Selected trace metals (As, Cd and Hg) distribution and contamination in the coastal wetland sediment of the northern Beibu Gulf, South China Sea

► Spatial and temporal distributions of As, Cd and Hg were presented. ► Mean sedimentation rates were 0.93-1.37 cm year−1 during 1920s to 2008. ► Metal content increased evidently in 1985-2008 due to anthropogenic impacts. ► Locally the surface sediments have potential ecological risk of As to benthos.