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As many as 5.25 trillion plastic particles weighing 250,000 tons are floating in the oceans, according to recent estimates. This presents a serious environmental challenge: in addition to chemicals in the plastics themselves, pollutants already dissolved in seawater can adsorb, or latch onto, these plastic fragments. These can be eaten by marine animals which mistake them for food and can pose a threat to seafood safety.

The IAEA uses nuclear and isotopic techniques to gain a better understanding of the effect microplastics have on organisms and to evaluate any additional contamination risks from associated pollutants. This includes the use of radiolabelled tracers in controlled aquaria to examine to what extent plastics can be further contaminated and transferred through the marine environment and up the food chain.   

Plastics accumulate in the oceans because of their slow degradation rates. Micro-plastics, plastics smaller than 5mm, originate from the weathering and disintegration of larger plastic debris, from pellets used in the manufacturing of plastics, from additives in cleaning and personal care products, and from synthetic clothing.

Due to their small size, microplastics may also enter internal organs, where they could potentially be vectors for the transfer of contaminants attached to them. These could include persistent organic pollutants like polychlorinated biphenyls (PCBs) as well as trace elements like mercury and lead. Plastics and any pollutants which accumulate on them, can enter the food chain and be transferred to humans through the consumption of seafood.

To help evaluate risks and strengthen seafood safety programmes, IAEA experts are conducting research using nuclear and isotopic techniques under controlled laboratory conditions to precisely quantify the movement, fate and impact of plastic particles and associated organic and inorganic contaminants on a range of aquatic biota such as fish and oysters. By using tracers such as carbon-13, and carbon-14, IAEA researchers can study how pollutants such as PCBs ‘attach’ themselves to microplastics in the environment and if they can dissociate or ‘detach’ from these plastics when ingested by marine animals.

IAEA researchers will also use tracers to study the movement and fate of microplastics within the animals to understand how they are taken up — whether via the digestive system or through gills depending on the organism as well as whether they can be eliminated or if they clog different organs. If plastics accumulate in the gut, for example, organisms could get a false sense of being full, which can negatively influence their nutrient intake.

This information will advance our understanding of the role of microplastics and associated contaminants in societally and commercially important marine organisms and help strengthen Member State seafood safety programmes. Understanding to what extent microplastics can transfer hazardous contaminants to marine biota is an issue of global concern, in particular for countries that rely on fisheries as a source of food and income.

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