Tiny Pollutants, Big Problems: The Impact of Microplastics on Water Quality

Jul 23

Did you know that by 2050, there could be more plastic in the oceans than fish? [1] One major culprit is microplastics. Microplastics have infiltrated every corner of our planet's water bodies, posing significant threats to both environmental and human health.

What are Microplastics?

Microplastics, defined as plastic particles less than 5mm in diameter, exist in two main forms: primary and secondary. Primary microplastics are intentionally manufactured small particles found in products like microbeads in cosmetics and microfibers from synthetic clothing. These particles are released into the environment through domestic and industrial use. In contrast, secondary microplastics result from the breakdown of larger plastic debris due to environmental factors such as UV radiation, wave action, and mechanical abrasion over time [2].

As plastics degrade, they do not disappear. Instead, they fragment into increasingly smaller pieces, eventually becoming microplastics. The widespread use of plastic for human consumption over the last century has caused microplastics to become ubiquitous, present in virtually every ecosystem on Earth. Microplastics have even been found in Mariana’s Trench, the deepest point on Earth, and in Arctic ice, highlighting the vast proportions of the plastic epidemic [3].

Sources of primary microplastics

Microbeads are minuscule plastic particles used as abrasives in cosmetics, cleansers, and toothpaste. Typically made of polyethylene or other polymers, these beads are designed to exfoliate or scrub skin. Recognizing their environmental impact, the U.S. Congress passed the Microbead-Free Waters Act in 2015 to prohibit their use in cosmetics and personal care products [4]. Despite legislative efforts and industry phase-outs, microbeads persist in waterways worldwide due to their previous extensive use and improper disposal practices.

Microfibers are tiny threads and fibers shed from synthetic textiles during washing. Clothing made from plastic-based materials like nylon, polyester, rayon, acrylic, and spandex releases microfibers into wastewater with every laundry cycle. These microfibers are too small to be effectively filtered out by conventional wastewater treatment plants, leading to their discharge into rivers, lakes, and oceans through effluent. Moreover, even if microplastics are partially removed during treatment, they often accumulate in sewage sludge, which can subsequently be used as fertilizer on agricultural fields. This cycle perpetuates their entry into the environment via runoff into water bodies [2].

Pathways of Microplastics into Water Bodies

One of the primary pathways of microplastics is through point sources, which include specific, identifiable sources of pollution. Wastewater treatment plants are a significant point source of microplastics. Despite the treatment processes designed to clean wastewater, many facilities are not equipped to filter out microplastics effectively. As a result, untreated or partially treated microplastics are discharged directly into rivers, lakes, and oceans. Studies have shown that these facilities can release substantial quantities of microplastics, primarily from household sources such as synthetic fibers shed during laundry [2].

Non-point sources of microplastic pollution are diffuse and harder to identify than point sources. One major non-point source is urban runoff, where microplastics from tire wear and paint particles are carried into water systems. Every time a vehicle travels, tiny fragments from tires are abraded and left on road surfaces. When it rains, these particles are washed into storm drains and eventually enter rivers and oceans. Similarly, paint particles from buildings and road markings degrade and are swept into water bodies through runoff. Agricultural runoff also plays a role, as microplastics used in agricultural films and containers find their way into streams and rivers [2].

Atmospheric deposition is another significant pathway through which microplastics enter water bodies. Recent research has revealed that microplastics can be transported over long distances by wind. Once airborne, these particles can travel thousands of kilometers before being deposited back onto the Earth's surface. This deposition occurs when microplastics settle from the air onto land and water surfaces. Rain and snow can wash these particles into rivers, lakes, and oceans, contributing to the contamination of even remote areas. Studies have found microplastics in the Arctic and other isolated regions, indicating the global reach of atmospheric transport [2].

Why are Microplastics Dangerous?

Toxic chemicals are used in the production of microplastics

Plastics are composed of polymers and often contain additives like color dyes, which can include toxic chemicals. Many of these additives are known or suspected carcinogens or endocrine disruptors, such as bisphenol A (BPA) and phthalates. These chemicals have adverse effects on development, reproduction, and neurological functions in both humans and other species [5].

The global market for plastics includes over 13,000 different chemicals, with more than 3,200 considered substances of potential concern due to their persistence, bioaccumulative properties, or toxicity. Despite this extensive use, many of these chemicals remain poorly studied, leaving their full toxicity uncertain. For instance, BPA, which can cross the blood-brain barrier, is linked to neuropsychological dysfunction and neurodegenerative diseases, and can impact DNA methylation and heart development [5].

Another significant source of concern is tire wear particles (TWPs), which release toxic chemicals like perfluorooctanesulfonic acid (PFOS) and 6PPD-quinone into the environment. These particles have been associated with mortality in salmonid fishes, highlighting their environmental toxicity [5].

Microfibers also contain a variety of chemicals, including dyes, antimicrobial agents, and water repellents, which can adversely affect human and environmental health. Textile chemicals are known to cause allergic reactions, carcinogenesis, and developmental abnormalities. Other sources of microfibers include cigarette filters and fishing gear, both of which release toxic chemicals such as polycyclic aromatic hydrocarbons (PAHs) and metals into the environment [5].

Microplastics accumulate toxins from the environment

Microplastics have a non-polar surface and a high surface area-to-volume ratio, which aids in the adsorption of various toxic chemicals from seawater. Their non-polar surface facilitates the adsorption of metal ions from the environment, as positively charged ions bind to negatively charged sites on the plastic surface, while their high surface area-to-volume ratio allows them to adsorb metals, pharmaceuticals, polycyclic aromatic hydrocarbons (PAHs), and PCBs [5].

Metal contaminants

Microplastics have a tendency to attract and accumulate metal contaminants from the environment. Research has shown that various types of microplastics, including polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP), can accumulate metals such as zinc (Zn), lead (Pb), cadmium (Cd), and copper (Cu). Studies conducted in different coastal regions have highlighted that LDPE, in particular, tends to accumulate higher concentrations of metals compared to other types of microplastics [5].

Many metals have toxic effects on marine organisms even at low concentrations. For example, mercury can impair neurological development and reproduction in marine mammals and fish. Lead and cadmium can disrupt metabolic processes and cause organ damage. Zinc, while essential in small amounts, can become toxic at higher concentrations, affecting cellular functions and growth in marine organisms. These metals can accumulate in their tissues over time, leading to the bioaccumulation of metals in top predators, such as large fish, marine mammals, and even humans who consume seafood [5].

Organic contaminants

Organic contaminants such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are commonly found attached to microplastic particles (MPs) across global marine environments. These contaminants adhere to the surface of microplastics due to their hydrophobic nature, which makes them more likely to attach to the non-polar surfaces of plastic particles floating in water bodies. As a result, microplastics can concentrate these harmful chemicals, potentially posing risks to aquatic organisms and ecosystems when ingested or absorbed by marine life [5].

PCBs and PAHs can mimic or interfere with hormones in organisms, disrupting normal endocrine function. This can lead to reproductive disorders, altered sexual development, and impaired fertility in exposed animals. Some PCBs and PAHs are also classified as probable human carcinogens. Long-term exposure to these contaminants has been linked to increased risks of lung, liver, skin, bladder, and gastrointestinal cancers in humans [5].

Pesticides

Microplastics have also been found to attract pesticides, including persistent organic pollutants like DDT and its derivatives. Studies have found significant concentrations of DDT, DDD, and DDE on microplastic particles collected from various global beaches. Additionally, studies examining seabirds' ingestion of microplastics found these particles contained various pesticides, indicating their potential to accumulate and transport harmful chemicals in marine environments [5].

Pesticides are designed to be toxic to specific pests, but they can also harm non-target organisms, including marine life. When marine organisms ingest microplastics laden with pesticides, they can experience acute toxicity, affecting their nervous system, immune function, and reproductive health. Specifically, DDT is known to act as an endocrine disruptor in various species, including humans. It can interfere with hormone systems, particularly estrogen signaling, leading to reproductive and developmental abnormalities in wildlife. In humans, exposure to DDT has been associated with increased risks of breast cancer and other hormone-related health issues. DDT and its metabolites also have neurotoxic effects. Chronic exposure to DDT has been linked to neurological symptoms such as tremors, seizures, and altered cognitive function in humans and wildlife [5].

PFAS

The presence of per- and polyfluoroalkyl substances (PFAS) in consumer products such as textiles, carpets, and plastics contributes to their release into the environment. These substances can interact with microplastics (MPs), forming complexes known as MP-PFAS. PFAS molecules, particularly those with long-chain structures, exhibit strong hydrophobic properties, enhancing their tendency to adsorb onto microplastic surfaces [5].

PFAS compounds, especially the long-chain varieties, have been associated with adverse health effects in humans, including developmental issues, immune system disruption, and potential carcinogenicity. Both microplastics and PFAS are highly persistent in the environment, meaning they do not easily break down over time and are likely to accumulate in ecosystems [5].

Routes of Human Exposure to Microplastics

Microplastics have been found in various environmental settings, including water sources intended for human consumption such as rivers, lakes, and groundwater. Humans are exposed to MPs through dermal contact, inhalation of airborne particles, and ingestion of contaminated food and water.

Drinking water

Microplastics have been detected in drinking water sources worldwide, including tap water and bottled water. These particles enter water systems through various routes, such as runoff from plastic waste, wastewater effluent, and atmospheric deposition. Once in water sources, microplastics can persist due to their resistance to degradation, potentially accumulating in drinking water supplies.

Notably, microplastic concentrations are higher in bottled water than in treated water. Microplastic concentrations were found to be highest in polyethylene terephthalate (PET) packaging compared to other materials, indicating that PET bottles contribute significantly to plastic pollution in water. Even seemingly non-plastic items like glass bottles may contain plastic components (e.g., plastic layers under caps) that can release microplastics into the water [6].

Research has demonstrated that mechanical stress, such as repeated opening and closing of bottlenecks, contributes substantially to microplastic contamination in bottled water compared to normal handling and use. Throughout their lifecycle, plastic bottles are exposed to various pressures and environmental conditions (e.g., UV exposure, temperature fluctuations) that can influence the release of microplastics into bottled water [6].

Food

Microplastics enter the food chain primarily through marine and freshwater ecosystems. Marine organisms, such as fish and shellfish, can ingest microplastics directly or indirectly through contaminated prey. Over time, these particles may accumulate in the tissues of aquatic organisms, leading to bioaccumulation as larger predators consume smaller ones. Consequently, humans can inadvertently ingest microplastics when consuming seafood. Additionally, microplastics have been found in other food sources, including sea salt, honey, and even beer, highlighting their widespread presence in the food supply and potential pathways for human exposure [7].

Inhalation

Recent studies have demonstrated that microplastics are present in the atmosphere, suggesting that inhalation is another route of human exposure. Airborne microplastics originate from various sources, such as the degradation of plastic debris, road dust from tires, and industrial processes. Once airborne, these particles can be inhaled and deposited in the respiratory tract. While the health implications of inhalation exposure to microplastics are still being investigated, there is concern that chronic exposure could contribute to respiratory and cardiovascular diseases, as well as other systemic effects [7].

Dermal contact

Dermal exposure to microplastics can happen when individuals come into contact with contaminated water or soil, or directly with particulate microplastics. Microplastics, especially very small synthetic fibers less than 25 μm in size, can potentially penetrate skin pores, which typically range from 40 to 80 μm in diameter, bypassing the outer layer of the skin. The extent of exposure through this route varies among individuals due to differences in skin pore size and individual susceptibility [7].

Impact of Microplastics on Human Health

Digestive system effects

When ingested, microplastics can cause physical irritation to the gastrointestinal tract, potentially leading to inflammation and various gastrointestinal symptoms such as abdominal pain, bloating, and changes in bowel habits. Moreover, these particles can alter the intestinal microbiome, disrupting the balance between beneficial and harmful bacteria. Chemical toxicity is also a concern, as microplastics can absorb and accumulate environmental toxins like heavy metals and polycyclic aromatic hydrocarbons, which further exacerbate gastrointestinal issues [7].

Respiratory system effects

Inhalation of airborne microplastics can induce oxidative stress in the airways and lungs, triggering respiratory symptoms such as coughing, sneezing, shortness of breath, fatigue, and dizziness. Studies have shown that nano-sized plastics can cause mitochondrial damage in human respiratory cells, while acting as carriers for other toxic substances like polystyrene (PS), which are harmful to lung health and increase the risk of conditions such as chronic obstructive pulmonary disease (COPD) [7].

Endocrine and reproductive system effects

Microplastics interfere with hormone production, release, transport, metabolism, and elimination, potentially causing endocrine disruption. This disruption can lead to various disorders, including metabolic issues, developmental abnormalities, and reproductive disorders such as infertility, miscarriage, and congenital malformations. Microplastics can absorb and release endocrine-disrupting chemicals like bisphenol A, exacerbating their impact on the endocrine and reproductive systems [7].

Immune system effects

Research indicates that microplastics may induce chronic inflammation and disrupt immune system homeostasis. Animal studies have shown that exposure to these particles can activate genes and proteins involved in immune responses, suggesting potential immune system dysregulation in humans exposed to microplastics [7].

Overall health implications

In vitro experiments with human cells and in vivo studies with animals have consistently demonstrated that microplastics elicit adverse health effects. These include inflammation, oxidative stress characterized by increased reactive oxygen species production, disturbances in lipid metabolism, dysbiosis of gut microbiota, and neurotoxicity. Experimental findings on animals exposed to microplastics further highlight disturbances in liver lipid metabolism, increased oxidative stress, and inflammation in organs such as the liver, kidneys, intestines, and brain [7].

Environmental and Ecological Consequences of Microplastics

Aquatic life

Microplastics pose significant threats to aquatic life, impacting various species through ingestion and entanglement. Fish, seabirds, marine mammals, and other wildlife often mistake small plastic particles for food, leading to ingestion. This ingestion can cause physical harm, blockages in digestive systems, and even death. Seabirds, for example, may inadvertently feed plastic to their chicks, resulting in reduced growth rates and reproductive success. Marine animals also risk becoming entangled in larger plastic debris, such as fishing nets and lines, leading to injuries, impaired movement, and sometimes death [8].

Bioaccumulation

Bioaccumulation is the process by which microplastics accumulate in organisms through ingestion and are stored in their tissues. In aquatic environments, organisms at lower trophic levels, such as plankton and filter-feeders like mussels, accumulate microplastics over time. As larger predators consume these smaller organisms, microplastics biomagnify up the food chain. This means that organisms higher in the food chain, including fish and marine mammals, accumulate higher concentrations of microplastics. Biomagnification increases the likelihood of exposure to microplastics for top predators and poses risks to species health and ecosystem stability [8].

Habitat disruption

Microplastics alter aquatic habitats, affecting species distribution and ecosystem dynamics. These particles can accumulate on the ocean floor, disrupting benthic habitats and altering sediment composition. Floating microplastics can create microenvironments that differ from natural conditions, influencing microbial communities and nutrient cycling. Additionally, microplastics can serve as vectors for other pollutants, such as heavy metals and persistent organic pollutants, which further degrade habitats and threaten ecosystem health [8].

Mitigation and Solutions

Waste management improvements

Advancements in waste management are crucial in mitigating microplastic pollution. Enhanced recycling technologies and increased recycling rates play pivotal roles in reducing the volume of plastic waste that enters the environment. Innovations in sorting techniques and infrastructure improvements have facilitated more efficient separation of plastic waste, thereby promoting circularity in plastic use and reducing the amount of plastic that ends up as litter or in natural ecosystems [9].

Upgrading wastewater treatment plants represents another critical step in mitigating microplastic release into aquatic environments. Traditional treatment methods often fail to capture microplastics effectively, allowing these particles to enter rivers, lakes, and oceans. By implementing advanced filtration systems and incorporating tertiary treatment processes, wastewater treatment plants can significantly reduce the discharge of microplastics into water bodies, thereby protecting aquatic ecosystems and preventing further contamination [9].

Innovative technologies

Nanotechnology holds promise in addressing microplastic pollution through advanced filtration systems. Researchers are exploring nanomaterials that can efficiently capture microplastics from wastewater and other sources. These technologies leverage the high surface area and adsorption capabilities of nanomaterials to trap microplastics before they reach natural ecosystems. Continued research and development in nanotechnology offer potential solutions to improve water quality and reduce environmental contamination caused by microplastics [9].

The development and adoption of biodegradable plastics represent another innovative approach to combating microplastic pollution. Biodegradable plastics are designed to break down more readily in natural environments compared to traditional plastics, reducing their persistence and potential impact on ecosystems. However, challenges remain in ensuring these alternatives meet performance standards and do not contribute to other environmental issues, such as increased greenhouse gas emissions during production [9].

Policy and legislation

Successful legislative measures, such as bans on microbeads in cosmetics and personal care products, demonstrate effective policy interventions to mitigate microplastic pollution. These bans restrict the use of plastic microbeads, which are prevalent in exfoliating scrubs and toothpaste, and have been significant contributors to microplastic pollution in aquatic environments. Such regulatory actions highlight the importance of proactive policies in eliminating sources of microplastics and promoting environmentally friendly alternatives.

International cooperation is essential in addressing the global nature of microplastic pollution. Collaborative efforts among nations are necessary to establish comprehensive frameworks and standards for managing plastic waste and preventing its entry into the environment. Coordination on research, data sharing, and best practices can facilitate the development of unified strategies to tackle microplastic pollution effectively on a global scale, ensuring sustainable use of plastic materials and safeguarding marine and terrestrial ecosystems.

Individual Actions to Reduce Microplastic Pollution

Consumer choices

Making eco-friendly product choices can significantly contribute to reducing microplastic pollution. Opt for products made from natural fibers and materials labeled as microplastic-free. Natural fiber clothing, bamboo-based items, and biodegradable alternatives can help minimize the release of microplastics into the environment. By supporting brands that prioritize sustainability and offer microplastic-free options, consumers can drive demand for environmentally responsible products.

Reducing reliance on single-use plastics is another impactful way individuals can mitigate microplastic pollution. Simple changes like carrying reusable bags, water bottles, and utensils can significantly decrease plastic waste generation. Choosing products with minimal plastic packaging and opting for reusable alternatives instead of disposable items further reduces the amount of plastic entering landfills and natural ecosystems. These actions not only lessen microplastic contamination but also promote a sustainable lifestyle [9].

Community involvement

Community engagement plays a vital role in addressing microplastic pollution at the local level. Participating in or organizing community events focused on cleaning local water bodies can directly mitigate microplastic contamination. These initiatives raise awareness about the environmental impact of plastics, encourage responsible waste disposal practices, and foster community stewardship of natural resources. By joining cleanup efforts and advocating for cleaner environments, individuals can contribute to preserving aquatic ecosystems and reducing the prevalence of microplastics in waterways.

Educational efforts

Increasing educational initiatives is essential to raise public awareness about the detrimental effects of microplastics. Educational programs in schools, community centers, and online platforms can inform individuals about the sources, impacts, and preventive measures related to microplastic pollution. Teaching about sustainable consumption habits, proper waste management, and the importance of reducing plastic use empowers individuals to make informed choices that support environmental conservation. By promoting knowledge and understanding of microplastic issues, educational efforts inspire collective action and encourage sustainable behaviors among communities.

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References

Jade Hall