Mercury inputs to Chinese marginal seas : impact of industrialization and development of China

Abstract

In the past decades, China has experienced substantial economic growth and industrialization. However, the effects of vast development of China on Hg input to the nearby oceans are still unclear. In this study, the influx and isotopic compositions of Hg in four 210Pb-dated sediment cores were examined to investigate changes in Hg deposition to the marginal seas off China over a century. Nearshore cores had higher Hg influxes than offshore cores. Increases of Hg influxes started since the 1950s, which coincides with China's economic development. Dramatic historical changes in Hg isotopic composition were observed in the cores (δ202Hg: −2.01‰ to −0.69‰; Δ199Hg: −0.16‰ to 0.31‰; n = 106). δ202Hg increased from the deep to the surface layers of the cores. The offshore cores mainly showed positive Δ199Hg values, but the pre-1950 samples had more positive Δ199Hg values than the younger samples. The nearshore cores mainly showed negative Δ199Hg values in the pre-1950s samples, but the younger samples showed Δ199Hg values close to zero. A triple-mixing isotope model, used to quantify the contribution of potential Hg inputs (e.g., direct discharge of industrial Hg, soil Hg, and precipitation-derived Hg), showed clear evidence of enhanced industrial Hg inputs to the ocean margin, but slightly decreased watershed soil Hg inputs in the last few decades. The variations of watershed-derived Hg were likely caused by the construction of impoundments in major rivers of China. This study demonstrates that mercury inputs to Chinese marginal seas have been largely altered due to the industrialization and economic development of China.