Simulated study on interactions between heavy metals and organic matter in contaminated soil.

In order to understand the interactions between accumulation of organic matter and heavy metals in contaminated soil, an incubation experiment was conducted by adding different levels of organic materials, Pb and Cu to soil. The soil microbial biomass, CO2-C released from incubated soil, and concentrations of heavy metals in particulate organic matter (POM) were monitored, the effect of organic matter on solubility of heavy metals (Pb, Cu) and those of heavy metal addition on respiratory intensity and mineralization of organic matter in contaminated soil were characterized. The results show that both soil microbial biomass and respiratory intensity decreased significantly with increasing addition of Pb and Cu, and thus increased accumulation of soil organic matter. Meanwhile, accumulation of organic matter declined water-extractability and mobility of the metals by formation of metal-enriched organic particles, and thus increased stabilization and sequestration of metals in the soil. It was also found that the POM has great potential to accumulate large amounts of metals by the creation of adsorption sites by microbial degradation of organic matter, with high affinities for metals thus stabilizing metal-POM. The experiments verified a mutual immobilization of metals and POM as organo-metallic complexes in contaminated soil. As a result, organic matter could be stabilized to some degree by metals due to an inhibition of microbial activity caused by toxic effects of metals and strong resistant of POM - heavy metals to biodegradation. This process would simultaneously lead to an increasing organic C and metal contents in the metal-contaminated soil.