Cadmium Bioaccumulation in Aquatic Oligochaetes Using a Biodynamic Model: A Review of Values of Physiological Parameters and Model Validation Using Laboratory and Field Bioaccumulation Data.

This study reviews certain physiological digestive parameters in the literature that could be used to predict tissue residues in aquatic oligochaetes using the biodynamic model. Predictions were evaluated with independently measured Cd bioaccumulation data in sediment bioassays and field oligochaetes. The parameter review focused on three species commonly used in ecotoxicity testing and bioaccumulation studies: Tubifex tubifex (Tt), Limnodrilus hoffmeisteri (Lh) and Lumbriculus variegatus (Lv). Median Ingestion rates (g g d, dw) at unpolluted conditions were 7.8 (Tt), 24.5 (Lh) and 11.5 (Lv), while results were lower (1.7-2.4) at polluted conditions. Assimilation efficiencies ranged from 3.4-19.6% (Tt), 2.7-16.1% (Lh), and 10.9-25.6% (Lv). The biodynamic model accurately predicted Cd tissue concentration in T. tubifex exposed to spiked sediments in laboratory bioassays. Comparisons of predicted vs. measured Cd tissue concentration in bioassays or field aquatic oligochaetes suggest that the biodynamic model can predict Cd tissue concentration within a factor of five in 81.3% of cases, across a range of measured tissue concentrations from 0.1 to 100 μg Cd g dw. Predictions can be refined by using physiological parameter values that have been measured under varying environmental conditions (e.g. temperature, dissolved oxygen). The model can underestimate tissue concentration by up to one order of magnitude when worms are exposed to highly contaminated sediments. Contrarily, predictions overestimate tissue concentration by up to two orders of magnitude when the measured Cd < 0.1 μg g dw, although in most cases these predictions do not fail bioaccumulation-based risk assessments, using a tissue threshold value of 1.5 μg Cd g dw.