Plastics are contaminants of emerging concern that can enter the environment from multiple sources, including via land application of treated sewage sludge (biosolids). Biosolids samples collected from 82 wastewater treatment plants across Australia and covering 34% of the population during census week in 2016 were quantitatively analyzed to estimate the release of seven common plastics. Quantitative analysis was performed by pressurized liquid extraction followed by double-shot micro furnace pyrolysis coupled to gas chromatography mass spectrometry. Ninety nine percent of the samples contained plastics (Σ₆Plastics) at concentrations of between 0.4 and 23.5 mg/g dry weight (median; 10.4 mg/g dry weight) while polycarbonate was not detected in any sample. Per-capita mass loads of plastics (Σ₆Plastics) released were between 8 and 877 g/person/year across all investigated wastewater treatment plants. Polyethylene was the predominant plastic detected, contributing to 69% of Σ₆Plastics. Based on the concentrations measured, it was projected that around 4,700 metric tons (Mt) of plastics are released into the Australian environment through biosolids end-use each year, equating to approximately 200 g/person/year, which represents 0.13% of total plastics use in Australia. Of this, 3,700 Mt of plastics are released to agricultural land and 140 Mt to landscape topsoil. Our results provide a first quantitative per-capita mass loads and emission estimate of plastic types through biosolids end-use.

Per-capita plastics released from WWTPs in Australian jurisdictions, compared to plastics consumption data in Australia

Benjamin Tscharke

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