Plastic and Microplastic in the Environment. Группа авторов

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      3.1.4 Associated Risk

      MPs can readily absorb harmful chemicals from the atmosphere and pathogenic contaminants due to its surface deposition (Verla et al. 2019). Along with their own harmful impacts, this MP has more associated risk when exposed to the environment, as they are breeding grounds for pathogens (Lu et al. 2019).

Plastic polymers are manufactured using chemical additives and other smaller monomer units, which give them the desired shape, structure, strength, and durability. These additives include wide ranges of chemicals like heavy metals; e.g. mercury, plasticizers, flame‐retardants, pigments, heat stabilizer filler, UV stabilizers, and many more, and this accounts for 4% of their total weight (Ambrogi et al. 2017). These chemicals tend to deposit over the MPs rather than dissolve in the water bodies (Ziccardi et al. 2016). When these chemicals leach into the environment due to photolysis chemical, and physical breakdown processes, they exhibit harmful impacts in every possible environment (air, water, or soil) as most of them are carcinogenic (Abdel‐Shafy and Mansour 2016). These MPs slowly degrade, and their surface area to volume ratio increases, which increases the chemical leaching (Chamas et al. 2020). These leached chemicals are mixed with the surrounding matrix and are transferred to the organism, causing bioaccumulation of these chemicals in them (Figure 3.3). If these MPs are directly eaten by primary consumers like zooplankton and then become prey by high trophic level, there is a high chance of bioaccumulation (Ziccardi et al. 2016).

Figure 3.3 Associated chemical toxicants entering marine organisms have potential health impacts.

      Fecal matter of zooplankton is an important component of marine organic matter and plays a significant role in the biological pump. The biological carbon pump is helpful in the transportation of carbon, nutrients, and energy to the deeper water sediments (Cisternas‐Novoa et al. 2019). Due to feeding on the MPs contaminated meals, their fecal pellets are highly susceptible to the persistent pollutants, hydrocarbons, and petroleum residue. Moreover, benthos feed upon these contaminated meals and are highly prone to bioaccumulation and biomagnification of these harmful chemicals.

3.2 Human Health Implication

The route of exposure of MPs to humans is mainly from inhalation, ingestion, and dermal contact (Prata et al. 2020). The plastics provide the food security by being less reactive and less expensive, therefore they are extensively used in the packaging of food, water, medicine, and the packaging industry in general. Studies reveal the presence of MPs in bottled mineral water (Weisser et al. 2021) and honey, among other foods. The main route of exposure to MPs are inhalation from the airborne MPs coming from the construction and demolition areas, industrial emissions, waste storage and disposal sites, such as landfill and waste reduction plants, where incineration of waste is done. These MPs are ingested along with food and water into the human body via dermal contacts, mainly by applying the cosmetics containing microbeads in them. However, fishes are a potential pathway for the entrance of MPs to human bodies (Barboza et al. 2020). The ocean is the largest producer of biomass and provides varieties of products which we use in our day‐to‐day life. There is a chance of toxicity due to xenobiotic compounds as well, which provide an important iodide source, i.e. salt. People are using cosmetics, toothpaste, and face scrubs, which have MPs of >1 μm, where the absorption of PE and PP particles in tissues can cause skin damage (Sharma & Chatterjee 2017). While our skin may provide a direct entry of MPs and other contaminants to our bodies, there are other routes which can cause direct exposure to them, such as sweat glands, open injury, and hair follicles. The microbeads present in the toothpaste are unintentionally swallowed, reach the gut, and may absorbed into the blood, which can cause chromosomal alteration, hormonal imbalance (which can lead to infertility), or cancer (Usman et al. 2020).

      Plastic polymer products are pervasive in human life; therefore, their particle exposure is inevitable for humans. Humans are highly exposed to the MPs problem as they are widely present in the air, water, and soil (Campanale et al. 2020).

      As foreign particles, MPs are resistant to the natural degradation process or defense mechanisms naturally present in one's body. They may cause particle toxicity, oxidative stress, disruption of immune function, or neurotoxicity (Prata et al. 2020).

      If MPs enter into the gut, they are not easily excreted by the body and may cause blockage of the gastrointestinal tract, which may disturb the function of the digestive system and lead to death (Wright et al. 2013). The immune system is unable to remove them, and this leads to chronic inflammation, which may cause neoplasia; a tumorous growth potentially capable of turning into a cancerous state (Prata et al. 2020). MPs, in sizes ranging from 0.2–150 μm have a high potency of translocation in humans across the cells to the lymphatic and circulatory systems, possibly through Peyer's patches of the intestine (Hussain et al. 2001). However, this process is not well known and needs further studies.

      Although human bodies are capable of excreting more than 90% of the MPs (Schwabl et al. 2019), its fate in the human body is not yet fully understood as it has associated risk of toxicity of chemicals like heavy metals (cadmium, lead, chromium etc.) (Massos & Turner 2017), hydrophobic organic pollutants (organo‐chloride, polyaromatic hydrocarbons, polychlorinated biphenyls etc.), and additive compounds (Wright & Kelly 2017). These chemicals are highly carcinogenic and easily transported to the lymphatic system (Wright & Kelly 2017). These chemicals are hydrophobic and easily adsorbed by MPs, and even a very small dose is sufficient to adversely affect the biological metabolism of humans and animals.

Due to its property of being an essential component in nutrition, common salt is extensively consumed by humans globally. Because it is also used in food preservatives, the human community consumes a small quantity of salt in almost every food item, which includes both the freshly cooked and preserved items like chips, aerated drinks, and packaged juice, etc. Salts are also found in cosmetics, pharmaceuticals, toothpaste, and other personal care products. Salts are deracinated from seawater or saline lakes, rocks, and wells. Sea salts are extracted by constructing shallow basins over salty and mineral‐rich lakes, generally referred to as salt evaporation ponds, where salts are obtained by the natural evaporation process. Prior to crystallization, the seawater is mixed with fresh water and then passed through a number of successive ponds to maintain a salinity gradient. These areas are highly prone to anthropogenic contaminants, mainly with MPs from marine debris, and this water circulation process adds contaminants into the water in the form of microbeads. Sea salts have higher MP contamination than a lake or rock salts (Peixoto et al. 2019). All these types of exposure to MP contaminants to the human body are still under investigation.

3.3 Conclusion and Future Perspective

      Microplastic waste is a matter of concern for researchers, if we don't find a remediation technique then the time is not far when our green planet would be wrapped in colorful plastics. This is quite evident from the oceans, where MPs have close interaction with all segments including biotic and abiotic. They enter into the organisms bodies via food and water as per their feeding habits. However, their harmful impacts on the body metabolism of organisms largely depend upon the particles size, and the biological processes governing their presence in organisms' bodies. The organisms' bodies have different development stages such as egg, larvae, adults etc., which would define their accumulation, fate, and impacts. Some creatures have a self‐defense mechanism that restricts them to feed upon these harmful MPs that others confuse with prey and consume in huge amounts. Sometimes, particles of size <5 mm can be successfully excreted out of the body, while sometimes they cause blockage of the digestive system and are fatal to organisms.

      Studies revealed the presence of MPs in sea products like common salts, which is the main source of dietary iodine to the