Comparative toxicity of the selenate and selenite to the potworm Enchytraeus albidus (Annelida: Enchytraeidae) under laboratory conditions

Selenium soil chemistry is complex. It is dominated by selenates, selenites and selenides. Selenate seems to be more toxic for soil animals than selenite. However, bioavailability of different selenium forms as selenate and selenite on soil animals is poorly known. In order to investigate whether higher toxicity of selenate over selenite is a stable phenomenon to the potworm Enchytraeus albidus , standard laboratory tests were conducted on a chernozem brown forest soil and on a meadow chernozem. Toxicity was expressed in terms of adult mortality (LC 50 ) and juvenile production (EC 50 ). Selenate toxicity, expressed on adult mortality and juvenile production, was more substantial than that of selenite if total (conc. HNO 3 + conc. H 2 O 2 soluble) concentrations were considered. No such difference was observed in the case of available (NH 4 -acetate + EDTA soluble) concentrations. E. albidus proved to be more sensitive to selenate and selenite status of the soil than any other animal species tested before. Soil pH between 5.8 and 7.6 did not influence toxicity. The toxicity of selenate and selenite is reverse in aquatic and soil environment in most cases. The reason for this needs further investigations.