, and snails) [44,58,7,70], and the stimulated biological digestive fluid can facilitate the desorption of pollutants from MPs [9,73]. Therefore, MPs might transfer pollutants into organisms as carriers and increase contact with organisms, thereby enhance the bioavailability of pollutants [4,62,79]. ...
Microplastics (MPs) may significantly affect the bioavailability of coexisting pollutants in soil by adsorption-desorption behavior. However, the mechanisms underlying these interaction remain unclear. Herein, the influence of unused polythylene mulch film-derived MPs (MFMPs) and farmland residual polyethylene mulch film-derived MPs (MFMPs-aged) on the adsorption-desorption behavior and bioavailability of atrazine (ATZ) in soil were investigated. The adsorption kinetics and the adsorption isotherms of ATZ on soil, MFMPs, and MFMPs-aged fitted well by the pseudo-second-order model and the Langmuir model, respectively. ATZ were easier to desorb from soil, MFMPs, and MFMPs-aged in the simulated earthworm digestive fluid than that in the CaCl2 solution. The adsorption and desorption capacities of MFMPs and MFMPs-aged for ATZ were higher than those of soil, especially for MFMPs-aged. The existence of MPs in soil strengthened the adsorption and desorption capacities of ATZ, and the strengthened effects were promoted by the addition amount and aging process of MPs. Moreover, the occurrence of MPs significantly increased the bioaccumulation of ATZ in earthworms, especially for MFMPs-aged. This study deepens the knowledge of the interaction mechanisms of mulch film-derived MPs and pesticide pollution.
... The spread of viable fungal spores passing through the gut of soil organisms is commonly described (Friberg et al., 2005). Once passing through the gut or digestive systems, protists and nematodes release indigestible particles (Rillig & Bonkowski, 2018). The uptake and release of P. brassicae was also observed by us in cultures (Supporting Information: File 1) suggesting that this might also occur in soils. ...
The clubroot pathogen Plasmodiophora brassicae is a major and growing problem for the cultivation of Brassica crops. As conventional control disease management methods are ineffective or prohibited due to their ecological impact, and crop resistance is frequently broken, biological control of the pathogen has become a key focus for the development of sustainable agricultural systems. Here we provide a perspective review on the unexplored impact of soil microbiome predators, and their potential use as biocontrol agents, using clubroot disease as an example. We highlight several pathways by which microbiome predators can reduce clubroot in soils, including directly through predation and indirectly by inducing a clubroot-suppressive microbiome. We further discuss how some microbiome predators might, in contrast, benefit clubroot disease spread through mechanisms such as phoresy toward hosts. We highlight that gaps in knowledge need to be filled that hinder wider application of microbiome predators against P. brassicae alone, and in combination with known biocontrol agents.
... can accumulate or reduce heavy metals including copper, arsenic, mercury, and chromium [76][77][78]. The majority of soil protists tested can ingest microplastic particles within their feeding size range, even at low particle concentrations [79,80], and may aid in degradation by fragmenting and oxidizing the plastics [81]. Considering the extreme diversity of rhizosphere protists, they could be an untapped resource for novel metabolic potential in the plant environment. ...
... High concentrations of polypropylene microplastics can affect the soil dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP), PO 4 3− , humic matter, and fulvic acid concentrations after 30 d of cultivation (Liu et al., 2017). Changes in soil physicochemical properties are indispensable for understanding the impact of microplastics on soil ecosystems (Rillig and Bonkowski, 2018). However, most previous studies on the impact of microplastics on soil characteristics were performed in the laboratory, thereby limiting our understanding of the potential effects of microplastics on the soil environment. ...
Microplastic residues pose one of the most serious environmental problems in areas where plastic mulch is used extensively. Microplastic pollution has potentially serious consequences for ecosystems and human health. Several studies have analyzed microplastics in greenhouses or laboratory climate-controlled chambers; however, field studies evaluating the effects of different microplastics on different crops in extensive farming are limited. Therefore, we selected three major crops, Zea mays (ZM, monocotyledon), Glycine max (GM, dicotyledon, aboveground-bearing), and Arachis hypogaea (AH, dicotyledon, belowground-bearing) and investigated the effect of adding polyester microplastics (PES-MPs) and polypropylene microplastics (PP-MPs). Our results demonstrate that PP-MPs and PES-MPs decreased the soil bulk density of ZM, GM, and AH. Regarding soil pH, PES-MPs increased the soil pH of AH and ZM, whereas PP-MPs decreased the soil pH of ZM, GM, and AH compared to controls. Intriguingly, different coordinated trait responses to PP-MPs and PES-MPs were observed in all crops. In general, commonly measured parameters of AH, such as plant height, culm diameter, total biomass, root biomass, PSII maximum photochemical quantum yield (Fv/Fm), hundred-gain weight, and soluble sugar tended to decrease under PP-MPs exposure; however, some indicators of ZM and GM increased under PP-MPs exposure. PES-MPs had no obviously adverse influence on the three crops, except for the biomass of GM, and even significantly increased the chlorophyll content of AH, specific leaf area, and soluble sugar of GM. Compared with PES-MPs, PP-MPs have serious negative effects on crop growth and quality, especially AH. The findings of the present study provides evidence for evaluating the impact of soil microplastic pollution on crop yield and quality in farmland and lay a foundation for future investigations on the exploration of MP toxicity mechanisms and adaptability of different crops to microplastics.
... According to the results of the ADM, most micro and macroplastic pollution will be observed in soil and terrestrial compartments. Studies that have addressed terrestrial plastic pollution also show high levels of microplastics in residential soil, agricultural soil and negative effects on soil communities (Cohen et al., 2021;Rehm et al., 2021;Rillig and Bonkowski, 2018;Tian et al., 2022). This study highlights the importance of including plastic pollution on land and effects to soil communities and terrestrial ecosystems. ...
Knowledge on environmental plastic emission and spatial and temporal accumulation is vital for the development of successful mitigation strategies and risk assessments of plastics. In this study, emissions of both micro and macro plastic from the plastic value chain to the environment were assessed on a global level through a mass flow analysis (MFA). All countries, 10 sectors, 8 polymers and 7 environmental compartments (terrestrial, freshwater or oceanic) are distinguished in the model. The results assess a loss of 0.8 million tonnes (mt) of microplastics and 8.7 mt of macroplastics to the global environment in 2017. This is respectively 0.2 % and 2.1 % of plastics produced in the same year. The packaging sector contributed most for macroplastic emissions, and tyre wear for microplastic emissions. With the MFA results, accumulation, degradation and environmental transportation are considered in the Accumulation and dispersion model (ADM) until 2050. This model predicts macro- and microplastic accumulation in the environment to 2.2 gigatonnes (Gt) and 3.1 Gt in 2050 respectively (scenario: yearly consumption increase of 4 %). This will be 30 % less when a yearly production reduction of 1 % until 2050 is modeled to 1.5 and 2.3 Gt macro and microplastics respectively. Almost 2.15 Gt of micro and macroplastics accumulate in the environment until 2050 with zero plastic production after 2022 due to leakage from landfills and degradation processes. Results are compared to other modeling studies quantifying plastic emissions to the environment. The current study predicts lower emissions to ocean and higher emissions to surface waters like lakes and rivers. Non aquatic, terrestrial compartments are observed to accumulate most plastics emitted to the environment. The approach used results in a flexible and adaptable model that addresses plastic emissions to the environment over time and space, with detail on country level and environmental compartments.
Microplastics (MPs) are emerging pollutants of terrestrial ecosystems. The impacts of MP particle size on terrestrial systems remain unclear. The current study aimed to investigate the effects of six particle sizes (i.e., 4500, 1500, 500, 50, 5, and 0.5 μm) of polyethylene (PE) and polyvinyl chloride (PVC) on soil respiration, enzyme activity, bacteria, fungi, protists, and seed germination. MPs significantly promoted soil respiration, and the stimulating effects of PE were the strongest for medium and small-sized (0.5–1500 μm) particles, while those of PVC were the strongest for small particle sizes (0.5–50 μm). Large-sized (4500 μm) PE and all sizes of PVC significantly improved soil urease activity, while medium-sized (1500 μm) PVC significantly improved soil invertase activity. MPs altered the soil microbial community diversity, and the effects were especially pronounced for medium and small-sized (0.5–1500 μm) particles of PE and PVC on bacteria and fungi and small-sized (0.5 μm) particles of PE on protists. The impacts of MPs on bacteria and fungi were greater than on protists. The seed germination rate of Brassica chinensis decreased gradually with the decrease in PE MPs particle size. Therefore, to reduce the impact of MPs on soil ecosystems, effective measures should be taken to avoid the transformation of MPs into smaller particles in soil environmental management.
Microplastic pollution is a research hotspot around the world. This study investigated the characteristics of microplastic pollution in the freshwater environments of 21 major cities across China. Through indoor and outdoor experimental analysis, we have identified the spatial and temporal distribution characteristics of microplastic pollution in China’s freshwater environments. Our findings indicate that the average concentration of microplastics in China’s freshwater environments is 3502.6 n/m3. The majority of these microplastics are fibrous (42.5%), predominantly smaller than 3 mm (28.1%), and mostly colored (64.7%). The primary chemical components of these microplastics are polyethylene (PE, 33.6%), polyvinyl chloride (PVC, 21.5%), polypropylene (PP, 16.8%), and polystyrene (PS, 15.6%). The abundance of microplastics in China’s freshwater environments generally tends to increase from west to east and from south to north, with the lowest concentration found in Xining, Qinghai (1737.5 n/m3), and the highest in Jiamusi, Heilongjiang (5650.0 n/m3). The distribution characteristics of microplastics are directly related to land use types, primarily concentrated in areas of intense human activity, including agricultural, transport, and urban land. Seasonal changes affect the abundance of microplastics, peaking in summer, followed by spring and autumn, mainly due to variations in rainfall, showing a positive correlation.
Microplastic (MP) release into the terrestrial environment has occurred since humans started manufacturing and using plastics. These tiny plastic particles can be found in various media, including the atmosphere, soil, freshwater, sediments, and organisms. MPs migrate through terrestrial environmental media due to wind, water, gravity, and biological processes. Although the variables that affect the migration process have been investigated in various settings, the mechanisms of MP migration in terrestrial environments have yet to be systematically characterized. This study classifies the migration mechanisms of MPs as physical, chemical and biological manners, and discusses the factors affecting migration mechanisms in dynamic factors, environmental factors and MP characteristics. Examining the action mechanisms of migration can establish a foundation for understanding the migration processes of MPs and provide a theoretical framework for modeling MP movement in environmental. Future research challenges include understanding the effect of MP characteristics in the migration process and simulating the migration of MPs in the environment in the long-term. Exploring the MP migration on various spatial and temporal scales, considering the life cycle of MPs is a worthy research direction.
Plastic products in plant production and protection help farmers increase crop production, enhance food quality, and reduce global water use and their environmental footprint. Simultaneously, plastic has emerged as a critical ecological issue in recent years, and its pollution has significantly impacted soil, water, and plants. Thus, this review examines the multifaceted problems of plastic pollution in agriculture as a risk to food security, the ecosystem, and the environment. The study's objective was to review and present the most recent information on using different plastic products in agriculture, the sources of plastic pollution, the advantages and drawbacks of using plastic products, and the strategies for mitigating plastic pollution in agriculture. Furthermore, after examining current plastic applications, benefits, adverse effects, and risks to soil, plants, and the environment, we addressed the requirements for technological advancements, regulations, and social processes that could contribute to mitigating plastic pollution in our ecosystems. We identified different pathways toward more sustainable use of plastics in agriculture and discussed future research directions.
Plastics have recently become an indispensable part of everyone’s daily life due to their versatility, durability, light weight, and low production costs. The increasing production and use of plastics poses great environmental problems due to their incomplete utilization, a very long period of biodegradation, and a negative impact on living organisms. Decomposing plastics lead to the formation of microplastics, which accumulate in the environment and living organisms, becoming part of the food chain. The contamination of soils and water with poly(vinyl chloride) (PVC) seriously threatens ecosystems around the world. Their durability and low weight make microplastic particles easily transported through water or air, ending up in the soil. Thus, the problem of microplastic pollution affects the entire ecosystem. Since microplastics are commonly found in both drinking and bottled water, humans are also exposed to their harmful effects. Because of existing risks associated with the PVC microplastic contamination of the ecosystem, intensive research is underway to develop methods to clean and remove it from the environment. The pollution of the environment with plastic, and especially microplastic, results in the reduction of both water and soil resources used for agricultural and utility purposes. This review provides an overview of PVC’s environmental impact and its disposal options.
Microplastic pollution has emerged as a new environmental concern due to our reliance on plastic. Recent years have seen an upward trend in scholarly interest in the topic of microplastics carrying contaminants; however, the available review studies have largely focused on specific aspects of this issue, such as sorption, transport, and toxicological effects. Consequently, this review synthesizes the state-of-the-art knowledge on these topics by presenting key findings to guide better policy action toward microplastic management. Microplastics have been reported to absorb pollutants such as persistent organic pollutants, heavy metals, and antibiotics, leading to their bioaccumulation in marine and terrestrial ecosystems. Hydrophobic interactions are found to be the predominant sorption mechanism, especially for organic pollutants, although electrostatic forces, Van der Waals forces, hydrogen bonding, and pi-pi interactions are also noteworthy. This review reveals that physicochemical properties of microplastics, such as size, structure, and functional groups, and environmental compartment properties, such as pH, temperature, and salinity, influence the sorption of pollutants by microplastic. It has been found that microplastics influence the growth and metabolism of organisms. Inadequate methods for collection and analysis of environmental samples, lack of replication of real-world settings in laboratories, and a lack of understanding of the sorption mechanism and toxicity of microplastics impede current microplastic research. Therefore, future research should focus on filling in these knowledge gaps.
Plastic pollution is widely recognized as a major environmental concern due to the entry of small plastic particles into the food chain, thereby posing potential risks to human health. However, the current understanding of microplastic (MP; <5 mm) particles in livestock, which serve as an important food source, is limited. This study aims to investigate the abundance and characteristics of MPs in edible tissues of cow and sheep, namely liver, meat, and tripe, obtained from butcher shops in five areas of Bushehr port, Iran. The average concentration of MPs in different tissues of cow and sheep were 0.14 and 0.13 items/g, respectively. Among the examined tissues, cow meat exhibited the highest concentration of MPs, with a concentration of 0.19 items/g. Nylon and fiber were identified as the predominant polymer types and shapes of MPs found in cow and sheep tissues, respectively. Furthermore, no statistically significant difference was observed in MP abundance across different tissues of cow and sheep. Significantly, this study highlights the elevated risks associated with exposure to MPs through the consumption of edible cow and sheep tissues, particularly for children who consume meat. The results underscore the potential transfer of MPs from the environment to livestock bodies through their food, potential accumulation within their tissues, and subsequent health risks for consumers.
Plastic products have become ubiquitous in society, and entered various ecosystems due to the massive scale of production. The United Nations Environment Program (UNEP) has listed microplastics (MPs), which form when plastic remnants degrade, as a global emerging pollutant, and the association between soil pollution and MPs has become a popular research topic. This paper systematically reviews research focusing on MP-related soil pollution from the past 10 years (2012-2022), with the identified papers demonstrating that interactions between MPs and soil aggregates has become a research frontier in the field. The presented research provides evidence that soil aggregates are important storage sites for MPs, and that storage patterns of MPs within soil aggregates are influenced by MP characteristics. In addition, MPs affect the formation, turnover, and stability of soil aggregates through the introduction of fracture points along with diverse physicochemical characteristics such as composition and specific surface area. The current knowledge base includes certain issues and challenges that could be addressed in future research by extending the spatial and temporal scales over which microplastic-soil aggregate interactions are studied, unifying quantitative and qualitative methods, and tracing the fates of MPs in the soil matrix. This review contributes to enriching our understanding of how terrestrial MPs interact with soil aggregates, and whether they pose a risk to soil health.
Over the past 50 years, the emergence of plastic waste as one of the most urgent environmental problems in the world has given rise to several proposals to address the rising levels of contaminants associated with plastic debris. Worldwide plastic production has increased significantly over the last 70 years, reaching a record high of 359 million tonnes in 2020. China is currently the world's largest plastic producer, with a share of 17.5%. Of the total marine waste, microplastics account for 75%, while land-based pollution accounts for responsible for 80-90%, and ocean-based pollution 10-20% only in overall pollution problems. Even at small dosages (10 μg/mL), microplastics have been found to cause toxic effects on human and animal health. This review examines the sources of microplastic contamination, the prevalent reaches of microplastics, their impacts, and the remediation methods for microplastic contamination. This review explains the relationship between the community composition and the presence of microplastic particulate matter in aquatic ecosystems. The interaction between microplastics and emerging pollutants, including heavy metals, has been linked to enhanced toxicity. The review article provided a comprehensive overview of microplastic, including its fate, environmental toxicity, and possible remediation strategies. The results of our study are of great value as they illustrate a current perspective and provide an in-depth analysis of the current status of microplastics in development, their test requirements, and remediation technologies suitable for various environments.
Microplastics (MPs) has been suggested that it can greatly affect soil greenhouse gases (GHGs) emissions via altering soil physical, chemical, and biological properties. However, the difference in GHGs emissions, especially for those from coastal wetland soils, between varied aged MPs was rarely explored and the underlying mechanisms of GHGs emissions affected by the aged MPs were poorly understood. Therefore, the implications of fibrous polypropylene MPs (FPP-MPs) exposure on N2O, CO2, and CH4 emissions were examined by a 60-day soil incubation experiment. Compared with the control, the additions of un-aged FPP-MPs with both two rates (0.2 and 2 %) and aged FPP-MPs with a low rate (0.2 %) showed an insignificant effect on N2O emission, while the aged FPP-MPs added with a high rate (2 %) resulted in a remarkably increase in N2O emission, especially for those of the 30-day-aged FPP-MPs. A significant increase in CO2 emission was only observed in the 30-day-aged FPP-MPs treatments, compared with the control, and a higher addition rate produced a higher increase of CO2 emission. Regarding CH4 emission, it was significantly increased by adding aged FPP-MPs, and a longer aging period or/and a higher addition rate generated a higher degree of promotion of CH4 emission. However, compared with the CO2 emission, the quantity of CH4 emission was extremely low. These increased GHGs emissions can be ascribed to the improvements in soil physical structure and other chemical properties (e.g., pH and contents of soil organic matter and dissolved organic carbon) and enhancements in the abundances of denitrification- and carbon mineralization-related microorganisms. Overall, our results highlight the risk of elevated GHGs emissions from the soil polluted with 30-day-aged FPP-MPs, which should not be ignored as long-term aged FPP-MPs continue to increase in coastal wetland soils.
Groundwater is the primary source of water that occurs below the earth's surface. However, the advancement in technology and the increasing population, which lead to the discharge of contaminants such as microplastics (MPs), have an adverse impact on the quality of groundwater. MPs are ubiquitous pollutants that are widely found throughout the world. The maximum abundance of MPs is 4 items/L and 15.2 items/L in groundwater at the specific location of China and USA. Various factors can affect the migration of MPs from soil to groundwater. The occurrence of MPs in water causes serious health issues. Therefore, taking appropriate strategies to control MP contamination in groundwater is urgent and important. This review summarizes the current literature on the migration process of MPs from soil to groundwater along with possible methods for the remediation of MP-polluted groundwater. The main objective of the review is to summarize the technical parameters, process, mechanism, and characteristics of various remediation methods and to analyze strategies for controlling MP pollution in groundwater, providing a reference for future research. Possible control strategies for MP pollution in groundwater include two aspects: i) prevention of MPs from entering groundwater; ii) remediation of polluted groundwater with MPs (ectopic remediation and in-situ remediation). Formulating legislative measures, strengthening public awareness and producing more environment-friendly alternatives can be helpful to reduce the production of MPs from the source. Manage plastic waste reasonably is also a good strategy and the most important part of the management is recycling. The shortcomings of the current study and the direction of future research are also highlighted in the review.
Microplastics are considered emerging pollutants. Their potential risks to the fragile ecosystem of the Qinghai-Tibet Plateau should not be ignored. In order to determine the types, distribution, and morphological characteristics of microplastics in the water and sediments of Qinghai Lake, 26 water and sediment samples were characterized. A stereoscopic microscope and Fourier transform infrared (FT-IR) spectroscopy were used. Furthermore, the source and distribution of the microplastics were identified using the geographic information system (GIS) kriging interpolation method. Our results demonstrated that the microplastics present in the water and sediments of Qinghai Lake were mainly composed of polyethene (PE) and polypropylene (PP). Considering that packaging materials and fibres from fishery products contain PE and PP, it is likely that they are the primary source of microplastics in Qinghai Lake. As a result, the most elevated levels are found at the Lake’s centre. Concerning sediments, the highest amount was found at the Erlang Sword Scenic Site, which may display most of the tourism activities in the area. These results further indicate that tourism activities may be the primary source of microplastics in Qinghai Lake. In order to ensure the sustainable development of the Qinghai Lake Basin, it is essential to improve the management of this tourist destination.KeywordsPollutant source monitoringPolymer type detectionPollution characteristicsSpatial distribution
The soil environment is a critical component of the global ecosystem and is essential for nutrient cycling and energy flow. Various physical, chemical, and biological processes occur in the soil and are affected by environmental factors. Soil is vulnerable to pollutants, especially emerging pollutants, such as microplastics (MPs). MPs pollution has become a significant environmental problem, and its harm to human health and the environment cannot be underestimated. However, most studies on MPs pollution have focused on marine ecosystems, estuaries, lakes, rivers, and other aquatic environments, whereas few considered the effects and hazards of MPs pollution of the soil, especially the responses of different environmental factors to MPs. In addition, when many MPs pollutants produced by agricultural activities (mulching film, organic fertilizer) and atmospheric sedimentation enter the soil environment, it will cause changes in soil pH, organic matter composition, microbial community, enzyme activity, animals and plants and other environmental factors. However, due to the complex and changeable soil environment, the heterogeneity is very strong. The changes of environmental factors may react on the migration, transformation and degradation of MPs, and there are synergistic or antagonistic interactions among different factors. Therefore, it is very important to analyze the specific effects of MPs pollution on soil properties to clarify the environmental behavior and effects of MPs. This review focuses on the source, formation, and influencing factors of MPs pollution in soil and summarizes its effect and influence degree on various soil environmental factors. The results provide research suggestions and theoretical support for preventing or controlling MPs soil pollution.
Microplastics are plastic particles with particle size less than 5 mm in the environment. As an emerging organic pollutant, the presence of microplastics in the soil environment has been widely noticed. Secondly, due to the overuse of antibiotics, a large amount of antibiotics that cannot be fully absorbed by humans and livestock enter the soil environment in the form of urine or manure, making the soil suffer from serious antibiotic contamination problems. To address the environmental problems of microplastics and antibiotic contamination in soil, this study was conducted to investigate the effects of PE microplastics on antibiotic degradation, microbial community characteristics and ARGs in tetracycline-contaminated soils. The results showed that the addition of PE microplastics inhibited the degradation of tetracycline, and significantly increased the organic carbon content and decreased the neutral phosphatase activity. The addition of PE microplastics significantly reduced the alpha diversity of soil microbial community. Compared to the single tetracycline contamination. In addition, combined contamination with PE microplastics and tetracycline significantly affected bacterial genera such as Aeromicrobium, Rhodococcus, Mycobacterium and Intrasporangium. Metagenome sequencing studies revealed that the addition of PE microplastics inhibited the dissipation of ARGs in tetracycline-contaminated soils. There were strong positive correlations between Multidrug, Aminoglycoside and Clycopeptide resistance genes and Chloroflexi and Proteobacteria in tetracycline contaminated soils, and there was a strong positive correlation between Aminoglycoside resistance genes and Actinobacteria in combined contamination of PE microplastics and tetracycline. This study will provide some data support for the current environmental risk assessment of the coexistence of multiple contaminants in soil.
In the cascade reservoirs, the interception and storage of upstream reservoirs led to significant changes in the inflow of downstream reservoir, which result in deviation of flood design standards and unreasonable flood limited water level (FLWL). This paper proposes a framework to design the reservoir’s seasonal FLWLs considering the influence of its upstream cascade reservoirs regulation. Firstly, the natural runoff of the reservoir is reduction calculated to the operation period which includes the discharge process calculation of upstream cascade reservoirs and interval flood encounter analysis. Further, an entropy weight-based improved Fisher optimal segmentation method is proposed for flood season staging, and then flood regulation calculation for the seasonal design flood process is conducted to determine the seasonal FLWL. Finally, the flood control risk and benefit analysis of the seasonal FLWLs is carried out. Taking China’s Three Gorges reservoir as a case, the flood season can be divided into three stages and the seasonal FLWL can rise to a certain extent compared with the original value. Compared to the original design standard, the average annual reservoir storage and power generation can be increased without increasing the risk of flood control.
Microplastics (MP) and nanoplastics (NP) contamination of the terrestrial environment is a growing concern worldwide and is thought to impact soil biota, particularly the micro and mesofauna community, by various processes that may contribute to global change in terrestrial systems. Soils act as a long-term sink for MP, accumulating these contaminants and increasing their adverse impacts on soil ecosystems. Consequently, the whole terrestrial ecosystem is impacted by microplastic pollution, which also threatens human health by their potential transfer to the soil food web. In general, the ingestion of MP in different concentrations by soil micro and mesofauna can adversely affect their development and reproduction, impacting terrestrial ecosystems. MP in soil moves horizontally and vertically because of the movement of soil organisms and the disturbance caused by plants. However, the effects of MP on terrestrial micro-and mesofauna are largely overlooked. Here, we give the most recent information on the forgotten impacts of MP contamination of soil on microfauna and mesofauna communities (protists, tardigrades, soil rotifers, nematodes, collembola and mites). More than 50 studies focused on the impact of MP on these organisms between 1990 and 2022 have been reviewed. In general, plastic pollution does not directly affect the survival of organisms, except under co-contaminated plastics that can increase adverse effects (e.g. tire-tread particles on springtails). Besides, they can have adverse effects at oxidative stress and reduced reproduction (protists, nematodes, potworms, springtails or mites). It was observed that micro and mesofauna could act as passive plastic transporters, as shown for springtails or mites. Finally, this review discusses how soil micro- and mesofauna play a key role in facilitating the (bio-)degradation and movement of MP and NP through soil systems and, therefore, the potential transfer to soil depths. More research should be focused on plastic mixtures, community level and long-term experiments.
In recent years, the prevalence and accumulation of microplastics (MPs) in the soil environment have raised worldwide concerns for their resistance to degradation and long-term ecological impacts. However, compared with aquatic ecosystems, there is still a lack of critical reviews on the ecological effects and effective remediation methods of MPs in soil. In this review, the distribution characteristics, sources and transportation, identification techniques of MPs are summarized, followed by an elaboration of the interactions between MPs contamination and soil ecosystems. Moreover, we generalized the effects and degradation mechanisms of different organisms on the degradation of MPs. There are a variety of microorganisms in the environment that can degrade MPs, but the enzymes that really work are yet to be explored. It may be a breakthrough in the field of biodegradation to transform the stability and performance of enzymes based on computer protein design. This review will guide researchers to further explore feasible approaches and formulate advanced remediation strategies for MPs contamination in the future.
Despite great general benefits derived from plastic use, accumulation of plastic material in ecosystems, and especially microplastic, is becoming an increasing environmental concern. Microplastic has been extensively studied in aquatic environments, with very few studies focusing on soils. We here tested the idea that microplastic particles (polyethylene beads) could be transported from the soil surface down the soil profile via earthworms. We used Lumbricus terrestris L., an anecic earthworm species, in a factorial greenhouse experiment with four different microplastic sizes. Presence of earthworms greatly increased the presence of microplastic particles at depth (we examined 3 soil layers, each 3.5 cm deep), with smaller PE microbeads having been transported downward to a greater extent. Our study clearly shows that earthworms can be significant transport agents of microplastics in soils, incorporating this material into soil, likely via casts, burrows (affecting soil hydraulics), egestion and adherence to the earthworm exterior. This movement has potential consequences for exposure of other soil biota to microplastics, for the residence times of microplastic at greater depth, and for the possible eventual arrival of microplastics in the groundwater.
Plastic debris is an environmentally persistent and complex contaminant of increasing concern. Understanding the sources, abundance and composition of microplastics present in the environment is a huge challenge due to the fact that hundreds of millions of tonnes of plastic material is manufactured for societal use annually, some of which is released to the environment. The majority of microplastics research to date has focussed on the marine environment. Although freshwater and terrestrial environments are recognised as origins and transport pathways of plastics to the oceans, there is still a comparative lack of knowledge about these environmental compartments. It is highly likely that microplastics will accumulate within continental environments, especially in areas of high anthropogenic influence such as agricultural or urban areas. This review critically evaluates the current literature on the presence, behaviour and fate of microplastics in freshwater and terrestrial environments and, where appropriate, also draws on relevant studies from other fields including nanotechnology, agriculture and waste management. Furthermore, we evaluate the relevant biological and chemical information from the substantial body of marine microplastic literature, determining the applicability and comparability of this data to freshwater and terrestrial systems. With the evidence presented, the authors have set out the current state of the knowledge, and identified the key gaps. These include the volume and composition of microplastics entering the environment, behaviour and fate of microplastics under a variety of environmental conditions and how characteristics of microplastics influence their toxicity. Given the technical challenges surrounding microplastics research, it is especially important that future studies develop standardised techniques to allow for comparability of data. The identification of these research needs will help inform the design of future studies, to determine both the extent and potential ecological impacts of microplastic pollution in freshwater and terrestrial environments.
This study reveals the diversity and distribution of two major ubiquitous groups of soil amoebae, the genus Acanthamoeba and the Myxomycetes (plasmodial slime-moulds) that are rarely, if ever, recovered in environmental sampling studies. We analyzed 150 grassland soil samples from three Biodiversity Exploratories study regions in Germany. We developed specific primers targeting the V2 variable region in the first part of the small subunit of the ribosomal RNA gene for high-throughput pyrotag sequencing. From ca. 1 million reads, applying very stringent filtering and clustering parameters to avoid overestimation of the diversity, we obtained 273 acanthamoebal and 338 myxomycete operational taxonomic units (OTUs, 96% similarity threshold). This number is consistent with the genetic diversity known in the two investigated lineages, but unequalled to date by any environmental sampling study. Only very few OTUs were identical to already known sequences. Strikingly different OTUs assemblages were found between the three German regions (PerMANOVA p.value = 0.001) and even between sites of the same region (multiple-site Simpson-based similarity indices <0.4), showing steep biogeographical gradients.
Background
Bacterivores, mostly represented by protists and nematodes, are a key component of soil biodiversity involved in soil fertility and plant productivity. In the current context of global change and soil biodiversity erosion, it becomes urgent to suitably recognize and quantify their ecological importance in ecosystem functioning.ScopeUsing meta-analysis tools, we aimed at providing a quantitative synthesis of the ecological importance of soil bacterivores on ecosystem functions. We also intended to produce an overview of the ecological factors that are expected to drive the magnitude of bacterivore effects on ecosystem functions.Conclusions
Bacterivores in soil contributed significantly to numerous key ecosystem functions. We propose a new theoretical framework based on ecological stoichiometry stressing the role of C:N:P ratios in soil, microbial and plant biomass as important parameters driving bacterivore-effects on soil N and P availability for plants, immobilization of N and P in the bacterial biomass, and plant responses in nutrition and growth.
Acanthamoeba is a very abundant genus of soil protists with fundamental importance in nutrient cycling, but several strains can also act as human pathogens. The systematics of the genus is still unclear: currently 18 small-subunit (SSU or 18S) ribosomal RNA sequence types (T1-T18) are recognized, which sometimes contain several different morphotypes; on the other hand, some morphological identical strains belong to different sequence types, sometimes appearing in paraphyletic positions. In this study, we cultivated 65 Acanthamoeba clones from soil samples collected under grassland at three separate locations in the Netherlands, in Sardinia and at high altitude mountains in Tibet. We obtained 24 distinct partial sequences, which predominantly grouped within sequence type T4 followed by T2, T13, T16 and "OX-1" (in the T2/T6 clade). Our sequences were 98-99 % similar, but none was identical to already known Acanthamoeba sequences. The community composition of Acanthamoeba strains differed between locations, T4 being the dominant sequence type in Sardinia and Tibet, but represented only half of the clones from soils in the Netherlands. The other half of clones from the Dutch soils was made up by T2, T16 and "OX-1", while T13 was only found in Sardinia and Tibet. None of the sequences was identical between localities. Several T4 clones from all three localities and all T13 clones grew at 37 °C while one T4 clone was highly cytopathogenic.
The quantitative uptake of suspended particles has been studied in 14 species of ciliated protozoa in terms of the maximum rate of water cleared at low particle concentrations and of the maximum ingestion rate at high particle concentrations. The results, supported by data from the literature, show that ciliates which feed on larger particles (> 1-5μm) compare favorably with metazoan suspension feeders with respect to the ability to concentrate dilute suspensions of particles. Species specialized on smaller food particles (0.2-1μm), the size range of most bacteria in natural environments, require a higher concentration of particles. Bacterial population densities which can sustain ciliate growth are found in sediments, waters rich in organic material, and in the early successional stages of decomposing organic material. This is not the case in open waters in general where bacterivorous ciliates cannot play a role as grazers of bacteria.
The quantitative uptake of latex beads of different sizes and of live cells by 14 species of ciliates was studied. The functional response (uptake rate as function of food particle concentration) can be fitted to a hyperbolic function and this can be explained in terms of the function of the mouth apparatus. Each species shows a distinct size spectrum of particles which are retained and ingested. These size spectra may be explained by mouth morphology, and particle size selection may play a role for niche separation of coexisting ciliates. Most bacterivorous holotrich ciliates retain particles down to 0.2μm and in one case down to 0.1μm; they retain particles between 0.3 and 1μm most efficiently. The spirotrich ciliates investigated do not retain particles smaller than 1-2μm.
Even though bacterivorous flagellates have been recognized as being able to structure the bacterial community, their behavioral basis for food selection is hardly known. We investigated the feeding behavior of the filter-feeding choanoflagellate Monosiga ovata and the raptorial-feeding kinetoplastid flagellate Rhynchomonas nasuta feeding on a bacterial community dominated by Pseudomonas putida and compared it to that of interception-feeding flagellates. M. ovata handles several food particles simultaneously. In contrast, R. nasuta handles only 1 particle at a time. The handling time for 1 prey particle is in the range of 3.7 s for R. nasuta but more than 300 s for M. ovata. The speed of food particles within the feeding current of M. ovata was only 9.3 +/- 5.7 mum s(-1) but due to the large surface of the collar the filtered water volume was 6.4 nl h-l and therefore comparable to that of interception-feeding flagellates of a similar size. Bacteria ingested by M. ovata were significantly smaller compared to the bacteria in the medium (p = 0.001). Size selection of food particles occurs during the processing of food items. This is in contrast to raptorial-feeding R. nasuta, which shows passive food size selection for bigger particles during the contact phase. Attachment of bacteria proved to be an efficient protection mechanism, defending them from being grazed by flagellates. There are significant species-specific differences in the processing of food particles which explain the coexistence of various bacterivorous nanoflagellates in the size range of 3 to 5 mum and indicate the existence of specific predation pressure on different bacteria.
Ingestion of picoplankton-size particles was studied in two marine ciliates, a typical grazer of pico- and nano-plankton, the oligotrich Strombidium sulcatum, and a bacteriovorous scuticociliate, Uronema sp. In laboratory experiments, both logarithmic- (food-unlimited) and stationary-phase (food-limited) populations were presented with particles of different sizes and surface properties: plain microspheres, protein-adsorbing carboxylate microspheres, fluorescently labelled heterotrophic bacteria, and cyanobacteria. In both log- and stationary-phase populations, Strombidium clearance rates varied linearly as function of prey size based on the ingestion of plain microspheres. In contrast, Uronema clearance rates were invariant with particle size for log-phase populations but increased with particle size in stationary-phase cells. Discrimination among prey with different surface properties was also dissimilar in the two ciliates. For Strombidium, log-phase populations cleared 1-μm-diameter plain microspheres at higher rates than those with carboxylate surfaces. The pattern was repeated by stationary-phase cells for both ~0.5- and 1-μm-diameter microspheres. In Uronema, there was no significant difference in clearance rates with surface property in log-phase populations, similar to the findings with regard to particle size. Only in stationary-phase populations of Uronema was some selection evident, as 0.97-μm carboxylate microspheres were cleared at rates higher than were 0.95-μm plain microspheres. Overall, selection was higher in stationary-phase ciliates, and Strombidium seemed to feed more size-selectively among picoplankton particles than did Uronema.
Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: (1) to summarise the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. We conclude by highlighting key future research areas for scientists and policymakers.
Soil pseudomonads increase their competitiveness by producing toxic secondary metabolites, which inhibit competitors and repel predators. Toxin production is regulated by cell-cell signalling and efficiently protects the bacterial population. However, cell communication is unstable, and natural populations often contain signal blind mutants displaying an altered phenotype defective in exoproduct synthesis. Such mutants are weak competitors, and we hypothesized that their fitness depends on natural communities on the exoproducts of wild-type bacteria, especially defence toxins. We established mixed populations of wild-type and signal blind, non-toxic gacS-deficient mutants of Pseudomonas fluorescens CHA0 in batch and rhizosphere systems. Bacteria were grazed by representatives of the most important bacterial predators in soil, nematodes (Caenorhabditis elegans) and protozoa (Acanthamoeba castellanii). The gacS mutants showed a negative frequency-dependent fitness and could reach up to one-third of the population, suggesting that they rely on the exoproducts of the wild-type bacteria. Both predators preferentially consumed the mutant strain, but populations with a low mutant load were resistant to predation, allowing the mutant to remain competitive at low relative density. The results suggest that signal blind Pseudomonas increase their fitness by exploiting the toxins produced by wild-type bacteria, and that predation promotes the production of bacterial defence compounds by selectively eliminating non-toxic mutants. Therefore, predators not only regulate population dynamics of soil bacteria but also structure the genetic and phenotypic constitution of bacterial communities.
Cells of Acanthamoeba castellanii (Neff) are known to form mature cysts characterized by a cellulose-containing cell wall when transferred to a nonnutrient medium. Amebas which engulfed latex beads before encystment formed mature cysts essentially devoid of bead material. The encystment of bead-containing cells appeared to be similar to that of control cells since no important differences between the two were observed with respect to cellular levels of glycogen or protein, cellulose synthetase activity, the amount of cyst wall polysaccharide formed, or the percentage of cysts formed. Actinomycin D and cycloheximide inhibited encystment as well as bead expulsion. Ultrastructural analysis revealed that the beads, which initially were contained in phagocytic vesicles, were released from the cell by fusion of vesicular membranes with the plasma membrane. Exocytosis was observed in cells after 3 hr of encystment, with most of the beads being lost before cyst wall formation. Each bead-containing vesicle involved in expulsion was conspicuously demarcated by an area of concentrated cytoplasm, which was more homogeneously granular than the surrounding cytoplasm. Beads were not observed in the cytoplasm of mature cysts but were occasionally found in the cyst wall.
Electron microscopic studies confirm and extend the conclusions derived previously from a quantitative biochemical study of the phagocytosis of polystyrene and polyvinyltoluene latex beads by Acanthamoeba (1). Latex beads 1.305, 1.90, and 2.68 micro in diameter are ingested individually, with each bead tightly surrounded by a membrane derived from the plasma membrane. Latex beads 0.557, 0.264, 0.126, and 0.088 micro in diameter are accumulated at the surface of the ameba and then phagocytosed, with many beads tightly packed within one membrane-bounded vesicle.
The influence of grazing by the bacterivorous nanoflagellate Ochromonas sp. strain DS on the taxonomic and morphological structures of a complex bacterial community was studied in one-stage chemostat experiments. A bacterial community, consisting of at least 30 different strains, was fed with a complex carbon source under conditions of low growth rate (0.5 day(-1) when nongrazed) and low substrate concentration (9 mg liter(-1)). Before and after the introduction of the predator, the bacterial community composition was studied by in situ techniques (immunofluorescence microscopy and fluorescent in situ hybridization), as well as by cultivation on agar media. The cell sizes of nonspecifically stained and immunofluorescently labeled bacteria were measured by image analysis. Grazing by the flagellate caused a bidirectional change in the morphological structure of the community. Medium-size bacterial cells, which dominated the nongrazed community, were largely replaced by smaller cells, as well as by cells contained in large multicellular flocs. Cell morphological changes were combined with community taxonomic changes. After introduction of the flagellate, the dominating strains with medium-size cells were largely replaced by single-celled strains with smaller cells on the one hand and, on the other hand, by Pseudomonas sp. strain MWH1, which formed the large, floc-like forms. We assume that size-selective grazing was the major force controlling both the morphological and the taxonomic structures of the model community.
Phagocytosis in the common grazing soil amoeba Acanthamoeba castellanii was characterized by flow cytometry. Uptake of fluorescently labelled latex microbeads by cells was quantified by appropriate setting of thresholds on light scatter channels and, subsequently, on fluorescence histograms. Confocal laser scanning microscopy was used to verify the effectiveness of sodium azide as a control for distinguishing between cell surface binding and internalization of beads. It was found that binding of beads at the cell surface was complete within 5 min and 80% of cells had beads associated with them after 10 min. However, the total number of phagocytosed beads continued to rise up to 2 h. The prolonged increase in numbers of beads phagocytosed was due to cell populations containing increasing numbers of beads peaking at increasing time intervals from the onset of phagocytosis. Fine adjustment of thresholds on light scatter channels was used to fractionate cells according to cell volume (cell cycle stage). Phagocytotic activity was approximately threefold higher in the largest (oldest) than in the smallest (newly divided) cells of A. castellanii and showed some evidence of periodicity. At no stage in the cell cycle did phagocytosis cease. Binding and phagocytosis of beads were also markedly influenced by culture age and rate of rotary agitation of cell suspensions. Saturation of phagocytosis (per cell) at increasing bead or decreasing cell concentrations occurred at bead/cell ratios exceeding 10:1. This was probably a result of a limitation of the vacuolar uptake system of A. castellanii, as no saturation of bead binding was evident. The advantages of flow cytometry for characterization of phagocytosis at the single-cell level in heterogeneous protozoal populations and the significance of the present results are discussed.
Protists include all eukaryotes except plants, fungi and animals. They are an essential, yet often forgotten, component of the soil microbiome. Method developments have now furthered our understanding of the real taxonomic and functional diversity of soil protists. They occupy key roles in microbial foodwebs as consumers of bacteria, fungi and other small eukaryotes. As parasites of plants, animals and even of larger protists, they regulate populations and shape communities. Pathogenic forms play a major role in public health issues as human parasites, or act as agricultural pests. Predatory soil protists release nutrients enhancing plant growth. Soil protists are of key importance for our understanding of eukaryotic evolution and microbial biogeography. Soil protists are also useful in applied research as bioindicators of soil quality, as models in ecotoxicology and as potential biofertilizers and biocontrol agents. In this review, we provide an overview of the enormous morphological, taxonomical and functional diversity of soil protists, and discuss current challenges and opportunities in soil protistology. Research in soil biology would clearly benefit from incorporating more protistology alongside the study of bacteria, fungi and animals.
Microplastics (MPs) are small (<5 mm diameter) but have clear implications for the environment. These artificial particles are found in and pose threats to aquatic systems worldwide. MPs have terrestrial sources, but their concentrations and fates in the terrestrial environment are poorly understood. Whilst global plastic production continues to increase, so do the environmental concentrations and impacts of MPs. In this first study of MPs in floodplain soils, we developed a method for identifying, quantifying, and measuring the sizes of most commonly produced MPs in soil by FT-IR microscopy. For small MP (<1mm) analysis, MP were separated by density separation and oxidation of organic matter. In this study we analyzed 29 floodplains in Swiss nature reserves associated with catchments covering 53% of Switzerland. We found evidence that 90% of Swiss floodplain soils contain MPs. The highest MP concentrations were associated with the concentration of mesoplastics (5 mm – 2.5 cm diameter), indicating plastic waste as source. Furthermore, MP concentration was correlated with the population of the catchment. The wide distribution of MPs, their presence in remote unsettled high mountain areas, decoupling of MEP and MP compositions, and the dominance of MPs by small (<500 µm diameter) particles, indicate that MPs enter soils via diffuse aeolian transport.
This article introduces a simple and cost-saving method developed to extract, distinguish and quantify light density microplastics of polyethylene (PE) and polypropylene (PP) in soil. A floatation method using distilled water was used to extract the light density microplastics from soil samples. Microplastics and impurities were identified using a heating method (3-5s at 130°C). The number and size of particles were determined using a camera (Leica DFC 425) connected to a microscope (Leica wild M3C, Type S, simple light, 6.4×). Quantification of the microplastics was conducted using a developed model. Results showed that the floatation method was effective in extracting microplastics from soils, with recovery rates of approximately 90%. After being exposed to heat, the microplastics in the soil samples melted and were transformed into circular transparent particles while other impurities, such as organic matter and silicates were not changed by the heat. Regression analysis of microplastics weight and particle volume (a calculation based on image J software analysis) after heating showed the best fit (y=1.14x+0.46, R(2)=99%, p<0.001). Recovery rates based on the empirical model method were >80%. Results from field samples collected from North-western China prove that our method of repetitive floatation and heating can be used to extract, distinguish and quantify light density polyethylene microplastics in soils. Microplastics mass can be evaluated using the empirical model.
Soils host the most complex communities of organisms, which are still largely considered as an unknown ‘black box’. A key role in soil food webs is held by the highly abundant and diverse group of protists. Traditionally, soil protists are considered as the main consumers of bacteria in soils. However, recent insights obtained using new methodologies, provide clear evidence for the trophic diversity of microbial eukaryotes, showing that non-bacterivorous soil protists (fungivores, omnivores, predators of other protists and nematodes), photosynthetic taxa and plant-as well as animal parasites might be equally important.
Plastics, despite their great benefits, have become a ubiquitous environmental pollutant, with microplastic particles having come into focus most recently. Microplastic effects have been intensely studied in aquatic, especially marine systems; however, there is lack of studies focusing on effects on soil and its biota. A basic question is if and how surface-deposited microplastic particles are transported into the soil. We here wished to test if soil microarthropods, using Collembola, can transport these particles over distances of centimeters within days in a highly controlled experimental set-up. We conducted a fully factorial experiment with two collembolan species of differing body size, Folsomia candida and Proisotoma minuta, in combination with urea-formaldehyde particles of two different particle sizes. We observed significant differences between the species concerning the distance the particles were transported. F. candida was able to transport larger particles further and faster than P. minuta. Using video, we observed F. candida interacting with urea-formaldehyde particles and polyethylene terephthalate fibers, showing translocation of both material types. Our data clearly show that microplastic particles can be moved and distributed by soil microarthropods. Although we did not observe feeding, it is possible that microarthropods contribute to the accumulation of microplastics in the soil food web.
A method based on Pressurized Fluid Extraction (PFE) was developed for measuring microplastics in environmental samples. This method can address some limitations of the current microplastic methods and provide laboratories with a simple analytical method for quantifying common microplastics in a range of environmental samples. The method was initially developed by recovering 101% to 111% of spiked plastics on glass beads and was then applied to a composted municipal waste sample with spike recoveries ranging from 85% to 94%. The results from municipal waste samples and soil samples collected from an industrial area demonstrated that the method is a promising alternative for determining the concentration and identity of microplastics in environmental samples.
Plastic debris is widespread in the environment, but information on the effects of microplastics on terrestrial fauna is completely lacking. Here, we studied the survival and fitness of the earthworm Lumbricus terrestris (Oligochaeta, Lumbricidae) exposed to microplastics (Polyethylene, <150 μm) in litter at concentrations of 7, 28, 45, and 60% dry weight, percentages that, after bioturbation, translate to 0.2 to 1.2% in bulk soil. Mortality after 60 days was higher at 28, 45, and 60% of microplastics in the litter than at 7% w/w and in the control (0%). Growth rate was significantly reduced at 28, 45, and 60% w/w microplastics, compared to the 7% and control treatments. Due to the digestion of ingested organic matter, microplastic was concentrated in cast, especially at the lowest dose (i.e., 7% in litter) because that dose had the highest proportion of digestible organic matter. Whereas 50 percent of the microplastics had a size of <50 μm in the original litter, 90 percent of the microplastics in the casts was <50 μm in all treatments, which suggests size-selective egestion by the earthworms. These concentration-transport and size-selection mechanisms may have important implications for fate and risk of microplastic in terrestrial ecosystems.
A recombination-deficient strain (EM 1035) of Escherichia coli (Migula) was used to test the ability of the marine zooflagellate Paraphysomonas vestita (Stokes) to discriminate between living and heat-killed prey of similar size and morphology. Cell division of EM 1035 was prevented by relatively short exposure to UV-irradiation. Fluorescent staining with rhodamine isothiocyanate did not affect the viability of the bacterial cells or the growth and feeding rates of the zooflagellate. P. vestita fed preferentially on living cells when presented with an equal density mixture of heat-killed and UV-irradiated (nondividing) cells. The flagellate discriminated between living and dead cells with a preference ratio of about 20 suggesting that chemosensory cues may be important in the feeding selectivity of some marine protozoans.
To determine if conidia of the nematophagous fungus Drechmeria coniospora are subject to predation by soil protozoa, several sandy soils were enriched with 109 conidia of this fungus per g dry soil. After incubation of the samples at 20°C for three weeks, a flagellate was detected as the most dominant mycophagous protozoan. Conidia of several fungi, with minimum diameters between 2 and 16 μm, supported growth of this flagellate, irrespective of pigmentation. Bacteria however could not be used for growth, although bacteria and also latex beads of the same size were ingested. This is, to our knowledge, the first report of an obligate mycophagous soil-borne flagellate. The flagellate was able to grow at the expense of the conidia of D. coniospora in liquid culture, with a specific growth rate of about 0.1 h−1; the optimum temperature was 20–24°C. Approximately 10 D. coniospora conidia were required for one flagellate division. In sterilized soil, enriched with 108D. coniospora conidia per g dry soil, the specific growth rate was 0.014 h−1, when the soil was at 50 or 65% of its water-holding capacity (WHC). In drier soil, i.e. 25% WHC, no growth took place. During growth of the flagellate in soil, the number of D. coniospora was reduced by about 20%, which was in the same order of magnitude as expected on the basis of the requirement of 10 D. coniospora conidia for one flagellate division. Since many conidia remained in the soil after growth of the flagellate, we concluded that although the flagellate is an interesting organism, it does not play a very important role in the survival of D. coniospora conidia in the soil.
Acanthamoeba sp. take up polystyrene and polyvinyltoluene latex beads. There appear to be no requirements for specific organic molecules for uptake providing the appropriate osmotic conditions are maintained. This requirement can be satisfied by glucose, mannitol, inulin, or proteose-peptone. The proper osmolarity depends on the previous history of the amoebas and they can adapt to an unfavorable osmolarity. Uptake is inhibited by 2 × 10-6 M dinitrophenol, 2 × 10-3 M cyanide, and 2 × 10-4 M azide but not by 4 × 10-2 M fluoride or 2 × 10-3 M iodoacetate. Uptake is optimal at 30-35°. A quantitative measure of bead uptake has been developed by application of the dioxane extraction method of J. Roberts and J. H. Quastel (Biochem. J. 89, 150 (1963)). The rate of uptake was found to be a linear function of the time of incubation and the concentration of cells over a broad pH range. Once taken in, beads are retained by amoebae for at least 4.5 hr. The rates of uptake of each of six different size beads (0.126-2.68 μ) were directly proportional to the concentration of beads; the data give straight line in a Lineweaver-Burk plot. When calculated on a weight basis, the values for Kb (concentration of beads resulting in half the maximal velocity) were identical for all six sizes of beads and the values for Vmax were the same for all sizes of beads within a factor of 2. Therefore, the kinetics of uptake are a function of bead mass (or volume) and not of bead number, surface area, or diameter. The uptake of beads is highly selective, there being essentially no uptake of [14C]glucose or [131I]albumin during the ingestion of 25-30% of the beads present in the same incubation medium. Ingestion of beads of diameter 2.68 μ was inhibited by the presence of beads of diameter 0.126 μ. Taken all together the data indicate that beads are bound to, and accumulate at, the cell surface until an optimum volume, approximately the same for all sizes, is reached, at which time the beads are ingested by a mechanism that excludes the incubation medium. This interpretation has been confirmed by electron microscopic observations which will be published elsewhere.
Acanthamoeba spp. are free-living predators that selectively feed on bacteria. Adherence of the bacterial food source to the trophozoite membrane is followed by internalisation and digestion. Through co-cultivation of A. castellanii and A. polyphaga, individually, with Xanthomonas maltophilia, Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa (despite the amoebicidal properties of the latter organism), specificity with regard to the preferred bacterial substrate was judged. X. maltophilia and P. aeruginosa adhered almost immediately forming a multilayered mantle of bacilli around trophozoites of both species of amoebae. E. coli adhered to fewer trophozoites and in smaller numbers. X. maltophilia was readily internalised after co-cultivation for 8 h, whereas P. aeruginosa, E. coli and S. epidermidis were not internalised even after co-cultivation for 24 h. These data suggest that the suitability of a bacterial food source for the Acanthamoeba spp. studied is associated not only with the proclivity with which the bacterial species binds to the trophozoite surface, but also with the rate of its internalisation.
Food selectivity and the mechanisms of food selection were analyzed by video microscopy for three species (Spumella, Ochromonas, Cafeteria) of interception-feeding heterotrophic nanoflagellates. The fate of individual prey particles, either live bacteria and/or inert particles, was recorded during the different stages of the particle-flagellate-interaction, which included capture, ingestion, digestion, and egestion. The experiments revealed species-specific differences and new insights into the underlying mechanisms of particle selection by bacterivorous flagellates. When beads and bacteria were offered simultaneously, both particles were ingested unselectively at similar rates. However, the chrysomonads Spumella and Ochromonas egested the inert beads after a vacuole passage time of only 2-3 min, which resulted in an increasing proportion of bacteria in the food vacuoles. Vacuole passage time for starved flagellates was significantly longer compared to that of exponential-phase flagellates for Spumella and Ochromonas. The bicosoecid Cafeteria stored all ingested particles, beads as well as bacteria, in food vacuoles for more then 30 min. Therefore "selective digestion" is one main mechanism responsible for differential processing of prey particles. This selection mechanism may explain some discrepancies of former experiments using inert particles as bacterial surrogates for measuring bacterivory.
Heterotrophic flagellates (HF) are known as most important grazers of bacteria in many aquatic ecosystem. HF cannot be treated as a black box since HF generally contain a diverse community of species significantly differing in their feeding behaviour and other ecological properties. Today it seems that the dominant taxonomic groups among heterotrophic nano- and microflagellate communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates, kathablepharids) and benthic communities (euglenids, bodonids, thaumatomonads, apusomonads, cercomonads) are relatively similar. HF among protista incertae sedis, often neglected in ecological studies, are abundant bacterivores in all investigated habitats. Recent studies of flagellate feeding processes indicated that there are significant species-specific differences and individual variability regarding the food uptake and food selection of bacterivorous flagellates: Variability of bacterivory is discussed regarding the prevailing feeding modes, the energy budgets, the considerable importance of slight deviations in the time budgets of feeding phases, the ingestion rates and the feeding microhabitat, respectively. The significant flexibility of the grazing impact of bacterivorous flagellate communities creates a complex top-down pressure on bacteria which should have lead to the evolution of efficient predator avoidance mechanisms in bacteria and should be at least partly responsible for the diversity of present bacteria.
Phagocytosis is the process that cells have evolved to internalise large particles such as mineral debris, which they store, or apoptotic cells and pathogens, which they have the capacity to kill and degrade. However, several important pathogens can suppress these killing functions and survive and multiply within phagosomes, causing disease. Recent advances in phagosome biology have been made possible largely by a model system that uses inert latex beads. The ability to purify latex bead-containing phagosomes has opened the door to allow comprehensive biochemical analyses and functional assays to study the molecular mechanisms governing phagosome function. These approaches have led to unique insights directly relevant for the understanding of the biology of intracellular pathogens and the ways by which they subvert their hosts.
Synthetic fabric fibers have been proposed as indicators of past spreading of wastewater sludge. Synthetic fiber detectability was examined in sludges (dewatered, pelletized, composted, alkaline-stabilized) and in soils from experimental columns and field sites applied with those sludge products. Fibers (isolated by water extraction and examined using polarized light microscopy) were detectable in sludge products and in soil columns over 5 years after application, retaining characteristics observed in the applied sludge. Concentrations mirrored (within a factor of 2) predictions based on soil dilution. Fibers were detectable in field site soils up to 15 years after application, again retaining the characteristics seen in sludge products. Concentrations correlated with residual sludge metal concentration gradients in a well-characterized field site. Fibers found along preferential flow paths and/or in horizons largely below the mixed layer suggest some potential for translocation. Synthetic fibers were shown to be rapid and semi-quantitative indicators of past sludge application.
Acanthamoebae, in common with other protozoa, readily endocytose particulate material, which in turn may lead to the spread of infectious disease.
Evaluation and quantification of plain and carboxylate FITC-microsphere association with acanthamoebal trophzoites was undertaken using a combination of flow cytometry and confocal microscopy. Trophozoites from strains and species of Acanthamoeba were exposed to plain and carboxylate FITC-microspheres. Microsphere size and aspects such as trophozoite starvation, maturity, and exposure to metabolic inhibitors were assessed.
All species and strains of Acanthamoeba readily endocytosed plain and carboxylate microspheres. Starving trophozoites significantly increased binding and potential ingestion of microspheres, whereas trophozoites of increasing maturity lost such abilities. Trophozoites showed a significant preference for 2.0- and 3.0-microm-diameter microspheres when compared with other sizes, which in turn could occupy much of the cytoplasm. The physiological inhibitors sodium azide, 2,4-dinitrophenol, and cytochalasin B reduced microsphere association with trophozoites; however, some microspheres still bound and associated with trophozoites after inhibitor exposure, a manifestation of both active and inactive agent involvement in microsphere endocytosis.
Even though the origins of microsphere binding by acanthamoebal trophozoite remains shrouded, the combination of flow cytometry and confocal microscopy supported synergistic quantification and qualification of trophozoite-microsphere endocytosis.
Table 1 Research priorities for studies on microplastic effects on soil protists, ranked by importance
- M Scheurer
- M Bigalke
Scheurer, M., Bigalke, M., 2018. Microplastics in Swiss floodplain soils. Environ. Sci.
Table 1
Research priorities for studies on microplastic effects on soil protists, ranked by importance.
Research priority (ranked)
Specific questions