The acute toxicity of cadmium to different larval stages of Chironomus riparius (Diptera: Chironomidae) and its ecological significance for pollution regulation.

Acute toxicity tests using a static-with-replacement testing procedure were carried out with the four larval instars of the freshwater detritivore Chironomus riparius (Meigen). Median lethal concentrations (10, 24, 48 and 96 h LC50's) indicated great differences in sensitivity to cadmium between instars. Larvae became more tolerant with increasing age, the most resistant stage (fourth instar) having a 24 h LC50 of 2,400 mg Cd l-1, approximately 950 times greater than the corresponding value of 2.1 mg Cd l-1 recorded for the most sensitive (first instar) stage. These observations are discussed in relation to the establishment of water quality standards.