Effects of Sand Filters in Wastewater Treatment Plants on Microplastic Output

Microplastics, pieces of plastic between 5mm and 0.3mm, have been found in oceans and freshwater systems and can carry bacteria that the usual suspended solids do not. They also have a high potential for bioaccumulation, as even the smallest organisms can ingest them because of their small size. Because the research on microplastics in freshwater is limited, I wanted to know if they could be detected in freshwater streams, if the amount increased downstream of wastewater treatment plants (WWTPs), and if sand filters in WWTPs decreased microplastic output. Samples were taken at eight sites in and around four WWTPs, two with sand filters and two without. Microplastics were found in all the samples, though there were more downstream of WWTPs. The effect of filters on microplastics downstream was that though the total weight of the microplastics per liter did not increase, the number of pieces did, and those pieces were much smaller than those found downstream of WWTPs with no filter.