Selenium uptake by larval Chironomus decorus from a Ruppia maritima-based benthic/detrital substrate

Abstract

Elevated levels of selenium have led to the contamination of several aquatic ecosystems. Much of the selenium contamination has resulted from agricultural irrigation and drainage of seleniferous soils. Disposal of selenium contaminated drainwater in evaporation ponds has led to selenium bioaccumulation and toxicity in waterfowl and shorebirds using these ponds. Studies have demonstrated that it is a seleno-amino acid that causes the observed toxicity. However, selenate is the dominant form of selenium in agricultural drainwater, and the biotransformation of selenate into seleno-amino acids has been shown to be greatly limited relative to the more reduced selenium species. We hypothesize that it is in the benthic zone, where the reducing environment facilitates conversion of selenate to selenium forms more conducive to biotransformation, that most biotransformation and subsequent bioaccumulation of seleno-amino acids takes place, and that movement of selenium into the benthic-detrital food chain is a key pathway leading to selenium bioaccumulation. This hypothesis was investigated by conducting laboratory benthic-detrital food chain experiments using the common evaporation pond macrophyte Ruppia maritima as the benthic-detrital substrate. Larval Chironomus decorus were reared on the contaminated Ruppia substrate, and the resulting bioaccumulation and toxicity in the larvae were determined.