Enrichment assessment of Sb and trace metals in sediments with significant variability of background concentration in detailed scale.

Variability of background concentration of toxic trace metal(loid)s in sediments can often lead to under/over-report of contamination level, even in detailed scale. In this study, both surface (5-10 cm) and subsurface (> 10 cm) sediments were collected at many sites in a small lake (0.528 km) with multi-function (irrigation, aquaculture, and watercourse) in an industrial area. Total concentration of trace metal(loid)s (Cd, Cr, Co, Cu, Ni, Sb, Pb, and Zn) and potential reference elements (Ti, Zr, Rb, and Li) were analyzed. The results showed that although the trace metal(loid)s were mainly lithogenic in subsurface sediments, the variability of baseline concentration was significant. For Sb, this variability was a result of alteration in hydrological parameters as well as sediment properties including Fe/Mn oxide contents, particle size distribution, and organic matter contents. Comparison of the normalized Sb concentration in samples from two sediment cores indicated that Ti is the best reference element for normalizing Sb to reduce the impact from particle size and natural source. Enrichment assessment using modified EFs (Ti as reference element) and I index (measured baseline concentration) suggested that about 70% of the surface sediments were at least moderately polluted by Sb in the lake, as a result of recent anthropogenic input, mainly from nearby industries, e.g., concrete factory and textile factory. Modified EFs should be used, instead of I index, when Sb enrichment was relatively low in sediment. The anomalies of Sb background concentration may need regulator attention when assessing the level of sediment contamination.