The potential of microplastic pellets as a vector to metal contamination in two sympatric marine species

Microplastics are a global threat to the marine environment due to the ever-growing use of plastic materials, to their abundance and widespread distribution. It is suspected that microplastic size range enables ingestion by many marine organisms. In addition, may release toxicants from paints, coatings and other additives resulting from the manufacturing process, as well as adsorb contaminants, such as metals, and thus act as carry-overs of toxicants. Consequently, there is a concern that microplastics, either pristine or resulting from ageing and fragmentation, can be vectors of marine pollutants via ingestion or release of compounds to the water column, then increasing bioavailability. The present work aimed at assessing the potential of microplastics as vectors of metal contamination to marine organisms by exposing, for 30 days, two sympatric coastal species, the fish Diplodus sargus and the decapod crustacean Palaemon serratus (juveniles), to pristine and coated polystyrene microplastics (c.a. 1 mm Ø). The coating consisted of a common anti-fouling paint containing copper and zinc. Through a whole-body histopathological screening involving both qualitative and semi-quantitative methods, it was shown that only fish ingested the spherical microplastics, which were present in the intestine, albeit without adverse effects. This indicates that fish are able to cope with microplastic ingestion and passage through the gut. In addition, no effects to metal intoxication were found in either species, suggesting that metal bioavailability was not significantly increased to cause harm. This may result from the fact that either metal is essential, therefore implying high tolerance and reduced toxicity. Altogether, the findings indicate reduced risk of these materials to act as vectors of metals from antifouling paints. Different morphoanatomical aspects and feeding behaviour of both species may explain the observed differences and the selective rejection of microplastics by shrimps.