Effects of Soil‐applied Sewage Sludge on Concentrations of Elements in Earthworms

Abstract Samples of earthworms ( Aporrectodea tuberculata [Annelida: Lumbricidae]) and their casts collected from field plots were analyzed by neutron activation analysis to evaluate the suitability of using earthworms to monitor the bioavailability of elements in soils, and to determine the effects of land application of sewage sludge on the concentrations of trace elements in earthworms. Culture of earthworms on soils treated with radioactive tracers shows that earthworms accumulate Cd, Co, Hg, and Zn, but not Hf, Sc, and Tb. The results for the earthworms from the field plots are corrected for the effects of contamination by uneliminated casts with the use of interelement ratios. The concentrations of Hg and Cr in the casts increase with increasing rates of sludge application, but the constant concentrations of these elements in the earthworms show that these elements are not bioavailable. The concentrations of Cd, Cu, and Zn in the earthworms increase, while those of Se decrease with increasing rates of sludge application. The very high concentrations of Cd in the earthworms, ranging from about 10 ppm in the control samples to over 100 ppm in the affected samples, show that earthworms efficiently accumulate Cd.