Ecological risk assessment and identification of sources of heavy metals contamination in sewage sludge from municipal wastewater treatment plants in the Metropolitan Area of Lima-Callao, Peru

Municipal sewage sludge is the major by-product generated in the wastewater treatment process with reuse potential, but the presence of heavy metals (HMs) can be a limiting factor, which is why more detailed studies on their potential risks to the environment are necessary. In this research, the concentrations of eight HMs in sewage sludge for agricultural purposes from 11 municipal wastewater treatment plants of the Metropolitan Area of Lima-Callao were evaluated, during the years 2015, 2017 and 2020. In order to determine pollution levels, ecological risk, risk to human health and identify the main sources of contamination, the geoaccumulation index, the potential ecological risk index, the carcinogenic and non-carcinogenic risk index, and multivariate statistical techniques (correlation analysis, principal component analysis (PCA) and hierarchical cluster analysis (HCA)) were applied. The results showed high levels of pollution by Cu and Zn, and low levels of As. Likewise, a moderate to very high ecological risk was recorded, with Cd and Cu being the ones with the highest potential of ecological risk, restraining the use of sewage sludge for agriculture. Considering the economic activities present in the study area, the PCA and the HCA revealed that contamination by HMs derived mainly from industrial, commercial, and domestic activities; however, service activities also contributed to the concentrations of HMs. Finally, the study identified Cd and Cu as the metals of greatest concern.