Toxicity bioassays of cadmium on selected freshwater invertebrates and the interaction of cadmium and zinc on the freshwater shrimp, Paratya tasmaniensis Riek

Abstract

In acute toxicity bioassays with cadmium sulphate at 15º C in soft water (total hardness 10 mg/l as calcium carbonate), the concentrations fatal to 50 % of the test animals were determined for five freshwater invertebrate species. The 96 hr median lethal concentration (LC50) of cadmium was 0.04 mg/l for the amphipod Austrochiltonia subtenuis Sayce, 0.06 mg/l for the shrimp Paratya tasmaniensis Riek, 0.84 mg/l for the ephemeropteran nymph Atalophlebia australis Walker, 250 mg/l for the zygopteran nymph Ischnura heterosticta (Burmeister) and well over 2000 mg/l for a trichopteran larva of the Leptoceridae. The bioassays on Paratya indicared that there may be seasonal differences in sensitivity to cadmium. The 96 hr LC50 for zinc for Paratya was 1.21 mg/l. Zinc and cadmium appeared to interact less than additively at concentrations below 1 toxic unit. Above this concentration, their interaction was strictly additive.