Application of a kinetic model of bioaccumulation across a pH and salinity gradient for the prediction of cadmium uptake by the sediment dwelling chironomidae

A kinetic model for the prediction of metal concentrations in aquatic organisms was applied for the prediction of cadmium concentrations in the sediment dwelling dipertan larvae, Chironomidae. Cadmium concentrations were determined in Chironomidae sampled along two distinct environmental gradients: (1) an acidity gradient(from pH 5.0-6.5) and (2) a salinity gradient (from 0 to 9.6 ppt). Comparison of predicted and observed values indicated that the kinetic model was successful in predicting concentrations in chironomids sampled along the acidity gradient but not the salinity gradient. Separation of routes of cadmium uptake into food and solute sources indicated that ingested sediment accounted for 60-100% of total invertebrate cadmium concentrations, however, the relative importance of water increased as a function of decreasing acidity and salinity. These results support the refinement of a kinetic model for predicting cadmium concentrations in sediment-living invertebrates, such as Chironomidae. By allowing for uptake from food and water the model highlighted the potential for routes of cadmium uptake to be pH and salinity dependent. For monitoring purposes, hath vectors and the potential for the relative importance for each vector to change needs to be considered when assessing the degree of metal exposure to sediment ingesting invertebrates which inhabit systems with either a natural or anthropogencially induced gradient in key water chemistry variables such as salinity or pH.