Adsorption of metals on aged microplastics in intensive mariculture areas: Aggravating the potential ecological risks to marine organisms

Field determination of the metal adsorption capacity of microplastics (MPs) by using a passive sampler had been done in typical subtropical mariculture area in China. The adsorption of eight metals (Fe, Mn, Cu, Zn, As, Pb, Cr and Cd) by five types of MPs (low-density polyethylene, polypropylene, polystyrene, poly(ethylene terephthalate) and poly(vinyl chloride) (PVC) was compared, including metal types, mariculture types (cage and longline culture), metal residue content in ambient environment, polymer types and particle sizes of MPs. The results showed that Cu, Zn, As, Cd, Pb and Cr in the mariculture environment were contaminated compared with the quality criteria. The concentrations of these six metals adsorbed on five MPs increased linearly with those in seawater. More enriched Cu and As in MPs in marine cage culture than in longline culture, due to the obvious endogenous pollution emissions for the artificial diets, fish medicine and disinfectants. Aged PVC with more cracks and pores showed higher metal adsorption capacity than any other polymers. MPs with a smaller size range of 50-74 μm tended to accumulate higher amounts of metals than those with a larger size range of 74-178 μm, consisting with the surface characteristics of MPs. The significant positive relationship between the concentrations of nutrients in seawater and the adsorption amounts of Cu, Zn and As on MPs implies that the eutrophication would promote their pollution. Based on the ecological risk assessment, the occurrence of MPs could aggravate the potential risk of metals to marine organisms in intensive mariculture areas. This is the first time to reveal the impacts of the adsorption of metals on aged MPs on the potential ecological risks of metals to organisms under the realistic environmental condition.