Polyethylene Terephthalate and Polycarbonate Microplastics in Sewage Sludge Collected from the United States

Microplastics (MPs) are emerging pollutants of public health and environmental concern. Sewage sludge is a sink for MPs that originate from domestic sources and can provide an indication of the magnitude of discharge of MPs by local populations. Nevertheless, reports of quantitative analysis of MPs present in sewage sludge are limited. In this study, 65 sewage sludge samples collected from sewage treatment plants (STPs) across the United States were analyzed for MPs originating from polyethylene terephthalate (PET) and polycarbonate (PC) using alkali-assisted thermal depolymerization and liquid chromatography-tandem mass spectrometry. PET and PC were detected in all sludge samples at concentrations (dry weight) in the ranges of 28-12000 mu g/g (median of 370 mu g/g) and 0.70-8400 mu g/g (median of 5.9 mu g/g), respectively. The concentrations of PET and PC varied, depending on the treatment capacity of the STPs. The annual environmental emission of MPs through sludge disposal was estimated at 3700000 kg/year for PET and 310000 kg/year for PC. Our results provide a emission of MPs through land application of sludge.