Trophic transfer, biomagnification and risk assessments of four common heavy metals in the food web of Laizhou Bay, the Bohai Sea

This study investigated the trophic transfer of four common toxic metals (Cd, Cr, Cu and Hg) in the food web and assessed their potential ecological risks in Laizhou Bay, a spawning area for fishery populations in the Bohai Sea, North China. Based on the predation relations of 43 species that were representatives of the main trophic levels (TLs), a simplified food web was constructed using stomach content analysis and stable nitrogen isotope ratio (δ15N) analysis. Using copepods as the baseline species (TL = 2.00), the TLs of the organisms ranged from 1.96 (Polychaeta) to 4.47 (Japanese flounder) and showed the following ranking order: predatory pelagic or demersal fish > medium demersal fish > crustacean, cephalopod, small pelagic or demersal fish > zooplankton and Polychaeta. The metals showed different trophic transfer behaviors in the food web. Hg and Cr tended to be efficiently biomagnified between TLs, along the main food chains and in the food web. Cu biodiluted significantly with increasing TLs, while Cd showed no biomagnification or biodilution trends in the food web. At low or moderate levels of Cd and Hg, potential ecological risks were detected in the water and sediments at only a few sites, indicating their overall low ecological risks in the environment. The metals in the important fishery species (four top predatory fish, two cephalopods and eight crustaceans) were below the permissible limits, except for Cd in octopus and paddle crab, which reached or exceeded the most restrictive criteria. Based on the provisional tolerable weekly intake (PTWI) criteria, the safe weekly human consumption levels by humans of the predatory fish, cephalopods and crustaceans were species-specific (0.20–4.44 kg) and should be cautiously assessed. [Display omitted] •A food web in LZB fishery ecosystem was built based on trophic relations.•Hg and Cr were clearly biomagnified in the food chains or food web.•Cu biodiluted and Cd showed no clear trend along LZB food web.•Metals showed low ecological or health risks in environment or fishery species.•Cd exhibited health risk to human from consuming octopus and crabs.