Microplastic Pollution in Soil and Water and the Potential Effects on Human Health: A Review

Abstract

The presence of microplastics in the environment has increased due to anthropogenic activities; it is estimated that 15 million kilograms of plastic waste accumulate in the ocean annually. Pollution permeates every inch of the ocean from microplastics in the food chain to plastic water bottles floating on the surface. This monolith of ocean pollution is made up of all kinds of marine debris and contains 1.8 trillion pieces of plastic, covering an area twice the size of Texas. The objective of this review is to show advances in the study of emerging problems, specifically in the presence of microplastics in water and soil and their potential effects on health. In addition, microplastics have synergy with residual contaminants that exist in the water such as textile waste, organic matter, pathogens, etc. This causes damage to aquatic organisms as it makes nutrient transfer more complex in many of these species. There is a report that estimates that liabilities related to plastic pollution will cost the industry 100,000 million dollars due to lawsuits for damages and losses, of which 20,000 million will occur in the United States. The study of the presence of microplastics in the environment can generate indicators of the current effect to generate public policies that try to control the growth of this pollutant in the environment. It is important to discuss all the routes of generation of microplastics, distribution, and cosmetics involved in fast fashion with glitter and to evaluate the physical, chemical, biological, and toxicological effects on the environment, proposing the path and future to be followed regarding this research topic.

1. Introduction

Marine pollution, unlike water pollution in general, focuses on artificial products that enter the ocean. In recent decades, it has really been evaluated how this aquatic habitat is affected by human activity. Plastic is already flooding the most remote places on the planet closer to our borders. It represents 95% of the waste present in the Mediterranean Sea, whose pollution accounts for the highest density of floating microplastics in its waters. Recently, it was thought that plastic pollution in the ocean came mainly from 20 rivers. However, according to a study published in May 2021, the plastic that floods the oceans reaches more than 1000 rivers around the world, complicating possible solutions [1].

Before 1972, the ocean was considered a bottomless space where all kinds of waste were dumped, ranging from sludge from wastewater treatment plants to chemical, industrial, and radioactive waste. The London Protocol was enacted in 1972 and later ratified in Spain in 1975. The agreement promoted regulatory programs and prohibited the dumping of hazardous materials into the sea. In 2006, an updated agreement came into force, establishing a strict list of materials and waste that cannot be disposed of in the ocean [2].

In the last two decades, the use of plastic has increased exponentially worldwide [3,4], due to its wide availability, low cost, and versatility [5]; its name derives from the Greek “Plastikos”, which refers to its ability to be deformed in different ways [6] Global plastic production dates to 1839, followed by long-lasting plastics in 1940 [7].

Table 1. Historical milestones in plastic development.

Year	Plastic Discovered	Source
1839	Polystyrene and vulcanized rubber	[9]
1860	Parkesine	[10]
1870	Celluloid	[10]
1907	Bakelite	[11]
1920	Polyvinyl chloride	[12]
1940	Advanced durable plastics	[7]

presents a brief condensation of the discovery of some relevant plastics in the history of humanity. If plastics are not controlled, it is estimated that 155–265 Mt of plastic will be produced annually by 2060 [8].

According to Lee et al. [13], ecotoxicity can be caused by the polymer itself, unreacted monomers, impurities (e.g., residual catalysts or reaction by-products), additives (e.g., stabilizers), or other substances within the polymer matrix (e.g., dyes, lubricants, or plasticizers). Various issues related to these have already been reported in marine organisms, such as malnutrition, inflammation, reduced fertility, and mortality [14,15]. The chemical components of environmental microplastics (MPs) are diverse and include plastic polymers, as well as additives that act as stabilizers, dyes, or oxidation retardants, most of which are endocrine disruptors, according to Bouwmeester et al. [16]. MPs can exist as fragments, films, fibers, and foam [17]. When determining the origin of microplastics in soils or groundwater, it is important to note that certain microplastic shapes are detached from different products [18,19].

Over time, microplastics have become a problem of great relevance to society; the degradation of superior plastics involves different organisms both in water and in soil. In addition, not only do they represent a risk to human development and health involving nervous tissue, oxidative stress, and the immune system, among others, but they also endanger microbiological life, and flora and fauna are potentially affected. Microplastics are usually generated from the degradation of anthropogenically generated plastics such as single-use bags and PET bottles, designed to contain some liquid and be discarded even if their degradation takes hundreds of years. And it is this degradation of long polymer chains that produces chains of less branching capable of being inserted in different environments such as rivers, lakes, algae, fauna systems, etc. [20]. The increase in this type of component has caused concern in different teams of researchers worldwide, as it generates uncertainty about the care of the environment and the species themselves.

A microplastic is defined as a particle with a diameter of less than 5 mm; this type of contaminant will prevail in the environment for hundreds of years due to its chemical stability [21]. They are mostly low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene tetraacetate (PET), and polyvinyl chloride (PVC) [22]. These pollutants come from two sources divided into primary and secondary [23]. According to Bouwmeester et al., the amount of PE and PP components is approximately 67% of all MPs. Primary sources are plastic particles added to personal care, beauty, and cosmetic products such as the glitter mentioned above. Figure 1 shows secondary sources, including those derived from the degradation of long-chain plastics such as physical and chemical processes and biodegradation that occurs due to erosion due to contact with water, air, and the sun. Thus, these particles are concentrated in different bodies of water such as rivers and lakes, as well as in crops, which directly impacts the environment. Microplastics, in addition to having different particle sizes, come in a wide variety of colors and shapes, which can be attractive to different marine organisms since they have sizes similar to the source of their nutrients [24]. Thus, many of these microplastics enter the organisms and begin a long chain of absorption and distribution, remaining in different organs and the entire digestive tract of higher species, even in tissue, which could put health at risk. In addition, organisms having a considerable intake of plastics are usually organisms with a low nutrient load when feeding the next member of the chain [25].

Micro- and nanospheres are particles with sizes of 1–1000 μm and 1–1000 nm, respectively. In the context of microplastics, these terms refer to synthetic polymers that are intentionally manufactured or the result of fragmentation of longer chains of plastic materials. Microbeads are often used in industry for personal care products, as exfoliating agents and as cosmetics, in addition to the biomedical area. Due to their size, they can easily enter the ocean, creating potential health and environmental risks.

On the other hand, nanospheres contribute to the growth of the problem of microplastics due to their larger surface area and can easily interact with biological systems; this allows them to easily penetrate cellular structures, promoting bioaccumulation and enhancing toxic effects.

Experiments with cells and animals have demonstrated the effects of MPs on various human body systems, including the digestive [26], respiratory [27], endocrine [28], reproductive [29], and immune systems [30]. Firstly, the digestive systems are affected when MPs are ingested, and physical irritation of the gastrointestinal tract can eventually cause inflammation, leading to various gastrointestinal symptoms [16].

Here begins the microplastic supply chain in human life. For instance, fish consumption introduces varying bioaccumulated doses resulting from the ingestion of primary organisms obtained from rivers and lakes. This is expected to impact not only biodiversity and the availability of fish—whose reproductive rates may decline due to nutrient depletion replaced by consumed plastics—but also potentially pose a risk to human health. Therefore, the study of microplastics, their accumulation, and their potential adverse effects on health must continue to be investigated across various scientific disciplines. Figure 2 shows the traditional life cycle of the plastics in the environment. Microplastic contamination of soil and groundwater is a potential risk for human health, plants, nematodes, soil properties, etc. There are some methods studied for remediation including pyrolysis, replacing plastics with biodegradable materials, plastic filters, etc. [31,32]. However, all these technologies need to be improved.

2. Microplastic Production

The principal secondary feeding mechanism through which microplastics enter the environment occurs after degradation caused by photodegradation, wind erosion, climate changes, and mechanical processes such as the downstream passage of plastic bags and bottles in rivers. These compounds, in addition to being ingested by small organisms, are very difficult to digest, leading to their accumulation throughout the entire food chain. Consequently, higher plastic concentrations in organisms are associated with more severe adverse health effects. Throughout the 21st century, various studies have demonstrated the presence of microplastics in plankton, fish, and seabirds [33,34]. Figure 3 shows the different types of plastics produced according to the particle size.

The influence of ocean currents, as well as their warming due to climate change and greenhouse gases, creates uncertainty regarding the expected abundance and typical accumulation of microplastics in water. Studies indicate that Antarctic waters do not yet show significant microplastic accumulation, attributed to the low levels of anthropogenic activity in the region [35]. Over the years, research on this issue has evolved from focusing on small regions to recognizing it as a global-scale problem. Nevertheless, a recent study reported the contribution of a wastewater treatment plant (WWTP) as a local source of MP particles in the region of the Antarctic for the first time. Micro-Raman analysis shows MPs from 64 to 159 particles per liter of wastewater. In addition, >90% of the identified particles were smaller than 50 μm. Among those analyzed, microplastics were identified as polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene, polyethylene terephthalate, and polystyrene [36].

Current research in the field primarily addresses the variation in microplastic concentrations in sediments, water, and soil. Traditionally, irrigation water for many crops comes from rivers near agricultural lands, making it a vector for the distribution of microplastics and thereby creating a more complex issue. Fibers and microplastics are easily ingested by terrestrial organisms, leading to accumulation in sediments. Studies show that the so-called vertical movement of microplastics, defined as the transfer of the contaminant between environmental agents, influences particle size and distribution in the environment [37]. At present, there are many papers on the adverse effects of microplastics on the marine environment, but the attention to pollution in terrestrial environments is very limited [38,39]. The microplastics accumulated in the land could migrate into the groundwater through the subsoil [40].

3. Microplastic Accumulation in Soil and Water

It is essential to consider the microplastics present in the soil, as they reduce the nutrient cycling of crops and the land in general. Ding et al. conducted a study in 2020 [41] where they established the concentration of microplastics in agricultural lands as 3410 pieces/kg of soil for agriculture. Here, the irrigation of crops is important, and fertilizers such as urea contribute to the increase in these particles. The use of coated fertilizers promotes the growth of some crops, as does the use of plastics in greenhouses for potato, strawberry, and blueberry production, among others. These plastics, exposed to sunlight, are considered the main source of microplastics in the soil [42]. These plastic covers are often used to maintain soil moisture for a longer time and the proper temperature of the soil [43], thus generating higher yields per square meter of crop and requiring less time for harvest. The use of activated sludge as fertilizers from wastewater treatment plants (WWTPs) promotes crop growth and maintains soil moisture [44].

Additionally, the improper disposal of urban waste is the main factor in the accumulation of microplastics in urban soils, as landfills are usually not designed to prevent the abrasion of plastics or degradation caused by wind and sunlight. Finally, if there is no proper waste separation, the biological degradation generated by organic waste also contributes to the breaking of polymer chains present in plastics. The only natural source of microplastics in the soil comes from forests and the degradation of lignocellulosic compounds, although this occurs in much smaller proportions [45,46].

Table 2. Summary of microplastic studies in soil and groundwater.

Microplastic Type	Size Range (mm)	Common Polymers	Sources
Fragments	0.02–0.2	Polypropylene, polyethylene	[50,51]
Fibers	0.02–0.05	Polypropylene, polyamide
Fibers	0.0–0.5	Polyethylene, polypropylene, high-density polyethylene
Fibers (Groundwater)	Variable	Polyethylene
Pellets (Groundwater)	Variable	Polypropylene, polystyrene

below shows the report of the dominant forms of microplastics in soil and aquifers. Although plastic fragments and films are the dominant microplastics, these will only be detectable in the soil and not in the subsurface water [47]. The presence of microplastics in groundwater is due to runoff caused by landfills [48]. When microplastics are found as fibers in the environment, they are generally due to asphalt processes and the production of synthetic textiles [49].

At the end of 2019, the COVID-19 pandemic, caused by SARS-CoV-2, began. Since it was declared a pandemic by the World Health Organization (WHO), each country implemented different methods to mitigate and combat the virus [52,53]. As a result, doctors recommended the use of face masks while the virus transmission pattern was being determined [54]. This reduces the number of times a person touches their mouth, nose, and face in general. According to the WHO, 89 million face masks were needed every month during the pandemic [55]. For example, China produced more than 14.8 million face masks monthly in February 2020, and more than 600 million masks were ordered in Japan for April 2020. This led to an uncontrolled increase in masks made from polymeric materials, usually made from polypropylene and polystyrene [56]. This demand, combined with the short use time for each mask, caused a serious problem, accumulating large amounts of plastic on roads, rivers, etc., even obstructing pipes. The excessive use of face masks created chaos in both terrestrial and aquatic environments. Additionally, many plastic bags, bottles, and containers were discarded [57]. These products encountered the environment in various ways. Initially, they were discarded as waste or thrown in public spaces, passing through various areas until they reached rivers, lakes, and oceans, creating new sources of microplastics. Face masks can be made from different materials and consist of four main parts: the inner layer (fiber material or nonwoven fabric), middle layer (melt-blown filter), outer layer (nonwoven fabric and colored), and ear bands (fiber material).

To better understand the issues involving microplastics, bioindicators have been used, including the honeybee (Apis mellifera), an insect that is fundamental to the preservation of various ecosystems. In this interaction, the honeybee suffers from the effects of habitat contamination, which, combined with other factors, has contributed to a massive population decline [58].

What makes this insect an excellent bioindicator of pollution is its ability to travel long distances, its small size that allows it to explore confined spaces, and its body, which can gather extensive information about the environment. Additionally, it can transfer contaminants even to its apicultural production [59,60,61].

It is presumed that these effects are primarily due to the presence of microplastics, which, through ingestion, end up being incorporated into their internal tissues. This leads to alterations in their natural microbiota, indirectly and negatively impacting their protection against adverse environmental factors such as microbial and viral pathogens. Consequently, this results in an increase in the diseases they develop and even their death [59,62].

In 2013, microplastics were first observed in honey, sparking a debate about whether these particles are harmful to bees [63]. In a study conducted by Edo et al., in 2021 [61], titled “Honeybees as Active Samplers for Microplastics”, published in the journal Science of the Total Environment, the objective was to demonstrate the presence of microplastics in bees collected from 19 apiary farms located in different areas of Copenhagen and suburban and rural regions of Denmark. The following results were obtained: 52% of the polymer materials found were fragments with an average 234 ± 156 µm diameter equivalent, and 38% were fibers with an average 64 ± 39 µm equivalent diameter. Furthermore, 13 types of microplastics were identified, with polyester being the most abundant, followed by polyethylene (PE) and polyvinyl chloride (PVC), and this trend was maintained across all three regions mentioned.

In another study conducted by Deng et al., in 2021 [59], which investigated the susceptibility of bees to viral infection through the ingestion of polystyrene (PS) microplastics in China, it was found that when bees interact with the environment, they can transport these fragments on their bodies and indirectly to their hives, promoting the accumulation of contaminants in apicultural products. This study was supplemented with a control group of bees, which were fed a sucrose solution containing polystyrene in varying amounts, along with the injection of synthetic RNA from IAPV to evaluate the physical and biological impact of the microplastic in the study. The results revealed that polystyrene was present in the midgut, where its integrity was affected, and then it translocated to the trachea and hemolymph, causing increased susceptibility to viral infections. The study also concluded that microplastics bioaccumulate in bees.

4. Effects of Microplastic on Health

Zhang et al., in 2022 [64], reported the ability of polystyrene micro- and nanospheres of four sizes (0.1, 0.5, 1, and 5 μm) to enter small intestine and colon epithelial cells, as well as their potential effects on these cells. They reported that the uptake of these nanospheres (PS-NPs) had greater potential to enter the cells compared to microspheres (PS-MPs). Similarly, they noted that PS-MPs did not have a significant effect on cell viability and apoptosis, but the group treated with high concentrations showed low toxicity in terms of oxidative stress levels and mitochondrial membrane potential. However, 5 μm PS-MPs had a significant effect on mitochondrial membrane potential, resulting in a high level of mitochondrial depolarization.

MPs act as vectors for various chemical agents present in soil and water where they adhere due to the large surface area of the nanospheres creating the Trojan Horse Effect that consists of the symbiosis of various chemical agents with MPs due to their hydrophobic nature; once they absorb heavy metals, these MPs are ingested by various organisms, which alters microbial interactions and causes bioaccumulation through the food chain. This phenomenon can trigger an adverse effect on human health, so more follow-up is needed on research in the area [65].

Although the presence and effects of MPs in marine environments have been studied, they have become a cosmopolitan issue, and possible human exposure pathways, such as through diet or inhalation, are being investigated. Observations of plastic microfibers in lung tissue biopsy samples and the ability of biopersistent particles larger than >100 μm to penetrate the gastrointestinal tract epithelium have been documented. Upon absorption, particles <2.5 μm and fibers are expected to pose the greatest concern in the lungs, while larger particles are worrisome in the gastrointestinal tract due to the presence of M cells in Peyer’s patches, capable of accumulating micrometer-sized particles, and the phenomenon of persorption [66]. Damage occurs due to the biopersistent nature of MPs, their hydrophobicity, and their unique surface chemistry, which cause inflammation. Toxicity is likely to have a cumulative effect that depends on the dose. The main human exposure pathways to MPs have been identified as gastrointestinal ingestion, pulmonary inhalation, and dermal infiltration [67].

Yan et al., in 2024, examined how polystyrene MPs (microplastics) affect the trophic transfer and biotoxicity of fluoxetine in a simple food chain involving Artemia nauplii and Danio rerio (zebrafish). The results showed that MPs increased fluoxetine accumulation in Artemia but reduced its accumulation in zebrafish due to different retention times between the organisms [68]. Fluoxetine accumulated in the shrimp was transferred to the fish through the food chain, although MPs mitigated this process by exerting a “cleaning” effect. Additionally, the biotoxic effects of fluoxetine related to neurotransmission in fish were reduced by MPs, while oxidative damage, apoptosis, and immune responses in zebrafish were exacerbated by MPs due to their stimulating effect.

In 2019, Fernández et al. [69] investigated the uptake, elimination, and accumulation of MPs (irregularly shaped high-density polyethylene particles, ≤22 μm in size) in mussels. The results showed that the uptake of MPs increased with higher concentrations and that mussels eliminated MPs at the same rate as similarly sized food, such as microalgae. Smaller MPs (2–4 μm) were eliminated less efficiently than larger ones. MPs, especially those smaller than 6 μm, remained in the digestive gland after 6 days of depuration. Mussels eliminated approximately 85% of the ingested MPs, with 2–6% retained. The study also noted a prolonged retention time for MPs, which contrasted with the generally accepted intestinal emptying times.

In 2024, a study was conducted on two commercially important fish species, Larimichthys polyactis and Collichthys lucidus, using stable isotope analysis to investigate how microplastics (MPs) accumulate in their food sources. The results revealed that the predominant forms, colors, and polymers of MPs in the region were fibers, blue, and PET. C. lucidus exhibited a broader isotopic niche and showed a greater tendency to accumulate MPs compared to L. polyactis. Biomagnification analysis indicated that the predominant MPs in terms of form, color, and polymer were magnified in both fish species, and MPs smaller than 3 mm showed significant biomagnification. Additionally, factors such as feeding strategies and habitat preferences may influence the ingestion of MPs by fish [70].

Similarly, Lu et al., in 2024 [71], analyzed this bioaccumulation effect by exposing Tenebrio molitor larvae to micro- and nanoplastics, which were subsequently used as a food source for mice (mammals). They observed that micro- and nanoplastics effectively translocate through the food chain, from lower to higher trophic levels, as the micro- and nanoplastics transferred along the food chain were later detected in the digestive, respiratory, and urinary systems of the mice. Intense fluorescent signals were observed in key organs such as the lungs, liver, intestines, brain, and kidneys, as well as in embryos.

However, it seems that the bioaccumulation behavior within the food chain depends on the system, as in 2022 [72], Covernton and collaborators studied the bioaccumulation of MPs in bivalves, crabs, echinoderms, and fish feeding at different trophic levels in three sites on the southern Vancouver Island. They found that smaller suspension-feeding and plankton-feeding fish tended to ingest more MPs relative to their body weight. Trophic transfer occurred between prey and predator in rockfish, but the higher concentrations of MPs in full stomachs compared to empty ones indicated a rapid excretion of ingested MPs.

Plastic bioaccumulation in the human body can potentially lead to a variety of health problems, including respiratory disorders such as lung cancer [73], asthma [74], and hypersensitivity pneumonitis [75], neurological symptoms like fatigue and dizziness, inflammatory bowel disease, and even alterations in the gut microbiota [76]. Most studies conducted to date have confirmed that nanoplastics and MPs can induce apoptosis in cells and have genotoxic and cytotoxic effects. Understanding the cellular and molecular mechanisms of plastic actions can help extrapolate the risks to humans [76].

A group of researchers identified the dynamics between polystyrene micro- and nanoplastics and four distinct human colorectal cancer cell lines (HT29, HCT116, SW480, and SW620). They observed that short-term exposure to 0.25 μm particles significantly amplified cell migration, potentially leading to pro-metastatic effects. They also reported the persistence and bioaccumulation of MNPs in colorectal cancer cell lines, key toxicological characteristics according to REACH (Regulation concerning the Registration, Evaluation, Authorization, and Restriction of Chemicals), and highlighted the potential of MNPs as hidden catalysts for tumor progression, particularly by enhancing cell migration and possibly stimulating metastasis. This finding sheds light on a significant and previously underexplored area of concern [77].

Due to the different backgrounds regarding the accumulation of plastic polymers in various organs of organisms, it is necessary to identify and compare the interactions to improve the monitoring and risk assessments of MPs. For this reason, working groups like that of D’Avignon and collaborators in 2023 [78] analyzed the effect of a single exposure in a trio of interacting freshwater animals (the quagga mussel Dreissena bugensis, a filter feeder; the amphipod Gammarus fasciatus, a deposit feeder; and the round goby Neogobius melanostomus, a benthivorous fish). They observed that filter-feeding species had higher MP content when exposed to suspended particles, while detritivores had a similar absorption from any of the routes. Mussels transferred microbeads to amphipods, and both invertebrates transferred microbeads to their mutual predator, the round goby. Round gobies generally showed low contamination from all routes (suspension, sedimentation, trophic transfer) but had a higher load of microbeads due to the predation of contaminated mussels. A higher abundance of mussels (10–15 mussels per aquarium, or ~200–300 mussels/m²) did not increase individual mussel loads during exposure, nor did it increase the transfer of microbeads from mussels to amphipods through biodeposition. This demonstrates the bioaccumulation of MPs within a food chain.

To identify how bioaccumulation or potential biomagnification of micro- and nanoplastics occurs, ref. [79] studied the bioaccumulation and expulsion tendency of two plastic particles of different sizes (1 and 2 µm), testing them on three human epithelial cell lines (liver, lung, and intestine). They observed different behaviors, with the highest absorption of plastic occurring in liver cells. A 60% reduction in the content of 1 µm particles in the cells was also seen after the plastic was removed. Finally, the viability and proliferation of the three human cell lines were not significantly affected by the 1 and 2 µm beads.

The cell- and dose-dependent cytotoxic effects of PET MPs, as well as the significant impact on HER-2-driven signaling pathways, have been studied. It was found that ingested MPs primarily accumulate in the gastrointestinal tract and, if smaller than 2 μm, can cross the gastrointestinal epithelium, leading to systemic exposure. These results suggest that PET MPs may interfere with HER2-driven signaling pathways, which are necessary for proliferation and survival in BT-474 and SK-BR-3 cells [67].

Basini et al., in 2022 [80], studied the impact of exposure to MPs on human embryonic kidney-293 (HEK-293) cells and immortalized human keratinocytes (HaCaT), considered model systems for healthy tissues, and on two breast cancer (BC) cell lines (BT-474 and SK-BR-3). Primary adipose stromal cells (ASCs) showed alterations in pro- and antioxidant cellular mechanisms, cell growth, and stimulation of inflammatory markers.

Since the consumption of MPs within the food chain is one of the main factors for their bioaccumulation in humans, Rahman et al., in 2024 [81], studied the specific distribution and variation of MPs in commercially captured fish (7 species, 140 individuals) collected from the two main fish distribution centers in Dhaka (Uttara and Jatrabari). Additionally, they examined the impact of MPs of different sizes on the growth of fish (Anabas testudineus) in a controlled experiment. They reported that the kidneys of market fish bioaccumulated the highest concentration of MPs (average, 59.1 MPs/g), followed by the liver (24.6 MPs/g) and intestines (18.6 MPs/g). MPs in the form of fibers were the most common in all fish (79–93%), except in Glossogobius giuris (where fragments were 51%). Fourier transform infrared (FTIR) spectroscopy analysis identified 19 different types of polymers, with high-density polyethylene (HDPE), ethylene-vinyl acetate (EVA), and polyamide (PA) commonly found in all organs. The experimental study confirmed that large PVC MPs (1.18 mm–300 μm) had a more negative impact on fish growth (length) and caused more physical deformities (particularly intestinal lesions) compared to small PVC MPs (150 μm–75 μm). As in previous studies, greater bioaccumulation of larger MP particles was observed.

Zhu et al., in 2020 [82], studied and collected data on the absorption, accumulation, and translocation of MPs in marine life, as well as their in vivo interactions with other persistent pollutants by analyzing edible oysters from the coast of China. They reported the presence of MPs in all oyster tissue samples studied, with an average concentration of about 4.53 items/g wet weight (24.49 items/g dry weight). MPs were translocated and primarily distributed in the gills and mantle of the studied oysters in the form of fibers, with cellophane and polyester being the most found materials. Excessive concentrations of trace metals (30.484, 4.415, 0.395, and 181.044 μg/g dry weight for Cr, Cd, Pb, and Cu, respectively) were detected in the oysters using inductively coupled plasma mass spectrometry. Trace metals such as Cr, Mn, Ni, Cu, Zn, Cd, and Pb were found to adsorb onto the surface of MPs isolated from the oysters.

Lu et al., in 2024 [83], studied the effects of long-term exposure to environmentally relevant doses of polystyrene nanoplastics (PS-NPs) on lipid accumulation in terms of autophagy and lysosomal mechanisms. They found that hepatic lipid accumulation was more pronounced in mice exposed to 100 nm PS-NPs compared to those exposed to 500 nm PS-NPs.

Since an increase in heavy metals has been reported in organisms containing MPs, Jia et al., in 2021 [84], studied the impact of MPs on the behavior of heavy metals in the aquatic environment and conducted batch experiments. In these experiments, MPs (0.001%, 0.01%, 0.1%) and heavy metals (50, 100 mg/kg Cu²⁺; or 25, 50 mg/kg Pb²⁺) were added individually or combined to soil for cultivating rapeseed (Brassica napus L.) in a greenhouse. The copper and lead contents in the rapeseed from the MP0.1+Cu100 and MP0.1+Pb50 treatments reached 38.9 mg/kg and 9.4 mg/kg, which were significantly (p < 0.05) higher than those from the Cu100 (35.3 mg/kg) and Pb50 (8.7 mg/kg) treatments, respectively. They reported that MPs in the soil facilitated the entry of heavy metals into the rapeseed plants. They also observed changes in malondialdehyde content, the activities of superoxide dismutase and guaiacol peroxidase, and sugar and vitamin C contents, indicating that MPs in the soil would cause more severe damage and degrade the quality of rapeseed plants.

Plastic polymers also contain additives such as bisphenols, in the case of PET. These have been shown to cause problems, as demonstrated in the study by Du et al., in 2020 [85]. To test whether prenatal exposure to bisphenols can increase the risk of respiratory diseases in children, they exposed pregnant mice to 0, 40, 400, and 4000 μg/kg of bisphenol F (BPF) during gestation and lactation. The results showed an inflammatory response in the lungs of female offspring exposed to BPF, characterized by infiltration of peribranchial inflammatory cells. Subsequent transcriptome analysis identified a total of 685 differentially expressed genes (DEGs) in the lungs of female offspring exposed to high doses of BPF, with 526 genes upregulated and 159 genes downregulated. This suggests potential pulmonary toxicity associated with BPF exposure during gestation and lactation.

Bisphenol M (BPM), an alternative to bisphenol A (BPA), is commonly used in various industrial applications. However, BPM is not a safe substitute for BPA due to its harmful effects on living organisms. Chen et al., in 2024 [86], evaluated the effect of BPM on mouse oocytes, where they observed a significant impact on the germinal vesicle breakdown (GVBD) rate and polar body extrusion (PBE) rate throughout the meiotic progression of mouse oocytes. This ultimately resulted in meiotic arrest and an increase in the acetylation level of α-tubulin in oocytes after treatment with BPM, leading to a reduction in microtubule stability. This causes a decrease in the stability of microtubules.

Table 3. Review of the most important MP effects on health.

Findings Reported by Researchers	Reference
Polystyrene micro- and nanospheres of different sizes can enter small intestine and colon epithelial cells, with nanospheres showing greater uptake. High concentrations of 5 μm PS-MPs significantly affected mitochondrial membrane potential.	[64]
Microplastic pollution is a global issue, with exposure pathways through diet, inhalation, and absorption. MPs <2.5 μm pose lung risks, while larger MPs impact the gastrointestinal tract.	[66]
Polystyrene MPs increase fluoxetine accumulation in Artemia but reduce it in zebrafish. MPs mitigate fluoxetine’s biotoxic effects on fish neurotransmission but exacerbate oxidative damage, apoptosis, and immune responses.	[68]
High-density polyethylene MPs (≤22 μm) were ingested by mussels, with smaller MPs (<6 μm) persisting in the digestive gland after depuration.	[69]
MPs in commercially important fish species (Larimichthys polyactis and Collichthys lucidus) were mainly fibers, blue in color, and PET-based. C. lucidus had a higher tendency for MP accumulation.	[70]
Micro- and nanoplastics translocate through the food chain, detected in key mammalian organs after ingestion by Tenebrio molitor larvae and subsequent consumption by mice.	[83]
Smaller fish species ingest more MPs relative to body weight, with rapid excretion in rockfish. Trophic transfer occurs between prey and predators.	[72]
MP bioaccumulation in humans is linked to respiratory disorders, neurological symptoms, inflammatory bowel disease, and gut microbiota alterations.	[73,74,75,76]
Polystyrene micro- and nanoplastics enhance cell migration in colorectal cancer cell lines, suggesting a pro-metastatic effect.	[77]
MPs bioaccumulate within food chains, with mussels transferring MPs to amphipods, which are then ingested by round goby fish.	[78]
MPs of different sizes (1 and 2 µm) showed varying bioaccumulation tendencies in human liver, lung, and intestinal epithelial cells, with the highest absorption in liver cells.	[79]
PET MPs can cross the gastrointestinal epithelium and interfere with HER2-driven signaling pathways, impacting cell survival.	[67]
MP exposure in HEK-293 and HaCaT cells alters oxidative mechanisms and inflammatory markers.	[80]
Market fish kidneys accumulated the highest MP concentrations, mainly fibers. Larger PVC MPs caused more growth defects in fish.	[81]
MPs were detected in oyster tissues, mainly in gills and mantles. Trace metals adsorbed onto MPs, increasing contamination risks.	[82]
Polystyrene nanoplastics exposure increased hepatic lipid accumulation in mice via autophagy and lysosomal pathways.	[71]
MPs facilitate heavy metal entry into rapeseed plants, affecting antioxidant enzymes and degrading plant quality.	[84]
Prenatal exposure to bisphenol F (BPF) led to lung inflammation and altered gene expression in offspring.	[85]
Bisphenol M (BPM) disrupted microtubule stability in mouse oocytes, causing meiotic arrest.	[86]

shows a summary of the information presented in this paragraph of the paper.

5. Bioremediation for Microplastic Exposure

Studies on the potential cytotoxic effects of micro- and nanoplastics, as well as their sources of bioaccumulation and biomagnification through trophic chains, are increasingly prevalent. However, another avenue of research focuses on potential mitigation strategies for the presence of these plastic polymers. Various solutions have been proposed, such as reducing the use of plastics that can degrade into MPs [87], investigating the presence of MPs in dental hygiene products, and proposing their removal from such products [88]. However, a significant challenge is the removal of such small particles from the environment, which is why bioremediation can be an option. This approach involves identifying the key pathways adopted by microbes to use plastic fragments as the sole carbon source for growth and development [89].

There are physical methods for remediation and removal of MPs such as filtration, sedimentation, magnetic separation, ultrasonic treatments, etc. However, they have many limitations in the removal of plastic particles [90,91]. Membrane filtration methods are used in secondary treatment and use methods with different pore sizes and techniques such as ultrafiltration, reverse osmosis, etc. One of the main disadvantages of these separation techniques is the operating conditions, for example, for filtration membranes, pressures of 10–100 bar are applied to force molecules from semipermeable membranes, basing their effectiveness on the size and weight of the particles to be removed. In addition, secondary compounds that can be attached to MPs such as heavy metals can be removed [92].

Considering the various remediation technologies for MPs and nanoparticles, microbial remediation is regarded as an eco-friendlier option. The microbial degradation of plastics is influenced by various biotic and abiotic factors, such as enzymatic mechanisms, substrate and co-substrate concentration, temperature, pH, and oxidative stress, among others [93]. Some alternatives that can be implemented to promote the bioremediation of these recalcitrant compounds include advanced enzymatic and molecular technologies, biomembranes, and activated sludge, among others [89].

An increasing number of microorganisms with the ability to degrade plastic polymers are being described. Pseudomonadota (Proteobacteria), Bacteroidota (Bacteroidetes), Bacillota (Firmicutes), and Cyanobacteria have been frequently reported in plastic biofilms and are capable of degrading plastics. Alternatively, plastic-degrading bacteria are being sought from marine environments, such as deep ocean waters and offshore areas, particularly Pseudomonas spp., Bacillus spp., Alcanivorax spp., and Actinomycetes [94]. Similarly, some fungi and marine algae have also demonstrated plastic-degrading capabilities [83].

Ekanayaka et al. (2022) [95] identified plastic-degrading fungi across eleven classes within the fungal phyla Ascomycota (Dothideomycetes, Eurotiomycetes, Leotiomycetes, Saccharomycetes, and Sordariomycetes), Basidiomycota (Agaricomycetes, Microbotryomycetes, Tremellomycetes, Tritirachiomycetes, and Ustilaginomycetes), and Mucoromycota (Mucoromycetes). Many of these microbial species degrade plastic polymers by producing enzymes that break them down. Some of the described enzymes belong to the hydrolase family, which includes esterases, lipases, depolymerases, and PETases—enzymes known to break down the carbon backbone of many commonly used plastics [96]. Additionally, oxidoreductase family enzymes have also been reported to play a role in plastic polymer degradation. However, this process typically involves a complex system of enzymes rather than a single one [97].

Since individual microbial strains often lack the complete set of enzymes required for efficient plastic degradation, the use of diverse microorganisms with complementary enzymatic activities is proposed as a promising solution for plastic waste treatment [98]. Due to the low degradation percentages achieved by many isolated microorganisms, synthetic microbial consortia have been developed. Systems biology tools and genetic engineering techniques can pave the way for bioremediation and plastic degradation [99]. Synthetic consortia involve selecting individuals with higher degradative activity and combining different species in the same medium. However, despite sounding promising on paper, microbial ecology is complex and challenging to predict, which is why this option is not always more efficient than a natural consortium. This is due to competitive interactions among microbes, where one microorganism can inhibit the degradative activity of another [100].

6. Policies for Avoiding Microplastic Accumulation

In 2018, the World Resources Institute (WRI) [101] led a project to develop a methodology and implement a report on single-use plastics and microplastics, providing a global review of national laws and regulations. This report stems from efforts to limit the manufacturing, importation, sale, use, and disposal of these products, aiming to mitigate their impact on marine debris. The report includes the application of bans on the manufacturing, use, distribution, importation, or exportation of single-use plastic products, specifying whether they apply to certain products, materials, or production processes; types of incentives and disincentives, such as taxes and fees; requirements like Extended Producer Responsibility (EPR) to promote a circular economy approach; recycling laws applied to plastic waste; and an overview of voluntary measures used to limit the use of microplastics.

According to the WRI report, 127 out of 192 countries reviewed have at least one piece of legislation to control the use of plastic bags. The earliest regulatory measures date back to the beginning of the century, and gradually, over the first decade, more countries began to implement similar measures. It is important to note that in some countries without national regulations, local governments (states, cities, and municipalities) have introduced their own.

In terms of regions, Europe leads with 44 countries having some form of legislation regulating the use of plastic bags, including all European Union member states except Belgium, which adopts a regional approach. The European Union has two major regulations on plastic waste management: Directive 94/62/EC on Packaging and Packaging Waste and Directive 2015/720 regarding the consumption of lightweight carrier bags.

African nations have progressively joined these initiatives, with 37 countries implementing measures, followed by 27 countries in Asia, 14 in Latin America and the Caribbean, and 5 in West Asia. In the United States and Canada, plastic use is regulated at the subnational level, involving private sector participation.

Figure 4 shows a summary of microplastics and their prevalence across continents. Europe records up to 2914 pieces/kg, followed by Australia with 2400 pieces/kg, the Americas with 1190 pieces/kg, East Asia with 1074 pieces/kg, and the Middle East with 205 pieces/kg.

Only a small number of territories have imposed total restrictions on all types of plastics for any use. Countries like Afghanistan, Bhutan, and Côte d’Ivoire have implemented complete bans on the import and distribution of plastics but only partial bans on local production. Most countries have opted for partial regulatory measures, specifically targeting material composition, particle size, or production volume.

Table 4. Countries implementing plastic bag thickness regulations.

Thickness Category (Microns)	Countries with Regulations
15 microns	Uzbekistan, Republic of Moldova
20–25 microns	Bangladesh, Botswana, China, Mongolia, South Africa
30 microns	Albania, Cambodia, Ethiopia, Mozambique, Nepal, Senegal, Uganda, etc.
35–40 microns	Tunisia, Vanuatu
50 microns	France, India, Italy, Madagascar, Pakistan, Romania, Monaco, Poland, UK, Andorra, Portugal, Cyprus
60 microns	Cameroon, Yemen, Malawi
100 microns and above	Eritrea, Jordan, Saudi Arabia

shows the countries with regulations on the thickness of plastic bags.

Additionally, 41 countries have implemented regulations concerning the materials used to produce plastic bags, 38 of which have banned non-biodegradable materials and promoted the use of compostable bags. Both Italy and Turkey require the use of recycled materials in bag production, mandating that at least 30% of the materials be recycled for food-grade bags and 10% for other permitted plastic bags. Countries like Austria base their regulations on the weight of the bags, which determines the percentage of recycled materials to be used in their production.

Table 5. Plastic bag material regulations by region.

Region	Country	Regulation Summary
Africa	Burkina Faso	Prohibition of production, import, marketing, and distribution of non-biodegradable plastic packaging and bags.
	Niger	Ban on plastic bags, except for those certified as biodegradable per standards.
Asia-Pacific	India	Thickness requirement (50 microns) does not apply to compostable plastic bags meeting prescribed standards.
	Republic of Korea	Biodegradable plastic bags may be distributed for free.
Europe	Austria	Plastic bags must include a minimum percentage of recyclable materials.
	France	Ban on single-use non-compostable plastic bags under 50 microns; bio-sourced content requirement to increase from 30% (2017) to 60% (2025).
Latin America	Colombia	Plastic bags must contain at least 40% post-consumer or post-industrial recycled material, following technical standards.
	Paraguay	Gradual transition from polyethylene bags to biodegradable alternatives.
West Asia	Saudi Arabia	Disposable plastic products (polypropylene and polyethylene) must be oxo-degradable and biodegradable per regulations.
	United Arab Emirates	Manufacturers and suppliers must comply with oxo-degradable bag standards before distribution.

presents examples of actions and materials proposed by various countries for plastic bag production.

In the countries not mentioned so far, less impactful regulations are in place. For example, countries like Antigua and Barbuda ban the import, distribution, and sale of plastic bags, imposing fines of up to USD 10,000, with exceptions for certain specific types. Others, such as Argentina, Belize, Mexico, Ecuador, and Honduras, only regulate solid waste disposal and the prohibition of microbeads in cosmetics and personal care products at the national level.

The particles present in such products, referred to as microbeads or microplastics (Article 269 of the General Health Law, Mexico) [102], are plastic particles smaller than 5 mm intentionally added for exfoliation and cleaning. These particles are not biodegradable in aquatic environments. “Rain-soft cosmetics” refers to any personal hygiene product for hair, skin, teeth, or oral care, including exfoliants [103].

Of the 192 countries studied by the WRI, only 8 have national laws regulating the manufacture of microbeads in personal care products. These countries are Canada, France, Italy, the Republic of Korea, New Zealand, Sweden, the United Kingdom, and the United States of America.

Table 6. Microbead laws and regulations.

Country	Law or Regulation Name
Canada	Microbeads in Toiletries Regulations (SOR/2017-111), 2 June 2017.
France	Reclaiming Biodiversity, Nature and Landscapes Act No 2016-1087 of 8, Article 124, August 2016.
Italy	General Budget Law 2018: Law no. 205 of 27, Art.1, Sections 543 to 548, December 2017.
Republic of Korea	Regulations on safety standards for cosmetics [Annex 1] {No. 2017-114, Notice, Article 3, 29 December 2017.
New Zealand	Waste Minimisation (Microbeads) Regulations 2017, under section 23(1)(b) of the Waste Minimisation Act 2008.
Sweden	Regulation amending Regulation (1998: 944) prohibiting etc. in certain cases in connection with handling, import and export of chemical products.
UK	The Environmental Protection (Microbeads) (England) Regulations 2017. The Environmental Protection (Microbeads) (Scotland) Regulations 2018. The Environmental Protection (Microbeads) (Wales) Regulations 2018. The Environmental Protection (Microbeads) (Northern Ireland) Regulations 2018.
US	Microbead-Free Waters Act of 2015.

provides a summary of the laws enacted in these countries to promote the elimination and regulation of microbeads.

As can be observed, there is a significant discrepancy in regulations regarding the presence of microplastics in water. While some countries have implemented strict measures, others consider only a few elements of interest in water. It is necessary to standardize an evaluation criterion, as discharges from all countries accumulate through various rivers in common areas. An example of the effort to harmonize regulations was proposed by UNEA in 2014, adopting Resolution 1/6 on “Marine Plastic Debris and Microplastics” [104]. At the conference in 2017, UNEA established an Expert Group on Marine Debris and Microplastics to conduct research and write reports. The first resolution adopted at the 2019 conference focused on marine litter and microplastics [105], with 49 countries committing to “prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities including marine debris and nutrient pollution” by 2025. The agenda for the UNEA 2022 meeting again included microplastics, and there was a proposal to develop an international convention specifically addressing marine microplastic pollution. Despite this, no significant progress has been made towards establishing such a treaty, and the current UNEA resolutions on marine microplastics remain non-binding [106].

The main problem is the existence of inadequate laws to regulate marine microplastic discharges, which stems from the absence of international criteria focused on addressing the issue caused by these particles in water. So far, the conventions that have been held only provide a vague idea of the guidelines that should be followed to tackle the problem, but there is no coherence or consistency in standards across different countries and regions [107]. Microplastic pollution in water is a global issue that requires a joint response from all nations, starting with local laws and extending to national governments. The more uniform the criteria for microplastic pollution become, the greater the progress in reducing ocean contamination [108].

7. Conclusions

Despite the efforts made, the amount of microplastics in the environment is expected to continue increasing due to both natural and anthropogenic effects. Today, microplastics are found in soil, water, and underground aquifers. Therefore, it is essential for interdisciplinary teams of researchers to join forces to address the various sources of MPs identified so far. The analyzed data revealed that based on particle size, micro- and nanoplastics may pose a more severe problem than initially anticipated, as they are present in all systems involving the food chain.

Furthermore, despite the increasing research on methods to mitigate MPs, these efforts are still insufficient to solve the issue of plastic pollution in the environment. Therefore, it is necessary to promote the conscious use of these plastic polymers and ensure their proper disposal. Additionally, alternatives for recycling large plastics should be sought to prevent their fragmentation into micro- and nanoplastics.

According to Mexican legislation, an addendum was made to Article 269, establishing the prohibition of the manufacture, import, and commercialization of cosmetic products containing microplastics. Among the consequences of products with microplastics is the transport of contaminants such as DDT, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls. When ingested by wildlife or humans (either directly or indirectly), these plastics contain high concentrations of these hazardous toxins, which bioaccumulate in the food chain, as described in the present research work.

Finally, in spite the efforts made to legislate and regulate the emission of first-generation microplastics, these regulations need to be strengthened and combined with various remediation techniques, both mechanical methods like filter installation and the use of fungi and bacteria to degrade and reduce the impact of MPs on the environment.