Organic matter associated heavy metals in polluted soils

The distribution of heavy metals in different size fractions of soils affects bioavailability of the metals. Understanding distribution of heavy metals in soils can provide useful information for evaluating environmental risk of the metals. In this study, both physical and chemical methods were applied to characterize organic matter-associated heavy metals in two metal-contaminated soil profiles. The results found that heavy metals, including Cd, Cu, Pb and Zn, in the soils were significantly enriched in particulate organic mater fractions (POM). The enrichment factor of Cd, Cu, Pb and Zn in 2mm POM fractions were 1.4~3.2, 2.5~2.6, 2.8~3.9 and 3.0~3.9, respectively, those in 0.05~1 mm POM fractions were 2.7~7.8, 3.2~6.4, 3.2~9.3 and 3.2~5.6, respectively. The enrich- ment was more significant in the 0.05~2 mm POM fractions than the 2 mm POM fractions. The enrichment of metals in the POM fractions was positively correlated with accumulation of the metals in the soils. The proportions of total heavy metals as organic matter-bound forms in the soils increased with increasing soil organic matter content. More than 40% of heavy metals in the surface soils were presented in organic matter bound forms.