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A straightforward method for measuring the range of apparent density of microplastics
Abstract
Density of microplastics has been regarded as the primary property that affect the distribution and bioavailability of microplastics in the water column. For measuring the density of microplastis, we developed a simple and rapid method based on density gradient solutions. In this study, we tested four solvents to make the density gradient solutions, i.e., ethanol (0.8 g/cm3), ultrapure water (1.0 g/cm3), saturated NaI (1.8 g/cm3) and ZnCl2 (1.8 g/cm3). Density of microplastics was measured via observing the float or sink status in the density gradient solutions. We found that density gradient solutions made from ZnCl2 had a larger uncertainty in measuring density than that from NaI, most likely due to a higher surface tension of ZnCl2 solution. Solutions made from ethanol, ultrapure water, and NaI showed consistent density results with listed densities of commercial products, indicating that these density gradient solutions were suitable for measuring microplastics with a density range of 0.8-1.8 g/cm3.
... As observed in Figure 2b, the latter outcome was due to the effect of air bubbles' presence and persistence on the PVC particles' surface. A similar phenomenon was observed in a previous study carried out to determine the behavior of polyester (PES) particles in NaI-and ZnCl2-water solutions both characterized by a density of 1.3 g/cm 3 [29]. This study showed opposite results for the ZnCl2 and NaI solution with PES particles, respectively, floating and settling. ...
... This study showed opposite results for the ZnCl2 and NaI solution with PES particles, respectively, floating and settling. This was probably ascribable to the higher surface tension within the ZnCl2 solution prompting the formation of bubbles on the PES surface [29]. In order to limit the air bubbles' influence on the PVC, larger particles were used during the density separation tests. ...
This work provides a comprehensive study of a density separation treatment through sucrose solution for the removal of microplastics (MPs) from marine sediments. The theoretical determination of flotation velocities for 1.0 mm diameter spherical MPs with a density of 1.3 g/cm 3 at various solution temperatures and sucrose contents was performed. An optimal velocity of 1.03 m/h was observed with a 70% sucrose solution at 50 °C. The validation of theoretical velocities was carried out through experimental tests at optimal operating conditions for polypropylene (PP), high-density polyethylene (HDPE), polylactic acid (PLA), and polyvinyl chloride (PVC) as target MPs. The results showed an experimental floating velocity slightly lower than the theoretical predictions for PP, HDPE, and PLA. PVC, instead, characterized by a higher density than the separation solution, showed a settling velocity 42% lower than the theoretical one. Further tests were performed to assess the solid-to-liquid (S/L) ratio effect on MPs' separation efficiency. The results showed an optimal S/L of 75 kg/m 3 with 80% PVC removal and total PP, HDPE, and PLA removal. Finally, the design and cost optimization of a longitudinal settling tank were proposed for the pilot/real-scale treatment. The observed outcomes provided in-depth details useful for the development of an environmentally sustainable treatment for the preservation of marine areas.
... For example, a study introduced a portable device using a saturated ZnCl 2 solution that yields a 95.8% separation efficiency. 81 Nevertheless, ZnCl 2 may react with carbonates in the sample, leading to sedimentation, and its corrosiveness may reduce otation efficacy. 82 Furthermore, this strategy has other drawbacks, including high costs, toxicity, and environmental damage owing to waste liquid disposal. ...
Microplastics (MPs) are a class of non-degradable pollutants of global concern. MPs ubiquitously exist in the natural environment and can get inevitably transferred to the human body. Although the impacts of MPs on the ecosystem are not clearly defined yet, their toxicity to human health is becoming a concern. The complexity of MPs caused by the presence of heavy metals and organic pollution further makes it a great challenge to analyze MPs rapidly and accurately. Demanding pretreatment and insufficient data acquisition seriously hinder the precise understanding of the risk of MPs to the ecosystem and human health. Herein, this review covers recent advances in the separation of MPs, identification, and quantification methods while discussing their mechanisms and efficacy. Furthermore, this review details the use of Fourier transform infrared spectroscopy, Raman spectroscopy, and mass spectrometry for the qualitative and quantitative analysis of MPs, offering a comprehensive overview of the up-to-date strategies that overcome current technological limitations. Finally, challenges and prospective outlooks for the rapid and accurate analysis of MPs are presented.
... The black polystyrene fragments were measured using particle analysis (Image J) and had a mean ferret diameter of 24.8 ± 16.4 µm. Density of each microplastic type was estimated using dilutions of sodium iodide in deionized water according to Li et al. (2018), resulting in density ranges of 1.3-1.4 mg ml − 1 , 1.1-1.2 ...
Microplastics are increasing in marine environments worldwide, but their fate is not fully understood. Reef-building corals are suggested to serve as sinks for microplastics via active removal through ingestion and passive removal by adhesion. However, it is unknown which type of plastics are more likely to be ingested or adhered to corals and whether water flow or coral morphology affects these processes. We exposed the corals, Leptoseris sp ., Montipora capitata , Montipora digitata , and Pocillopora acuta to weathered polyester fibers, acrylic fibers, and polystyrene fragments under three unidirectional flow regimes (2.6, 5.0 and 7.5 cm s − 1 ). Adhesion rates were 3.9 times higher than ingestion rates and fibers were the dominant type of microplastics for both ingestion and adhesion. Flow significantly affected adhesion but not ingestion. Species was a significant factor for both ingestion and adhesion, but we did not find a significant correlation to morphological traits for either process. Moreover, on M. capitata , we observed higher adhesion rates on exposed skeleton than live tissue, suggesting that M. capitata actively removes microplastics from its surface and that non-living sections of reefs may also serve as an important sink for microplastic pollution. Our data revealed that processes that influence coral and microplastic interactions are complex but appear to be species-specific and are likely influenced by feeding strategies and other characteristics of corals. We also highlight the potential for non-living structures on reefs to serve as microplastic sinks.
Polymer identification of plastic marine debris can help identify its sources, degradation, and fate. We optimized and validated a fast, simple, and accessible technique, attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), to identify polymers contained in plastic ingested by sea turtles. Spectra of consumer good items with known resin identification codes #1-6 and several #7 plastics were compared to standard and raw manufactured polymers. High temperature size exclusion chromatography measurements confirmed ATR FT-IR could differentiate these polymers. High-density (HDPE) and low-density polyethylene (LDPE) discrimination is challenging but a clear step-by-step guide is provided that identified 78% of ingested PE samples. The optimal cleaning methods consisted of wiping ingested pieces with water or cutting. Of 828 ingested plastics pieces from 50 Pacific sea turtles, 96% were identified by ATR FT-IR as HDPE, LDPE, unknown PE, polypropylene (PP), PE and PP mixtures, polystyrene, polyvinyl chloride, and nylon.
Microplastic pollution is increasingly becoming a great environmental concern worldwide. Microplastics have been found in many marine organisms as a result of increasing plastic pollution within marine environments. However, the relationship between micoplastics in organisms and their living environment is still relatively poorly understood. In the present study, we investigated microplastic pollution in the water and the mussels (Mytilus edulis, Perna viridis) at 25 sites along the coastal waters of China. We also, for the first time, conducted an exposure experiment in parallel on the same site using M. edulis in the laboratory. A strong positive linear relationship was found between microplastic levels in the water and in the mussels. Fibers were the dominant microplastics. The sizes of microplastics in the mussels were smaller than those in the water. During exposure experiments, the abundance of microbeads was significantly higher than that of fibers, even though the nominal abundance of fibers was eight times that of microbeads. In general, our results supported positive and quantitative correlations of microplastics in mussels and in their surrounding waters and that mussels were more likely to ingest smaller microplastics. Laboratory exposure experiment is a good way to understand the relative impacts of microplastics ingested by marine organisms. However, significant differences in the results between exposure experiments and field investigations indicated that further efforts are needed to simulate the diverse environmentally relevant properties of microplastics.
Microplastic pollution is recognized as an emerging threat to aquatic ecosystems. One of the main environmental risks associated with microplastics is their bioavailability to marine organisms. Up to date, ingestion has been widely accepted as the sole way for the animals to uptake microplastics. Nevertheless, microplastics have also been found in some organs which are not involved in the process of ingestion. We hypothesize that the animal might uptake microplastics through adherence in addition to ingestion. To test this hypothesis, we collected mussels from the fishery farms, conducted exposure/clearance experiments and analyzed the accumulation of microplastics in specific organ of mussels. Our studies clearly showed the uptake of microplastic in multiple organs of mussels. In the field investigations, we found that the abundance of microplastic by weight but not by individual showed significant difference among organs, and the intestine contained the highest level of microplastics (9.2items/g). In the uptake and clearance experiment, the accumulation and retention of microfibers could also be observed in all tested organs of mussels including foot and mantle. Our results strongly suggest that adherence rather than ingestion led to the accumulation of microplastics in those organs which are not involved in ingestion process. To our best knowledge, it is the first time to propose that adherence is a novel way for animals to uptake microplastics beyond ingestion. This new finding makes us rethink about the bioavailability, accumulation and toxicity of microplastics to aquatic animals.
The incidence of microplastics in marine environments has been increasing over the past several decades. The objective of this study was to characterize the size and shape dependent effects of microplastic particles (spheres, fibers and fragments) on the adult daggerblade grass shrimp, Palaemonetes pugio. Grass shrimp were exposed to 11 sizes of plastic; spheres (30, 35, 59, 75, 83, 116, and 165 µm), fragments (34 and 93 µm), and fibers (34 and 93 µm) at a concentration of 20,00 particles/400 mL (= 50,000 particles/L) for three hours. Following exposure, grass shrimp were monitored for survival, ingested and ventilated microplastics, and residence time. Mortality ranged from 0-55%. Spheres and fragments under 50 microns were not acutely toxicity. Spheres and fragments greater than 50 microns had mortalities ranging from 5-40%. Mortality was significantly higher at 93 µm fibers than other sizes tested (p < 0.001). The shape of the particle had a significant influence on the number of particles ingested by the shrimp (p < 0.001). The residence time of particles in the gut ranged from 27-75 hours with an average at 43.0 ± 13.8 hours. Within the gills, the residence time ranged from 27-45 hours with an average of 36.9 ± 5.4 hours. Results from this study suggest that microplastic particles of various sizes and shapes can be ingested and ventilated by adult daggerblade grass shrimp, resulting in acute toxicity. This article is protected by copyright. All rights reserved.
The presence of microplastic (MP) in the aquatic environment is recognized as a global-scale pollution issue. Secondary MP particles result from an ongoing fragmentation process governed by various biotic and abiotic factors. For a reliable risk assessment of these MP particles, knowledge about interactions with biota is needed. However, extensive testing with standard organisms under reproducible laboratory conditions with well-characterized MP suspensions is not available yet. As MP in the environment represents a mixture of particles differing in properties (e.g., size, color, polymer type, surface characteristics), it is likely that only specific particle fractions pose a threat towards organisms. In order to assign hazardous effects to specific particle properties, these characteristics need to be analyzed. As shown by the testing of particles (e.g. nanoparticles), characteristics other than chemical properties are important for the emergence of toxicity in organisms, and parameters such as surface area or size distribution need consideration. Therefore, the use of “well-defined” particles for ecotoxicological testing (i.e., standard particles) facilitates the establishment of causal links between physical-chemical properties of MP particles and toxic effects in organisms. However, the benefits of well-defined particles under laboratory conditions are offset by the disadvantage of the unknown comparability with MP in the environment. Therefore, weathering effects caused by biological, chemical, physical or mechanical processes have to be considered. To date, the characterization of the progression of MP weathering based on powder and suspension characterization methods is in its infancy. The aim of this commentary is to illustrate the prerequisites for testing MP in the laboratory from 3 perspectives: (i) knowledge of particle properties; (ii) behavior of MP in test setups involving ecotoxicological test organisms; and (iii) accordingly, test conditions that may need adjustment. Only under those prerequisites will reliable hazard assessment of MP be feasible. Integr Environ Assess Manag 2017;13:500–504. © 2017 SETAC
Key Points
Understanding the environmental behavior of microplastic (MP) requires extensive knowledge about its physical–chemical characteristics; the relevance and implementation of an improved particle characterization for meaningful ecotoxicological testing is elaborated in this commentary. Microplastic in water bodies must be perceived as a mixture of particles with diverse characteristics, and the importance of single parameters for assessing the environmental hazard of MP will be prospected. Because MP in the environment is subject to changes due to weathering processes, the investigation of both pristine and weathered MP under controlled laboratory conditions is recommended, and challenges regarding the characteristics of weathered particles are discussed. An improved particle characterization of MP is the basis for understanding the relevant differences between well-defined and weathered as well as environmental MP and the key to interpreting ecotoxicological data and finally improving hazard assessment.
Microplastic is an umbrella term that covers many particle shapes, sizes, and polymer types, and as such the physical and chemical properties of environmental microplastics will differ from the primary microbeads commonly used for ecotoxicity testing. In the present article, we discuss the physical and chemical properties of microplastics that are potentially relevant to their ecotoxicity, including particle size, particle shape, crystallinity, surface chemistry, and polymer and additive composition. Overall, there is a need for a structured approach to the testing of different properties to identify which are the most relevant drivers of microplastic toxicity. In addition, the properties discussed will be influenced by and change depending on environmental conditions and degradation pathways. Future challenges include new technologies that will enter the plastic production cycle and the impact of these changes on the composition of environmental microplastics.
Integr Environ Assess Manag 2017;13:470–475.
Microplastics [MPs], now a ubiquitous pollutant in the oceans, pose a serious potential threat to marine ecology and has justifiably encouraged focused biological and ecological research attention. But, their generation, fate, fragmentation and their propensity to sorb/release persistent organic pollutants (POPs) are determined by the characteristics of the polymers that constitutes them. Yet, physico-chemical characteristics of the polymers making up the MPs have not received detailed attention in published work. This review assesses the relevance of selected characteristics of plastics that composes the microplastics, to their role as a pollutant with potentially serious ecological impacts. Fragmentation leading to secondary microplastics is also discussed underlining the likelihood of a surface-ablation mechanism that can lead to preferential formation of smaller sized MPs.
These test methods describe the determination of the specific gravity (relative density) and density of solid plastics in forms such as sheets, rods, tubes, or molded items. 1.2 Two test methods are described: 1.2.1 Test Method A—For testing solid plastics in water, and 1.2.2 Test Method B—For testing solid plastics in liquids other than water. 1.3 The values stated in SI units are to be regarded as the standard.
Marine microscopic plastic (microplastic) debris is a modern societal issue, illustrating the challenge of balancing the convenience of plastic in daily life with the prospect of causing ecological harm by careless disposal. Here we develop the concept of microplastic as a complex, dynamic mixture of polymers and additives, to which organic material and contaminants can successively bind to form an ‘ecocorona’, increasing the density and surface charge of particles and changing their bioavailability and toxicity. Chronic exposure to microplastic is rarely lethal, but can adversely affect individual animals, reducing feeding and depleting energy stores, with knock-on effects for fecundity and growth. We explore the extent to which ecological processes could be impacted, including altered behaviours, bioturbation and impacts on carbon flux to the deep ocean. We discuss how microplastic compares with other anthropogenic pollutants in terms of ecological risk, and consider the role of science and society in tackling this global issue in the future.