Trace metals contamination and sedimentation flux of the East China Sea

Abstract

The distributions, contamination status and annual sedimentation flux of trace metals (Cu, Fe, Mn, Ni, Pb and Zn) in surface sediments of the East China Sea (ECS) were studied in the present work. The concentration ranges of trace metals in surface sediments of the ECS were as follows: Cu, 4.29-41.5 mug/g; Pb, 10-44.8 mug/g; Zn, 18.2-114 mug/g; Ni, 8.17-48.64 mug/g; Mn, 152- 1152 mug/g ; Fe, 0.62-3.97 % and Al, 4.35-8.49 %. The spatial distribution of the trace metals generally exhibited higher concentration in the inner shelf and decrease with seawards. However, higher Mn concentration comparable to the inner shelf was seen at some stations of the middle shelf. The calculations of enrichment factor (EF), trace metals concentration normalized to aluminum concentration, showed that the lead (1.2-4.4) was the most contaminated element, but the Cu (0.1-1.3) was the least contaminated element among the elements studied. The sequences of the average enrichment factor of trace metals are Pb > Hg > Zn > Mn - Fe > Ni > Cu. The results of EF may suggest that the contamination of trace metals in the middle and outer shelves of the ECS was still minor. Finally, based on the results obtained in the present study and the data of mass accumulation rate (MAR) from literature, the annual sedimentation fluxes of trace metals in the ECS were calculated. The calculated area is divided onto five zones based on the mass sedimentation rate and the calculated area is approximate 50% of the total area of the ECS. The annual sedimentation fluxes of each element are as follows: Cu, 31 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> t/y; Fe, 34.8 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> t/y; Mn, 90.7 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> t/y; Ni, 44.8 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> t/y; Pb, 43.2 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> t/y; and Zn, 108 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> t/y, respectively. The higher sedimentation flux of trace metals was found in the inner shelf, suggesting that the riverine suspended particulate matters from the Yangtze River were mostly deposited in the inner shelf.