Distribution and Behaviors of Cd, Cu, and Ni in the East China Sea Surface Water off the Changjiang Estuary

Abstract

Trace metal (Cd, Cu, and Ni) distributions and behaviors in surface waters of the East China Sea continental shelf were investigated during an expedition conducted in June 2004. Dissolved and particulate trace metal concentrations, as well as fractions of dissolved trace metals, fractionated based on their different chemical affinities to ion exchangers, were determined using ultra-clean techniques and graphite furnace atomic absorption spectrometry (GFAAS). Large variations of dissolved (< 0.45 μm) metal concentrations in the East China Sea shelf waters were found (n = 16) and ranged between 0.036 - 0.287 nM for Cd, 0.87 - 8.66 nM for Cu, and 2.66 - 6.04 nM for Ni. Particulate metal contributions were highest near the river mouth. Dissolved Cd and Ni were predominantly present (98% for Cd and 86% for Ni) as Chelex-labile fractions in the shelf waters. The anionic-organic metal fractions accounted for, on average, 8% for Cu, < 1% for Cd, and 1% for Ni. The dissolved "inert" metal fractions, on average, were 32% for Cu, 2% for Cd, and 13% for Ni. Dissolved Cd, Cu, and Ni were linearly correlated with salinity and can be explained by a three or two-endmember mixing model. For Cu, all three dissolved fractions had inverse correlations with salinity and organic Cu accounted for a significant fraction of the total dissolved Cu suggesting that Cu is bioactive, but its association with biogeochemical processes in the shelf water was less important than mixing process.

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