Determining sediment quality criteria and ecological risk thresholds for cadmium in sediment using equilibrium partitioning and bioassays: a case study of Baiyangdian Lake

We quantified the ecological risks posed by cadmium (Cd) in Baiyangdian Lake (BYDL) sediments, and established region-specific sediment quality criteria (SQC) and risk thresholds, using an approach that combined benthic bioassays with an improved version of the equilibrium partitioning (EqPA) method that incorporated acid volatile sulfide (AVS)-bound and residual fraction correction terms. The resulting SQC for Cd in BYDL sediments was 9.01 mg/kg, which was substantially higher than other threshold effects level (2.58 mg/kg) and is attributable to the suppression of Cd bioavailability by AVS in the sediments (average logKp = 3.86). Furthermore, we conducted a 21-day exposure experiment using the native bivalve <i>Anodonta woodiana</i> at Cd concentrations between 1 and 20 mg/kg. Significant impacts were observed at concentrations ≥15 mg/kg, including reduced survival (70%), increased tissue accumulation (4.93 mg/kg), and the inhibition of the superoxide dismutase and carboxylesterase enzymes (>40%). By integrating the data from the benthic bioassays, enzyme activity analysis, and the EqPA method, we determined an ecological risk threshold of 10-15 mg/kg for Cd in BYDL sediments. This region-specific threshold can support targeted sediment management in BYDL, and the combined EqPA-bioassay approach provides a method for developing sediment quality benchmarks elsewhere.