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Recently, studies on microplastics (MPs) have increased rapidly due to the growing awareness of the potential health risks related to their occurrence. The first part of this review is devoted to MP occurrence, distribution, and quantification. MPs can be transferred from the environment to humans mainly through inhalation, secondly from ingestion, and, to a lesser extent, through dermal contact. As regards food web contamination, we discuss the microplastic presence not only in the most investigated sources, such as seafood, drinking water, and salts, but also in other foods such as honey, sugar, milk, fruit, and meat (chickens, cows, and pigs). All literature data suggest not-negligible human exposure to MPs through the above-mentioned routes. Consequently, several research efforts have been devoted to assessing potential human health risks. Initially, toxicological studies were conducted with aquatic organisms and then with experimental mammal animal models and human cell cultures. In the latter case, toxicological effects were observed at high concentrations of MPs (polystyrene is the most common MP benchmark) for a short time. Further studies must be performed to assess the real consequences of MP contamination at low concentrations and prolonged exposure.
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Microplastics in the Environment: Intake through the Food
Web, Human Exposure and Toxicological Effects
Concetta Pironti 1, , Maria Ricciardi 1 ,† , Oriana Motta 1 ,* , Ylenia Miele 2, Antonio Proto 2
and Luigi Montano 3, 4,*
Citation: Pironti, C.; Ricciardi, M.;
Motta, O.; Miele, Y.; Proto, A.;
Montano, L. Microplastics in the
Environment: Intake through the
Food Web, Human Exposure and
Toxicological Effects. Toxics 2021,9,
Academic Editors: Andreu Rico and
Roberto Rosal
Received: 31 July 2021
Accepted: 14 September 2021
Published: 16 September 2021
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1Department of Medicine Surgery and Dentistry “Scuola Medica Salernitana”, University of Salerno,
Via S. Allende, 84081 Baronissi, Italy; (C.P.); (M.R.)
2Department of Chemistry and Biology, University of Salerno, Via Giovanni Paolo II, 84084 Fisciano, Italy; (Y.M.); (A.P.)
3Andrology Unit and Service of Lifestyle Medicine in UroAndrology, Local Health Authority (ASL) Salerno,
Coordination Unit of the Network for Environmental and Reproductive Health (Eco-FoodFertility Project),
“S. Francesco di Assisi Hospital”, 84020 Oliveto Citra, Italy
4PhD Program in Evolutionary Biology and Ecology, University of Rome “Tor Vergata”, 00133 Rome, Italy
*Correspondence: (O.M.); (L.M.); Tel.: +39-089-963-083 (O.M.)
These authors contributed equally to this paper as first authors.
Recently, studies on microplastics (MPs) have increased rapidly due to the growing
awareness of the potential health risks related to their occurrence. The first part of this review
is devoted to MP occurrence, distribution, and quantification. MPs can be transferred from the
environment to humans mainly through inhalation, secondly from ingestion, and, to a lesser extent,
through dermal contact. As regards food web contamination, we discuss the microplastic presence
not only in the most investigated sources, such as seafood, drinking water, and salts, but also in
other foods such as honey, sugar, milk, fruit, and meat (chickens, cows, and pigs). All literature data
suggest not-negligible human exposure to MPs through the above-mentioned routes. Consequently,
several research efforts have been devoted to assessing potential human health risks. Initially,
toxicological studies were conducted with aquatic organisms and then with experimental mammal
animal models and human cell cultures. In the latter case, toxicological effects were observed at high
concentrations of MPs (polystyrene is the most common MP benchmark) for a short time. Further
studies must be performed to assess the real consequences of MP contamination at low concentrations
and prolonged exposure.
microplastic; nanoplastic; environment; food web; human exposure; toxicological effects
1. Introduction
Plastics are widely employed in many applications, ranging from food packaging
to technological devices and disposable medical equipment, thus making them present
in everyday human life. However, the consequential human exposure to microparticles
derived from plastic materials could have, over time, harmful effects. In literature, a
large number of studies are dedicated to the transport of microplastics in the food web
through air, water, and soil environments; their persistent nature can be very toxic to
humans. Plastic debris is defined as microplastics (MPs) by the National Oceanic and
Atmospheric Administration (NOAA) when the particles have a diameter lower than 5 mm.
The classification of microplastics is also based on their source: microplastics are defined
as primary if released intentionally in the environment and secondary if they are released
indirectly by deterioration processes. Microbeads and abrasives in personal care products
and cleaning formulations are examples of primary MPs intentionally included in products
and used in the manufacturing of plastic materials [
]. Secondary microplastics can derive
from the deterioration, fragmentation, or improper disposal in the environment of large
Toxics 2021,9, 224.
Toxics 2021,9, 224 2 of 29
pieces of plastic, such as plastic films, household garbage, atmospheric deposition, and
vehicle emissions [
]. Mixtures such as paints can release both primary and secondary
microplastics: primary when the paint is in its fluid form and secondary if small particles
detach from the dried paint (for example, fragments of ships and boats) [5].
Microplastics can have different shapes (fibers, fragments, spheres, beads, films, flakes,
pellets, and foam) depending on the original form of the plastics, the deterioration processes
occurring on the plastic surface, and the residence time in the environment [
]. The
potential of microplastics to cause physical harm to organisms is affected by their size and
shape [
]. In fact, although large microplastics are not taken up by most plants and soil
organisms, small particles (e.g., nanoplastics) can be easily taken into cells, thus generating
an environmental risk [10,11].
Concerning plastic shape, some studies suggest that fibers are more toxic on ma-
rine invertebrates with respect to fragments and spheres having the same polymer ma-
trix [
]. In addition to petroleum-based plastic fibers, man-made cellulose fibers (e.g.,
viscose/rayon) have also been detected in different environmental matrices (deep-sea
sediment [
], macroinvertebrates [
], fishes [
]), thus increasing the interest of the
scientific community in this kind of plastic pollution, which is usually underestimated. This
type of fiber is biodegradable in the natural aquatic environment, so it is not considered
an environmental issue in itself. However, the additives it contains may be harmful to
aquatic organisms.
In fact, the presence of organic and inorganic additives and traces of monomers, met-
als, or other compounds that can be released represents a more toxic source of pollution for
human health than the MP fragments themselves [
]. For example, chemicals such
as bisphenol A [
] and phthalates [
] are often found in association with microplastics;
these endocrine disruptors can be very hazardous for humans [
]. Other adverse
effects on the environment derive from the fact that the MPs can also act as vectors for other
contaminants [
] (e.g., potential human pathogens [
], organic pollutants [
], heavy
metals [
]). In fact, the adsorption of persistent organic pollutants (POPs), mainly poly-
cyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated
diphenyl ethers (PBDEs), and dichlorodiphenyltrichloroethane (DDT) on microplastics
has been reported [
]. Trace elements were found in combination with microplastics
in the marine zooplankton of the Mediterranean Sea. Aluminum, iron, chromium, zinc,
nickel, molybdenum, manganese, lead cobalt, and copper were found at concentrations
of mg/kg while arsenic, vanadium, rubidium, and cadmium at level of µg kg1[30]. The
levels of aluminum, copper, and zinc registered were comparable with the values found in
microplastics collected in England and Brazil, while the levels of iron and manganese were
lower in the samples collected in the Mediterranean Sea [3133].
Microplastics may concentrate in the human body through various exposure pathways
(see paragraph on “Implication of microplastic contamination on human health”), such
as inhalation of dust and direct consumption of food contaminated by microplastics. In
fact, the maximum estimated intakes of microplastic from dust ingestion for adults and
children are about 1000 and 3000 particles per year, respectively [
]. At present, knowledge
of the effects and toxicity of microplastics to humans is very limited, and the research
on the trophic transfer of microplastics in the food web to humans is key to preventing
microplastic contamination problems.
This review covers some environmental routes (water, air, and soil) of microplastics
contamination into the food web, describing their effects on human health, and presents
new and relevant studies on their occurrence, fate, and behavior.
2. Methodology
The authors thoroughly reviewed the literature related to microplastics, finding that
current research is predominantly focused on environmental contamination rather than
human health interactions. This review went through under a three-pillar approach: (1) de-
lineation of the urgency and seriousness of microplastics in the food web by emphasizing
Toxics 2021,9, 224 3 of 29
the various ways that microplastics interact with the human body; (2) impacts of microplas-
tics on water, air, and soil properties through multiple aspects, as well as the potential
risks when dispersed into other environment media, transferred along the food chain, and
accumulated by animals, plants, and humans; (3) determination of contamination and
accumulation of MPs in water, soil, air, and food, particle toxicity, and the proposal of
future research directions according to the existing literature. The keywords “microplas-
tic”, “environment”, “food web”, “human exposure”, and “toxicological effects” were
selected individually or jointly to search for relevant information on Web of Science, Sco-
pus, and Google Scholar. Key literature published between 2004 and 2021 (up to June) were
assimilated and analyzed.
3. Occurrence, Analysis, and Abundance of Microplastics in the Environment
Microplastic pollution was first observed in the marine environment: in the 1970s,
spherules, disks, and pellets were detected on the surface of the Sargasso Sea [
], on the
coasts of New England [
], in the surface waters of the Atlantic Ocean [
], and in the
surface waters of the Pacific Ocean [
]. Recently, the attention of researchers has moved to
wastewater, rivers, and lakes [
]. Due to the increasing interest in this field, several
review articles [
] were published in the last few years, with the aim of giving an
overview of microplastic presence in different water matrices all over the world, analytical
methods for their detection, and possible consequences to human health [
]. The
occurrence of microplastics in the water environment was widely discussed in our recently
published review, which focused on their abundance in different water matrices and their
distribution worldwide [
]. In contrast, the present review mainly deals with the transport
of this contaminant to humans through the food web, with only an introduction of the
pollution of the different environmental compartments.
As regards the origin of MP contamination in water environments, the main sources
are improperly disposed plastic wastes from land and, to a lesser extent, derivatives from
marine activities, such as the fishing industry employing plastic equipment [
]. The
fragmentation of plastic debris in water leads to the contamination of aquatic species
through active and passive intakes, with consequent transfers within the food web [54].
More recently, microplastics have been recognized as air pollutants [
]. Alongside
other atmospheric contaminants such as nitrogen oxides [
], hydrogen sulfide
carbon dioxide [
], persistent organic pollutants [
], and BTEX [
], their concen-
tration should be regularly monitored to ensure human safety. Several studies have shown
that atmospheric microplastic particles can be carried to remote areas by atmospheric events
such as winds [
], ocean currents [
], river outflow, and drift [
]. Airborne
MPs may be deposited in aquatic environments and soils via dry or wet deposition [
with a consequent spatial distribution and temporal variability of their abundance [
As a consequence, microplastics have been detected even in remote areas such as the
Antarctic and the South Indian Ocean.
The estimated amount of annual plastics discharged to the soil is much higher than
that released in the oceans [
], so the terrestrial environment can be considered an impor-
tant sink for microplastics [
]. However, microplastic pollution in the soil environment
has been largely overlooked for several years [
], gaining attention since 2012, when
Rilling [
] identified the possibility of microplastic occurrence in the terrestrial environ-
ment and the need for studies for their estimation. The low number of investigations
is probably due to the unavailability of suitable analytical methods for microplastics in
soils [
]. Plastic mulch films, compost and municipal solid waste, biosolids such as anaer-
obic digestate and sewage sludge, irrigation and flooding of wastewaters, atmospheric
deposition, illegal dumping of waste, and plastic-coated fertilizers represent the principal
sources of microplastics in soil [81,8892].
The collection and treatment of samples are the most important steps to obtaining
a satisfying determination of microplastic pollution without contamination. Different
sampling techniques are required according to the type of environmental matrix considered.
Toxics 2021,9, 224 4 of 29
For the water compartment, the main sampling methods are sediment recovery from the
seafloor, beaches, and estuaries, beachcombing for the shoreline, observation by divers, use
of marine trawls to collect particles within the water column, and examination of plastic
fragments ingested by marine organisms [2,7].
Regarding atmospheric microplastics, most of the studies have employed a passive
sampling of deposited material [
], while only a few studies have used active sam-
pling [9698], often in comparison with passive ones.
The two sampling methodologies provide different information regarding microplas-
tics in the air. In particular, passive samplers give an estimation of the number of deposited
microplastics onto the surface of a certain place during a specific time-lapse, while active
devices return the number of microplastics in the air mass that may not be deposited [99].
Once sampling has been carried out, the analysis of MPs can be done through several
procedures such as separation, identification, and quantification. Sieves usually achieve the
first step of microplastics separation, with mesh sizes ranging from 0.038 to 4.75 mm and
filters with small mesh sizes (0.02–5
m) [
]. For small particles (dimensions < 1
many studies have reported the use of active (e.g., field flow fractionation technique) [
and passive separation (e.g., chromatographic techniques such as hydrodynamic chro-
matography) [103,104].
Particle visualization, as well as the evaluation of color, shape, and light transmission,
is important for identifying microplastics in sample materials or debris (e.g., shell fragments,
algae, sand, and glass) [
] and distinguishing plastic from non-plastic particles [
]. Large
microplastics (1–5 mm) are identified with the naked eye, and an optical microscope can
be used for smaller microplastics to obtain images for analysis, which provide the shape
and number of the microplastic particles. More advanced techniques, such as SEM-EDS
(scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy) [
were recently reported in the literature to characterize the morphology of ultra-small
plastic particles and facilitate the differentiation of microplastics from other plastic-like
particles [
]. Lastly, the characterization of samples in terms of chemical composition,
i.e., polymer type, is mainly performed by FT-IR (Fourier transform infrared spectroscopy)
and Raman spectroscopy [
]. These are useful techniques for identifying the polymeric
composition of microplastics of different types (with sizes
m) since they require
small sample amounts and limited sample preparation. Moreover, these spectroscopies are
complementary vibrational techniques. Generally, signals with strong IR intensity have
weak Raman intensity and vice versa. For instance, carbonyl groups, being polar functional
groups, are well detected by IR, whereas aromatic bonds and double bonds are better
identified using Raman [109].
The analytical techniques described in this section are used for the identification
of microplastics in all the environmental compartments, i.e., water, air, and soil. The
quantification of MPs is still a great challenge due to their special chemical and physical
properties (very high molecular weights, poor solubility in most solvents). Although
new accurate and sophisticated analytical methods have been reported for microplastic
detection and characterization, FT-IR and Raman spectroscopy remain the most commonly
used for identifying the polymeric composition of microplastics, accompanied by visual
characterization through optical microscopy.
4. Microplastic Transport in the Food Web and Consequent Human Exposure
As reported above, microplastics can be generated through several mechanisms and can
be transported across different environmental compartments, reaching the food web and,
finally, the human body. Figure 1shows the main pathways of food contamination through
soil/water/atmosphere. Human ingestion of contaminated food and beverages is a con-
cern [
], even if it seems to be unappreciated compared to environmental implications.
Toxics 2021,9, 224 5 of 29
Figure 1. Scheme of food web contamination due to MP pollution.
In this paragraph, we discuss peer-reviewed papers on MP contamination in edible
animal species (seafood and chicken) and food samples such as salt, sugar, honey, milk,
fruit, soft drinks, and drinking water.
Food and beverage samples must be pretreated to avoid large errors in the results.
For example, drinking water samples were filtered, in parallel, through stainless steel
filters [
]. A flowmeter was connected to all the outlet tubes of the filtration units to
quantify the volume of filtered water. At each sampling position, the setup was primed for
ten minutes prior to applying filters. Finally, the filters were transferred to glass Petri dishes,
covered with 70% ethanol, and stored at
C until further processing. Salt samples can
be treated with hydrogen peroxide to digest possible organic content [
]. Fish samples
can be caught using different types of gear and transported to fishing harbors in ice chests
and later transferred to another ice chest and stored at
C before the analysis [
Similarly, chicken feces and other food samples are frozen before the analysis to avoid
decomposition [115].
Sometimes fishes and mussels are collected from the sea and kept alive to study how
they interact with MPs. In these cases, they can be held in fiber-glass tanks with artificial
seawater to acclimatize to laboratory conditions, and then microalgae or shrimps are added
to feed the animals [116,117].
Once the exposure time is completed, it is necessary to extract the MPs and remove
fats, proteins, sugars, and other substances through digestion with acids, alkali, oxidizing
agents, and enzymes. Sometimes, multiple digestion steps are required to improve the
analysis. The analytic techniques for particle characterization and chemical composition are
the same discussed in the paragraph “Occurrence, analysis, and abundance of microplastics
in the environment”.
4.1. Seafood
The marine environment is the most studied system for MP contamination, and sea
products (e.g., wild animal species, algae, sea salts) [
] are one of the primary sources
of food for humans [
]. Consequently, several studies have investigated microplastic
occurrence and abundance in marine species, expressing MP concentration as the number
of particles/g or particles/individual [
]. There are two different mechanisms to
describe how MPs reach the organs of fish. MPs may be captured actively (by confusion
with prey), passively (e.g., gill water filtration), and through the ingestion of contaminated
prey [139].
Shellfish (including crustaceans and bivalves) and other fish species are often con-
taminated with microplastics. Microplastics were detected in the 25 species contributing
Toxics 2021,9, 224 6 of 29
most to global sea fishing, including the Atlantic cod (Gadus Morhva), the European hake
(Merluccius Merluccius), the red mullet (Mullus Barbatus), and the European pilchard (Sar-
dina Pichardus) [
]. Miranda and Carvalho-Souza [
] also found microplastics in the
digestive tract of two important species of edible fish (Scomberomorus Cavalla and Rhizo-
prionodon LandII) from the Brazil’s eastern coast, although, in some cases, this would not
be a big health concern as the GI tract is discarded during processing. However, scientific
studies have analyzed the accumulation of microplastics in other species such as D. Labrax,
T. Trachurus, and S. Colias specimens from Portuguese coastal waters [
]. In this case,
a different amount of plastic debris that could be explained by various mechanisms of con-
tamination (passive, active, and through contaminated prey) was observed for each species.
S. Colias showed a higher percentage of microplastic contamination in the gastrointestinal
tract (62%) than the other species (42%), probably due to some distinct ecological features
(e.g., time spent in areas closer to shore, feeding ecology) and physiological differences
(e.g., water filtration rates, elimination processes) [114].
Among the 150 fishes analyzed, the percentage value obtained of 35% is comparable
to the corresponding values reported in the literature: 19.8% of 263 fishes from Portuguese
coastal waters, 38% of 120 fishes from the Monolego River estuary in Portugal, 58% of 1337
fishes from the Mediterranean Sea, and 65% of 178 fishes from the Red Sea [
]. In the
Persian Gulf, a wide variety of pelagic and benthic species was investigated: about 128
marine organisms, divided into 3 fish species, 1 prawn species, and 1 crab species. The
results found that the MPs were located in the muscles and gills of the individuals [
In this case, the adsorption in muscles could show toxicological effects since all particles
were equally transferred to the next level of the food web. Microplastic fibers were recently
detected on the external surface and in the gastrointestinal tract of clupeid fishes (larval and
juvenile stages) from the Mediterranean Sea, i.e., Sardina pilchardus (0.53 items/specimen)
and Engraulis encrasicolus (0.26 items/specimen). Since these clupeids are among the main
food sources for several marine species, these results give rise to concern relating to the
possible transfer of microplastics through the marine food web and into humans [109].
The uptake of MPs is also influenced by the chemical and physical composition of
water, in particular by salinity. A study of fishes in the Saudi EEZ of the Arabian Gulf,
based on 15 individuals of Lethrinus nebulosus, 20 Gerres acinaces, 20 Siganus canaliculatus,
6Liza parsia, 10 Scomberomorus commerson, 20 Euthynnus affinis, 20 Epinephelus coioides,
20 Rastrelliger kanagurta, and 9 individuals of Carangoides malabaricus, indicated that only
5.71% of samples ingested MPs. The lower value is probably due to the presence of
microplastics in the sea surface microlayer and, consequently, less availability for ingestion
by fishes [
]. In the marine food web, consumers or predators can ingest MPs through
prey items such as polychaetes, mollusks, small crustaceans and arthropods, annelids,
and fish larvae. So even though the gastrointestinal tract is discarded during processing,
the presence of MPs in the gastrointestinal tract of marine organisms has raised concern
worldwide as seafood can be a significant source of MPs in humans [
]. A study on
the gastrointestinal tracts of tiger shrimp (P. monodon) and brown shrimp (M. monocerous),
commercially important shellfish species of Bangladesh, evaluated the presence of MPs
averaging 3.40
1.23 and 3.87
1.05 particles/g of the gastrointestinal tract; FTIR data
confirmed particles of polyamide-6 and rayon polymers, the common raw materials of
ropes, fishing nets, floats, fish baskets/bags, and coatings used in the sea [147].
Moreover, the contamination of MPs involved not only fish from the sea; this could be
a warning for freshwater fishing and fish farming industries to introduce more controls.
Cultured organisms can be exposed to high levels of MPs, as evidenced by the analysis of
fish meals from three different Malaysian commercial brands [
]. In the study, a total of
336 particles was isolated, and 64.3% were identified as MPs; micro-Raman spectroscopy
confirmed that the most abundant isolated polymer was PE (63.0%), followed by PP (27.8%),
PET (8.8%), and NY (0.4%).
A useful tool for quantifying the level of microplastic contamination within the fresh-
water food web is stable isotope analysis [
]. This technique measures the relative
Toxics 2021,9, 224 7 of 29
abundance of stable isotopes, giving an isotopic ratio, expressed as
], and
providing information about the origin of a sample [
]. It has been widely used in
food analysis [
], medical diagnostics [
], monitoring of air quality [
], and
characterization of commercial cleaning products [
]. It has been recently employed to
evaluate the presence of microplastics [
] and to discriminate between polymer sources
(petroleum and plant-derived) [
]. The carbon stable isotope ratio (
C) and nitro-
gen stable isotope ratio (
N) were used to quantify trophic niches for macroinvertebrates
and fish within the Garonne River. The abundance of ingested microplastics varied be-
tween macroinvertebrates and fish and was not significantly related to pollution; moreover,
it increased with the size of organisms and was affected by the origin of the resources
consumed by fish. The authors assert that results of isotopic analysis suggest the absence
of microplastic bioaccumulation in freshwater food webs and the dominance of direct
(accidental) consumption; therefore, the stable isotopic ratio is very useful for a deeper
understanding of microplastic ingestion by wild organisms [149].
These studies will not only be beneficial to understanding the distribution and migra-
tion of microplastics in marine ecosystems but also provide an important reference for the
protection and governance of seafood.
4.2. Salt for Human Consumption
In the last few years, several studies regarding the microplastic contamination of salt
intended for human consumption [
] have been published and discussed [
Salts provide essential nutrition elements and, thanks to their chemical characteristics and
low cost, are used in food preservation methods (e.g., fruits, cheese, cereals, drinks). Other
uses for salt, for example, are in the cosmetic and personal care product industry and the
pharmaceutical industry (as an additive, stabilizer, and thickener).
MPs have been found in the commercial salts of 128 brands from 38 different sources in
numerous countries spanning over five continents in the period 2015–2018 [
]. MP abun-
dance in table salt was different among the countries under study: the lowest values were
detected in China (600 particles/kg) [
] and the United States
(800 particles/kg)
while higher values were discovered in Italy (8000 particles/kg) [
], Indonesia
(10,000 particles/kg)
], and Croatia (20,000 particles/kg) [
]. The particles iden-
tified in sea salt were made of cellulose, cellophane (CPH), polyethylene-vinyl acetate
(PEVA), PA, polyacrylonitrile (PAN), polyalkene, poly(1-butene), PET, poly(metylacrylate),
PP, phenoxy resin (PR), polyurethane (PU), polyvinyl chloride (PVC), and paraffin wax.
The results of a meta-analysis [
] proved that the microplastic content in salt strongly
depends on its origin; in particular, sea salt is the most contaminated, followed by lake salt,
rock, and well salt. The microplastic contamination of salts can derive from the alteration of
larger plastic pieces through biological, photo, and/or mechanical degradation in the envi-
ronment or from the direct input of particles from industrial processes and the manufacture
of a wide diversity of everyday-use products. The high amount of microplastics in sea salt
derives from the fact that it is produced from the evaporation of seawater, which often
contains harmful microplastics. Hence, recently, a coagulation process was developed for a
clean sea salt production by removing microplastics from seawater, showing interesting
results [175].
Consequently, maximum human exposure is estimated to be 6110 microplastic par-
ticles per year, confirming salt as a microplastic carrier. To illustrate human risk, several
authors estimated the annual consumption of microplastic particles through sea salt. The
values are 37 [
], 64–302 [
], 40–680 [
], 510 [
], and 1000 particles [
] based on
human ingestion of 5 g of salt per day, the recommended intake threshold by the World
Health Organization [
]. However, the actual salt intake can be much higher (10 g/day
worldwide [
]) than the recommended one, thus increasing the human ingestion of MPs
derived from salt.
Toxics 2021,9, 224 8 of 29
4.3. Drinking Water
Freshwater bodies are the predominant drinking water source for human consump-
tion. In literature, some scientific papers introduced the role of potable water as a suspect
potential source of MPs [
]. The presence of fibers in surface water is, therefore, pre-
sumably caused by the inflow of sewage water. Freshwater has been shown to contain PE
and PP, comprising up to>90% of MPs in drinking water, and also PET, PS, PVC, polyester
(PES), PA, polytetrafluoroethylene (PTFE), and RY, the materials commonly used in various
products, in particular, food and cosmetic packaging, houseware, and toys [
]. Some stud-
ies analyzed water samples in Germany, including raw water, drinking water, tap water,
and bottled water [
]. Water samples taken at different positions within the drink-
ing water supply chain (raw water and drinking water) have shown an average microplastic
concentration of 700 particles/L (range 0–7000 particles/L) [
]. The detected microplas-
tic particles were small fragments (size range 50–150
m) of polyester, polyvinylchloride,
polyethylene, polyamide, and epoxy resin, probably introduced during drinking water pu-
rification and transport. Other authors have investigated microplastic abundance in bottled
water from diverse packages (single-use plastic bottles, reusable plastic bottles, beverage
cartons, and glass bottles); however, no statistical differences were observed among sam-
ples [
]. Microplastics in the size range of 5–100
m were detected in concentrations
from 11
8 (beverage cartons) to 118
88 (returnable plastic bottles) particles/L [
]. In
contrast, a higher microplastic amount in mineral water from reusable PET bottles (average
5432 microplastics/L) compared to single-use PET bottles (
2649 ±2857 particles/L)
and also a high microplastic content
(3074 ±2531 microplastics/L)
in glass bottles were
observed in the size range of 1–5
m [
]. Microplastic abundance in raw and treated wa-
ter was determined from three drinking water treatment plants in urban areas of the Czech
Republic [
]. Microplastic content was significantly lower in treated (from
338 ±76
28 particles/L) compared to raw water (from 1473
34 to 3605
497 particles/L),
and most of the particles were within the size range of 1–10 µm.
The detected microplastic concentrations in treated water are not negligible and
suggest that potable water could be an important source of microplastics to humans.
Recently, the World Health Organization [
] has reported that the microplastic content
in tap water is about 5 particles/L, with a consequent daily dose of microplastics of
10 particles, considering a human water intake assumption of 2 L/day [
]. A significant
increase in the amount of microplastic intake must be considered in individuals who drink
water only from plastic bottles compared to those who consume only tap water (additional
90,000 annual microplastic particles compared to 4000).
4.4. Soft Drinks
Beverages intended for human consumption are divided into groups of alcoholic and
non-alcoholic drinks. Beers, wines, and spirits are classified as common alcoholic drinks,
while non-alcoholic drinks include tea, coffee (hot and cold), soft drinks, milk, chocolate,
carbonated, and non-carbonated sweetened drinks.
In Mexico [
], a total of 57 beverage products, including cold tea, soft drinks, energy
drinks, and beers, was investigated to develop baseline data on the levels of MPs. Chemical
characterization results allow for the distinction of different forms of MPs (fibers and
fragments) and various sizes of 0.1–3 mm with different colors (blue, red, brown, black,
and green). The chemical nature of MPs obtained by micro-Raman spectroscopy indicated
contamination from synthetic textiles and packaging in the beverage products; indeed, the
particles identified were PA, poly(ester amide), acrylonitrile, butadiene, styrene, and PET,
the most common raw materials of these commercial products [
]. A possible source of
contamination could be the water used in the bottling industry production of soft drinks,
which comes from various supply sources: groundwater, surface water, a public water
network, or rainwater [
]. Considering that the international market of drinking water
has an annual volume of over 245 billion liters, small quantities of MPs in drinks can also
have harmful effects on human health due to accumulation and interaction with other
Toxics 2021,9, 224 9 of 29
compounds. An appropriate study
in vivo
is necessary to preserve and understand all
possible implications.
In German beers, a 2014 study investigated microplastic contamination and found
fibers, fragments, and granules after filtration through a 0.8
m cellulose filter, except
for wheat beers that could percolate and were filtered through a 40
m sieve [
However, there were many criticisms of the results because researchers affirmed that
contamination could not have originated from the raw material, but there were artifacts due
to laboratory contaminations. In 2018 [
], the MP contamination of American beers was
evaluated: the samples were filtered with an 11
m pore size, and the authors postulate that
product processing might be the most important factor explaining human contamination.
4.5. Milk
Dairy milk products are a part of globalized commodities for regular income; world
exports expanded to 75 million tons (in milk equivalents), and global milk output in
2018 was estimated at 843 million tons [
]. However, the industrial process of milk
production has been subjected to many technological developments to improve hygiene
and human health, which have influenced milk composition [
]. Considering the intense
processing of milk, the possible risks of milk contamination from microplastics may occur
from poor cleanliness procedure equipment, the surrounding environment, as well as water
supply conditions and the inadequate handling of milk. The presence of MPs in dairy milk
products was detected in Mexico [
], where 23 milk samples from 5 international and
3 national brands were analyzed. All samples analyzed included microplastics. Scanning
electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) was
used to examine the surface morphology and elemental composition of microplastics in
milk samples. A total of 150 microplastic particles were confirmed in 23 milk samples,
with an average concentration of 6.5
, lower than any reported levels in
liquid food products, confirming the ubiquity of MPs in samples and showing variability
in the range of 3–11
]. The most common contaminants in milk
samples are the thermoplastic sulfone polymers that are used in the ultrafiltration and
microfiltration membranes in food and dairy industry processing. High pressure and
continuous chemical and physical stress can damage the membranes, peeling off particles
from filters, and, thus, may be a source of microplastics in fluid milk samples. The release
of microplastics from milk raises serious concerns because the main consumers of milk
are infants.
Infant feeding bottles, commonly made of PP, can release microplastics in milk, as
evidenced in the paper of Li et al. [
]. In this study, the authors also estimated the intake
of MPs on all the continents. The average daily consumption of PP MPs by infants was
estimated to be 1,580,000 particles per capita, with a range of 14,600–4,550,000 particles,
depending on the region. Infants in Africa and Asia have the lowest potential exposure
to MPs from PP bottles, with rates of 527,000 and 893,000 particles per day, respectively.
Infants in South America have medium exposure levels (1,010,000 particles per day),
whereas Oceania, North America, and Europe have the highest levels, corresponding
to 2,100,000, 2,280,000, and 2,610,000 particles per day, respectively. The average value
corresponds to about 3000 times the total adult consumption of MPs from water, food, and
air (up to 600 particles per day for adults).
4.6. Honey, Sugar, and Fruit
The analysis of 19 samples of honey coming from different countries revealed a high
concentration of microplastic particles [
]. In 2019, the Swiss Beekeepers Association
started new research to understand the origin of MP contamination in honey. Therefore,
they discriminated beehives made of wood from those made of polystyrene to explore
the significant contamination source in honey. For these particle classes, they were able to
identify the particle materials using attenuated total reflection–Fourier transform infrared
spectroscopy (ATR-FTIR) and Raman techniques, which, in some cases, even allowed them
Toxics 2021,9, 224 10 of 29
to relate the particles to their specific origin. The results do not provide any evidence
for notable contamination in honey from environmental sources, but some microscopic
particles could be related to beekeeper activities [
]. Microplastics were also discovered
in honey from Ecuador, with a concentration of 54 and 67 particles/L in industrial and
craft honey, respectively [
]. This microplastic contamination of food products probably
originated from atmospheric contribution during production processes.
The mean values of microplastics in sugars (excluding the cane sugar sample) were
123 fibers/kg and 32
7 fragments/kg, with the maxima of 388 and 270, respectively.
For these samples, no distinction was made between colored and transparent particles.
International sugar suppliers usually offer purities
99.8%, where these sugars will contain
a maximum of 0.2% foreign matter. However, despite the large numbers of foreign particles
found in both honey and sugars, they will most probably not exceed any governmental or
industry limits [197].
Very recently, microplastics were detected, for the first time, in edible fruits
(52,600–307,750 particles/g)
and vegetables (72,175–130,500 particles/g) in the size range
of 1.36–3.19
m, with apples and carrots being the most contaminated samples (estimated
daily intakes of MPs in the range of 2.96 ×104–1.41 ×106particles/kg/day) [200].
4.7. Chicken, Cows, and Pigs
In 2017 [
], MP transfer from soil to chickens was investigated for the first
time in traditional Mayan home gardens in Southeast Mexico. The authors analyzed
the concentration of MPs in soil, earthworm casts, chicken feces, crops, and gizzards
(used for human consumption) and observed that the concentrations increased from
(0.87 ±1.9 particles/g)
to earthworm casts (14.8
28.8 particles/g) to chicken feces
129.8 ±82.3 particles/g)
. Chicken gizzards contained 10.2
13.8 microplastic particles/g,
while no microplastic was found in crops. Most recently, it has also been reported that
microplastic contaminants can be present in chicken meat and feces [
]. Other researchers
have evaluated the use of a rapid method based on attenuated total reflection mid-infrared
(ATR-MIR) spectroscopy combined with chemometric techniques to identify the level of
contamination in chicken meat with microplastics polystyrene (particle size 100
m) and
polyvinyl chloride (particle sizes 3 µm, 100 µm, and 2–4 mm) [203].
The occurrence of microplastics in livestock and manure has been reported in 19 dif-
ferent farms in South China, where pigs, poultry, and cows are raised [
]. PP and PE in
colorful fibers and fragment types were the most abundant MPs. Livestock and poultry
animals can eliminate MPs when eating polluted feeds. MPs can also reside in the digestive
system, despite the high levels of digestive juices; thus, MPs can pass through the digestive
system and remain in the manure. After the contaminated feces is used for composting,
agricultural soil can be polluted by the MPs present in the compost. Another source of
MP contamination for meat is the packaging used: extruded polystyrene microplastics can
contaminate meat at 4–18.7 particles per kg of food [205].
These are very small examples of MP contamination in edible animals, and they are
not sufficiently representatives of a real meat contamination issue.
4.8. Some Considerations of Food Web Contamination
Based on the studies discussed above, great efforts have been devoted to microplastic
detection in sea products, drinking water (raw, treated, and stored in different packages),
and salts for human consumption, while only a few studies have been conducted on other
foods such as honey, sugar, fruit, and chickens. This higher number of studies is probably
due to the easy transport of microplastics from a polluted water environment to related
food products. Several factors are responsible for an MP presence in food products. The
contamination can be related to environmental sources (contamination of water, soils, and
air) [
] and manufacturing processes such as the materials used during the filtration step
of beer and milk [199].
Toxics 2021,9, 224 11 of 29
MP contamination can also be due to packaging, such as bottled drinking water,
beer, milk, and refreshments [
], extruded polystyrene for meat [
], and take-out food
containers. In a study published in 2020, four plastic containers made of polypropylene
(PP), polystyrene (PS), polyethylene terephthalate (PET), and paperboard coated with PE
were analyzed: the highest microplastic abundance was found in the containers made of
PS [
]. Based on the MP abundance of food containers and take-out order frequency,
human microplastic intake is estimated as 12–203 items per week. The packaging material
has less effect on beer since, in most cases, beer is packaged in glass bottles and aluminum
cans [199].
MP occurrence in food and beverages is recapped in Table 1. The estimated intake
of MPs through inhalation and ingestion is reported in Table 2. Among various foods
investigated, salt is the one that releases the least microplastics, while a high intake of
microplastics can occur through milk stored in PP bottles used for infants. As regards
meat and seafood, the dose of MPs ingested depends on dietary habits: for example, in the
UK, where people eat less seafood, the MP intake is minor compared to Mediterranean
countries [208].
Table 1. Occurrence and quantification of microplastics in foods and beverages.
Sample Sampling Location Abundance
Average (Range)
Range Polymer
Type Ref.
European anchovies Mediterranean Sea (Gulf
of Lions) - 0.124–0.438 mm PE,
styrene/acrylonitrile [123]
Bivalves (Mytilus edulis
Crassostrea gigas)Germany and Brittany (FR) 0.36–0.47 particles g1>0.005 mm - [136]
Mussels (Mytilus edulis)French–Belgian–Dutch coastline
(FR, BE, NL) 0.2–0.5 particles g10.015–1 mm - [135]
Dogfish, hake, red
Galician coast, Cantabrian coast,
Gulf of Cadiz, Spanish
Mediterranean coast (ES)
1.56 ±0.5
particles/individual 0.38–3.1 mm - [121]
Semipelagic fish Mallorca and Eivissa (Balearic
Islands, ES) 3.75 (2.47–4.89)
particles/individual 0.5 mm - [132]
Pelagic and
Plymouth (UK) 1.90
particles/individual 0.13–14.3 mm PA, cellulose, RY [131]
Benthic and
pelagic fish Portugal coast (PT) 0.27 ±0.63
particles/individual 0.217–4.81
(average 2.11) mm PP, PE, ALK, RY,
PES, NY [133]
Different fish
Mediterranean coast of Turkey
particles/individual average 0.656 mm polystyrene:
isoprene, PE, PP [126]
Red mullet
(Mullus surmuletus)
Palma, Port d’Andratx, Port
d’Alcúdia, Cala Ratjada and
Santanyí(Mallorca, ES)
particles/individual -PET, CPH,
Polyacrylate, PAN [120]
Deep benthic
invertebrates Rockall Trough, Scotland (UK) 1.582 ±0.448 particles g10.023–6.25
(average 1.191) mm ALK, PES [124]
Benthic organisms South Yellow Sea (North China
and South Korea, CN, KR) (1.7–47.0) particles g10.05–5 mm PP, PE, PS, PET, NY [137]
(Mytilus edulis)Coastal water of China (CN)
1.5–7.6 particles g10.033–4.7 mm CPH, PET, PES [129]
Different fish
species Rapa Nui (Easter Island, CL) 2.5
particles/individual 0.2–5 mm PE, PP [134]
Bivalve (oyster, mussel,
Manila clam and
South Korea (KR)
0.97 (0–2.8)
0.15 (0–1.8) particles g10.1–0.2 mm PE, PP, PS, PES,
PEVA, PET, PUR [122]
fish South China sea (CN)
Stomach: 1.96
particles/individual and
1.56 particles g1;
Intestine: 1.77
particles/individual and
4.89 particles g1
<1 mm CPH, PA, PET, [138]
Indian white shrimps Kochi, Southwest India (IN)
0.04 particles g10.157–2.785 mm PA, PES, PE, PP [125]
Sea salt, lake salt,
rock/well salt China (CN)
550–681 particles kg1
(sea salt)
43–364 particles kg1(lake salt)
7–204 particles kg1(rock/well salt)
0.1–1 mm PET, PE, PB, PP,
PES, CPH [170]
Ocean salt, sea salt, rock
salt United States (USA) 47–806 particles kg10.1–5 mm [166]
Sea salt Italy (IT) 1600–8200 particles kg10.004–2.1 mm [168]
Sea salt Croatia 13,500–19,800 particles kg10.015–4.6 mm PP [168]
Toxics 2021,9, 224 12 of 29
Table 1. Cont.
Sample Sampling Location Abundance
Average (Range)
Range Polymer
Type Ref.
Sea and lake salt
Australia (AU), France (FR), Iran
(IR), Japan (JP), Malaysia (MY),
New Zealand (NZ), Portugal
(PL), South Africa (ZA)
1000–10,000 particles kg10.2–1 mm
Sea salt Indonesia (ID) 100 particles kg10.1–2 mm PE, PET, PP [165]
Drinking water, soft
drinks, and milk
Drinking water Oldenburg-East-Frisian water
board, Germany (DE) 0–7000 particles L10.05–0.150 mm PES, PVC, PE, PA,
EP [181]
Drinking water Germany (DE)
11 ±8 particles L1
(beverage cartons)
118 ±88 particles L1
(returnable plastic bottles)
0.005–0.1 mm PET, PE, PA, PP [184]
Drinking water Bavaria, Germany (DE)
4889 ±5432 particles L1
(reusable PET bottles)
2649 ±2857 particles L1
(single-use PET bottles)
3074 ±2531 particles L1
(glass bottles)
0.001–0.01 mm
copolymer, PP, PE,
Drinking water Czech Republic (CZ)
338 ±76 to 628 ±28 particles L1
(treated water)
1473 ±34 to 3605 ±497 particles L1
0.001–0.1 mm
PTT, PVC (raw
PVC (treated
Cold tea, soft drinks,
energy drinks, beers Mexico City, Mexico (MX)
11 ±5.26 particles (cold tea)
40 ±24.53 particles (soft drinks)
14 ±5.79 particles (energy drinks)
152 ±50.97 particles
(0–28 ±5.29 particles L1) (beers)
0.1–3 mm PA, PET, PEA, ABS [189]
Beer Germany (DE)
2–79 particles L1(fibers)
12–109 particles L1
2–66 particles L1
Beer Germany (DE)
16 ±15 particles L1(fibers)
21 ±16 particles L1(fragments)
27 ±10 particles L1(granules)
Beer USA 0–14.3 particles L10.1–5 mm [166]
Milk Mexico City, Mexico (MX) 6500 particles m30.1–5 mm Polysulfone [195]
Honey, sugar, and fruit
Honey Germany (DE), France (FR), Italy
(IT), Spain (ES)
166 ±147 particles kg1(fibers)
9±9 particles kg1
0.01–9 mm [197]
Honey Germany (DE)
10–336 particles kg1
2–82 particles kg1
0.01–several mm [209]
Honey Switzerland (CH)
32–108 particles kg1
8–28 particles kg1(other)
PET [198]
Honey Ecuador (EC) 54 particles L1(industrial honey)
67 particles L1(craft honey) 0.013–0.25 mm PP, PE, PAAm [199]
Sugar Germany (DE), France (FR), Italy
(IT), Spain (ES)
217 ±123 particles kg1(fibres)
32 ±7 particles kg1(fragments) [197]
Fruit and vegetables Catania, Italy (IT)
52,600–307,750 particles g1(apples)
98,325–302,250 particles g1(pears)
65,025–201,750 particles g1
26,375–75,425 particles g1(lettuce)
72,175–130,500 particles g1(carrots)
0.00156–0.00319 mm
0.00187–0.00259 mm
0.00186–0.00295 mm
0.00218–0.00278 mm
0.00136–0.002 mm
Chicken, cows, and
Chicken feces Campeche, SE Mexico (MX) 129.8 ±82.3 particles g10.1–5 mm [201]
Chicken gizzards Campeche, SE Mexico (MX) 10.2 ±13.8 particles g10.1–5 mm [201]
Toxics 2021,9, 224 13 of 29
Table 1. Cont.
Sample Sampling Location Abundance
Average (Range)
Range Polymer
Type Ref.
Poultry, pigs, cows South China (CN)
902 ±1290 particles kg1
(pig manure)
667 ±990 particles kg1
(poultry manure)
74 ±129 particles kg1
(cow manure)
139 ±115 particles kg1(pig feeds)
96 ±109 particles kg1
(poultry feeds)
36 ±63 particles kg1
(cow feeds)
<5 mm PP, PE, PET [204]
Abbreviations. MO: microscope; FTIR: Fourier transform infrared spectroscopy; RMS: Raman spectroscopy; SEM: scanning electron
microscope; FTIR-ATR: Fourier transform infrared spectroscopy–attenuated total reflectance; SEM-EDX: scanning electron microscopy
with energy dispersive X-ray analysis; PE: polyethylene; PP: polypropylene; PS: polystyrene; PVA: polyvinyl alcohol; PVC: polyvinyl
chloride; PES: polyester; PET: polyethylene terephthalate; PUR: polyurethane; PA: polyamide; NY: nylon; CPH: cellophane; RY: rayon; EP:
epoxy resin; ALK: alkyd resin; PAN: polyacrylonitrile; PMMA: poly(methyl methacrylate); ABS: acrylonitrile butadiene styrene; PEVA:
polyethylene-vinyl acetate; PAAm: polyacrylamide; PB: poly(1-butene); PBA: polybutylacrylate; PTT: polytrimethylene terephthalate; PEA:
Table 2. Estimated intake of microplastics through inhalation, food and beverages, and packaging.
Sample Origin Estimated Intake Ref.
Air (inhalation) Europe (UE) 26–130 particles/day/capita
272 particles/day/capita [210,211]
Dust Tehran, Iran (IR)
107–736 particles/year/capita
(adults, normal exposure)
353–2429 particles/year/capita
(adults, acute exposure)
644 particles/year/capita
(children, normal exposure)
3223 particles/year/capita
(children, acute exposure)
Seafood Europe and American countries 518–3078 particles/year/capita [141]
Seafood UK
Other countries such as France,
Belgium, and Spain
123 particles/year/capita (UK)
4620 particles/year/capita [208]
Australia, France, Iran,
Japan, Malaysia, New Zealand,
South Africa
37 particles/year/capita [164]
Salt Turkey
249–302 particles/year/capita (sea salt)
203–247 particles/year/capita (lake salt)
64–78 particles/year/capita (rock salt)
North Sea Salt,
Celtic Sea Salt,
Mediterranean Sea Salt
Mediterranean Sea Salt
Utah Sea Salt
Himalayan Rock Salt Mined
Hawaiian Sea Salt Ocean
Baja Sea Salt Ocean
Atlantic Sea Salt Ocean
Pacific Sea Salt
40–680 particles/year/capita [166]
Salt Spain 510 particles/year/capita [163]
Salt China (CN) 1000 particles/year/capita [170]
Drinking water Asia, USA, and Europe 3000–4000 particles/year/capita [187]
Drinking water America
4000 particles/year/capita (consumers of tap water)
90,000 particles/year/capita (consumers of water from
plastic bottles)
Drinking water, salt, and beer
USA 5800 particles/year/capita [166]
Milk (Infant exposure) Asia, Europe, America, Oceania,
527,000 and 893,000 particles/day/capita (Asia
and Africa)
2,100,000 particles/day/capita (Oceania)
2,280,000 particles/day/capita (North America)
2,610,000 particles/day/capita (Europe)
Fruit and vegetables Italy (IT) 29,600–1,416,000 particles/kg/day [200]
Meat (food packaging) France (FR) 0.1–515.2 mg/year/capita [205]
Take-out containers China (CN) 2977 particles/year/capita [207]
Toxics 2021,9, 224 14 of 29
All these studies suggest a not-negligible ingestion of microplastic particles. However,
these examples are still too few to be sufficiently representative of true microplastic contam-
ination, so further studies need to be performed in order to have more data on the human
ingestion of microplastics from foods different from those related to the water environment.
Considering these results, toxicological and epidemiological studies need to be performed
to investigate more deeply the possible consequences of microplastics found in foods on
human health.
5. Implication of Microplastic Contamination on Human Health
5.1. Possible Routes for Human Exposure to Microplastics
The human body’s exposure to microplastics passes through different routes: inges-
tion [
], inhalation [
], and dermal contact [
] (Figure 2). Each of these routes of
exposure is related to a particular environment and its chemical–physical characteristics.
Figure 2.
Schematic representation of exposure to microplastics through three routes: ingestion,
inhalation, and dermal contact.
In the previous paragraph, we underlined the occurrence and abundance of mi-
croplastics in the air and soil web and their transport within the food web, from seafood
to beverages and fruits. Considering the high microplastic concentrations detected, the
above-mentioned exposure routes can represent important issues for human health.
MPs can have potential adverse effects on human health [
], such as inflammation
and secondary genotoxicity [
], and their accumulation can induce or enhance an immune
response [
]. Inhaled microplastics can translocate into the respiratory epithelium via
diffusion, direct cellular penetration, or active cellular uptake, as reported for other non-
biological micro-and nanoparticles [
]. The preliminary effects of microplastic inhalation
were studied in workers involved in plastic processing. Histopathological analysis of the
lungs of these workers showed interstitial fibrosis and granulomatous lesions, postulated
to be acrylic, polyester, and nylon dust [
]. The comparison between the number of
microplastics absorbed by inhalation and that by ingestion (through the food web) was
also reported in the literature [
]. It was observed that the amount of inhaled MPs was
from 3 to 15 times higher than the ingested ones, so the levels of MP ingestion by humans
are minimal compared to exposure [208].
Dermal contact with microplastics is considered a less significant route of exposure,
usually associated with exposure to monomers and additives, such as the endocrine
disruptors bisphenol A and phthalates, from the daily use of common appliances [
For instance, dermal uptake was investigated in rainbow trout. There is evidence for the
Toxics 2021,9, 224 15 of 29
uptake of 1
m latex spheres from the surrounding water, with particles localizing and
persisting in the surface and sub-surface epidermal cells of the skin and in phagocytes
underlying the gill surface [
]. In humans, surgical sutures in medicine, i.e., braided
polyester and polypropylene, are known to induce low inflammatory reactions and a
foreign body reaction with fibrous encapsulation. Moreover, human epithelial cells suffer
oxidative stress from exposure to microplastics and nanoplastics as well [218].
Persorption is considered as a possible route of uptake in the gastrointestinal tract, and
it describes the mechanical kneading of solid particles (up to 130
m diameter) through gaps
in the single-layer epithelium at the villus tips and into the circulatory system
Samples of persorption were obtained using PVC particles (5–110
m) as a model of non-
degradable microparticles, following exposure via feeding or rectal administration, in rats,
guinea pigs, rabbits, chickens, dogs, and pigs. Persorption has also been reported in human
subjects by using starch particles (200 g) that led to granules being observed in urine,
bile, cerebrospinal fluid, peritoneal fluid, and breast milk [
]. Peyer’s patches of the
ileum (the third portion of the small intestine) are considered the major sites of uptake and
translocation of particles in the gastrointestinal tract. The uptake of plastic microspheres
m) by Peyer’s patches has been reported in mammalian models such as rats, with
an estimation of 60% of PS nanoparticle (60 nm) uptake occurring via Peyer’s patches in
rats following 5-day oral dosing. The accumulation of MPs in this compartment could
interfere with endogenous microparticle uptake and, consequently, immunosensing and
surveillance, compromising local immunity [111].
Obviously, a real estimation of the number of microplastics accumulated in the human
body is difficult to obtain. Only a few studies have performed human exposure assessments
for MPs, considering total intake from different routes [
]. In a recent study, a
probabilistic model was used to estimate child and adult exposure to MPs and their
accumulation during life [
]. The model considered the ingestion of food (fish, salt,
mollusks, and crustaceans) and beverages (tap water, bottled water, beer, and milk) and
inhalation through the atmosphere as the main routes of exposure to quantify microplastic
intake. Moreover, it included intestinal absorption and biliary excretion to assess MP
accumulation. The results highlighted a small contribution of microplastics to total chemical
intake compared to other more hazardous contaminants with the same exposure routes,
e.g., benzo(a)pyrene, di(2-ethylhexyl)phthalate, 3,30,4,40,5-pentachlorobiphenyl, and lead.
Notwithstanding the above, human exposure to MPs remains not-negligible, thus
warranting investigations on their effects on humans.
5.2. Toxicological Studies and Consequences to Human Health
Adverse effects of environmental exposure to MPs have been mostly studied using
marine organisms (77%) and freshwater organisms (23%), while research involving terres-
trial organisms is still in its beginnings [
]. Often, aquatic organisms at the start of
the trophic web are considered since the plastic contamination of such species has become
the main topic in bioaccumulation and biomagnification dynamics [
]. For example, a
recent study suggested that aquatic microplastic pollution could affect the growth and
feeding behavior of Artemia salina, a planktonic organism used as a primary food source
for many farmed species [
]. In particular, brine shrimps easily internalized 10
polystyrene microspheres through filtration. In the absence of a food source, this phe-
nomenon also occurred at low concentrations (1 MPs/mL), whereas, in the presence of a
food source (Dunaliella salina), microplastics were ingested only at higher concentrations
(10–100 MPs/mL). MP uptake, in a dose-dependent manner, caused lower ingestion of
a nutritional food source, which led to a developmental delay and a reduction in total
body length.
In the last few years, the impact of microplastics and nanoplastics on the human
body has been analyzed in both
in vitro
in vivo
studies [
]. The toxicological
hazard of microplastic and nanoplastic exposure to humans through oral ingestion was
recently assessed [
]. Several toxicological studies on ingested microplastics are reported
Toxics 2021,9, 224 16 of 29
in the literature, most of which used polystyrene particles as a benchmark material for
more complex microplastics, while only a few examples regarded polyethylene [
However, none of the studies considered human exposure to real-life microplastic samples
but evaluated the toxicological effects of PS plastic particles on cell cultures [
] and
also experimental mammal animal models [
]. Moreover, the toxic effects strongly
depended on the dose, dose rate, and duration of exposure used in the experiments. The
majority of studies on polystyrene particles in cell cultures considered short-term exposure
to high microplastic concentrations and showed toxicological effects on parameters such
as oxidative stress [
], inflammation [
], mitochondrial dysfunction [
lysosomal dysfunction [
], and apoptosis [
], whereas only a few studies investigated
genotoxicity [
] (see Figure 3for the main toxicological effects found in cell cultures).
Figure 3.
Toxicological effects of polystyrene microparticles on cell cultures: oxidative stress, apopto-
sis, inflammation, mitochondrial and lysosomal dysfunction, and genotoxicity.
In contrast to these data, obvious indices of toxicity have not been demonstrated in
animal models. Concerning particle size, more toxic results are observed for PS particles
that are less than 100 nm with respect to particles larger than 100 nm. Moreover, it was
observed that in the functionalization of PS particles, both carboxyl groups (-COOH) and
amine groups (-NH
) make microparticles more toxic than non-functionalized ones [
In the case of polyethylene particles, studies have suggested that these microplastics
generate only inflammatory reactions.
Since inhalation is one of the main routes for human exposure to microplastics, some
studies have regarded the effects of polystyrene nanoparticles (PS-NPs) on human lung
epithelial A549 cells, usually used as a model for human alveolar type II pulmonary epithe-
lium [
]. It has been shown that PS-NPs might directly interfere with membrane
transporter (P-glycoprotein/MDR1) function in A549 cells, in an amount that depends
on their size and surface properties, resulting in a possible influence on the disposition
of xenobiotic and endogenous substrates [
]. Moreover, PS-NPs are rapidly internal-
ized by A549 cells, affecting their viability, apoptosis, and cell cycle and disturbing gene
transcription and protein expression [
]. The results of this study clearly showed that
knowledge of parameters such as the concentration of particles, diameter, and exposure
time is necessary to assess the toxicological effects of these particles on human alveolar ep-
ithelial A549 cells [
]. Recently, the combined toxicity of PS-NPs and phthalate esters on
A549 cells was also investigated. At a greater concentration of PS-NPs, these particles have
a dominant role in the combined cytotoxicity observed in mechanisms of oxidative stress
and inflammatory reactions [
]. Moreover, to evaluate the potential toxicological effects
of microplastics, A549 cells were exposed to polystyrene microplastics. The inhibition of
cell proliferation and major changes in cell morphology were observed, confirming that
microplastics have a potential for harm to humans [253].
Toxics 2021,9, 224 17 of 29
Moreover, A549 cells were used to assess the toxicity of polyvinyl chloride (PVC)
microparticles since the inhalation of PVC dust has been associated with pulmonary
diseases [
]. PVC microparticles produced
in vitro
cytotoxicity and inflammatory
potential for several rat and human pulmonary cells, perhaps due to the presence of
residual additives [254,255].
Considering ingestion as another important exposure route for humans, the interac-
tion of PS-NPs with human intestinal cells and intestinal translocation was studied using
in vitro
models [
]. No significant cytotoxic effect and no adverse effects in
the integrity or permeability of the barrier mode were detected [
]. Nevertheless, the
studies confirmed the capability of particles to cross the epithelial barrier of the digestive
system, which should not be underestimated because of other possible long-term impli-
cations [
]. Factors affecting the cellular uptake of PS-NPs were also investigated in
different cell lines [
]. Experiments performed using carboxylated PS-NPs (40 and
200 nm of diameter) revealed that NPs enter cells via active energy-dependent processes for
all cell types but exploit different uptake mechanisms depending on cell type [
]. More-
over, surface charge is the main parameter influencing cellular uptake efficiency, whereas
compositional elements, aggregation/agglomeration, and protein corona formation results
are less relevant [259].
As previously mentioned, MPs can adsorb chemicals such as heavy metals, persis-
tent organic pollutants plasticizers [
], antioxidants and slip agents [
], and some
potential pathogens [
] on their surface, increasing the exposure of humans to toxic
chemicals and additives. For example, high concentrations of phthalates and organophos-
phorus esters have been detected on some beached microplastics based on PP flakes and
PS foams [
]. Moreover, MPs containing high levels of potentially bioavailable toxic
substances (e.g., lead, cadmium, organochlorine compounds, copper, zinc, and hydrocar-
bons) may represent a significant ecotoxicological risk for the early life stages of aquatic
organisms [
]. As a catalytic surface, microplastics can also affect biochemical processes
in organisms, increasing intakes and accumulations of pollutants in organisms [
]. It has
been documented how aged plastics strengthen their ability to absorb chemicals because of
weathering. Some studies have shown the bioaccumulation of chemicals from plastics in
organisms [
] and the presence of potentially pathogenic bacteria on microplastics [
Furthermore, biofilm communities on microplastics from three marine ecosystems (the
Baltic, Sargasso, and Mediterranean seas) were characterized using high-throughput 16S
rRNA gene sequencing. As a result of this investigation, MPs were found to be a possible
reservoir of rare and understudied microbes, hence encouraging future studies in this
field [
]. MPs colonized by potential pathogens showed a close relationship with coral
diseases, with the possibility of disease 4–89% greater than a plastic-free condition [
]. In-
creased exposure to microplastics can cause immune disorders, neurodegenerative diseases,
and cancer [212,265].
Another important issue arises from the ability of microplastics to accumulate over
time and to be bio-persistent [
]. An artificial
in vitro
digestion protocol (considering the
three digestive compartments: mouth, stomach, and intestine) allowed us to analyze the
effects of gastrointestinal passage on the physiochemical particle characteristics of the most
environmentally abundant materials, such as PE, PP; PVC, PET, and PS [
]. The SEM
results demonstrated a high resistance of all MPs to the artificial digestive juices compared
to the influence of the positive controls of hydrochloric acid, nitric acid, and acetone.
Moreover, a cross-disciplinary review discusses and evaluates the potential impacts of
microplastics on human health through diet and environment [
]. There was no evidence
of increased cancer risk for nylon flock workers, although they had a higher prevalence of
respiratory diseases (dyspnea, coughing, reduced lung capacity, and wheezing) [
Ultimately, several toxic effects of plastic particles were observed, but they mainly
occurred for particle sizes smaller than 5
m at a concentration much higher than human
exposure, demonstrating hazard rather than risk for human health, so the same effects
at low concentration must be verified. Epidemiological studies must be carried out to
Toxics 2021,9, 224 18 of 29
assess the real consequence of microplastic contamination at concentrations in the range of
human exposure.
5.3. Future Trends: Occurrence in Body Fluids and Related Effects
The above-discussed papers assert an elevated microplastics intake, so a deeper
investigation on the translocation and accumulation of MPs in the human body is needed
to better characterize their potential to harm humans. In fact, MP occurrence and detection
in the fluids of the human body remain a poorly investigated field but could be very useful
for assessing the interaction of plastic particles with the human body.
In a recent study, the presence of microplastics in human stool was investigated [
All samples analyzed (from 3 men and 5 women) contained microplastics (size range of
m), with polypropylene and polyethylene terephthalate as the most abundant
polymers and an average concentration of 2 particles/g of fecal matter.
Surprisingly, microplastic fragments were also detected in human placenta samples
collected from six consenting women with uneventful pregnancies [
]. Analysis by Ra-
man microspectroscopy was able to detect 12 pigmented microplastic fragments (
5–10 µm
in size) in 4 placentas, mainly polypropylene. The presence of microplastics in the human
placenta is a matter of great concern, so further studies should be performed to evaluate if
it can result in harmful effects on pregnancy.
These results encourage the search for microplastics in human fluids, and other
investigations should be carried out to assess how microplastics interact with the human
body and reach its fluids. A significant issue to consider in microplastic determination is
the contamination of samples due to airborne microplastics. Consequently, great attention
must be paid to sample treatment to avoid the misidentification of microplastics in human
samples, especially for low size particles (<10 mm), and enlarge the number of samples
collected. Therefore, in the near future, new methodologies should be developed to count
and characterize MPs in body fluids, avoiding interferences as much as possible.
Moreover, more international and cross-disciplinary research focusing on the toxi-
cology of these particles is urgently needed to fully understand the long-term effects on
humans and help health organizations to provide prevention guidelines.
6. Conclusions
Plastic microparticle accumulation in the environment leads to stress on ecosystems.
In this review, we analyzed the most recent literature related to microplastics in the envi-
ronment and food, the potential route of exposure for humans, and toxicological effects.
We have underlined how several literature studies have detected high microplastic con-
centrations in the environment, with the consequent transport of these particles within
the food web, from seafood to beverages and fruits. A higher number of studies have
researched the contamination of sea products, drinking water (raw, treated, and stored in
different packages), salts for human consumption, and honey, sugar, fruit, and chickens.
All these studies suggest a not-negligible ingestion of microplastic particles through food
consumption. Several toxic effects of ingested microplastics, mainly PS, were reported to
occur at high microplastic concentrations compared to human exposure, demonstrating
a hazard for human health. Further studies must be performed to assess the real conse-
quences of microplastic contamination at concentrations in the range of human exposure.
Increasing awareness of the potential and growing risks to human health has not been
accompanied by considerable efforts to establish the influence of microplastic abundance
on human health
in vivo
, most probably because of the lack of standardization of sampling
methodologies and the separation of MPs. This review aims to guide future researchers into
a deeper investigation of the processes involved in MP uptake, the potential mechanisms
of toxicity, and health effects.
Toxics 2021,9, 224 19 of 29
Author Contributions:
Conceptualization: O.M., A.P. and L.M. Data curation: C.P. and M.R. Formal
analysis: C.P. and M.R. Funding acquisition: O.M. and A.P. Investigation: C.P., M.R. and Y.M.
Methodology: C.P., M.R. and Y.M. Project administration and resources: O.M. and A.P. Software:
C.P., M.R. and Y.M. Supervision and validation: O.M., A.P. and L.M. Visualization: C.P., M.R., Y.M.,
O.M. and A.P. Writing original draft: C.P. and M.R. Writing–review and editing: O.M. and L.M. All
authors have read and agreed to the published version of the manuscript.
This work was financially supported by Fondi di Ateneo per la Ricerca di Base “FARB
2020”, University of Salerno.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Acknowledgments: The authors gratefully acknowledge Antonio Faggiano for graphics support.
Conflicts of Interest: The authors declare no conflict of interest.
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... Due to the small size of the particles, MPs are intensively distributed in the environment via water and wind. MPs are found all over the globe: in the air, soil, and water, in polar ice, at the depths of the seas, and in living organisms [1][2][3]. In this regard, the question of the impact of MPs on human health is pertinent. ...
... People consume MPs mainly via water and food, and the first target of their action is the gastrointestinal tract [3]. It is possible that the worldwide increase in the incidence of inflammatory bowel diseases (IBDs), including ulcerative colitis, is associated with an increase in the number of MP particles in the environment [12]. ...
Full-text available
Microplastic pollution poses a threat to human health. It is possible that the increase in the incidence of inflammatory bowel disease is associated with exposure to microplastics. We investigated the effect of the consumption of polystyrene microparticles with a diameter of 5 μm at a dose of 2.3 mg/kg/day for 6 weeks on morphological changes in the colons of healthy male C57BL/6 mice and of mice with acute colitis induced by a 1% dextran sulfate sodium solution (DSS). In healthy mice, microplastics caused an increase in the number of endocrine cells, an increase in the content of highly sulfated mucins in goblet cells, an increase in the number of cells in the lamina propria, and a decrease in the volume fraction of macrophages. Microplastic consumption caused more severe acute colitis, which is characterized by a greater prevalence of ulcers and inflammation and a decrease in the content of neutral mucins in goblet cells.
... This promotes the accumulation of plastics (plastic nanomaterials and plastic micromaterials) in the environment and, consequently, in living organisms through the food chain [10]. Plastic accumulation can cause lung, intestinal, kidney, cardiac, and liver diseases, in addition to genetic mutations, nervous system degradation, and decreased fertility in humans and animals [11][12][13][14][15]. ...
Full-text available
Paper is a biodegradable material, but in food packaging, its hygroscopicity and porosity can cause food contamination due to the exchange of gasses and liquids with the environment. Therefore, it is important to use biodegradable materials for paper coatings, such as nanocellulose, which is chemically compatible with paper but less hygroscopic. The objective of this study was to evaluate the effectiveness of nanofibrillated cellulose (NFC) as a paper coating. NFC produced from bleached eucalyptus pulp was used as a coating on kraft paper sheets produced from Pinus pulp. To prepare the coating, two thicknesses of wet nanocellulose (1 mm and 2 mm) were tested, and two nanocellulose films made with the same thicknesses were evaluated. The morphological, physical, mechanical, and thermal properties of the composites were investigated. The presence of NFC improved the surface of the paper by filling the pores; consequently, the density and barrier properties were also improved. All mechanical properties were improved, with the highest increases observed for bursting and tensile strength; however, the films showed low bursting index values and null values for the tearing index. The thermal stability of the paper with NFC coatings met the minimum requirements for food packaging.
... Plastic is a toxic and poisonous substance that takes a long time to decompose, resulting in pollution or contamination of the environment, ecosystem, and living organisms on earth. The material of plastic production is polymeric, including polyvinyl chloride (PVC), polyethylene terephthalate (PET or PETE), the Higher or lower density of polyethylene (HDPE or LDPE), polystyrene (PS), polypropylene (PP), and other plastics listed in Table 1 [2,3]. Table 1. ...
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The study aimed to review the ingestion of microplastics by aquatic animals in the South East Asia and the impacts of this ingestion on the environment, human health, and species health, as well as to explore technologies for remediation. Microplastic particles range in size from 1 to 5 microns and are the result of the breakdown of larger, original plastic particles. Microplastic was defined in 2011, but the majority of people did not view it as a serious pollutant or act accordingly. Microplastic is a serious pollutant that has prompted increased research and experimentation since 2005. Microplastics are so small that they can enter the tissues and organs of aquatic animals. Malaysia produces a quantity of plastic waste and receives plastic waste from other countries for disposal. The effects of microplastic on aquatic animals have been studied in relation to the ecosystem cycle and food chain. The presence of microplastic in aquatic animals has detrimental effects on the environment, human health, species health, and the ecosystem. Physical, chemical, and biological technologies are provided, as well as a combination of two technologies, for the remediation of microplastic, which aids in the removal of microplastic from the environment and the reduction of microplastic in aquatic animals. These technologies aim to reduce the concentration of microplastics in water bodies, preventing their ingestion by aquatic animals. However, their efficiency in tropical regions may vary, depending on the specific environmental conditions. It requires continued research, policy, and public awareness to mitigate the impacts of microplastics on the environment and human health. In addition, microplastics generate some challenges and opportunities for reducing microplastics' impact on humans and the environment in the future.
... Sea foods such as fish, marine animal species, and microalgae are primary sources of foods in human diet [58,59]. Additionally, different brands of salts are used by humans, which provides essential nutrients, as well as acts as a food preservative [60]. In the period 2015-2018, a study showed that MPs were found in 128 brands of commercial salts [61], thus indicating how deep the roots of MPs toxicity may have spread in the food chain. ...
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Over the last century, accumulation of microplastic has emerged as a greater threat to the environment, plants, microorganisms and even human beings. Microplastics can be intentionally produced for industries such as cosmetics, or they may be unintentionally generated from degradation of bulk plastic debris. Furthermore, mismanagement of plastic waste is a major source of microplastics. When ingested, microplastics can alter several physical, chemical and biological processes in living organisms. Thus, their toxicity silently spreads its roots into the biosphere. Unfortunately, current strategies for the elimination of microplastics are not sufficient for their complete removal and degradation. Therefore, the adoption of green innovative technologies is the first step toward a microplastic-free environment. However, advances for its effective degradation and elimination are hindered by our limited understanding. This literature study investigates microplastic comprehensively, covering their sources, fate, ecological impacts and their effects on biological processes. It includes an analysis of microplastics in Indian rivers, explores methods for its eradication and degradation, emphasizes plastic recycling and offers future recommendations to pave way toward achieving a microplastic-free environment. Graphical Abstract
... Children and infants are at a significant potential risk of inhaling MPs, which is about five times more than adults . Food security and human health are put at risk when people consume contaminated food, which inevitably exposes them to microplastics (Pironti et al. 2021). The quantity and size range of MPs in various foodstuff are described in Table 1. ...
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Microplastics (MPs) are biologically active environmental pollutants having signifcant impact on the ecosystem and human health. MPs have been reported to increase oxidative stress, resulting in tissue damage, developmental abnormalities, metabolic disorders, epigenetic changes, abnormal reproduction, and reduced gamete quality. At present, most of the existing literature has focused on the efects of MPs on the reproduction of various aquatic organisms; however, the efects of MPs on mammalian reproduction specifcally humans are least studied except a few ones fragmentally discussing the efects of MPs on gametogenesis in human. This review discusses efects of MPs on male and female reproduction with a focus on diferent metabolic pathways involved in compromised gamete quality, gamete toxicity, apoptosis, and DNA damage.