The relationship of Chironomus riparius larval Se body burden and body concentration to larval dry mass and effects on sensitivity to selenium.

Selenium as selenite was added to laboratory cultures of Chironomus riparius. In two sets of cultures, substrate-bound Se concentrations were typically 10(3) times dissolved Se concentrations, while in the other set dissolved Se concentrations were about 10 to 50 times substrate-bound Se concentrations. Body burdens of individual second-, third-, and fourth-instar larvae and eviscerated fourth-instar larvae were measured. Regressions of Se body burden on larval dry mass found evidence for separate intercepts but common slopes for each instar, and Se body concentrations were diluted by growth. The derivation of body concentration from body burden as a function of larval dry mass was used to derive a model of body burden and body concentration as a function of instar. Toxicity tests were performed to check for a change in sensitivity to Se as a function of culture Se concentration. Larval Se concentrations were highly correlated with dissolved Se concentrations but not with substrate-bound Se concentrations. Increases in Se in substrate caused no sensitization, while increases in dissolved Se caused desensitization. We concluded that covariates such as larval dry mass should be incorporated when deriving water quality criteria.