Assessing the Impacts of Land Spreading Water-Treatment Residuals on the Anecic Earthworm Lumbricus terrestris, Soil Microbial Activity, and Porewater Chemistry

Abstract

Water-treatment residuals (WTRs), by-products of drinking water clarification, are increasingly recycled to land to promote circular economy and reduce disposal costs, yet there is a lack of published literature on their effects on soil ecology. In the present study, the effects of WTRs on earthworm growth, soil respiration, and soil porewater chemistry were investigated throughout a 7-wk outdoor mesocosm trial. We derived WTRs from both aluminum and iron coagulants and applied them to a loam soil at 0 to 20% (w/w). In addition, soil from a field that had received long-term WTR applications and that of an adjacent nontreated reference field were included in the study. Earthworm mass increase was significantly higher in all but one laboratory-treated soil when compared to the control. Furthermore, a linear regression model was used to predict increases in weekly soil respiration based on the application rates of both Al and Fe WTRs. In addition, a significant increase in soil respiration was observed from the treated farm soils during the first 4 wk of the trial. Measured sodium, magnesium, potassium, and iron porewater concentrations were higher in the treated farm soils than the reference site soil in a majority of samples, although these differences may be related to land management. Laboratory-treated soils had elevated porewater arsenic concentrations (e.g., ~17 µg L–1 in controls vs ~62 µg L–1 in the 20% w/w Al WTR treatment in week 1), whereas porewater nickel concentrations were, respectively, elevated and lowered in Al WTR– and Fe WTR–amended samples. Overall, observed disturbances to soil ecology were determined to be minimal. Environ Toxicol Chem 2021;40:1964–1972. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.