Fate and Impacts of Microplastics in the Environment: Hydrosphere, Pedosphere, and Atmosphere

Abstract

Plastic litter is on the rise where plastic waste ends up in undesignated areas such as the coastal shorelines, where the plastic is exposed to environmental conditions. As a result, the degradation and decomposition of plastics occur, leading to the formation of smaller fragments of plastics, termed microplastics. Microplastics have recently been considered as an emerging class of contaminants due to their ecotoxicological impact on the aquatic environment as well as soil matrix. Microplastics are of a size less than 5 mm and are produced from either a primary source (such as plastic pellets, and beads in makeup products) or a secondary source (such as the wear and tear of normal-use plastics and washing of clothes and textiles). Microplastic pollution is spread across the hydrosphere, pedosphere, and atmosphere, and these environmental zones are being studied for microplastic accumulation individually. However, there exists a source–sink dynamic between these environmental compartments. This study reviews the available literature on microplastic research and discusses the current state of research on the fate and transport of microplastic in the hydrosphere, pedosphere, and atmosphere, explores the ecotoxicological impact of microplastics on aquatic and soil communities, and provides prospective future research directions and plastic waste management strategies to control microplastic pollution. While the fate of microplastics in the hydrosphere is well-documented and researched, studies on understanding the transport mechanism of microplastics in the pedosphere and atmosphere remain poorly understood.

Full text

Citation: Haque, F.; Fan, C. Fate and
Impacts of Microplastics in the
Environment: Hydrosphere,
Pedosphere, and Atmosphere.
Environments 2023,10, 70.
https://doi.org/10.3390/
environments10050070
Academic Editors: Teresa A.
P. Rocha-Santos and Ana
Luísa Patrício da Silva
Received: 27 March 2023
Revised: 22 April 2023
Accepted: 23 April 2023
Published: 24 April 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
environments
Review
Fate and Impacts of Microplastics in the Environment:
Hydrosphere, Pedosphere, and Atmosphere
Fatima Haque and Chihhao Fan *
Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei 106319, Taiwan;
fatimah@alumni.uoguelph.ca
*Correspondence: chfan@ntu.edu.tw
Abstract:
Plastic litter is on the rise where plastic waste ends up in undesignated areas such as
the coastal shorelines, where the plastic is exposed to environmental conditions. As a result, the
degradation and decomposition of plastics occur, leading to the formation of smaller fragments of
plastics, termed microplastics. Microplastics have recently been considered as an emerging class of
contaminants due to their ecotoxicological impact on the aquatic environment as well as soil matrix.
Microplastics are of a size less than 5 mm and are produced from either a primary source (such as
plastic pellets, and beads in makeup products) or a secondary source (such as the wear and tear
of normal-use plastics and washing of clothes and textiles). Microplastic pollution is spread across
the hydrosphere, pedosphere, and atmosphere, and these environmental zones are being studied
for microplastic accumulation individually. However, there exists a source–sink dynamic between
these environmental compartments. This study reviews the available literature on microplastic
research and discusses the current state of research on the fate and transport of microplastic in the
hydrosphere, pedosphere, and atmosphere, explores the ecotoxicological impact of microplastics
on aquatic and soil communities, and provides prospective future research directions and plastic
waste management strategies to control microplastic pollution. While the fate of microplastics in the
hydrosphere is well-documented and researched, studies on understanding the transport mechanism
of microplastics in the pedosphere and atmosphere remain poorly understood.
Keywords: microplastics; hydrosphere; pedosphere; atmosphere; ecotoxicology
1. Introduction
Plastic production began in the 1950s, resulting in plastic waste of 359 million tons
globally in 2018 [
1
,
2
]. Plastic waste is estimated to further increase by 276 million tons by
2025 [
3
]. This increase in plastic waste will place a huge burden on the existing plastic
management system because 78% of the plastic waste is handled via recycling, incineration,
and landfilling and the remaining 22% remains as mismanaged plastic waste [
4
,
5
]. It
is estimated that approximately 5.3 to 14 million tons of mismanaged plastic waste end
up being discarded as litter along the coastlines each year, out of which 10% enters the
hydrosphere and accumulates over time [
3
,
6
]. Plastic with sizes greater than 5 mm are called
macroplastics [
7
]. Once exposed to the environment, macroplastics undergo weathering
and degradation and result in the formation of microplastics with sizes less than 5 mm [
8
,
9
].
Environmental weathering results in plastic degradation in which long-chain polymers
are broken into smaller ones [
10
]. Weathering mechanisms including abiotic degradation
such as UV radiation, heat, and chemical reactions lead to plastic breakdown or fragmenta-
tion via mechanical stress or chemical oxidation [
11
]. Another notable degradation mecha-
nism is the biotic degradation caused by enzymatic processes as well as bio-disintegration,
in which plastics are fragmented into small pieces (e.g., the composting processes) [9].
Microplastics originate from various sources, and depending on their source, mi-
croplastics can be classified into primary and secondary microplastics [
12
,
13
]. Primary
Environments 2023,10, 70. https://doi.org/10.3390/environments10050070 https://www.mdpi.com/journal/environments

Environments 2023,10, 70 2 of 20
microplastics are minute plastic particles designed for commercial applications such as
cosmetic products. These are mainly composed of polyethylene (PE), polypropylene (PP),
polystyrene (PS), polyethylene terephthalate (PET) polymer, and acrylic or polyvinyl chlo-
ride (PVC) [
14
–
17
]. Primary microplastics usually enter the aquatic environment through
household sewage discharge or via air-blasting technology [
18
]. Other primary microplas-
tic examples include the use of acrylic or polyester in paint products and high-pressure
scrubbers [16,19].
Weathering and degradation of macroplastics result in the generation of secondary
microplastics [
20
]. Exposure to ultraviolet (UV) radiation catalyzes the photooxidation of
plastic, causing it to become brittle and fragment into microplastics [
9
]. One of the main
sources of secondary microplastics includes effluent from wastewater treatment plants
where they are found in the secondary treatment process of a wastewater treatment plant
after passing through the primary unit [
12
]. Another source of secondary microplastics
includes the wearing of plastics. Microplastics are released as a result of laundry activities
where the microplastics present in clothing products are released into the water [
21
], the
use of fishing gear including nets and ropes [
22
], tearing of rubber tires of automobiles [
23
]
as well as the wear and tear of household items such as plastic home furniture [24].
Microplastics are of increasing concern due to the ecotoxicological risks they pose to
aquatic and soil organisms as well as humans. Microplastic ingestion by a range of species
can result in bioaccumulation and biomagnification through the food chain. Microplastics,
possessing a size of less than 5 mm, are small enough to be readily consumed by marine
organisms [
25
]. As a result, primary consumers will assimilate the microplastics, pass them
on to their secondary consumers, and ultimately reach the human table, thus disrupting
the food chain [
26
]. Furthermore, microplastics can act as carrier vectors for heavy metals
and other pollutants such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated
biphenyls (PCBs) due to the hydrophobic nature of their surfaces [12,27,28].
After the Sustainable Development Goals (SDGs) were proposed by the United Na-
tions (UN), innumerable advocates have shifted economy-based development strategies
to measures that aim toward achieving an ever-lasting sustainable environment. The
United Nations Sustainable Development Goals (UN SDGs) assigned Goal 14 specifically
to conserve and use the oceans, seas, and marine resources sustainability and recognize
microplastics as emerging contaminants [
29
]. There is abundant literature discussing the
source and transport of microplastics in the hydrosphere, pedosphere, and atmosphere.
However, the fate and transport of microplastics in the environment in total, along with
their ecotoxicological impact on environmental organisms, are elusive. In this study, we col-
lated the review of microplastics in the three main zones of the environment—hydrosphere,
pedosphere, and atmosphere—and offer a single platform for readers to gain informa-
tion on the fate and transport of microplastics in the environment. Therefore, this review
aimed to provide a comprehensive understanding and the current state of research on
(i) the fate and transport of microplastic in the pedosphere, hydrosphere, and atmosphere;
(ii) the ecotoxicological impact of microplastics on aquatic and soil communities; (iii) the
prospective future research directions and plastic waste management strategies to control
microplastic pollution.
2. Sources and Types of Microplastics
Depending on their source, microplastics can be categorized into primary and sec-
ondary microplastics, as summarized in Table 1. There are six major types of observed
microplastics, based on their chemical composition and density including polystyrene
(PS), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropy-
lene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). All the rest
can be categorized as “others” (e.g., nylon, polyester) [
30
,
31
]. The common sources of PS
include cosmetic products (such as exfoliator beads found in facial scrubs), plastic furniture,
kitchenware, single-use plasticware, and plastic packaging materials. Clingy plastic wraps
and films, juice boxes, wire insulations, and disposable shopping bags are the sources of

Environments 2023,10, 70 3 of 20
LPDE. The main source of HDPE includes toys, shampoo bottles, recycle bins, cereal box
liners, and pipe systems. For PP, the common sources include straws, fishing gear (nets
and ropes), tapes, carpets, and camping items. PVC fittings and pipe accessories are the
major sources of PVC. The main sources of PET include food packaging, take-away food
containers, and textiles [
32
–
35
]. In addition to the differentiation based on the chemical
composition and density, microplastics can also be classified based on shape. Therefore,
microplastics may be categorized into pellets, microbeads, foams, fibers, films, fragments,
and microfibers [36].
Table 1. Categories of microplastics and their applications.
Category Common Applications References
Primary source
These include plastic pellets, exfoliator beads
present in facial scrubs and cleansers, sparkles
found in nail polish and make-up products, and
plastics used in air-blasting technology.
[14–17]
Secondary source
Water and wastewater
treatment plants discharge
Microplastics smaller in size may go untrapped
in the primary unit of the wastewater treatment
plant and enter the secondary units. These
include microfibers from washing clothes.
[12,37]
Wear and tear from normal
plastic use
Examples include the washing of clothes and
textiles during laundry, fishing activities, wear
and tear of rubber tires of automobiles, and
degradation of household items and plastic
furniture.
[21–24]
Airborne dust
These include plastic dust released from
activities such as plastic manufacturing, the
incineration of plastic waste, traffic emissions,
weathering of roads and streets, and urban
mining activities. Indoor airborne microplastics
come from plastic items used in household
including food packaging, plastic wear, and
plastic furnishings.
[38–41]
Secondary microplastics
The decomposition and weathering of
macroplastics generate secondary microplastics.
For example, the degradation of plastic litter
such as disposable plastic cutlery, plastic cups,
and food containers that end up being dumped
on coastal shorelines.
[9]
3. Transport of Microplastics
In the environment, microplastics can be transported through atmospheric or aquatic
currents depending on their weight and density [
42
]. Rainfall, surface runoff, and ocean
circulation are the possible routes that transfer microplastics from the pedosphere to the
hydrosphere. Not only can microplastics be transported from land to water, but they can
also travel from water to land due to ocean circulation [
43
]. Moreover, lighter and smaller
microplastics can be carried by the wind as airborne microplastics and consequently be
transported to remote areas such as glacier zones and high mountains. While lighter
microplastics can be relocated across the pedosphere by wind, denser microplastics might
accumulate or be buried in the pedosphere (soil) [
13
]. Heavy rainfall and surface runoff
from agricultural lands and urban areas can transport microplastics to surface waters
(the hydrosphere). Studies have shown that agricultural practices involving the use of
plastic mulches to improve crop growth or domestic sewage sludge as a soil amendment
may introduce microplastics to the soil [
44
,
45
]. Additionally, stormwater runoff carries
the microplastics resulting from the normal wear of tires on the road to neighboring

Environments 2023,10, 70 4 of 20
surface waters [
13
]. Moreover, airborne microplastics consisting of light fibers from clothes,
landfills, and waste incineration can be transported over long distances to remote areas
and be deposited via atmospheric fallout [
46
,
47
]. Figure 1shows a schematic of the
global distribution of microplastics in the environment. The following subsections discuss
the fate of microplastics in the different environmental compartments: the hydrosphere,
pedosphere, and atmosphere.
Environments 2023, 10, x FOR PEER REVIEW 4 of 21
and be deposited via atmospheric fallout [46,47]. Figure 1 shows a schematic of the global
distribution of microplastics in the environment. The following subsections discuss the
fate of microplastics in the dierent environmental compartments: the hydrosphere,
pedosphere, and atmosphere.
Figure 1. Microplastic distribution in the environment. The schematic represents the horizontal and
vertical distribution of the microplastic in the hydrosphere. Water current and wind current result
in the hydrosphere and atmospheric microplastic transfer, respectively, and result in microplastic
transfer to remote areas such as Arctic zones.
3.1. Fate of Microplastics in the Hydrosphere
The hydrosphere is the primary sink for microplastics, where human activities such
as tourism and wastewater treatment result in depositing microplastics in aquatic habitats
[48]. For instance, seven million microplastic items are released every day into the aquatic
habitat via wastewater treatment plant euents [48,49]. Depending on the physical
properties (e.g., shape and size), density, and chemical composition, microplastics can
either accumulate in the hydrosphere (i.e., their immediate source of disposal) or travel to
other remote environment areas such as glacial zones through various transport
mechanisms [50,51,52]. Among the microplastics present in the hydrosphere, 70% of them
are stored in the sediments of the aquatic body, and approximately 15% of microplastics
remain in the suspended form [28]. The mechanisms for the fate and distribution of
microplastics in the hydrosphere are not well-dened due to the degree of variation in the
dierent plastic degradation pathways as well as the water dynamics such as ocean
currents and wind currents, the velocities and intensities of which depend on climatic
conditions. However, two probable pathways for microplastic distribution in the
hydrosphere have been proposed: horizontal and vertical distributions.
Horizontal distribution is governed by water circulation velocity, precipitation, and
wind current, which determine the transport of plastic lier from the pedosphere into the
hydrosphere [53,54,55]. Upon entering the aquatic environment, plastic lier is exposed
to ocean current abrasion, abiotic disintegration, or biotic degradation. Microplastics of
dierent shapes, sizes, densities, and chemical compositions are formed, and those having
a density greater than the surrounding water will sink to the boom of the aquatic system,
whereas the lighter ones can remain suspended in the surface water [32]. The diameter of
the microplastics aects its transport under dierent water dynamics, which determines
the horizontal distribution of the microplastic. For example, the river bed slope in the
Rhine river resulted in the transport of microplastics over longer distances due to the
increased velocity as the result of the river bed slope [56]. The water conditions such as
river bed form, the ow velocity of sea, river, ocean and other water bodies, water level,
and water current impacts the transport of microplastics in the hydrosphere. In the case
Figure 1.
Microplastic distribution in the environment. The schematic represents the horizontal and
vertical distribution of the microplastic in the hydrosphere. Water current and wind current result
in the hydrosphere and atmospheric microplastic transfer, respectively, and result in microplastic
transfer to remote areas such as Arctic zones.
3.1. Fate of Microplastics in the Hydrosphere
The hydrosphere is the primary sink for microplastics, where human activities such as
tourism and wastewater treatment result in depositing microplastics in aquatic habitats [
48
].
For instance, seven million microplastic items are released every day into the aquatic habitat
via wastewater treatment plant effluents [
48
,
49
]. Depending on the physical properties (e.g.,
shape and size), density, and chemical composition, microplastics can either accumulate in
the hydrosphere (i.e., their immediate source of disposal) or travel to other remote environ-
ment areas such as glacial zones through various transport mechanisms [
50
–
52
]. Among
the microplastics present in the hydrosphere, 70% of them are stored in the sediments
of the aquatic body, and approximately 15% of microplastics remain in the suspended
form [
28
]. The mechanisms for the fate and distribution of microplastics in the hydrosphere
are not well-defined due to the degree of variation in the different plastic degradation
pathways as well as the water dynamics such as ocean currents and wind currents, the
velocities and intensities of which depend on climatic conditions. However, two probable
pathways for microplastic distribution in the hydrosphere have been proposed: horizontal
and vertical distributions.
Horizontal distribution is governed by water circulation velocity, precipitation, and
wind current, which determine the transport of plastic litter from the pedosphere into
the hydrosphere [
53
–
55
]. Upon entering the aquatic environment, plastic litter is exposed
to ocean current abrasion, abiotic disintegration, or biotic degradation. Microplastics of
different shapes, sizes, densities, and chemical compositions are formed, and those having
a density greater than the surrounding water will sink to the bottom of the aquatic system,
whereas the lighter ones can remain suspended in the surface water [
32
]. The diameter of
the microplastics affects its transport under different water dynamics, which determines
the horizontal distribution of the microplastic. For example, the river bed slope in the
Rhine river resulted in the transport of microplastics over longer distances due to the
increased velocity as the result of the river bed slope [
56
]. The water conditions such as

Environments 2023,10, 70 5 of 20
river bed form, the flow velocity of sea, river, ocean and other water bodies, water level,
and water current impacts the transport of microplastics in the hydrosphere. In the case of
rivers, dam and reservoir constructions can affect the water velocity and impact the fate of
microplastics [
57
]. Based on the velocity and flow direction of the regional wind and water
currents, the suspended microplastics can either return to the coastal shorelines/beaches or
be transported to remote regions [
12
,
48
,
58
], and the microplastics will remain suspended at
the water surface. As per data from 2010, approximately 5–13 million tons of macroplastics
enter the hydrosphere (ocean) [
3
], and 7–35 thousand tons of microplastics remained in
suspended form [59].
Another distribution pathway is vertical distribution, where heavier microplastics
sink to the water bed including seabeds, riverbeds, and ocean beds. Vertical distribution
in the hydrosphere includes vertical turbulent mixing, which is governed by the water
velocity and flow of direction; biota transfer, which depends on the movement of aquatic
organisms; biological fouling and aggregate/cluster formation, which is governed by the
presence of organisms present in the hydrosphere including microorganisms, bacteria,
plankton, and algae [
32
,
60
,
61
]. Biological fouling and aggregate formation are affected
by a number of factors such as microplastic characteristics (type, chemical composition,
surface morphology) as well as hydrosphere characteristics (temperature, pH, types of
microbes present) [
62
–
65
]. For example, in the Arabian Gulf, the surfaces of PET and PE
microplastics underwent biofouling as a result of the presence of different microbes and
plankton [
66
]. The process of biological fouling mainly comprises three steps: first, the
microbes and nutrients present in the hydrosphere attach to the microplastic’s surface [
67
];
subsequently, extracellular polymeric substances are released by the microorganisms to
form a biofilm that further attracts other marine invertebrates and aquatic life; second, the
attached microbes release extracellular polymeric substances (EPS) to further attract more
microbes and nutrients [
68
]; finally, a clustered mass of microplastics with flocculant and
nutrients eventually becomes denser and sinks to the bottom.
Table 2summarizes the studies on the occurrence and identification of microplastics in
the hydrosphere including sediment, deep-sea [
69
,
70
], shorelines [
71
], freshwater, river [
72
],
oceans [
42
,
73
], and coral reefs [
74
]. The deep-sea has been termed a global sink for mi-
croplastics, as evidenced by the first experimentally-based study conducted by Woodall
et al. [
69
]. The vertical distribution of microplastics results in the accumulation of microplas-
tics in the sea sediments, and a study conducted by Van Cauwenberghe [
75
] suggested
deep-sea sediments as the hot spot for microplastic accumulation. Other studies have
reported microplastics in the sediments in the range of 8 pieces/kg to 600,000 pieces/kg
sediment [76,77]. Another potential sink of microplastics in the hydrosphere is coral reefs.
An area of ~250,000 km
2
has been shown to assimilate microplastics at the annual rate of
1.5 ±1.9 % from surrounding waters during their growth [74].
Table 2. Occurrence of microplastics (MPs) in the hydrosphere.
Location Sink Type Sample Collection Analysis Result Summary Reference
Mediterranean Sea, South
West Indian Ocean, and
North East Atlantic
Ocean.
Deep sea
sediments
12 sediment cores
and 4 coral samples
were sampled
MPs were extracted by
sequential extraction using
sodium chloride solution. The
MPs were characterized using
FTIR.
All samples
contained MPs.
Characteristics of MP:
diameter <0.1 mm,
and fiber shaped.
[69]
Sandy beaches of
Australia, Oman, Chile,
USA, Philippines,
Portugal, Azores,
Mozambique, and the
United Kingdom.
Shoreline
Shoreline sediments
were sampled up to a
depth of 1 cm.
MPs were extracted using
sodium chloride solution
followed by filtration. The MPs
were characterized using FTIR.
MPs concentration of
8–124 MPs per 1000
mL of the sediment
was quantified.
These included PS,
PP, PE, acrylic, and
polyamide fibers.
[71]

Environments 2023,10, 70 6 of 20
Table 2. Cont.
Location Sink Type Sample Collection Analysis Result Summary Reference
Southern Ocean, North
Atlantic Ocean, Gulf of
Guinea, and
Mediterranean Sea.
Deep-sea
sediments
Sediment samples
were sampled up to a
depth of 1.2–4.8 km.
MPs were extracted using wet
sieves, followed by density
floatation using sodium iodide
solution. MPs were
characterized using
micro-Raman spectroscopy.
MPs of size 75–160
microns were found
in the samples.
[75]
Irish continental shelf Marine
sediments
Sediment box cores
were collected from
11 sites up to a depth
of 4.5 cm.
MPs were extracted by density
flotation using sodium poly
tungstate. MPs were
characterized using FTIR.
62 MPs were
recovered from 10
stations out of 11.
[70]
Western North Atlantic
Ocean and Caribbean Sea
Regional water
gyre
6100 surface
plankton net tows
were sampled.
MPs were handpicked. The
characterization method was
not mentioned.
MPs were identified
in the ocean gyre. [42]
Laboratory experiment Coral reefs
4 reef-building coral
species were exposed
to PE (200
particles/L).
Research
duration-18 months.
MPs were extracted from the
coral reefs using sodium
hypochlorite. MPs were
characterized using a
microscope and FTIR.
Coral reefs can trap
MP in their tissue as
well as the skeleton.
[74]
Northeast Pacific ocean Surface water
Zooplankton samples
collected from the
surface water
(n = 595).
MPs were sieved and
handpicked. They were
characterized using a
microscope and FTIR.
MPs were identified
in all the samples. [77]
3.2. Fate of Microplastics in the Pedosphere
In the literature, most of the research as focused on the hydrosphere as a sink for
microplastics, and very few studies have discussed the role of the pedosphere as a potential
sink for microplastics. For example, a European farm was reported to be able to deposit
an average of 50,000 tons of microplastics annually [
44
,
78
]. In light of such a finding,
the destructive impact of microplastics on soil organisms (both flora and fauna) should
be further investigated. There are two potential sources of microplastics contaminating
the pedosphere: domestic and agricultural activities. Domestic activities such as tourism
result in the disposal of plastic products and single-use plastics that accumulate on land as
plastic litter. As per the data, the plastic litter predominantly consists of at least 90 million
daily grocery bags [
79
], which end up as mismanaged plastic waste. Once exposed to
the environment, plastic litter undergoes deterioration and releases microplastics into
the soil. It has been estimated that around 300 million tons of microplastics are present
in the soil [
80
]. Another potential source of microplastics in the pedosphere relates to
agricultural activities such as the application of polymer-coated fertilizers, slow-release
fertilizers, composting, organic fertilizers, plastic mulches (made up of polyethylene), and
irrigation water containing microplastics (usually synthetic fiber) [
13
,
81
–
86
]. Liu et al. [
87
]
reported that over two decades, the concentration of wasted plastic mulch in China’s
agricultural field has increased by four times (up to 1.2 million tons). Plastic mulch and
other fertilizers added to the soil undergoes numerous weathering processes, thus releasing
MPs in the soil [
83
]. Browne et al. [
71
] found that the composition of the synthetic fiber
in the wastewater consisted of polyester (67%) and acrylic (17%), which was similar to
the composition of textiles, which implies that the main source of microplastics in the
wastewater was from washing clothes. Sewage sludge is treated by anaerobic digestion and
aerobic composting and the sludge-fertilizer thus formed is applied to the soil [88]. These
microplastic-contaminated sludge fertilizers introduce MPs into the pedosphere [
89
]. For
example, Zhang et al. [
90
] reported that the utilization of sludge-based fertilizer resulted
in an increase in the microplastic concentration in the soil by approximately 60 times.
Agricultural runoffs tend to transport the microplastics to nearby water bodies, but a
portion of the microplastics can be entrapped in the soil.

Environments 2023,10, 70 7 of 20
The fate and transport of microplastics in the soil are not well-reported. The movement
of MPs in the soil is complex and is primarily governed by bioturbation (i.e., the transfer of
microplastics from the surface soil into deeper layers) (Figure 2) [
91
]. Bioturbation is medi-
ated by soil fauna such as earthworms, soil larvae, and vertebrates (e.g., moles, mice, snakes,
and rabbits). These soil faunae can mediate soil vertical mixing via burrowing actions
(mimicking a mechanical mechanism) or by ingesting the microplastics and translocating
them into deeper soils while moving downward [
91
,
92
]. Several experimental studies show
the transport of microplastics in the soil via bioturbation. For example, Zhu et al. [
93
]
reported that the scraping and chewing actions of mites and collembola on plastics resulted
in the migration and transport of MPs in the soil. Earthworms result in the migration of
MPs both by external attachment as well as an internal attachment (via ingestions and
excretion), thus facilitating the lateral and vertical transport of MPs in the soil [
92
,
94
]. Other
routes of MP transport in the soil include root movement and expansion [
91
,
95
], tillage
activities [
96
], and the harvest of tuber crops such as potatoes and carrots. The downward
movement of microplastics would also be influenced by several parameters including the
wetting–drying cycle, soil pore space, soil type, moisture content, precipitation, temper-
ature, and leaching [
97
,
98
]. The shape, size, and composition of the microplastics also
determine their transport in the soil. Certain microplastics such as polystyrene can form
aggregates with soil under the influence of soil organic carbon, pH, and the cation exchange
capacity of the soil [
99
,
100
]. However, more research is needed to gain deeper insights into
the influence of soil properties and external factors on the migration of MPs in the soil.
Environments 2023, 10, x FOR PEER REVIEW 8 of 21
Figure 2. Microplastic transport in the soil. Bioturbation and ingestion by soil organisms are the
main routes for microplastic transfer into deeper soil layers. As a consequence, microplastics interact
with the POPs and heavy metals present in the soil, which can be bioavailable to plants.
Table 3. Occurrence of microplastics (MPs) in the pedosphere.
Location
Sink Type
Sample
Collection
Analysis
Result Summary
Reference
Bohai Sea and
the Yellow Sea
coastlines,
Shandong
Province, East
China.
Coastal beach
soils
Soil samples (n
= 120) were
sampled from
53 sites along
the coastline
(~3000 km).
MPs were extracted by
density separation
using sodium chloride
and sodium iodide
solution. The MPs
were characterized
using
stereomicroscope,
SEM, and ATR-FTIR.
MPs of size <5 mm were
found in all samples in the
range of 1.3–14,712.5 MP/kg
soil. These included PE, PP,
and PS.
[101]
Vegetable
farmlands and
riparian forest
zone around
Dian Lake,
Yunnan, China
Greenhouse
soil and forest
zone soil
Soil samples
were collected
(n = 50).
MPs were extracted
using sodium iodide
solution followed by
hydrogen peroxide.
The MPs were
characterized using a
stereomicroscope.
MPs were identied in the
range of 7100 to 42,960
MP/kg. The size of 95% of
the sampled MP is in the
range of 1–0.05 mm. These
predominantly included
plastic bers.
[96]
Agricultural
elds (n = 31) in
Chile where
sludge-based
fertilizers were
applied.
Agricultural
soil
Top soil (0–25
cm) was
sampled from
each
agricultural
eld.
MPs were extracted by
density separation
using sodium chloride
and zinc chloride. MPs
were characterized by
stereomicroscope.
MPs of size 0.16–10 mm
were found in the samples.
These predominantly
included bers (>97%).
[102]
Vegetable
farmland,
Shanghai, China.
Vegetable soil
Soil samples (n
= 3) were
collected from
shallow (0–
MPs were extracted
using sodium chloride
solution followed by
hydrogen peroxide.
MPs were
MPs of size 20 microns–5
mm were found in the
samples. These
predominantly included
[103]
Figure 2.
Microplastic transport in the soil. Bioturbation and ingestion by soil organisms are the main
routes for microplastic transfer into deeper soil layers. As a consequence, microplastics interact with
the POPs and heavy metals present in the soil, which can be bioavailable to plants.
Table 3summarizes the field monitoring work on the occurrence of microplastics in
the soil matrix. Zhou et al. [
101
] investigated the distribution of microplastics in the coastal
shorelines of Bohai Sea and Yellow Sea of China. Various types of microplastics were found
in the sampled soil including PE, PP, and PS with an average concentration of 7350 MP/kg.
Zhang and Liu [
96
] conducted a study on the vegetable farmlands and riparian forest zone
around Dian Lake, China, and found microplastics in the soil aggregate fractions with an
average concentration of 18,760 MP/kg. Corradini et al. [
102
] investigated microplastic
contamination in agricultural fields in Chile and found that the microplastic concentration
in the soil increased with the increasing rate of the application of sludge-based fertilizer. In
the suburbs of Shanghai, microplastics were detected in the soils of the rice–fish co-culture
ecosystem (8.1–12.5 MP/kg) and vegetable farmlands (65.1–90.9 MP/kg) [103,104].

Environments 2023,10, 70 8 of 20
Table 3. Occurrence of microplastics (MPs) in the pedosphere.
Location Sink Type Sample
Collection Analysis Result Summary Reference
Bohai Sea and the
Yellow Sea
coastlines,
Shandong
Province, East
China.
Coastal beach soils
Soil samples
(n = 120) were
sampled from
53 sites along the
coastline
(~3000 km).
MPs were extracted by
density separation
using sodium chloride
and sodium iodide
solution. The MPs
were characterized
using
stereomicroscope,
SEM, and ATR-FTIR.
MPs of size <5 mm
were found in all
samples in the
range of
1.3–14,712.5
MP/kg soil. These
included PE, PP,
and PS.
[101]
Vegetable
farmlands and
riparian forest
zone around Dian
Lake, Yunnan,
China
Greenhouse soil
and forest zone soil
Soil samples were
collected (n = 50).
MPs were extracted
using sodium iodide
solution followed by
hydrogen peroxide.
The MPs were
characterized using a
stereomicroscope.
MPs were
identified in the
range of 7100 to
42,960 MP/kg. The
size of 95% of the
sampled MP is in
the range of
1–0.05 mm. These
predominantly
included plastic
fibers.
[96]
Agricultural fields
(n = 31) in Chile
where
sludge-based
fertilizers were
applied.
Agricultural soil
Top soil (0–25 cm)
was sampled from
each agricultural
field.
MPs were extracted by
density separation
using sodium chloride
and zinc chloride. MPs
were characterized by
stereomicroscope.
MPs of size
0.16–10 mm were
found in the
samples. These
predominantly
included fibers
(>97%).
[102]
Vegetable
farmland,
Shanghai, China.
Vegetable soil
Soil samples (n = 3)
were collected
from shallow
(0–3 cm) and deep
soils (3–6 cm).
MPs were extracted
using sodium chloride
solution followed by
hydrogen peroxide.
MPs were
characterized using a
stereomicroscope and
µFTIR.
MPs of size
20 microns–5 mm
were found in the
samples. These
predominantly
included fibers,
fragments, film,
and pellets.
[103]
Shanghai, China.
Soil from rice–fish
co-culture
ecosystem
1 kg of wet soil
was collected from
each site (n = 3).
MPs were extracted
using sodium chloride
solution followed by
hydrogen peroxide.
MPs were
characterized using a
stereomicroscope and
µFTIR.
MPs of size <5 mm
were found in the
samples. These
predominantly
included fibers,
fragments, film,
and granules.
[104]
3.3. Fate of Microplastic in the Atmosphere
Since the hydrosphere and pedosphere are possible sinks for microplastics, attention
has been extended to exploring the transport pathways from the origins to the ultimate
sink for microplastics. Thus, the microplastics in the atmosphere become an issue of
interest [
105
,
106
]. Microplastics with a small size and low density can be suspended in the
wind current and transported over a long distance [
107
]. It has been reported that airborne
microplastics, also known as atmospheric microplastic particles, can be transported from
ocean surfaces in low-latitude zones to remote areas including the Arctic zones [
43
,
108
–
111
].
The available studies on atmospheric microplastics are limited and do not provide a clear
understanding of the fate and distribution of microplastics in the atmosphere because most

Environments 2023,10, 70 9 of 20
of the studies have been short-term monitoring works. For example, Dris et al. [
46
] and
Klein and Fischer [
110
] conducted experiments to identify and characterize microplastics
in the atmosphere over 12 months. Therefore, long-term monitoring works on atmospheric
microplastics are deemed necessary.
Atmospheric microplastics are considered a category of emerging contaminants
given the rising concern that the inhalation of microplastics can be detrimental to hu-
man health [
112
–
116
]. During the outbreak of the COVID-19 pandemic, surgical masks
were worn, which became a new source of microplastics. These masks, which were com-
posed of PP, PE, and PS, presented a direct route of inhalation that reaches the human
lungs [11,117,118].
The distribution and transport of atmospheric microplastics are governed by the wind
current speed and directions, up/down drafts, convection lift, and turbulence. They affect
the transport and fate of microplastics between the various environmental compartments—
the hydrosphere, pedosphere, and atmosphere [
105
,
111
]. Atmospheric microplastics can
travel to remote areas and be deposited through the precipitation of rain and snow. Since
rain and snow precipitation are two probable pathways for atmospheric microplastic depo-
sition, more research is needed to understand the impact of rainfall/snowfall events and
draw correlations between microplastic deposition and climatic conditions. Microplastics
have reached remote areas including Arctic Sea Ice (38–234 particles per cubic meter) [
52
],
Fram Strait [
119
], the Italian Alps (Forni Glacier, 74.4
±
28.3 particles per kilogram of sedi-
ment) [
109
] as well as the Vatnajökull ice cap in Iceland [
120
]. In the Arctic zones, snowfall
is one of the primary methods of atmospheric deposition for microplastics. The mechanism
of microplastic entrainment in glacier ice has been proposed by Van Sebille et al. [
121
], who
indicated that microplastic scavenging might occur during the ice formation process. Ice
crystals are formed that cover the surface of the sea. Subsequently, continuous agglomer-
ation of thick ice crystals occurs, resulting in the storing of more microplastics in deeper
layers of the ice crystals.
Table 4summarizes the available literature on atmospheric microplastics. Strong
wind and rainfall events resulted in the deposition of atmospheric microplastics in the
urban cities of Paris and Hamburg, where ~120 MP/m
2
and 275 MP/m
2
, respectively,
are deposited daily [
110
,
122
]. Cai et al. [
47
] reported the deposition of atmospheric mi-
croplastics in the city of Dongguan, China, which comprised both non-fibers and fibers
(mean 244 MP/m
2
daily). Atmospheric deposition was found to be higher in coastal
areas where wind currents are stronger (e.g., in Yantai, a coastal city in China), and an
atmospheric microplastic deposition of 602 MP/m
2
per day was reported [
123
]. In remote
areas, atmospheric deposition can be lower compared to the microplastic source because
there is a possibility of microplastics being deposited during long-distance transport. In
the Pyrenees Mountains, an average microplastic particle deposition of 365 MP/m
2
per
day has been reported [
108
]. Higher atmospheric microplastic deposition can be correlated
to higher human activities. For instance, Shanghai has a higher population density and
industrialization compared to Paris. Liu et al. [
109
] reported that Shanghai experienced a
greater atmospheric microplastic deposition of 4.18 MP/m
3
whereas Paris experienced an
atmospheric microplastic deposition of 2.84 MP/m3.
Table 4. Occurrence of microplastics (MPs) in the atmosphere.
Location Sample Type Analysis Result Summary Reference
Paris, France
Atmospheric fallout
A stainless-steel funnel was
used for the continuous
sampling of microplastics.
Samples were then filtered.
The MPs were characterized
using a stereomicroscope and
µFTIR.
MPs of various sizes were found
in the samples (predominantly
200–600 µm (42%) and
600–1400 µm (40%)).
Atmospheric microplastic
deposition of 120 MP/m2per
day. These included fibers.
[46]

Environments 2023,10, 70 10 of 20
Table 4. Cont.
Location Sample Type Analysis Result Summary Reference
Shanghai, China
Suspended
atmospheric
microplastics
A suspended particulate
sampler was used to collect the
samples. MPs were
characterized using a
stereomicroscope and µFTIR.
MPs were identified to have a
maximum deposition rate of 4.18
MP/m3. The size of more than
50% of the sampled MP is in the
range of 23–500 µm. These
predominantly included PET, PE,
and rayon.
[111]
Pyrenees
Mountains, Europe.
Atmospheric dry
and wet deposition
MPs were characterized using
a stereomicroscope and
µRaman.
Average microplastic particle
deposition of 365 MP/m2per
day. These predominantly
included PS, PE, PP, PVC, and
PET.
[108]
Yantai, China. Atmospheric
deposition
MPs were characterized using
a stereomicroscope and
µ
FTIR.
MPs of size 100–300 µm were
found in the samples.
Atmospheric microplastic
deposition of 602 MP/m2per
day. These predominantly
included fibers.
[123]
Dongguan city,
China.
Indoor and outdoor
dust
MPs were characterized using
a stereomicroscope and
µ
FTIR.
Atmospheric microplastic
deposition of 244 MP/m2per
day. These predominantly
included PP, PE, and PS.
[47]
Hamburg,
Germany.
Atmospheric fallout
MPs were characterized using
µRaman.
Atmospheric microplastic
deposition of 275 MP/m2per
day. These included
predominantly PE.
[110]
4. Impacts: Implications on the Soil, Water, and Biological Communities
This section reviews the impact of microplastics present in the hydrosphere and
pedosphere on aquatic organisms and soil organisms. Atmospheric microplastics eventually
enter the hydrosphere or pedosphere upon deposition, therefore, the impact of atmospheric
microplastics is not discussed separately.
4.1. Ecotoxicological Impact on Aquatic Biota
Microplastics are considered emerging contaminants due to their ecotoxicological im-
pact on aquatic biota. Because of their small size, microplastics can be readily taken up by
aquatic organisms including fishes, invertebrates as well as coastal birds and animals [
124
].
Many studies have been conducted on fish to understand the fate of bioavailable microplas-
tics in aquatic organisms. Table 5lists several studies exploring the effect of microplastic
ingestion on aquatic organisms. Studies on fish such as European Bass, Goldfish, Fathead
minnow, and Japanese medaka have confirmed the presence of microplastics (such as PS,
PVC, and PE) in their organ tissues [
125
,
126
]. In addition to fish, microplastics were also
detected in springtails, shrimps, and oysters [
127
–
129
]. The ecotoxicity of microplastics
impacts the health of the exposed aquatic organisms in different pathways including a
reduction in growth, dysfunction of the reproductive system, and influence on the egg’s
hatching [
130
,
131
], causing physical, chemical, and biological damage to aquatic organisms.
Examples of physical damage include damage to the gastrointestinal tract, which can lead
to the organism’s death and affect the mortality rate [
132
–
134
]. Chemical damage includes
the impact on the enzyme activities in organisms. For example, in the presence of PE and
heavy metal chromium (Cr), the uptake of Cr in Common Goby fish increased, which led
to a decrease in acetylcholinesterase (AchE) enzyme activity and resulted in acute toxic-
ity [
135
]. Examples of biological damage include gene manipulation and the development

Environments 2023,10, 70 11 of 20
of resistance genes for antibiotics and heavy metals [
136
]. Microplastics enter the food chain
and result in biomagnification where the microplastics are initially ingested by primary
consumers (e.g., small fishes, algae), and eventually reach the secondary consumers (e.g.,
larger fishes and birds), ultimately reaching the tertiary consumers (humans). As a result,
microplastics translocate through the food chain and disrupt it [
137
]. Microplastics may
also act as vector carriers for heavy metals and environmental pollutants. They can adsorb
these pollutants and mediate their transfer into the environment, thus exposing aquatic
organisms to these pollutants [
138
]. For example, PE microplastics have been shown to
interact with co-pollutants such as zinc oxide, resulting in increased microalgal growth in
the marine environment [
139
]. Microplastics are also found in larger aquatic biotas such as
whales [140], seals [141], sea urchins [142], walruses [143], and turtles [144].
Table 5. Impact of microplastics on aquatic biota.
Organism Aquatic Biota type Type of MP Impact Reference
Dunaliella salina Marine microalgae PE
MPs interact with zinc oxide and leach the
pollutant, thus making it unavailable for
the microalgae. This resulted in enhanced
microalgal growth.
[139]
Common goby
(Pomatoschistus
microps)
Fish PE
The presence of microplastics along with
heavy metal chromium (Cr) resulted in a
decrease in acetylcholinesterase (AchE)
activity.
[135]
Japanese medaka
(Oryzias latipes)Fish PE Disruption of the normal functioning of
the endocrine system. [145]
European sea bass
(Dicentrarchus
labrax)
Fish PVC Intestinal damage. [146]
European sea bass
(Dicentrarchus
labrax) larvae
Fish PE Injuries and ulceration in the intestines. [147]
Goldfish (Carassius
auratus)Fish PS, PE MPs were detected in the digestive tract. [125]
Fathead minnow
(Pimephales promela)Fish PS MPs suppress the immunity of fish. [126]
Marine copepod
(Tigriopus japonicus)Invertebrate PP MP ingestion and reduction in their
fecundity. [127]
Insects (Trichoptera,
Plecoptera, and
Coleoptera)
Invertebrate Polyester MP accumulation in the invertebrates. [133]
Gammaridae,
Asellidae, Tubificidae,
and Chironomidae
Invertebrate PE, PP, PVC, and
others MP accumulation in the gut. [134]
Shrimps
(Metapenaeus
monoceros,
Parapeneopsis
stylifera, and
Penaeus indicus)
Invertebrate
PP, PE, polyamide,
nylon, polyester,
and PET
MPs were detected in the gastrointestinal
tract and gut. [128]
Oysters (Ostrea
edulis)Invertebrate HDPE
Ingestion of HDPE resulted in greater
respiration rates in oysters, affecting the
mortality rate.
[129]

Environments 2023,10, 70 12 of 20
Table 5. Cont.
Organism Aquatic Biota type Type of MP Impact Reference
Sea urchins Invertebrate PE MP ingestion detected. [142]
Humpback whale
(Megaptera
novaeangliae)
Mammals PE, PP, PVC, PET,
nylon
Microplastics accumulated in the
gastrointestinal tract. [140]
Green turtle
(Chelonia mydas)Reptile PS, PE
The presence of microplastics in the beach
sand resulted in disruption of the nesting
ground for turtles and a delay in egg
hatching.
[144]
Walrus (Odobenus
rosmarus)Animal PE, PP, polyamide,
polyester, acrylic MP detection in the walrus feces. [143]
Fur Seals
(Arctocephalus
australis)
Animal
Microfibers (type of
MP not
determined)
MPs were detected in the seal feces. [141]
4.2. Ecotoxicological Impact on Soil Biota
Microplastics can act as carriers for environmental contaminants such as persistent
organic pollutants (POPs) [
148
]. POPs are present in wastewater effluents, urban runoffs,
and leachates from landfill. POPs that are commonly present in agricultural soil include
polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides,
and herbicides [
149
]. Microplastics can absorb and transfer the POPs and pose a threat
to the pedosphere biota. In a study by Bakir et al. [
150
], the interaction between PVC,
PE, and various POPs were investigated, showing that a plastic–POP mixture poses a
considerable environmental threat. As previously mentioned, microplastics can absorb
heavy metals on their surface. If the soil environment is contaminated with heavy metals,
microplastics may act as vector carriers for the heavy metals and mediate their transfer into
the deeper soil layers or make it available to the plants for uptake after their entrance to
the soil media [
151
]. The interaction between heavy metal and microplastics is governed
by their chemical and physical characteristics such as specific surface area and molecular
polarity [
152
]. Microplastic accumulation in soil has a detrimental effect on the animals
residing in the pedosphere. Microplastics are not readily digested by animals and it is
difficult for them to pass the undigested microplastics through their gut, thus leading to
microplastic accumulation in the animals’ bodies [
153
–
156
]. For example, mice residing in
soil contaminated with PS exhibited intestinal damage and reduced metabolic rate [
157
].
However, smaller organisms such as earthworms can digest microplastics, but microplastics
might damage their intestinal tract and impact their survival [
93
,
158
]. Table 6lists the
recent studies on the effects of microplastics on the soil biota. The summarized results
show that the predominant ecotoxicological effect of microplastics on the soil biota includes
growth and reproduction inhibition, damage to the gut lining, an increase in mortality rate,
damage to enzyme activities, and decreased immune responses [
45
,
103
,
159
]. Microplastics
also have detrimental effects on plants. For example, wheat and spring onions showed
reduced root and shoot biomass when growing in soil contaminated with LDPE, PS, HDPE,
PP, and PET [
160
,
161
]. More research is needed to understand the role of microplastics on
soil biota.
Table 6. Impact of microplastics on the soil biota.
Organism Soil Biota Type Type of MP Impact Reference
Wheat (Triticum
aestivum L.) Plant LDPE
Adverse impact on plant biomass, thus
affecting vegetative and reproductive
growth.
[161]

Environments 2023,10, 70 13 of 20
Table 6. Cont.
Organism Soil Biota Type Type of MP Impact Reference
Spring onion
(Allium fistulosu)Plant PS, HDPE, PP, PET Changes in the leaf traits and plant
biomass. [160]
Mice Residing animals PS Reduced metabolic rate. Intestinal
damage. [157]
Terrestrial snail
(Achatina fulica)Residing animals PET
Liver damage and misfunctioning of liver
enzymes. Disruption of digestion. [155]
Soil nematode
(Caenorhabditis
elegans)
Worms like animals
PS Disruption of motion and reproduction.
Growth disruption. [132]
Soil springtail
(Folsomia candida)
Worms like animals
PE
Decrease in reproduction rate. Damage to
gut microbes. [153]
Soil springtail
(Lobella sokamensis)
Worms like animals
PE, PS Locomotion disruption. [154]
Earthworm (Eisenia
fetida)Worm LDPE, PS Increase in enzyme activities including
catalase and peroxidase. [27]
Earthworm (Enchy-
traeuscrypticus)Worm PS
Decrease in body mass and damage to the
intestinal gut lining. [93]
Earthworm (Eisenia
andrei Bouché)Worm PE Reduced immune response. Gut damage. [45]
5. Prospective Future Research Directions and Plastic Waste Management Strategies
Microplastics are regarded as a category of emerging contaminants and pose an eco-
toxicological threat to aquatic, soil, and atmospheric ecosystems. In this review, the fate
and distribution of microplastics in the major environmental compartments (i.e., the hydro-
sphere, pedosphere, and atmosphere) were discussed. While atmospheric microplastics
can be transported over a long distance via the wind current and are eventually deposited
into the hydrosphere or pedosphere, the ecotoxicological effects of microplastics in the
aquatic and soil habitat were summarized. Based on the discussion in the manuscript,
perspectives on future research directions and plastic waste management strategies are
outlined. (a) Currently, most of the microplastic research focuses on the aquatic envi-
ronment. However, the microplastic distribution and accumulation in the pedosphere
and atmosphere remain to be explored. The pedosphere as well as the atmosphere are
involved in the microplastic source–sink dynamics, therefore, future research could focus
on these environmental compartments including large-scale monitoring and quantifica-
tion. (b) Only limited studies have been conducted to monitor soil data to understand
the distribution of microplastics in the pedosphere or atmosphere. The data relating to
the transfer of microplastics through the deeper soil layers or the atmosphere are not as
extensive as those available for the hydrosphere. Therefore, an attempt could be made to
fill in this gap to enhance the understanding regarding the movement of microplastics in
the environment. (c) As previously mentioned, microplastics may act as vector carriers
for other contaminants (e.g., POPs and heavy metals). There is a knowledge gap on the
adsorption and desorption mechanism of these contaminants onto the microplastics, which
need to be further investigated. (d) From the investigations reviewed in this manuscript, the
microplastic extraction and analytical techniques primarily consisted of initial microplastic
separation, followed by digestion and characterization using microscopic images or FTIR.
Aquatic, soil, and atmospheric microplastics are being collected from different environment
matrices. The microplastic extraction and analytical techniques should be standardized for
the different environmental scenarios to characterize the microplastics qualitatively and
quantitatively. It may not be scientific enough to use the same detection and characteriza-
tion protocols for the microplastics extracted from these three diverse environmental zones.

Environments 2023,10, 70 14 of 20
(e) The ecotoxicological impact of microplastics on the soil biota, especially earthworms,
has been well-reported and studied. However, only limited papers have discussed the
impact on plant species. Since microplastics can be bioavailable for plant uptake, they can
also carry certain contaminants. Therefore, it is important to study the effect resulting from
microplastics on plant performance. (f) The impact of microplastics on tertiary consumers
such as soil animals (e.g., poultry and rabbits) is missing. Since these animals can be a
source of food for humans, it is important to conduct field studies to examine the accu-
mulation of microplastics in soil animals. (g) The atmospheric transport of microplastics
plays an important role in the transport of microplastics in the environment. However, the
transport mechanism of microplastics within the air is not well-studied, nor is it known to
what extent atmospheric microplastic deposition results in aquatic or soil contamination.
Therefore, further research is needed to fill this gap in source–pathway–sink processes.
Since atmospheric microplastics can be deposited via snowfall in the glaciers where they
can be stored, studies should be implemented to measure the atmospheric microplastic flux
to quantify its contributions to the glaciers’ sink.
Having outlined the prospective future directions on microplastics, we hereby dis-
cuss different strategies for plastic waste management to control microplastic pollution.
Government plays an important role in reducing microplastic pollution and to promote
sustainable plastic waste management. Here are a few actions that can be taken at the
government level. (a) Identify the responsibilities of different states and municipal corpo-
rations in the production, use, recycling, and disposal of plastic wastes, and implement
corrective measures such as environmental taxes for sectors generating plastic pollution.
(b) Raise the public awareness of microplastic pollution and its impact through education
and workshops. This includes creating a nexus of collaborations between environmental
protection organizations, non-governmental organizations, and scientists to initiate public
participation. (c) Limit the flow of plastics wherever possible such as reducing/prohibiting
the use of single-use plastics. (d) Collaborate with researchers to understand where plas-
tic pollution can be prevented early in the life span of plastic production. For example,
improved microplastic removal processes in wastewater and sewage treatment will help
reduce the amount of microplastics from entering aquatic and terrestrial habitats. (e) Limit
the use of microplastic-contaminated wastewater for irrigating agricultural soils and de-
velop a protocol to monitor the usage of sludge-based fertilizers. (f) Promote the use of
biodegradable plastics such as polyhydroxyalkanoates (PHA) and poly(lactic) acid (PLA)
that can be derived from microorganisms and microalgae [
162
] or natural fibers rich in
polysaccharides, lipids, and proteins [
2
]. In summary, controlling the microplastic release
at the source is necessary to prevent aquatic and soil biota exposure to microplastics.
Author Contributions:
Conceptualization, F.H. and C.F.; writing—original draft preparation, F.H.;
writing—review and editing, F.H. and C.F.; supervision, C.F. All authors have read and agreed to the
published version of the manuscript.
Funding:
This research was funded by National Science and Technology Council, Taiwan with the
grant number NSTC 109-2313-B-002-049-MY2 and the APC was funded by National Science and
Technology Council.
Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Conflicts of Interest: The authors declare no conflict of interest.
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