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Plastic in the food chain – a threat to human health?

There is growing concern that toxic chemicals from plastic debris, especially micro- and nanoplastics, are making their way into the food chain. But are they harmful? Anthropogenic marine debris has been observed throughout the ocean, from beaches and shallow coral reefs to the deep sea. Plastic particles have been found in hundreds of species of marine organisms, including many species of fish and shellfish sold for human consumption. A recent study found plastic in one out of every four fish purchased from markets in the United States and Indonesia (Rochman et al., 2015). Globally, average per capita fish consumption is nearly 20 kg per year and seafood equates to nearly 17 per cent of the world’s protein consumption (FAO, 2014), so there is a potential pathway for human exposure to plastic.

Plastic on the plate Assessing the risks to human health from marine plastic is a complex process and there is still a lot of debate over the quantity of plastic being ingested from seafood and whether it has the potential to affect the health of consumers. Consumption of filter feeding invertebrates, such as mussels and oysters, appears the most likely route for human consumption of microplastics, because people eat the whole organism including the gut. It has been shown that mussels can retain some plastic in their circularity system for over 48 days (Browne et al., 2008). It is estimated that high consumers of mussels in Belgium could ingest up to 11,000 pieces of microplastic in a year (an average of 90 particles per meal over 122 meals; Van Cauwenberghe and Janssen, 2014). The presence of microplastic particles in seafood could pose a human health risk (Van Cauwenberghe and Janssen 2014; Bouwmeester et al., 2015), especially if, following ingestion, the particles move from the digestive system to come into contact with organs and tissues. However, there is currently no evidence of ingested microplastics moving from the gut into other parts of the human body (Galloway, 2015). In contrast to microplastics, it is thought that nano-sized material (less than 100 nm) may be more readily absorbed through the digestive system into the body. Evidence for this comes largely from studies investigating the ingestion of engineered nanospheres as a method of drug delivery, where they have been seen to cross the gut barrier and enter the circulatory system (e.g. Hussain et al., 2001). Bouwmeester et al. (2015) reviewed laboratory studies that demonstrate uptake of nanoparticles bymarine organisms, including mussels and scallops. However, they conclude

that there is insufficient evidence to determine whether the absorbed nanoparticles can go beyond the circulatory system and enter cells. There is also some debate about the extent of nanoplastics in the ocean. It has been suggested that they are produced from the fragmentation of larger plastic particles, helped by both physical and microbial processes (Cozar et al., 2014 and Lawet al., 2014). At present it is technically difficult to detect nanoparticles in tissue or in the marine environment, so new detection methods are required to determine the extent and fate of these particles (Bouwmeester et al. 2015). What about the chemicals? In addition to the potential physical effects of ingesting plastic, there may also be associated chemical toxicity. Marine debris has been shown to contain a cocktail of chemicals including monomers and additives like flame retardants, antioxidants, UV-stabilizers and plasticizers. There is research that indicates that some of these chemicals can act as endocrine disruptors in humans (reviewed in Talsness et al., 2009). Chemicals of particular concern are phthalates and bisphenol A (BPA), which animal studies suggest may impair reproductive function and be carcinogenic, even at very low doses (Meeker et al., 2009; vom Saal et al., 2007). However, even though phthalates and BPA have been in commercial use for over 50 years, studies into the effects on humans are limited. Several studies have explored possible associations between phthalates and conditions such as altered semen quality and shortened gestation, although data are limited and the results inconclusive (Hauser and Calafat, 2005). A hazard analysis of plastic polymers identified polyurethanes (used in hard plastic parts and

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