Effects of multiple annual biosolids applications on the soil concentrations of metals, organochlorine pesticides and polychlorinated biphenyls in a field trial in Victoria, Australia

Biosolids are organic solids derived from sewage treatment processes with one of the common reuse options for biosolids being application to agricultural land as a soil amendment for fertiliser value. However, biosolids often include relatively high concentrations of potential contaminants. While there have been many studies investigating the risks of contaminants in biosolids after one application to soil, there have been far fewer studies researching the risks from multiple biosolids applications on working farms. Thus, the aims of this study were to assess the potential for soil contamination after four annual applications of biosolids to a pasture used for grazing cattle and silage production in Victoria, Australia. The study was the first to investigate the effects of multiple biosolids additions on soil concentrations of organochloride pesticides and polychlorinated biphenyls. The results demonstrated that Cu and Zn were the limiting contaminants measured, with soil concentrations above some Australian soil guidelines, but not Receiving Soil Contaminant Levels, after four biosolids additions. In addition, despite being required by government policy, all soil and biosolids concentrations of organochloride pesticides and polychlorinated biphenyls were very low with almost all measurements below detection limits. As such, rather than concentrating on organochloride pesticides and polychlorinated biphenyls, we suggest measurement and risk assessment efforts may be better directed towards emerging contaminants in biosolids, for example, per- and poly-fluoroalkyl substances, pharmaceuticals, chemicals in personal care products, and microplastics.