Cadmium accumulation in the freshwater isopod Asellus racovitzai: the relative importance of solute and particulate sources at trace concentrations

摘要

A stable isotope tracer technique was used to evaluate the relative importance of particulates and water as respective sources of cadmium (Cd) uptake in the freshwater isopod Asellus racovitzai (Isopoda, Crustacea). 113~Cd(NO_3), was applied to the sediment at a nominal concentration of 20.0 ng g~-1, and 114~Cd(NO_3)_2 was added to the overlying water (nominal concentration of 4.4 ng g~-1), in the same test systems. Asellids added were either free-ranging on the sediment surface, where they were exposed to both parti- culate and water sources of Cd, or were enclosed in dialysis 'tubes', 10 cm above the sediment surface, and were therefore exposed to Cd in water only. By analysis of both isotopes, uptake vectors could be determined simultaneously. After 7 days of exposure, average 114~Cd concentrations in 'free' asellids were 15.6 ± 2.0 μg/g, compared with 10.4 ± 1.8 μg/g in 'tube'-held asellids (P < 0.05), i.e. at least 60/100 of accumulated 114~Cd was from water. Furthermore, water-spiked 114~Cd was accumulated in asellids to tissue concentrations that were more than four-times greater than sediment-spiked 113~Cd. When the sediment organic content was increased (20/100 peat moss), total Cd concentrations in both overlying water and asellids were significantly lower (P < 0.01), com- pared with the mineral sediment treatments, and Cd accumulation in tube and free asellids was similar. This study shows that water is an important vector of Cd accumulation in A. racovitzai, and factors that lower Cd concentrations in solution (such as increased organic content of sediment), decrease Cd bioaccumulation.