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Impacts

There is, currently, very little evidence of the impact that microplastics can have on humans.

 

For human health, it is the smallest particles – micro- and nano-particles which are small enough to be ingested – that are of greatest concern. There are several ways by which plastic particles can be ingested: orally through water, consumption of marine products which contain microplastics, through the skin via cosmetics (identified as highly unlikely but possible), or inhalation of particles in the air.

 

It is possible for microplastics to be passed up to higher levels in the food chain. This can occur when a species consumes organisms of a lower level in the food chain which has microplastics in the gut or tissue. The presence of microplastics at higher levels of the food chain (in fish) has been documented.

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One factor which possibly limits the dietary uptake for humans is that microplastics in fish tend to be present in the gut and digestive tract — parts of the fish not typically eaten. The presence of microplastics in fish beyond the gastrointestinal tract (e.g. in tissue) remains to be studied in detail. Micro- and nanoplastics in bivalves (mussels and oysters) cultured for human consumption have also been identified. However, neither human exposure nor potential risk have been identified or quantified.

 

Plastic fibres have also been detected in other food items; for example, honey, beer and table salt. But the authors suggested negligible health risks as a result of this exposure.

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Levels of microplastic ingestion are currently unknown. Even less is known about how such particles interact in the body. It may be the case that microplastics simply pass straight through the gastrointestinal tract without impact or interaction. A study of North Sea fish, for example, revealed that 80 percent of fish with detected microplastics contained only one particle — this suggests that following ingestion, plastic does not persist for long periods of time. Concentrations in mussels, in contrast, can be significantly higher.

 

What could cause concern about the impact of microplastics? Three possible toxic effects of plastic particle have been suggested: the plastic particles themselves, the release of persistent organic pollutant adsorbed to the plastics, and leaching of plastic additives.

 

There has been no evidence of harmful effects to date – however, the precautionary principle would indicate that this is not evidence against taking exposure seriously.

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Since microplastics are hydrophobic (insoluble), and are have a high surface area-to-volume ratio, they can sorb environmental contaminants. If there was significant accumulation of environmental contaminants, there is the possibility that these concentrations could ‘biomagnify’ up the food chain to higher levels. Biomagnification of PCBs varies by organism and environmental conditions; multiple studies have shown no evidence of uptake by the organisms of PCBs despite ingestion whilst some mussels, for example, have shown capability to transfer some compounds into their digestive glands.

 

To date, there has been no clear evidence of the accumulation of persistent organic pollutants or leached plastic additives in humans. Continued research in this area is important to better understand the role of plastic within broader ecosystems and risk to human health.

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