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.