Trace metal geochemical associations in sediments from the culture-bed of Anadara granosa

Abstract

Geochemical associations of certain trace metals in sediments from the culture-bed of Anadara granosa were studied. Trace metals were sequentially extracted from texturally homogeneous sediments collected along the mudflat of Kuala Juru, Malaysia. Mean total concentrations of Cd, Cu, Fe, Mn, Ni, Pb, and Zn were 2.5, 41, 11 485, 197, 19, 44, and 266 μg g −1, respectively. Mean concentrations of Cd, Cu, Fe, Mn, Ni, Pb, and Zn in the non-residual fraction on the other hand, were 1.0, 17, 4566, 138, 14, 13, and 210 μg g −1, respectively. These concentrations accounted for 40, 42, 40, 70, 76, 30, and 29% of total metal concentrations present in sediments, respectively. In the nonresidual fraction, 6.8% Cd, 4.9% Cu, 0.04% Fe, 13% Mn, 8% Ni, 12% Pb, and 9.8% Zn and 4.9% Cd, 1.1% Cu, 1.1% Fe, 13% Mn, 3.7% Ni, 7.5% Pb, and 10% Zn were present in the exchangeable and easily reducible fractions, respectively. In the moderately reducible fraction, 40% Cd, 6.9% Cu, 49% Fe, 11% Mn, 1.1% Ni, and 21% Zn were demonstrated to be associated with this fraction. Lead was, however, not detected in this fraction. Most trace metals were shown to be associated with the organic/sulphide fraction having 48, 87, 50, 64, 87, 80, and 59% of Cd, Cu, Fe, Mn, Ni, Pb, and Zn, respectively. It appears that the exchangeable, easily reducible and moderately reducible fractions in most cases are considered to be geochemically insignificant in the sorption of trace metals in partially anaerobic sediments investigated. The organic/sulphide fraction was, however, assumed to have an important role as a reservoir for trace metals in the sediments. As these metals were poorly concentrated in the exchangeable phase, the present results tend to indicate that the economically important bivalve, A. granosa is not at risk of being heavily contaminated by toxicologically significant trace metals.