Metal adsorption by microplastics in aquatic environments under controlled conditions: exposure time, pH and salinity

In recent decades there has been a significant increase in the presence of plastics in the environment, particularly in the marine environment, due to its great applicability in all fields of life. The effects of chronic ingestion of contaminated microplastics are still unknown, but several studies suggest that there is a potential gateway to the trophic network, especially when these plastics support other pollutants harmful to human life and act as a vehicle of entry into the organisms, making them more bioavailable. For this reason, the present work aims to evaluate the adsorption capacity that microplastics have for different metals depending on the physicochemical conditions of the aquatic environments (exposure time, pH, salinity). To do this, two types of microplastics were selected (polypropylene and polyethylene), and a group of two essential metals (Cu, Zn) and two toxic ones (Cd, Pb) were evaluated. Virgin pellets of both, polyethylene and polypropylene, were able to adsorb metals (Cu, Cd, Pb, Zn) in the aquatic environment, although the adsorption was low in most of the cases. Only minor differences were found in the adsorption capacity of the two studied materials. The exposure time showed an important effect regarding the adsorption capabilities of pellets, showing different adsorption rates for different metals. However, all studied metals showed the same behaviour in relation to pH and salinity, increasing the adsorption percentages as pH increase, and decreasing the adsorption percentages when salinity increase for lower salinities.