[Influence of speciation on the bioavailability of particle-bound cadmium in sediments]

In the present work, the impact of speciation on the bioavailability of cadmium in sediments was investigated. Bioaccumulation of cadmium adsorbed on various (hydr)oxide minerals, i.e. ferric hydroxide, aluminum hydroxide and manganese dioxide, by bivalve Meretrix meretrix Linnaeus, was measured using a suspending system. The results showed that the bioavailability of cadmium was significantly different for different minerals. At Cd concentration of 70 mg/kg, the accumulation of Cd by clams in Cd-Fe(OH)3 and Cd-Al(OH)3 system was not detectable after 22 days of exposure. In comparison, the clams absorbed appreciable amount of Cd from 70 mg/kg of Cd-MnO2 system. An average uptake rate of (0.0094 +/- 0.0010) microg/(g x d) for 70 mg/kg Cd-MnO2 was obtained by linear fitting curve (r2 = 0.853 9, p < 0.000 1). When Cd concentration was increased to 140 mg/kg, bioaccumulation of Cd from Cd-Fe(OH)3 system was still not observed, while for the clams cultivated in Cd-Al(OH)3 and Cd-MnO2 systems, Cd was apparently assimilated in the body of the animals. The uptake rates were determined to be (0.0166 +/- 0.0017) microg/(g x d) for Cd-Al(OH)3 and (0.024 8 +/- 0.0017) microg/(g x d) for Cd-MnO2. Generally, The bioaccumulation sequence of the Cd-(hydr) oxides is Cd-MnO2 > Cd-Al (OH)3 > Cd-Fe (OH)3. The type of minerals determines both assimilation efficiency and ingestion rate, consequently controls the bioaccumulation of adsorbed cadmium.