Heavy-Metal Rankings Across Sediment Risk, Seafood Bioaccumulation and Dietary Hazard in the Maowei Sea, China

Sediment indices usually set heavy-metal priorities in mariculture bays, but uptake and regulation vary among taxa, so seafood priorities may differ. In a single-season survey of the Maowei Sea (Beibu Gulf) in April 2022, seven metals were measured in water (27 stations), sediment (15 stations) and seven commercial taxa, each represented by the mean of 12 separately analysed station composites. We compared their rankings across sediment risk, bioaccumulation and dietary hazard. Cd and Hg contributed 85% of the sediment ecological risk index. Biota-sediment accumulation factors were highest for Cd in clams, Zn in oyster, Cu in crustaceans and Hg in fish. At an assumed 10% inorganic-As fraction, dietary hazard indices exceeded 1 for hard clam (1.44) and mitten crab (1.04). At 5%, no taxon exceeded 1. Under both fractions, the leading dietary metal in most taxa was As or Cu, not Cd or Hg. Cd or Hg took over in clams and fish at lower fractions, but not in crustaceans or oyster. In this survey, sediment rankings were a weak guide to seafood priorities, which argues for monitoring by taxon and metal. Measuring tissue As speciation should come first, since the dietary ranking depends on it.