The agony of choice: Advancing sediment hazard assessment by using avoidance behaviour assays with Lumbriculus variegatus.

Sediments play a key role in chemical partitioning in aquatic ecosystems, acting as sinks for lipophilic and persistent compounds. However, sediment hazard assessment is limited, often underestimating risks by focusing on short-term, lethal endpoints. Behavioural assays, although underused for sediment-dwellers, can provide faster, more sensitive assessments. This study adapted soil avoidance methods for sediment, testing avoidance in Lumbriculus variegatus exposed to lead, bixafen, and fluoxetine. We compared survival with conventional one-compartment (contaminated sediment only) and two-compartment (contaminated vs. control) assays. The two-compartment test detected significant avoidance at concentrations up to 428 times lower than survival and showed effects when conventional assays failed to detect any (e.g., for bixafen). It revealed significant responses at environmentally relevant levels (0.19 mg/kg fluoxetine, 550 mg/kg lead) and provided insights into chemical sensing and non-monotonic dose-response curves. Two-compartment avoidance assays are rapid, sensitive, and relevant for future sediment hazard assessments with potential population-level implications.