Accumulation patterns of trace metals in freshwater isopods in sediment bioassays—Influence of substrate characteristics, temperature and pH

Abstract

Asellus aquaticus (L.) was exposed in microcosms to littoral sediments from Lake Ketelmeer (River Rhine estuary) and from a control site in order to study effects of substrate characteristics, temperature and pH on the kinetics of trace metal accumulation. Elimination patterns were studied in parallel experiments with preloaded animals kept on control sediment or in test water. In a 50 day semistatic bioassay at three different temperatures (5, 10 and 20°C) and two pH levels (7.3 vs 8.1) a highly significant accumulation of Cd, Pb, Cu and Zn by the isopods was observed. No net uptake was recorded in animals kept on control substrates. The most marked accumulation by Asellus was noted for the non-essential trace metals Cd and Pb. Element-specific effects of sediment characteristics and temperature were encountered on sediment-water partitioning (Cd, Cu and Zn) and on accumulation and elimination kinetics (Cd, Cu and Pb). No significant effects were observed for the different pH levels. Accumulation of Cd and Cu increased significantly with temperature. Pb concentrations in animals exposed at 20°C were found to be significantly lower compared to other temperatures. The accumulation of Zn appeared to be unaffected by temperature. Two distinct elimination patterns were observed. Elimination of Cd and Cu was absent at the higher temperatures. A slight elimination of these metals was recorded only in some of the treatment groups at 5°C. Both elements seemed to be stored in stable body compartments. A relatively rapid elimination, not affected by temperature, was observed for Pb (biological) half-life: 8–15 days) and Zn (half-life: 21–44 days); above the control sediments Asellus maintained a Zn concentration of c. 100–150 μgg −1 (dry wt). Several explanations for the observed accumulation patterns and temperature effects are presented. The results indicated that freshwater isopods could be suitable organisms for bioassays and biological monitoring studies on the bioavailability of sediment-bound trace metals.