ECOTOXICOLOGICAL BIOASSAYS OF THE EARTHWORMS ALLOLOBOPHORA CALIGINOSA SAVIGNY AND PHERETIMA HAWAYANA ROSA TREATED WITH ARSENATE

Little research has been carried out on the effect of arsenate on earthworms. Ecotoxicological laboratory tests are fundamental tools for assessing the toxicity of arsenate to soil organisms. In this study, the impact of arsenate on the survival, reproduction and behaviour of the endogenic earthworms Allolobophora caliginosa and the anecic earthworms Pheretima hawayana has been quantified. The 96-h LC 50 of arsenate was estimated as 233.43 mg arsenate Kg^-1 soil. d.w. for P. hawayana which is significantly higher than that of A. caliginosa 147.24±27.16 mg arsenate kg^-1 soil d.w. The number of juveniles of P. hawayana was significantly higher than that of A. caliginosa at the arsenate concentrations 180, 240 and 400 mg kg^-1 soil dry weight. With the exception of the control (6.5 mg arsenate kg^-1 soil.d.w.), P. hawayana showed an avoidance behaviour for soils treated with all tested concentrations. A. caliginosa preferred soils treated with 6.5, 60, 110, 180 mg arsenate kg^-1 soil d.w., while the avoidance behaviour has been recorded only at 240 and 400 mg arsenate kg^-1 soil. d.w. This means that A. caliginosa individuals feed less when exposed to arsenate. On the contrary, the P. hawayana worms could be escaped into their deep vertical burrows when exposed to arsenate.