Can passive samplers replace biota in risk assessment of resuspended contaminated sediments?

Resuspension of contaminated sediments elevates turbidity and mobilises sediment‑bound polycyclic aromatic hydrocarbons (PAHs) into the water column, increasing their bioavailability and toxicity to aquatic organisms. Passive samplers (PS), which accumulate the freely dissolved fraction of contaminants, have the potential to replace biota as a non‑invasive tool for estimating exposure and toxicity. In the field, it remains unclear how PS uptake relates to organism bioaccumulation and toxicity, especially under varying turbidity, and whether PS data can reliably predict PAH-induced effects. We exposed PS and the red macroalga Ceramium tenuicorne to PAH-spiked sediment along a 1.1–7.5 NTU turbidity gradient and measured PAH uptake in both. Also, photosynthetic inhibition in C. tenuicorne was used as a response variable and related to the PAH uptake in both matrices. We found that PS linearly predicts algal bioaccumulation, and that adding turbidity as a covariate significantly improved the model, explaining 56% of the contaminant load in the algae. When combined with turbidity, PAH levels in PS predicted algal photoinhibition with slightly higher variance than the internal-dose model (54% vs 48%), with chemical activity ( a ) used as the common dose metric in all cases. The combination of a PS and the area under the turbidity curve provided a statistically supported proxy for algal PAH bioaccumulation. Both terms had positive effects and captured phototoxic responses, resulting in 26–79% reductions in photosynthesis activity. These findings highlight the importance of including turbidity as a key confounding factor in environmental monitoring and risk assessment of sediment-associated pollutants in coastal and shallow areas.