Environmental risk assessment of sludge spreading in agriculture using toxicological thresholds representative of soil biological communities

Abstract

The reuse of sludge for agricultural purposes is one of the strategies used worldwide to reduce landfill disposal whilst restoring the fertility of the soil, in a circular economy approach. This agricultural practice in Italy is regulated by the Italian Legislative Decree (LD) No. 99 of January 27, 1992, which provides chemical limits for some substances and the maximum admissible quantities of sludge that could be spread. In the present work, a synthetic index for estimating the environmental risk associated with sludge spreading is developed and experimentally applied, simulating the spreading of five different sludges. Environmental Risk Index (ERI) was estimated by taking into account the legal limits and the Predicted No Effect Concentrations (PNECs), which were specifically derived to Italian soils in this study, considering toxicological data referred to biotic communities living in Italy. Spreading simulations showed a “possible” hazard with respect to limits under LD No. 99/1992, and a “moderate” hazard level with respect to PNECs, mainly due to Dioxins and Furans, and Ni respectively (within the parameters considered by law). Whereas further studies are needed to estimate PNECs for other substances such as Plant Production Products (PPPs) and pharmaceuticals in order to preserve the structure and the functions of the soil ecosystem, the application of ERI showed a discrepancy between the list of parameters laid down in the regulation and the list of the most important environmental parameters for which soil-specific PNECs were inferred, with respect to the biological communities present in Italy. Given that, the list of substances of interest to be searched for in sludge and soil should be the same, giving priority to those that show the greatest ecotoxicological risks, such as PFAS. The weighted and integrated approach used in this study goes beyond the classic tabular approach of simple legal chemical limits providing with a more realistic framework for an integrated environmental risk assessment.