Use of embedded Chelex chelating resin and sediment toxicity bioassays with medaka embryos to determine the bioavailability and toxicity of lead-contaminated sediment.

The aquatic sediment acts as a reservoir for multiple sources of pollutants including toxic metals. Most analytical methods used for estimating the bioavailability of sediment heavy metals have not been biologically validated by correlation with an aquatic organism's response. A reliable whole-sediment contacting toxicity assay using vertebrate species is lacking and the exposure routes for sediment metals are unclear. This study established a novel bio-analytical approach involving the Chelex-100 resin detection system and sediment toxicity assessment with embryo-larval stages of medaka fish (Oryzias latipes) to evaluate the bioavailability and toxicity of lead (Pb) contamination in sediment to fish. Treated fish exposed to the Pb-spiked artificial sediment with whole-sediment exposure showed more dose-dependent toxic responses than those from pore- or overlying-water exposure extracted from the same sediment. The Chelex-100 resin-extractable Pb content was highly correlated with mortality, total malformation and Pb bioaccumulation in medaka embryos or hatchlings from Pb-spiked sediment at environmentally relevant concentrations. The environmental sediment with higher contents of clay or organic carbon showed lower potency of releasing Pb from sediment to overlying water, as compared to those observed with artificial sediment. Our results suggest that the bio-analytical method can be practically applied in situ to evaluate the adverse effect of heavy metal-contaminated sediment on the aquatic ecosystem.