Microplastics in Human Consumption

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lack of proper mechanisms for municipal solid waste (MSW) management often leads to the accumulation of waste piles with plastic debris; such dumps also become a major contributor of plastics to water bodies

The plastic wastes on reaching the water bodies or on the way may get disintegrated into smaller pieces; such fragmented plastics of less than 5 mm size are referred to as ‘microplastics’ (MPs) – a recent addition to the class of contaminants of emerging concern (CEC).

Bakelite was the first plastic synthesized in the 1920s; later plastics production increased during the Second World War in order to meet the demand from the military

annual production of plastics from 30 million tons in the 1970s has become more than 359 million tons in 2018 (Plastics Europe, 2019

Besides the increase in plastic production, another change noticed in the plastic industry in the last few decades was a shift from the production of durable plastics to single-use plastics. Much of the single-use plastics (SUP) such as LDPE, HDPE, PS and EPS production is from Northeast Asia (China, Hong Kong, Japan, Republic of Korea and Taiwan) followed by North America, the Middle East and Europe (UNEP, 2018).

Based on the thermal properties such as melting and cooling capacities, plastics are grouped into two categories: thermoplastics and thermosets.

Thermoplastics can be melted and hardened by heating and cooling respectively. In other words, such plastics can be reheated, reshaped and frozen repeatedly. The most common thermoplastics are high-density polyethylene (HDPE), polyethylene terephtalate (PET), polyvinyl-chloride (PVC), polypropylene (PE), low-density polyethylene (LDPE), expanded polystyrene (EPS), polystyrene (PS), polycarbonate (PC), polypropylene (PP), polylactic acid (PLA) and polyhydroxy alkenoates (PHA

Thermosets are plastics that, on heating, undergo a chemical change and form a stable three-dimensional network; thus these plastics cannot be remelted and reformed, hence they are “non-reversible plastic”. Common examples of thermosets are polyurethane (PUR), epoxy resins, phenolic resins, urea-formaldehyde (UF) resins, silicone, vinyl ester and acrylic resins

the plastic particles depending on size have different nomenclature (Figure 1.1): macroplastics (≥ 25mm); mesoplastics (5 to 25 mm); microplastics (1 μm to 5 mm); and nanoplastics (<1 µm) (Crawford and Quinn, 2016). Apart

Primary microplastics are synthesized plastic particles of microscopic size often referred to as pellets or beads for various applications. Resin pellets are used as raw materials in the plastic industry for the production of various plastic articles (Peng et al., 2017). Microbeads find their applications in cosmetics mainly as exfoliating materials, abrasive agents in detergents and air blast media; hygiene and personal care products such as soaps, hand and facial cleansers, toothpaste, shower gels and shampoos (Arthur et al., 2009; Cole et al., 2011; Fendall and Sewell, 2009; Siegfried et al., 2017; Peng et al., 2017).

Secondary microplastics originate from fragmentation and disintegration of larger plastic materials mostly plastic wastes discarded. The breakdown of plastic debris may occur due to the sunlight (UV radiation) or the mechanical action of wind/waves or biological means

Fragment (FR)
< 5 mm–1 mm
Plastic piece of irregular shape with a size of 1 mm to 5 mm along its longest dimension
Microfragment (MFR)
< 1 mm–1 µm
Plastic piece of irregular shape with a size of 1 µm to 1 mm along its longest dimension
Pellet (PT)
< 5 mm–1 mm
Small spherical-shaped plastic piece with a size of 1 mm to 5 mm in diameter
Microbead (MBD)
< 1 mm–1 µm
Small spherical-shaped plastic piece with a size of 1 µm to 1 mm in diameter
Fiber (FB)
< 5 mm–1 mm
Plastic piece of a strand or filament with a size of 1 mm to 5 mm along its longest dimension
Microfiber (MFB)
< 1 mm–1 µm
Plastic piece of a strand or filament with a size of 1 µm to 1 mm along its longest dimension
Film (FI)
< 5 mm–1 mm
Plastic piece of a thin membrane or sheet with a size of 1 mm to 5 mm along its longest dimension
Microfilm (MFI)
< 1 mm–1 µm
Plastic piece of a thin membrane or sheet with a size of 1 µm to 1 mm along its longest dimension
Foam (FM)
< 5 mm–1 mm
Plastic piece of foam or foam-like plastic material or sponge with a size of 1 mm to 5 mm along its longest dimension
Microfoam (MFM)
< 1 mm–1 µm
Plastic piece of foam or foam-like plastic material or sponge with a size of 1 µm to 1 mm along its longest dimension

A recent estimate (Geyer et al., 2017) states that about 79% of the plastic wastes so far generated remains in landfills or solid waste dumps or in the environment, while 12% has been incinerated and only 9% has been recycled

Similar is the case with laundry wastewater from individual houses; either manual wash or washing machine effluents carry MPs such as microfibers of polyester and nylon from cloths of synthetic fabric. Around 1,900 fibers per garment were reported from the effluent of a domestic washing machine (Browne et al., 2011).

Wind also acts as a dispersing means of plastic debris, mainly from the waste piles, dump yards and landfills (Barnes et al., 2009). The presence of MPs as fibers in atmospheric fallout, indoor and outdoor air has been reported (Dris et al., 2016, 2017). However, a number of studies reported the MPs in the air environment as less.

Given the longevity of MPs as hundreds and thousands of years, their presence in water bodies has been reviewed extensively in the literature. As far as the fate of MPs in sea/ocean waters is concerned, MPs are subjected to the following four mechanisms: sedimentation, shore deposition, nano-fragmentation and ingestion by organisms

The most important concern of risks of MPs in oceans and seas is due to the ingestion of MPs by a variety of organisms in the aquatic environment (Peng et al., 2017). Around 180 species including fish, turtles, birds and mammals have been reported to be ingesting MPs. The ingested MPs have been reported from different tissues and organs including gills, digestive glands, stomach and hepatopancreas

Several studies have documented the presence of MPs in marine biotic products – mainly the seafood items – like clams, fishes and crabs (Van Cauwenberghe and Janssen, 2014; Li et al., 2015). Similarly, sea salt – the abiotic product from the sea – is also reported to have microplastics (Yang et al., 2015; Karami et al., 2016). Hence, consumption of seafood and salt could be a significant route of exposure to MPs in humans.

many researchers have reported polyethylene (PE) as the dominant type of polymer in marine fishes, followed by polyethylene terephthalate (PET) and polypropylene (PP). Studies on freshwater fishes confirm polypropylene as the predominant polymer while polyester was common in estuarine fishes

When global studies on MPs contamination of salt are screened, around 27 polymer types have been detected from the different types and brands of salt samples, with dominant polymers of polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP) as reported by Lee et al. (2019).

Despite the fact that drinking water occupies a major portion of the human diet by supplying required minerals and trace nutrients, the reports on MP contamination of potable water remain limited.

Apart from drinking water, beer, the predominant beverage being consumed, has also been reported to have MP contamination.

MPs are also witnessed in beverages including potable water, soft drinks, energy drinks and beer;

Koelmans et al. (2019) have reviewed the global scenario of MP contamination in drinking water. The review indicates most detected polymers were PE, PET and PP while PMMA, PU, PS and PVC were found rarely.

Panno et al. (2019) investigated the MP contamination in springs and well water of two Karst aquifers (Karst aquifers are a special type of fractured rock aquifers) in Illinois, USA, and found MPs as well as other anthropogenic contaminants in Karst groundwater systems. They have reported a maximum concentration of 15.2 particles/L and all the MPs were fibers in shape.

Strand et al. (2018) sampled drinking water from 17 sites around Denmark; 50 L of samples per site were collected directly from taps filtered through stainless steel filters (10 μm) into a closed steel filter system in order to prevent contamination. The findings of this study showed 30 MP-like particles per 50 L as the highest abundance; however, further analysis revealed only 3% of the MP-like particles were verified as MPs, while the rest of the particles were either cellulose-like material (76%), unknown (7%), protein-like (4%) or poor spectra (10%).

In Germany, 38 mineral waters (packed in 15 different returnable and 11 single-use plastic bottles, three beverage cartons and nine glass bottles) were analyzed for microplastic contamination. MP contamination was found in every type of water, between 5 and 20 μm in size (almost 80%). The average MP content was 118 ± 88 particles/l in returnables, 14 ± 14 particles/l in single-use plastic bottles, 11 ± 8 particles/l in beverage cartons and 0–253 particles/l in glass-bottled waters. The study also revealed the polymer of the MPs correlates with the materials the bottles/cartons were made-up of

This industry spends 3–4 L of freshwater for the production of 1 L of soft drinks (Grumezescu and Holban, 2018).

As far as the drinking water supply is concerned, the presence of a higher abundance of MPs was noted in the raw water prior to treatment; after treatment, a reduction in the number of MPs has been observed consistently by many authors.

general, natural and synthetic polymers such as cellulose, natural gas, crude oil and coal are used to produce plastics through two main processes: polymerization and polycondensation. In order to add strength and improve the quality of the plastics, a few additives (phthalates, bisphenol A, polybrominated diphenyl ethers and metals or metalloids) are added besides different colorants. It is to be noted that some of these additives are endocrine disruptors or carcinogenic, thus becoming a matter of concern to human health (Revel et al., 2018).

the consumption of MP-contaminated food items by humans can lead to health issues due to: (1) the physical nature of the MPs, mainly their size and shape; (2) the leaching of additives from MPs, i.e. chemicals like phthalates, bisphenols, colorants, etc.; (3) the substances adsorbed on the surface of MPs and (4) the microbial consortia of the biofilm found on the surface of the MPs.

the predominant mode of MP intake is through ingestion. Consumption of seafood items contaminated with MPs has been identified as a major means of MP intake by humans; consumption of sea salt also leads to MP intake. Tap water, bottled water and beverages also serve as sources of MPs in the human body.

Cox et al. (2019) have studied the quantity of MPs entering the human body through consumption (ingestion). Accordingly, the daily (average) concentration of MP intake by an adult male is 142 and for adult females it is 126; for male and female children the intake is 113 and 106 respectively. They have also calculated the concentration of MPs present in common human food items, for example, 1.48MPs/g of seafood, 0.11 MPs/g of salt, 0.44MPs/g of sugar, 94.37MPs/L of bottled water and 32.27MPs/L of alcohol.

studies are limited on the health impacts of MPs on human systems. The potential impacts reported in studies are oxidative stress, inflammatory responses, disruptions of gut microorganisms, functional impacts on the gastrointestinal tract, epidermis and lung failure (Wright and Kelly, 2017; Smith et al., 2018

Microplastics of smaller dimensions, mostly synthetic fibers, entering the human respiratory system can cause inflammatory and cytotoxic effects along with respiratory distress (Hurley et al., 2016; Dehghani et al., 2017; Prata 2018; Rezaei et al., 2019; Dong et al., 2019).

MPs from toothpaste when swallowed unintentionally can enter into the gastrointestinal tract; such ingestions can lead to alterations in chromosomes causing obesity, infertility and cancer (GESAMP, 2015; Sharma and Chatterjee, 2017

Many of these additives such as phthalates, BPA and polybrominated diphenyl ether (PBDEs) are endocrine-disrupting chemicals (McGrath et al., 2017; Serrano et al., 2014; Lu et al., 2013). Liver function changes, insulin resistance, damages to a developing fetus and neurological functions are some of the toxic effects of BPA (Srivastava and Godara, 2013). Phthalate esters may lead to abnormal sexual development and birth defects (Cheng et al., 2015). A few plastics like styrofoam contain carcinogenic chemicals like benzene and styrene; these chemicals are highly toxic if consumed and might damage the lungs, reproductive systems and nervous system (Yang et al., 2011).

Heavy metals adsorbed over the surface of MPs may also get leached out in the digestive tracts of human beings. Apart from the adsorbed heavy metals, a few plastics like vinyl window blinds and plastic jewelry have lead as plastic stabilizers added during production. Exposure to lead may increase the risk of hypertension and negatively affect the kidneys and nervous system in adults, while decreased IQ level and reduced growth are the effects in children

The predominant means of entry of MPs into human body has been reported to be ingestion, i.e. through consumption of MP-contaminated food items (like fishes, prawns, crabs, salts, sugar, bottled water, honey, beer, etc.). However, inhalation of dust also leads to a substantial quantity of MPs’ entry into the human body; other means are through direct contact on the skin by the use of personal care products like shampoos, cleansers, toothpaste, etc. The additives in the plastic particles, chemicals and heavy metals adsorbed over the MPs all together cause human health issues when the MPs gain entry into the human body. Some of the health issues reported in the literature due to MPs are inflammation, oxidative stress, necrosis, apoptosis, endocrine disruption, immune disorder and cancer.

there exists debate on the size of MPs that gain entry into human organs/cells, the subsequent fate and the impacts of MPs on the human body. Most of the studies report that MPs of less than 20 µm should be able to penetrate organs, and particles measuring 10 µm should be able to access all organs and cross the cell membranes. There also exist studies reporting MPs found in human stool indicating that larger-sized particles (50 to 500 µm) are removed from the human body by the excretory system

Generated at: 2023-06-13-21-51-45