Assessment of metal concentrations in lake sediments of southwest Japan based on sediment quality guidelines

Abstract

Geochemical analysis of the bottom sediments of Lakes Banryoko, Onbe, Hamahara and Kijima in Shimane prefecture of southwest
Japan was carried out to determine their metal concentrations, and to assess the potential for ecological harm by comparison
with sediment quality guidelines. The work conducted includes water quality measurement, and analyses of trace and major elements
and rare earth element (REE) of sediments. Results showed that water quality of the lakes contrasts slightly between their
upper and lower parts. Average abundances of As, Pb, Zn, Cu, Ni, and Cr in Banryoko sediments were 27, 33, 90, 27, 25, and
46ppm, respectively, compared to 31, 52, 175, 44, 44, and 75ppm at Onbe, 11, 26, 96, 13, 13, and 35ppm at Hamahara, and
24, 43, 193, 31, 12, and 30ppm at Kijima. These concentrations exceeded the lowest effect level that has moderate impact
on aquatic organisms as proposed by the New York State Department of Environmental conservation. Pb and Cu abundances are
comparable to the Coastal Ocean Sediment Database threshold, while As and Zn exceed this value, indicating the concentrations
of these metals are potentially toxic. Increases in the abundances of these metals in lake sediments are probably related
to the reducing condition of the sediments, anthropogenic sources and surface soil erosion. The REE patterns of sediments
in the study areas are broadly comparable to the average upper continental crust, but show some contrast between lakes due
to differing source litho type. Significant positive correlations between Fe2O3 and As, Pb, Zn, and Cu were found in the sediments, suggesting these metals may be adsorbed on Fe oxides in the lake sediments.