Bioavailability of trace metals in sediments from Daya bay nature reserve: Spatial variation, controlling factors and the exposure risk assessment for aquatic biota

• Multiple forms and spatial variations of trace metals in sediments were analyzed. • Ocean dynamics facilitates the release of bioavailable metals from sediments. • The bioavailability of trace metals is influenced by SOM and salinity. • Risks of trace metals and mixtures to aquatic biota were assessed using DGT. Determining the ecological risk and environmental significance of trace metal bioavailability is critical for the sustainability of the marine environment and bioresources. The spatial variation, controlling factors and ecological risks of the bioavailability of trace metals (V, Cr, Ni, Cu, Zn, As, Cd and Pb) in Daya Bay sediments were analyzed using BCR sequential extraction and diffusive gradient in thin films (DGT). Differences in concentration distributions between the anthropogenic impact zone (AIZ) and the marine disturbance zone (MDZ) revealed the accumulation of anthropogenic metals in sediments, and that the ocean dynamic conditions promoted the release of bioavailable metals from nature sediments. Fine-grained sediments rich in organic matter possessed more bioavailable metals on the surface. The negative correlations between salinity and the non-residual fractions (F123) suggests that salinity has the potential to inhibit the bioavailability of trace metals. Risk assessment based on total concentrations and acid soluble fractions (F1) showed that Cd was the dominant contributing element to the potential ecological risks with 55.8 %. The evaluation via DGT-labile concentrations indicated that Cu was the element of priority concern for aquatic exposure risk with a risk probability of 7.45 %, and the joint risk probability for metal mixture toxicity was 12.27 %. The exposure risk for aquatic biota was shown as molluscs (9.37 %) > algae (6.82 %) > crustaceans (6.21 %) > invertebrates (6.07 %) > fish (2.61 %). The results provide new clues for risk assessment and management of trace metals in coastal sediments.