Sediment mercury concentration of a subtropical mangrove wetland responded to Hong Kong-Shenzhen industrial development since the 1960s

Mercury (Hg) in coastal wetlands is of great concern due to its acute toxicity. We measured the total Hg content (THg) from a 210Pb-dated sediment core obtained from the Futian mangrove wetland in Shenzhen Bay, South China to explore the historical variation and possible sources. Our results extend the sediment THg record back to 1960 and reveal three distinct intervals. Interval I (1960-1974) has low and increasing THg values, averaging 83.0 mu g/kg; Interval II (1975-1984) witnesses a remarkably increase, peaking in 1980 (261.6 mu g/kg) then remaining elevated; Interval III (1985-2014) shows a steady reduction, averaging 118.4 mu g/kg. The good cor-relation among THg, TOC, and Hg/TOC, and the downstream decrease in monitoring sediment THg consistently suggest that the bulk THg are mainly sourced from the Shenzhen River discharge. The different timing in in-dustrial development attributes the elevated THg concentrations during 1975-1984 to Hong Kong industrial sewage pollution.