Currently, the world faces a period of rapid changes with technological developments revolutionizing the way people live and, simultaneously, leading humankind to the global catastrophe of resource scarcity and climate change. The environment suffers from microplastics (further referred to as MPs) released by the degraded synthetic clothing, cosmetics, plastic bags, bottles, and containers. Although plastic products are already an essential part of people’s lives, they pose a serious environmental threat in the form of MPs articles damaging the biosphere’s health.
The Problem of Plastic Waste
Products made of plastic are popular due to the presence of their different types and the ability to take all sorts of sizes, colors, and shapes. Plastic might be produced from such natural materials as oil and coal, and it is not biodegradable. Hence, it can harm the environment for centuries. Annually, about 400 million tons of plastics are manufactured, and approximately 160 million tons of them are single-use plastic (“What Is the Problem”). Over eight million tons of plastic garbage enter the oceans, escaping from the land around the globe, primarily from beaches and ships or carried by the rivers. For example, “every day seven million cardboard coffee cups are thrown away but only one in 400 are recycled” (“What Is the Problem”). Not all types of plastic might be recycled due to the techniques by which it is produced or the high cost and complexity of recycling.
MPs Forming Process
MPs are tiny plastic particle with a diameter of less than five mm that appears as a result of the larger plastics breakdown or commercial product development. It is a significant pollutant posing a threat to animal health and the environment. There are primary (commercial use including cosmetics, microfibers shed from textiles like fishing nets, and others) and secondary (for example, the breakdown of plastic bottles) categories of plastic (“Microplastics”). The so-called breakdown secondary category results from the plastic’s exposure to ocean waves, sun radiation, and other environmental factors.
Particle Absorption by Animals
From plankton to whales, from commercial seafood to drinking water, different marine organisms contain MPs. It is noteworthy that the typical water treatment facilities are unable to remove all the MPs particles, which, in turn, often bind with various harmful chemicals before marine organisms ingest them. Nevertheless, most countries struggle to reduce MPs contamination in the environment. In 2017, the United Nations resolution addressed MPs and the regulations needed to reduce their impact on human health, wildlife, and oceans (“What Is the Problem”). Yet, there is no firm scientific evidence of whether MPs consumption damages animal or human health and the real threats they might pose.
Threat to Human
People are exposed to MPs environmentally, and the routes of such exposure include dermal contact, inhalation, and ingestion. Particle toxicity, inflammation, and oxidative stress might cause toxicity. In turn, inflammation can result in neoplasia and increase the particles translocation. MPs may play a significant role in immune function disruption and neurotoxicity (Prata et al.). People at risk include those working at factories making plastics and products made of them. The employees of waste management, aquaculture facilities, and wastewater treatment are also under threat. The cruise ship, fish farming industries, and shipping staff are at risk either (“What are Microplastics”). Individuals using specific skincare products and toothpaste containing plastic microbeads, going to coastal or ocean waters, and visiting shorelines are also exposed to MPs’ influence.
The Danger of Transmission on Trophic Chains
The MPs trophic transfer process, for instance, in top marine predators, is currently poorly understood. The in-nature studies practical limitations were resolved by the use of wild fish caught in captive seals. The extensive contamination controls revealed that “half of the scat sub-samples and a third of fish contained 1–4 MPs” (Nelms et al.). Hence, it is likely that trophic transfer is a major, although indirect, MPs ingestion pathway. The point is that MPs are significantly bioavailable both through direct ingestion and indirect trophic transfer from the prey. Although the latter was studied in laboratories for low-trophic level organisms, there is still a lack of empirical evidence in terms of high-trophic taxa. Differentiating between indirectly and directly ingested MPs is the primary difficulty of in-nature studies.
In the survey conducted by Nelms et al., the researchers resolved the issue through analyzing the scat’s (Halichoerus grypus) sub-samples and the Atlantic mackerel’s (Scomber scombrus) whole digestive tracts. The excess organic material was removed utilizing the enzymatic digestion protocol. Hence, synthetic particles could be visually detected without damaging them. FTIR (Fourier-Transform Infrared) spectroscopy was used to confirm the polymer type. Nelms et al. concluded that “trophic transfer represents an indirect, yet potentially major, the pathway of microplastic ingestion for any species whose feeding ecology involves the consumption of whole prey.” The resolution of limitations was hindered by the ethical constraints lying in subjecting large marine organisms to laboratory investigations.
In terms of physical effects, the MPs’ bio persistence might cause a chain of biological responses such as genotoxicity, inflammation, apoptosis, oxidative stress, and necrosis (Write and Kelly). Hence, a range of specific outcomes includes fibrosis, tissue damage, and carcinogenesis. The polymer’s composition establishes chemical effects that lead to the unreacted residual monomers and unbound chemicals leaching. Additionally, potential consequences include “the desorption of associated hydrophobic organic contaminants (HOCs)” (Write and Kelly). Digestive transit forms the corona on MPs that might consist of antigens and toxins. Write and Kelly claim that “in addition to hydrophobicity and charge, shape and age (surface pits and cracks) of the particle will impact the extent of this, as particle morphology is linked to the surface area” (Write and Kelly). The issue of corona’s impact on toxicity and particle uptake has already been widely researched in terms of therapeutic perspective, especially in nano plastics. Nevertheless, the corona’s development of environmental MPs is still largely unstudied.
Additional Problem with MPs
Sorption of Toxic Substances
In terms of toxic substances sorption, “the octanol-water partition coefficients (Kow) of organic chemicals, physical-chemical characteristics of MPs, weathering/aging degree of MPs, solution chemistry (e.g., salinity and pH), and temperature were found to be important factors for the sorption of chemicals in MPs” (Wang et al.). Currently, a significant concern is the disruptive endocrine properties of chemicals recognized as EDCs (Endocrine Disrupting Chemicals) or potential EDCs.
A compilation of their lists was developed by IPCP – the International Panel on Chemical Pollution. In general terms, the research on animals revealed non-linear low-level exposures to EDCs leading to permanent and transient changes. It results from their ability to compete with, disrupt, or mimic the endogenous hormones systems. Consequently, they might cause low birth rates, impaired reproduction, potential biodiversity loss, metabolism problems, thyroid function issues, and hormone-sensitive cancer types. The researchers suggest that “embryo and developmental periods are critical-sensitive periods to EDCs.13 EDCs may cause effects in cellular and/or animal models at deficient concentrations” (Gallo et al. 13). Currently, there are no scientific studies that correlate the direct consumption of polluted with EDCs and/or contaminated with MPs shellfish and fish.
Therefore, the consequent disruptions in the endocrine system and overall human health are neither deeply studied, and the main reason for it is the issue’s complexity. In 2018, the FAO report on food safety concluded that “basic toxicological data on the consumption of micro and nanoplastics in humans for a food risk safety assessment are essential lacking” (Gallo et al. 13). Additionally, “the available data of toxicokinetics only include absorption and distribution, whereas no information is available on metabolism and little on excretion” (Gallo et al. 13). It is yet unknown whether ingested MPs might be degraded into nanoplastics. Moreover, no accurate are available on the potential effect of processing and cooking seafood at high temperatures on the MPs toxicity.
Release of Poisonous Compounds into the Body
When ingested or inhaled, MPs tend to bioaccumulate exerting localized particle toxicity through enhancing or inducing an immune system response. Chemical toxicity arises through the local leaching of endogenous additives, component monomers, or adsorbed pollutants of the environment. Therefore, after dietary exposure, absorption in humans is plausible. It is evidenced by synthetic particles’ ability less than 150 mm in size to pass through the gastrointestinal epithelium in mammals, causing systemic exposure. Nevertheless, scientists insist that no more than 0,3% of those particles are likely to be absorbed (Campanale et al.). In turn, a lower fraction (around 0,1%) containing particles more prominent than 10 mm can reach both cellular membranes and organs and pass through both the placenta and a blood-brain barrier (Campanale et al.). The overall opinion is that the concentrations of exposure are likely to be low (Campanale et al.). However, data about nano plastics and MPs in the environment is still insufficient due to the technical and analytical complications to characterize, extract, and quantify them from the matrices of the environment.
MPs cause not only physiological effects arising through their ingestion. Additional chemical hazards are posed by plastic containing suspected and known chemicals that can disrupt the endocrine system as contaminants and additives (Gallo et al. 13). Although plastic is not the exclusive way marine organisms become exposed to harmful chemicals, there is evidence, and the scientific community is genuinely sure of its significant contribution to complex chemical contaminants’ mixtures exposure.
Currently, all the MP’s implications are not yet precisely understood and studied. Understanding their impact involves considerable complexity due to various chemical-physical properties making MPs multifaceted stressors. On the one hand, they fill the ecosystems with toxic chemicals, being themselves the transport vectors. On the other hand, the hazardous chemicals cocktail is added to MPs in their production, prolonging their life cycle and increasing their polymer properties.
It is essential to proceed with the primary scientific research on potential influence on overall human health, particularly endocrine systems. Particular attention should be paid to indirect and direct ingestion of marine nano- and MPs in developing stages. Technology transfer and innovations should be promoted to encourage plastic waste prevention, support implementation, and further develop safer alternatives to persistent plastics. It is also crucial to assist the economies in transition, Small Island Developing States, and developing countries with environmentally efficient management and sound collection of plastic packaging and waste.
Campanale, Claudia, et al. “A Detailed Review Study on Potential Effects of Microplastics and Additives of Concern on Human Health.” International Journal of Environmental Research and Public Health, vol. 17, no. 14, 2020, p. 1212.
Gallo, Frederick, et al. “Marine Litter Plastics and Microplastics and Their Toxic Chemicals Components: The Need for Urgent Preventive Measures.” Environmental Sciences Europe, vol. 30, no. 1, 2018, p. 13.
“Microplastics.” National Geographic, n.d. 2020. Web.
Nelms, Sarah E., et al. “Investigating Microplastic Trophic Transfer in Marine Top Predators.” Environmental Pollution, vol. 238, 2018, pp. 999-1007. Web.
Prata, Joana Correia, et al. “Environmental Exposure to Microplastics: An Overview on Possible Human Health Effects.” Science of the Total Environment, vol. 702, 2020. Web.
Wang, Fen, et al. “Sorption of Toxic Chemicals on Microplastics.” Microplastic Contamination in Aquatic Environments, 2018, pp. 225-247.
“What are Microplastics?” ToxTown, n.d. 2020. Web.
“What is the problem with plastic?” BBC, 2020. Web.
Write, Stephanie, and Frank Kelly. “Plastic and Human Health: A Micro Issue?” Environmental Science and Technology, vol. 51, no. 12, 2017.