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The exponential utilization of plastics and their recalcitrant nature results in their extensive environmental accumulation, a pressing environmental problem that modern societies are currently facing. The presence of plastic waste in different environmental matrices can seriously affect life forms, ecosystems, and the economy. Furthermore, plastic wastes can break down into smaller pieces called microplastics (MPs) and nanoplastics (NPs), leading to new interactions with the environment and living organisms. Therefore, there is an urgent need to provide sustainable and cost-effective solutions for their mitigation. The first half of this review discusses the characteristics, sources, distribution, and adverse consequences of MPs and NPs. The latter half discusses mitigation strategies based on the utilization of enzymes as green catalytic tools. Enzymatic approaches outstand as effective sustainable strategies for microplastic degradation since plastic-degrading enzymes can specifically target the polymer structure for their further degradation. In addition, we have also discussed the novel approaches to enhance the performances and stability of natural enzymes including immobilization methods onto different materials and nanomaterials. Finally, possible key directions are also provided for future research considerations to find a practical, feasible, and environmentally friendly strategy to tackle the current crisis of plastic pollution.
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Green Analytical Chemistry 3 (2022) 100031
Contents lists available at ScienceDirect
Green Analytical Chemistry
journal homepage:
Environmental impact and mitigation of micro(nano)plastics pollution
using green catalytic tools and green analytical methods
María Fernanda Cárdenas-Alcaide
, José Alfonso Godínez-Alemán
Reyna Berenice González-González
a , b
, Haz M.N. Iqbal
a , b ,
, Roberto Parra-Saldívar
a , b ,
Tecnologico de Monterrey, School of Engineering and Sciences, Monterrey 64849, Mexico
Tecnologico de Monterrey, Institute of Advanced Materials for Sustainable Manufacturing, Monterrey 64849, Mexico
Micro- and nano-plastics
Green catalysis
Emerging pollutants
The exponential utilization of plastics and their recalcitrant nature results in their extensive environmental accu-
mulation, a pressing environmental problem that modern societies are currently facing. The presence of plastic
waste in dierent environmental matrices can seriously aect life forms, ecosystems, and the economy. Fur-
thermore, plastic wastes can break down into smaller pieces called microplastics (MPs) and nanoplastics (NPs),
leading to new interactions with the environment and living organisms. Therefore, there is an urgent need to
provide sustainable and cost-eective solutions for their mitigation. The rst half of this review discusses the
characteristics, sources, distribution, and adverse consequences of MPs and NPs. The latter half discusses miti-
gation strategies based on the utilization of enzymes as green catalytic tools. Enzymatic approaches outstand as
eective sustainable strategies for microplastic degradation since plastic-degrading enzymes can specically tar-
get the polymer structure for their further degradation. In addition, we have also discussed the novel approaches
to enhance the performances and stability of natural enzymes including immobilization methods onto dierent
materials and nanomaterials. Finally, possible key directions are also provided for future research considerations
to nd a practical, feasible, and environmentally friendly strategy to tackle the current crisis of plastic pollution.
1. Introduction
Plastics are polymeric materials used extensively due to their ex-
cellent physicochemical properties and industrial viability [1] . Ap-
proximately, 367 million tons of plastics were produced and dis-
tributed worldwide [2] . Plastics are low-cost, lightweight, versatile,
durable, formable, corrosion, and heat-resistant materials that have con-
tributed to the industrial development of society [3] . These plastics
are categorized based on their physical and chemical properties into
thermoplastics and thermosets that include polyvinyl chloride (PVC-
U), polystyrene (PS), polypropylene (PP), high-density polyethylene
(HDPE), low-density polyethylene (LDPE), polyethylene terephthalate
(PET), and others [4] . Plastic is widely used in the food industry as
a common material for food packaging; however more sustainable
biodegradable alternatives have been reported to reduce the harmful
eects of conventional polymeric substances [5] . Similarly, it has been
Abbreviations: COVID-19, Coronavirus disease 2019; FTIR, Fourier-transform infrared spectroscopy; GC-MS, Gas chromatography–mass spectrometry; GI, Gastroin-
testinal; HDPE, High-density polyethylene; LDPE, Low-density polyethylene; MNPs, Micro- and nano-plastics; MPs, Microplastics; NPs, Nanoplastics; PA, Polyamides;
PAC, Polyacrylic; PE, Polyethylene; PET, Polyethylene terephthalate; PP, Polypropylene; PS, Polystyrene; PVC-U, Polyvinyl chloride; SEM, Scanning electron micro-
Corresponding authors at: Tecnologico de Monterrey, School of Engineering and Sciences, Monterrey 64849, Mexico.
E-mail addresses: (R.B. González-González), ha (H.M.N. Iqbal), (R. Parra-Saldívar) .
1 These authors contributed equally to this work and should be considered equal rst authors.
reported the use of biodegradable polymers for dierent applications
such as coating for fertilizers [6] and the preparation of membranes for
biogas upgrading [ 7 , 8 ].
Despite its world usage and high value to economics, plastic has a
slow degradation rate, which represents a serious social, environmen-
tal, and economic threat [9] . The lack of eective waste management,
disposal measures, and sustainable recycling and elimination methods
of plastic has led to its accumulation in the environment [3] . These is-
sues and the unrestrained production and consumption of plastics con-
tribute rapidly to climate change [10] . Greenhouse gas emissions occur
at every stage of the plastic lifecycle (extraction, transportation, ren-
ing, and manufacturing), with estimations such as 1.7 gigatons of CO
2015 [11] . Furthermore, poor management and disposal of plastic have
led to accumulation in ecosystem matrices such as oceans, landlls, and
dumps. Marine plastic pollution destabilizes ecosystems and is detrimen-
tal to aquatic species and habitats [12] , representing a major concern for
Received 21 July 2022; Received in revised form 19 August 2022; Accepted 31 August 2022
2772-5774/© 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license ( )
M.F. Cárdenas-Alcaide, J.A. Godínez-Alemán, R.B. González-González et al. Green Analytical Chemistry 3 (2022) 100031
biodiversity. Large plastic entanglements for marine animals are widely
reported, with registries of over 350 species entangled in plastic debris
[13] . Almost 284 million metric tons of plastic garbage were generated
in 2020 and it is estimated that 12000 million tons of plastic residues
will be generated by 2050 [14] . This uncontrolled waste generation was
notable during coronavirus disease 2019 (COVID-19) pandemic, with an
overow of plastic-based packaging and medical product responsible for
a 44.8 and 13.2% increase in plastic waste [15] .
During their degradation period, plastics lose their integrity and
break down into smaller pieces and particles, raising another environ-
mental concern. These tiny particles are called microplastics (MPs) and
nanoplastics (NPs). The presence of micro and nanoplastics (MNPs) re-
sults in new interactions with the environment and living organisms.
MPs are ingested by multiple organisms, from phytoplankton to higher
tropic levels, including mammals, birds, and sh, increasing their toxic
potential and impacting the biosphere [14] . MPs also have deep im-
plications for terrestrial ecosystems. Terrestrial soils show toxicity and
environmental eects due to the contamination of soil, ora, and fauna
[16] . MPs are exposed to organisms such as earthworms, responsible for
shaping the physical properties of soils, resulting in deep implications
for the terrestrial ecosystems [17] . On the other hand, NPs represent a
higher hazard due to their size range and permeability, allowing cells
and tissues to enter more easily [16] . NPs such as polystyrene can pro-
duce DNA damage, mutagenesis, and cytotoxicity [18] . In contrast with
MPs and macroplastics, the size of NPs penetrates the circulatory sys-
tem of species such as juvenile carps, bursting biochemical responses,
and tissue lessons [19] .
The need for public awareness regarding MNPs is crucial, and reme-
diation techniques are yet to be studied and implemented. Techniques
to manage macroplastic debris have been established, such as recycling,
incineration, bioremediation, and landlls [4] . Nonetheless, there is an
opportunity area in remediation techniques for MNPs and new strategies
need to be addressed to overcome their limitations. Some common reme-
diation methods for MNPs include membrane technology, phytoremedi-
ation, biodegradation, biotechnology, and photocatalysis [18] . Physical
processes such as membrane, disc, sand, or granulated lter technologies
involve ltration, adsorption, or sedimentation of MNPs. These meth-
ods show high eciency and can be used on a large scale with excellent
results [ 18 , 20 ]. Biological degradation techniques are also suitable for
treating MNPs waste due to their low energy input, eco-friendliness, and
low carbon emission [21] . In these methods, invertebrates, and microor-
ganisms such as bacteria, algae, and fungi break down MNPs’ long car-
bon chains into simpler monomers through enzymatic degradation [22] .
Biological catalysts or enzymes promote the biodegradation of complex
plastic polymers into harmless end products, such as carbon dioxide,
water, and biomass [23] . However, the eciency of these plastic de-
grading enzymes is much lower than other remediation techniques and
new green catalysts technologies need further exploration [22] .
Understanding the characteristics, sources, pathways, environmen-
tal distribution, and harmful eects of MNPs is of great importance and
the rst approach to solving the scope of this environmental concern. At
the same time, it is worth exploring contemporary and sustainable re-
mediation techniques such as biodegradation which can mitigate MNPs
pollution. Therefore, this review seeks to analyze the characteristics of
micro and nano-plastics and present recent advances in green catalytic
tools and enzymatic technologies for the degradation of plastic polluting
2. Sources, characteristics, and distribution of micro- and
2.1. Classification, characteristics, and emission sources of micro- and
Microplastics are dened as plastics smaller than 5 mm in diameter.
Fragmentation of MPs results in the formation NPs, which encompass
sizes of 1–100 nm. MNPs are produced due to the low degradability
rate of macroplastics and other weathering conditions and pathways
( Fig. 1 ). During its lifetime, plastics encounter physical, chemical, and
biological transformations that produce micro and nano-plastics, such
as hydrolysis, photooxidation, chemical oxidation, thermal eects, and
biodegradation [24] .
MNPs can be divided into primary MNPs, which are processed plas-
tic particles, and secondary MNPs, which are plastic debris that de-
grades from large pieces of plastics. Primary MNPs originate from plastic
pellets and microbeads found in personal care products to function as
lm-forming agents, functionalized polymers, hydrophilic agents, and
silicones [25] . When plastics enter the environment, they weaken due
to exposure to UV radiation, weathering, and physical abrasion which
eventually turns large pieces of debris into MNPs. For instance, MNPs
are formed and released from the surface of the plastic through de-
lamination, which occurs when the plastic interacts with wind, waves,
and other abrasive interactions like exposure to salt [ 26 , 27 ]. Even me-
chanical recycling of plastic wastes unintentionally generates secondary
MNPs, leading to a greater pollution emission to the aquatic environ-
ment [28] . In addition, the photodisintegration caused by intense UV
radiation induces the oxidation of the polymeric matrix resulting in
serious fragmentations [22] . These oxidative processes depend on en-
vironmental factors (e.g., UV exposure, temperature, soil composition,
moisture) and plastic characteristics (e.g., chemical structure, morphol-
ogy, crystallinity) [29] .
Plastic chemical structures and stability will determine their path-
way to the environment as MNPs. Plastics like PS, PET and PVC are least
stable to photodegradation and outdoor wearing due to their atomic
structure. PET is highly susceptible to biodegradation and has a more
elevated chance of turning into MPs and NPs [26] . Physical character-
istics such as shape, density, and composition of MNPs will determine
the distribution in water bodies and terrestrial ecosystems [24] . MPs
with a lower density than water bodies such as PE, PP, and expanded
PS are more prone to appear on open water bodies (surface waters and
shores) than more dense polymers such as PVC and PET; on the other
hand, higher density MPs such as PVC and PET tend to rest in sediments,
beaches, subsurface and deep-sea waters [26] .
2.2. Occurrence of micro- and nano-plastics
The presence of MNPs has been identied in the hydrosphere,
lithosphere, atmosphere, and biosphere. This includes all major rivers,
oceans, and urban areas [14] . MNPs can be detected in most water bod-
ies, sediments, and soils and are absorbed by dierent aquatic and ter-
restrial organisms [22] . Most studies regarding MNPs pollution are con-
centrated on aquatic environments [ 25 , 30 ]. Due to human industrializa-
tion and urbanization, plastic waste ends up in the marine environment
through hydric cycles, urban waterways, sewage, and industrial wastew-
ater connected to all oceans and coastal areas [ 14 , 31 ]. Consequently,
MNPs are mostly distributed in all types of water bodies. According to
recent studies, urban streams and glaciers have the highest concentra-
tions of MPs among all water bodies as a result of transport processes
that start in urban areas [32] .
MNPs in water bodies are mainly composed of types of plastic such as
polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl
chloride (PVU-CU), which can be detected on coastal water bodies such
as beaches and rivers and deep-water bodies such as oceans, reefs, and
lakes. However, MNPs can be found throughout aquatic environments
all around the world, with dierent compositions and particle sizes
across various recent studies ( Table 1 ) [33–37] . For example, during a
recent study conducted during an Antarctic expedition, concentrations
with an average of 0.10 ± 0.14 and 1.66 ± 1.20 items/m
3 were de-
tected in surface and subsurface water samples respectively [33] . MNPs
are likely to have existed for a long time on these waters, which is at-
tributed to the accumulation of particles during snow depositions with
limitations to be washed o [32] . These samples contained varied com-
M.F. Cárdenas-Alcaide, J.A. Godínez-Alemán, R.B. González-González et al. Green Analytical Chemistry 3 (2022) 100031
Fig. 1. Sources of micro(nano)plastics waste and their pathway to the environment. Created with and extracted under premium membership.
Table 1
Occurrence of micro(nano)plastics in aquatic environments.
Location Sample type Concentration Plastic size range Composition Ref.
Antarctica Surface waters 0.10 ± 0.14 particles/m
3 0.18–4.97 mm PET, PP, PE, AC [33]
Antarctica Subsurface 1.69 ± 1.21 particles/m
3 0.14–4.99 mm PP, PET, PE, PAN, PS, PA, PVC [33]
Caspian Sea, Iran River 40 460 particles kg
1 200–5000 𝜇m PP, PA, PS [34]
Zhuhai, China Seawater 10.00 ± 27.50 particles/L 101–500 𝜇m PE, PP, PS, PVC [36]
Faafu Atoll, Maldives Reef 0.26 particles/m
3 50 𝜇m –1 mm PE, PET, PVC [35]
Fuerteventura, Spain Wastewater 4.4–40 items/L 200–400 𝜇m PES, PP, PE [37]
Abbreviations: PE (Polyethylene); PP (Polypropylene); PS (Polystyrene); PAC (Polyacrylic); PVC-U (Polyvinyl chloride); PET
(Polyethylene terephthalate).
positions that included PET, PE, and PP in their majority. Furthermore,
studies have been conducted on the occurrence of MNPs in freshwater
on continental landmasses and transitional ecosystems. These types of
water bodies are the source of plastic particles in marine ecosystems.
For example, ding a study on the Qarasu River in Iran, samples were
performed to study the excess of MPs near pollution sources [34] . The
mean abundance of MPs of 10 sampling stations was 40 460 parti-
cles/kg, ranging from 200 to 5000 𝜇m. There was a high occurrence of
plastic bers and particles composed of PP, PE, and PA.
New information regarding MNPs, and marine wildlife has also been
found. MNPs may deeply aect marine fauna from zooplankton, inverte-
brates, and larval sh to sea turtles, marine birds, and bigger sh species
[18] . Therefore, studies of marine ecosystems are crucial and coral reefs
are valuable sample locations. In a study conducted in a Maldivian coral
reef in Faafu Atoll, samples were collected from sediments and seawater
samples. Despite the remote location from local urbanization, an aver-
age concentration of 0.26 particles/m
was found [35] . Another study
was conducted to investigate MPs in seawater and oysters along the
coastline of Zhuhai, China. This study showed the relation between the
presence of MPs and their harmful eects on the aquatic fauna. The
abundance of MPs was in the range of 0.14–7.90 particles/g and 10–
27.50 particles/L in seawater [36] . The analysis of marine species and
water samples is a promising form of study to determine the level of
pollution in dierent aquatic environments.
Pollution in agroecosystems with MNPs is also of great interest due
to the alteration of biological, chemical, and physical processes and soil
ecosystems caused by MNPs. The use of wastewater, sewage sludge, and
biosolids in agriculture leads to a high microplastic loading [ 29 , 37 ].
One of the latest contributions to these studies was performed by Pérez-
Reverón et al. [37] who studied wastewater and soil samples on the vol-
canic island of Fuerteventura in Spain. After the physicochemical anal-
ysis of the wastewater samples, dierent MPs, such as bers, fragments,
microbeads, and lms were found, establishing a relationship between
MPs and wastewater irrigated soils.
2.3. Environmental distribution of micro- and nano-plastics
The environmental distribution of MNPs is inuenced by many
ecosystem components and transporting agents. The degree of MNPs
pollution is distributed between environmental systems such as air,
soil, sediments, marine water, and freshwater [38] . MNPs have spread
around the world’s oceans, from surface water to deep trenches. Fresh-
water is also a source of MNPs, as it functions as the transport medium
to all types of marine ecosystems (lakes, rivers, oceans). Tons of MNPs
circulate in the atmosphere, allowing them to reach distant locations
such as mountains, plateaus, polar regions, and even the troposphere
[3] .
M.F. Cárdenas-Alcaide, J.A. Godínez-Alemán, R.B. González-González et al. Green Analytical Chemistry 3 (2022) 100031
MNPs are accumulated in the soil, and they persist aecting biodi-
versity and organisms. Plastic particles are distributed from farmlands,
landlls, littering, atmospheric deposition, and surface runo to soil
ecosystems [39] . Leachate and landlls are important sources of MNPs
with a high abundance of MNPs in many samples. About 99.4% of MPs
in landll sites are related to plastic waste buried in landlls [40] . Other
inputs such as agricultural, urban, recreational, and industrial land con-
tribute signicantly to MNPs loads in soils and other ecosystems such as
freshwater bodies and oceans [16] . Once MNPs enter the surface soil,
they can migrate to lower and deeper soils through leaching, bioturba-
tion, dry-wet cycles, root water movements, and agricultural activities
[3] .
Plastic debris transported from land sources enter the ocean. Land-
based debris contributes 80% of ocean plastic waste with MNPs dis-
tributed around shorelines, beaches, bottom sediments, and seawater
[39] . Accumulation of plastic particles has been detected in the open
ocean from the Atlantic and the Pacic Ocean and the Caribbean and
Mediterranean Sea [38] . It is estimated that 4.85 trillion microplastics
are accumulated on the global ocean surface [3] . Wastewater is a dis-
tribution source for MNPs and most importantly for NPs. Wastewater
treatment plants receive tons of waste from municipal, industrial, do-
mestic, and stormwater sources. These wastes are not correctly treated
before they are released into fresh and sea water bodies. Not all NPs are
removed eciently at wastewater treatment stages, so they pass through
and may be released into marine environments [41] .
Atmospheric transport is another form of distribution of MNPs that
can pose a threat to fragile areas and ecosystems due to its versatility.
Human-linked activities like road trac, vehicle movement, tire fric-
tion, and road surface are major sources of atmospheric MNPs [14] . At
the same time, MNPs’ abundance is dependent on meteorological fac-
tors and dry and wet depositions that cause long-range dispersion and
transport to the surrounding environments [3] . Microplastics suspended
in the air could represent a serious human health issue and detections of
MNPs in the atmosphere of metropolitan areas show very high concen-
trations. For instance, an annual estimation of 120.7 kg of MPs is sus-
pended through Shanghai air currents [16] . MNPs have also been found
during interactions between the atmosphere and other interfaces, such
as glacial, snow, or urban dust. High concentrations of MPs have been
found in the Arctic and European snow with ranges from 0 to 154,000
particles/L [25] .
3. Harmful effects of micro- and nano-plastics
MNPs on the dierent ecosystems, such as water, air, and land, has
received attention from the scientic community because their persis-
tence can cause serious harmful eects to the environment and human
health directly and indirectly ( Fig. 2 ).
3.1. Effects on the environment
The main sources of MNPs in the ocean are river transportation and
coastal discharge. Lately, atmospheric deposition seems to be a poten-
tial source of MNPS as well. Over the years, it has been estimated that
freshwater transports between 70% and 80% of MNPs from the terres-
trial to the marine environment [42] . On the surface of water bodies,
MNPs can become habitats for viruses and bacteria due to their low
density, easy suspension, and strong hydrophobicity. When MNPS accu-
mulate microbial populations, they form microbial lms that later trans-
fer to the deep ocean. Several studies analyze the ecological toxicity of
MNPs that are frequently ingested by marine organisms. A study on crus-
taceans from China demonstrated that the ingestion of these MNPs can
cause severe risks including acute poisoning symptoms, endocrine dis-
ruption, and reproductive toxicity [ 43 , 44 ]. Bivalves, including oysters,
clams, shellsh, and mussels, have also been used as research models
because they are a key food source for humans and the food they ingest
goes directly to their digestive system. Studies on a group of blue mus-
sel larvae exposed to MNPs showed that their growth was not aected
but developed abnormal and malformed. Another investigation reported
that oysters at an exposure of 50 nm NPs decrease their fertilization
rates and embryo-larval development. Freshwater organisms also have
attracted substantial interest since humans have much more contact
with this environment. Diverse research has reported the inuence of
MNPs on their growth, development, and behavior. A study exposed Ze-
brash ( Danio rerio ) to all four common MNPs, such as polyamides (PA),
PE, PP, and PVC and the results revealed intestinal damage and split-
ting of enterocytes [44] . Plastic particles with color are commonly used
to increase the attractiveness and longevity of plastics. Numerous stud-
ies on colored MNPs proved that specic colors are more ingested by
specic marine organisms. For example, blue-colored PP and PE MNPs
were the most common color found in the stomachs of bluegill ( Lep-
omismacrochirus ) and longear sunsh ( Lepomis megalotis ). White and un-
colored MNPs were mostly found in Asian clams ( Corbicula fluminea ).
This ingestion of MNPs caused adverse eects that inevitably lead to
a decrease in their growth and reproduction, such as blocked digestive
tracts, lacerations, inammatory responses, respiration problems, false
sense of satiation or/and decient predator avoidance [42] .
MNPs are released into the atmosphere by several sources, such as
synthetic textiles (e.g., clothing, furnishings, carpeting), abrasion of ma-
terials, and resuspension of MNPs from waste, landlls, and emissions
[ 45 , 46 ]. Due to their small size and low density, plastic particles can
easily be suspended in the air. Thus, they perform as good carriers of
dierent organic pollutants in the air and transport them over long dis-
tances, followed by their wet or dry deposition on oceans, freshwater
systems, and land [ 16 , 44 ]. Comparing this migration process of MNPs
to aquatic transportation, airborne transportation has fewer topographic
limitations. Airborne MNPs are easily transported in multiple directions
and exhibit a long persistence. Recently, a trajectory analysis indicated
that approximately 218 MPs are transported for a distance up to 95 km.
An estimation of the standard daily average MPs fallout in Greater Paris
reported 118 particles/m
per day. An evaluation of Shanghai’s air re-
ported an amount of transportation of 120.7 kg of suspended MPs per
year. A research group reported a count of 44 bers, 249 fragments,
and 73 lms m
2 deposited per day in the pristine French Pyrenees
catchment. Another study revealed an important amount transported
via the atmosphere and deposited via wet deposition on the Arctic and
European snow of 0–14.4 ×10
N liter
and 0.19 ×10
0.19 ×10
154 ×10
N liter
N liter
, respectively [16] . In addition, ev-
idence has proved the presence of MNPs in high elevated glaciers of
the Tibetan Plateau. Although outdoor exposures are a major issue, in-
door exposure measures revealed daily deposition rates of 1600 11000
, depending on the indoor type and lifestyle [46] .
MNPs, as a result of fragmentation of plastic due to temperature and
photo-oxidation, contaminates soil by penetrating soil layers and mainly
come from dierent sources including recycling of sludge, wastewater
irrigation, fertilizers, landlling, biosolids, or other [ 44 , 45 ]. Recently,
the amount of MNPs that are transferred to soil exceeds the amount of
MNPs present in the ocean. The presence of MNPs aects the physic-
ochemical properties of the soil such as porosity, soil structure, water
holding capacity, soil bulk, and others. A study revealed that PP MNPs
stimulate enzyme activity and increase the amount of dissolved organic
carbon, nitrogen, and phosphorus. A similar study reported that PE and
PVC-U reduce the diversity of the bacterial community and increase
the activity of urease and phosphatase. Another research also proved
that LDPE aects the microbial communities depending on the expo-
sure time. MNPs also inuence the physiological activities of organisms
in the soil habitat and reect in growth inhibition and damage to the
intestinal and immune systems, among other adverse eects. Scientists
found that nematodes easily ingest MNPs and accumulate them in the
middle and then in other parts of the gut. Also, evidence showed that
earthworms exposed to 0.2–1.2% of PE MPs suer from inhibition in
their growth and die when exposed to a concentration of 1–2%. In addi-
M.F. Cárdenas-Alcaide, J.A. Godínez-Alemán, R.B. González-González et al. Green Analytical Chemistry 3 (2022) 100031
Fig. 2. Harmful eects of plastics on the environment and human health across their life cycle. Created with and extracted under premium mem-
tion, MNPs aect plant growth and germination, interfering with plant
roots’ uptake of water and nutrient [44] .
To get a better perspective on the impact of MNPs pollution there
are some key parameters to focus on. MNPs with a smaller size show
a greater biological impact than those have a larger size. Similarly, the
shape is also a key factor, irregular particles seem to induce more phys-
ical impact in comparison to round particles. Finally, concentration has
substantial importance in toxicological studies since in vivo and in vitro
research uses higher concentrations of MNPs than those that are in the
environment [16] . However, the distribution of MNPs on all components
of the environment and the harmful eects on living organisms need to
be further studied to accurately estimate the impact of MNPs pollution.
3.2. Effects on human health
Humans are constantly exposed to sources of MNPs, including food,
medicine, clothing, dust, and cosmetics [47] . Three primary entry routes
contribute to the total amount of MNPs present in the human body: In-
gestion, inhalation, and skin contact. Recently, direct ingestion of plas-
tic particles, especially PET, PS, and PP MNPs, has gained substantial
scientic and public attention because it is the most signicant way in
which humans consume MNPs [ 25 , 48 ]. An estimation of the number
of MNPs consumed from the average intake of food revealed that the
average annual consumption is in the range of 39 000 to 52 000 parti-
cles and including a water intake from a bottled source and tap water,
one person could be ingesting 90 000 particles and 40 000 particles
per year, respectively [49] . A recent study analyzed water samples from
popular brands of mineral bottled water and showed that nine of the
eleven brands investigated contained dierent amounts of MNPs [50] .
Similar studies have also shown direct ingestion of MNPs via the con-
sumption of alcohol, salt, sugar, honey, milk, and other food or drink
items regularly consumed by humans [
25 , 51 ]. An extensive and increas-
ing body of evidence suggests that MNPs end in diverse consumed items
via animals ingesting MNPs in the environment, contamination during
production, and/or plastic packaging [49] . Plastic particles can reach
the gastrointestinal system through contaminated food products or af-
ter inhalation through mucociliary clearance, a mechanism that involves
the movement of particles from the respiratory system. Consequently,
several biological responses can be observed, such as inammation, in-
creased permeability, and a change in the gut microbe composition and
metabolism [47] . After ingestion, particles could be absorbed through
phagocytosis or endocytosis and inltrate the microfold cells (M-cells)
in the Peyer’s patches. Many negative health concerns derive from the
absorption of MNPs, such as particle toxicity, chemical toxicity, and the
introduction of pathogens and parasite vectors. The interaction between
NPs and molecules within the gastrointestinal (GI) tract, such as pro-
teins, lipids, carbohydrates, nucleic acids, ions, and water, results in the
encompass of NPs by a collection of proteins known as a ‘corona’. PS
NPs may develop in dierent forms of complex coronas, depending on
the conditions they are in. Additionally, studies have demonstrated that
protein corona changes within an in vitro model representing human di-
gestion, improving the translocation of NPs [48] . The same mechanisms
could apply to MPs as their translocation to the circulatory system af-
ter ingestion has been proved in vivo [47] . However, the risk of direct
ingesting MNPs is not entirely known since there is very little research
reported. Most use PS nanoparticle models, excluding other main poly-
meric materials present in the environment.
The second major route of human exposure to MNPs is via inhalation.
Plastic particles in the atmosphere are in direct and continuous contact
with humans. An evaluation of MPs in the air estimated an individual in-
halation of 26–130 airborne MPs per day [47] . Even though some MNPs
inhaled may be removed by immune mechanisms such as sneezing, cilia
M.F. Cárdenas-Alcaide, J.A. Godínez-Alemán, R.B. González-González et al. Green Analytical Chemistry 3 (2022) 100031
oating, etc., the small-sized bers are extremely dicult to remove
due to their high surface area and high penetration potential [ 42 , 44 ].
In addition, the pollutants act as oxidants, causing oxidative stress, in-
ammation, and carcinogenesis [51] . A large body of evidence proves
that synthetic textile workers that are constantly exposed to small plastic
bers, such as nylon, PS, PE, and PP, are more susceptible to develop-
ing respiratory diseases and lung cancer. The risk of cancer is related
to chronic pulmonary inammation and oxidative stress [42] . Through
inhalation, MNPs may end up embedded deep into the lungs and stay on
the alveolar resulting in lung damage. The alveolar surface area of the
lungs measures approximately 150 m
and has a thin tissue barrier that
allows NPs to permeate through it, proving that they can translocate
across dierent body parts. However, the absorption of plastic particles
in the lungs depends on several factors such as hydrophobicity, surface
charge and functionalization, surrounding protein coronas, and particle
Dermal exposure is likely to be considered the least signicant route
of exposure. The potentially harmful eects of MNPs are related to the
constant dermal exposure to plastic particles, such as dust, synthetic
bers, and microbeads in cosmetics. The stratum corneum is the out-
ermost layer of the epidermis that protects the skin forming a barrier
against injuries, chemicals, and microbial agents. Considering MNPs are
hydrophobic, the absorption of contaminated water through the stratum
corneum is not expected. However, MNPs could enter the body through
hair follicles, skin wounds, or sweat glands [48] . If the skin is dam-
aged by UV rays or small tears, MNPs may be able to penetrate the
skin barrier. Studies have also shown that medical devices implanted in
the human body, including PE articulating spacers, cosmetic and dental
implants, etc., also allow MNPs particle production and their posterior
translocation to other parts of the body [42] . In addition, research has
reported that human epithelial cells can also suer oxidative stress from
exposure to MNPs. It is worth noting that there is still a lack of data on
the direct human health implications and more research should be done
in the future to fully understand the impact of MNPs on the human body
[16] .
4. Enzymes in microplastic degradation
The enzymatic degradation consists of the use of enzymes as nat-
ural biocatalysts to break down complex organic compounds such as
plastic polymers into smaller units. The resulted products are consid-
ered more benign for the environment, such as water, carbon dioxide,
and biomass [23] . The enzymatic degradation can be experimentally
detected through dierent strategies such as visual observation, plastic
properties modications, weight reduction, carbon dioxide evolution,
and chromatography, among others [52] .
Plastic-degrading enzymes have been discovered in microorgan-
isms; more than 90 microorganisms, including fungi and bacteria, have
demonstrated abilities to degrade plastic wastes in vitro environments
[53] . Considering the huge abundance of MPs and NPs in the envi-
ronment and the prodigious metabolic and genetic diversity of micro-
bial communities, dierent microorganisms have developed capacities
in plastic utilization. It is assumed that the plastic-degrading enzymes
identied to date are only a fraction of the enzymes involved in the
degradation of plastics. Thus, the research community has shown in-
creasing interest in the discovery of new plastic-degrading enzymes, us-
ing metagenomics as a tool with great potential for this purpose [54] .
The typical procedure to identify plastic-degrading enzymes follows a
culture-based approach, where target microorganisms are grown from
environmental samples and then screened for a specic activity.
Two main categories of plastic-degrading enzymes are actively im-
plicated in the biodegradation of polymer structures: extracellular and
intracellular enzymes [ 23 , 55 ]. Dierent activities have been ascribed
to each type of enzyme. The extracellular enzymes have been more
widely studied for plastic biodegradation, showing a wide variety of
functions like oxidative and hydrolytic activities. Their main role in plas-
tic degradation is during the depolymerization process, which consists
of breaking down the long carbon chains presented in complex poly-
mers into short polymer intermediates. The resultant smaller molecules
(oligomers, dimers, or monomers) can access the semi-permeable outer
membranes and be used as carbon sources by microbial cells to release
carbon dioxide [ 23 , 53 ]. The decrease in the molecular weight of the
polymeric structure is a critical process during the degradation; smaller
molecules are more easily transported through the cell membrane, and
they are suitable substrates for some enzymes than can only act on
smaller molecules.
Lipases, proteases, and cellulases are some examples of extracellular
hydrolase enzymes involved in breaking down long-chain polymers into
smaller molecules. In general, these enzymes cause hydrolytic cleavage
of the long chains forming smaller units that are easier to transport and
assimilate into the cell for subsequent enzymatic degradation and ulti-
mately the release of environmentally harmless products [56] . For in-
stance, three hydrolases presented in Flavobacterium strains were found
responsible for the degradation of nylon [57] . Similarly, Shah et al.
[58] reported Bacillus subtilis MZA-75 as a polyurethane degrading bac-
teri isolated from soil. Extracellular and cell-associated esterases were
employed to utilize polyurethane as a carbon source. MPs degradation
was demonstrated through dierent techniques including FTIR, SEM,
and GC-MS. Although evidence of mineralization of ester hydrolysis
products into carbon dioxide and water was presented, further studies
were suggested to exactly dene the biodegradation mechanism for its
eective employment in waste management [58] . Esterases have been
widely explored in plastic degradation since they can hydrolyze esters
presented in the polymeric structure or produced during previous oxi-
dation reactions [59] .
Glycoside hydrolases have also been associated with MPs degrada-
tion; Yoshida et al. [60] isolated Ideonella sakaiensis 201-F6, a novel bac-
terium able to use poly(ethylene terephthalate) as carbon and energy
source. Two enzymes were responsible for hydrolyzing poly(ethylene
terephthalate) and producing ethylene glycol and terephthalic acid,
monomers that are safer for the environment [60] . More recently, El-
sayed and Kim [61] performed lab-scale experiments to measure the
kinetic constants for the degradation of high-density polyethylene us-
ing lipase, cellulase, and protease. Dierent experimental conditions
were evaluated such as temperature and enzyme concentration. The au-
thors concluded that degradation was mainly caused by the surface’s
rapid destruction and the polymer’s shape by its collision with enzymes.
Among the enzymes tested, protease was the most ecient, whereas li-
pase showed the lowest eciency. However, regardless of the hydrolase
used, increasing the enzyme concentration and higher temperatures led
to enhanced degradation performances. The enhanced degradation of
polyethylene under thermophilic temperatures and higher doses of en-
zymes are associated with an increase in collisions between the polymer
and the enzymes [61] .
Overall, hydrolases have demonstrated an active role in the degrada-
tion of MPs presented in wastewater through their eective catalytic re-
actions. Current microbial degradation processes are slow or ineective
for complete plastic degradation. Moreover, petroleum-based plastic
usually possesses chemical and physical properties that provide higher
resistance to enzymatic degradation, hindering the action of naturally
occurring plastic-degrading enzymes. However, the extraction and ma-
nipulation of microbial enzymes are considered a valuable approach for
improving the degradation performance, being currently an important
research area [ 56 , 62 ]. Typically, microorganisms with plastic-degrading
capacities are grown in a plastic-rich media and isolated for taxonomic
identication. Enzymes are then extracted from the cultured microor-
ganisms and subjected to plastic degradation experiments. Finally, tech-
niques like mass-spectrometry can be useful to determine the sequence
of the plastic-degrading enzyme and biochemical assays to determine
the optimal conditions and specicity [52] . In this manner, the iden-
tication of plastic-degrading enzymes requires molecular biology and
M.F. Cárdenas-Alcaide, J.A. Godínez-Alemán, R.B. González-González et al. Green Analytical Chemistry 3 (2022) 100031
The catalytic eciency of plastic-degrading enzymes can be en-
hanced through protein engineering, which is a recently emerging re-
search area. Dierent strategies to maximize depolymerization e-
ciency have been explored such as: improving the enzyme thermosta-
bility, strengthening the binding of the substrate to the active site
of the enzyme, enhancing the interaction substrate-enzyme, reducing
the eect of inhibitory products/intermediates, and combining dier-
ent enzymes to form bifunctional catalysts, among others. In this re-
spect, Zhu et al. [54] have successfully summarized the most recent
advances in protein engineering applied to plastic-degrading enzymes.
The evolution of this research topic might lead to great improvements
in the utilization of microorganisms as a sustainable waste-management
Another innovative method to remove MPs and NPs consists of
the immobilization of enzymes on functional supports including dif-
ferent nano-scaled materials. This might result in greater ecien-
cies and advantageous features associated with recyclability. Dierent
nanoparticle-enzyme complexes can be formed with variations in their
properties and performance. In this context, inorganic nanoparticles
have demonstrated great potential as enzyme support due to their high
surface area and well-dened pore distribution and geometry, which in
turn allow higher enzyme loadings [23] . Recently, Schaminger et al.
[63] immobilized a PET-degrading enzyme (PETase) on superparamag-
netic iron oxide nanoparticles. The immobilization was performed via
His-tag increasing enzyme stability and allowing high loads of PETase.
Immobilization on magnetic support enabled a simple magnetically re-
covery. Moreover, reusability tests suggested that the catalytic system
maintained approximately 50% of the initial catalytic activity after 10
cycles [63] . Similarly, Jia et al. [64] immobilized PETase enzyme de-
rived from Ideonella sakaiensis onto cobaltous phosphate nanoparticles.
Their results demonstrated that using nanostructures as supports fa-
vored the stability of the enzyme; the immobilized enzyme exhibited
75% of the initial eciency after 12 days, which was much higher than
the one presented by the free enzyme. The remarkable better stability
and performance towards the degradation of PET by the immobilized
enzyme system was attributed to the unique nanostructure (nanoow-
ers) of the support [64] .
Dierent enzymes have been also immobilized on inorganic nanos-
tructures. For instance, Krakor et al. [65] immobilized lipase and cuti-
nase on SiO
nanoparticles and Fe
nanostructures via co-
valent bonding. The prepared catalytic systems showed high stabil-
ity and eciency to degrade polycaprolactone. On the other hand,
carbon-based materials have also presented potential as support for
plastic-degrading enzymes. Hegde and Veeranki [66] immobilized
two recombinant cutinases on chitosan beads due to the abun-
dant and biocompatible nature of chitosan. Immobilization was per-
formed through covalently coupling with glutaraldehyde, showing
more than 70% of immobilization under optimal conditions. More-
over, reusability tests after 10 cycles showed 80% of eciency,
demonstrating chitosan as a candidate to assist in enzymatic catalysis
[66] .
Carbon-based nanomaterials are receiving increased research inter-
est because of their additional benets including higher surface area,
easy surface modication, and stability. In this respect, carbon nan-
otubes have been explored to attach dierent enzymes aimed to de-
grade dierent pollutants such as dyes [ 67 , 68 ]. Fewer studies related to
immobilized enzymes on carbon-based nanomaterials were found. As a
representative example, Costa et al. [69] evaluated the degradation of
4-methoxyphenol used as a plastic additive by immobilizing laccase on
functionalized multi-walled carbon nanotubes. Carbon nanotubes were
modied using dierent strategies to increase the immobilization e-
ciency; the best results were obtained from carbon nanotubes oxidized
with nitric acid due to the higher content of surface groups containing
oxygen. Under optimal conditions, the laccase-carbon nanotubes com-
plexes showed excellent immobilization eciency (100%) and stability
at high temperatures.
5. Analytical methods to analyze MNPs
For proper mitigation of MNPs from dierent environmental matri-
ces, highly eective and robust analytical-based detection methods are
of supreme interest. Classically, the rsthand identication and quanti-
cation of plastic-contents persistence in water bodies is done by visual
inspection for MPs [70] , which sometimes fails to detect MNPs. Thus, it
is important to establish and follow biotechnological advances to iden-
tify and characterize plastic-contents persistence at nanoscale to moni-
tor MNPs at large and NPs, in particular. There are several steps involved
prior to reach the detection of MNPs, for instance, (a) sampling, (b) ex-
traction and/or cleanup, and (c) determination [ 71 , 72 ]. Owing to the
diverse variations, such as sampling matrices, MNPs occurrence level,
sample preconditioning and/or pretreatment, detective tools, several in-
practice analytical methods are not coherent in their handling and detec-
tion mechanisms. However, all chemical and physical detection meth-
ods share the basic handling measures and characteristic procedures
with the same central skeleton. Considering the above-mentioned vari-
ations, results also vary in each adopted method. Fig. 3 shows a funda-
mental overview of dierent sampling routes, treatment, and detection
procedures [71] . Various techniques, including visual detection though
microscopy (light), SEM, FTIR, Raman spectroscopy, atomic force mi-
croscopy based infrared spectroscopy, ow cytometry, matrix-assisted