2 years ago
23 July, 2021
Plastics are mostly manufactured materials derived from crude oil. They are lightweight, inexpensive to produce and have many different structures and uses. Most plastics have one thing in common; they are durable, and it is difficult for microorganisms to break them down. This is an advantage to the user. But it is a disaster for the environment and a potential threat to human health.
Over time plastics disintegrate into smaller and smaller pieces. Microplastics are pieces of plastic less than 5 mm in size that is found in the environment (1). They are insoluble in water and may take decades or centuries to break down.
Microplastics arise following the environmental disintegration of plastics or are intentionally produced (2). Examples of the latter include microfibres used to make synthetic textiles, microbeads used in toothpaste and face creams, infill material for artificial turf, and nurdles – small plastic pellets that are the raw material for manufacturing many plastic products.
Microplastics are found all over the globe, from the deep-sea ocean bed to the snow of Mt Everest (3). They are present in oceans, rivers and lakes, in agricultural soils, in the air we breathe, in products we use, the water we drink and in the food we eat. They have been detected in sugar, salt, honey, beer and a variety of seafood (2). And they are found in our own guts and stools (4).
Nanoplastics – microplastics less than 1000 nanometres (less than 10-3 mm) – have been detected in animal organs, including the brains of fish and the liver of mice (5). They have also been found in human tissues, including the placenta (6).
Human exposure to microplastics occurs largely through ingestion, originating from food, especially seafood such as crustaceans (e.g. shrimp) and bivalves (e.g. oysters), or from food packaging material.
A new and concerning study found polypropylene infant feeding bottles can release millions of microplastic particles per litre into infant formula (7). This occurs during formula preparation, as bottles are routinely exposed to high-temperature water and shaken, releasing microplastics into the liquid formula. Plastic tea bags and water bottles also release high quantities of microplastics into liquid contents (8).
We breathe in microplastics from, for example, microfibres released from textiles, erosion of car tyres and dust. They may also enter our bodies via skin contact, for example, through the application of personal care products such as sunscreens.
Microplastics pose significant environmental and health concerns because of their persistence in the environment, potential toxicity and their ability to absorb contaminants and pathogens from the environment. However, the long-term effects of microplastics on human health are currently unknown (9).
Raw materials and chemical additives are incorporated into plastics during their manufacture, and these may be later released into the environment. Examples of additives include plasticisers used to soften plastics, UV stabilisers used to help prevent degradation, flame-retardants to help prevent products from catching fire, sealants and dyes. Many of these are persistent organic pollutants and/or endocrine-disrupting chemicals (EDCs) that interfere with hormone function and so may be detrimental to animal or human health (2).
Microplastic particles can bind to chemical pollutants found in the environment. The concentration of such pollutants in microplastics in oceans can be millions of times higher than in the seawater itself (10). This is concerning because if they are ingested by marine organisms such as fish, they are getting a strong dose of toxic chemicals, which may be passed on to any fish-eater – including humans.
Nutrients and organic matter adsorbed from surroundings by microplastics can enable microbial biofilms to form. Biofilms are communities of microorganisms that stick to the surface of an object by secreting a slimy, glue-like substance. They often harbour pathogens, including food poisoning bacteria, which can be ingested by marine organisms such as fish, and filter feeders such as oysters, mussels and scallops, which may be later consumed by humans (11).
Most studies that examine the health effects of microplastics have used animal subjects. It has been shown that ingestion of microplastics causes an inflammatory response, can damage the gut, disrupt gut microorganisms, cause organ damage, and affect reproduction or metabolism. Breathing in microplastics may cause inflammation and chemical toxicity and introduce pathogenic microorganisms into the body. Microplastics introduced through skin contact can cause skin damage due to local inflammation and cellular toxicity (11).
Studies have yet to demonstrate a link between microplastics and breast cancer risk, but such a link is feasible.
Plastic components such as bisphenols and additives, including phthalates, heavy metals such as cadmium, PFAS or flame retardants, all leach from microplastics. Many are EDCs that can act as oestrogen mimics at low concentrations, and so may increase breast cancer risk (12). Microplastics often contain a mixture of EDCs, which may be particularly harmful. Exposure to oestrogen mimics during critical windows of development, especially during early life, may cause changes in breast development which increase the risk of breast cancer later in life (12).
The presence of microplastics can increase the biological accumulation of persistent organic pollutants in aquatic species, for example,* PCBs in rabbitfish (13), or ** PAHs in mussels (14). Exposure to these cancer-causing compounds through consumption of seafood may also increase breast cancer risk (12).
Ingestion of microplastics can cause acute and chronic inflammation and irritation. This may potentially lead to DNA damage and promote cancer (9).
Plastics are useful materials that have become essential to modern life. They are lightweight, flexible and durable and have helped improve our lives in many ways, from their uses in medicine to food packaging.
But plastics and microplastics are significant sources of pollution; hundreds of thousands of tonnes of microplastics are now floating on the global sea surface (15).
There are various ways we can help prevent this from worsening. The simplest place to begin is to buy fewer products containing plastic.
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