Assessment of tolerance limits of petroleum residues in soil organic matter: sorption of dichlorobenzene by soil.

Soil organic matter can protect plants and microorganisms from toxic substances. Beyond the tolerance limit, the toxicity of petroleum pollution to soil organisms may increase rapidly with the increase of petroleum content. However, the method for evaluating the petroleum tolerance limit of soil organic matter (SOM) is still lacking. In this study, the petroleum saturation limit in SOM was first evaluated by the sorption coefficient (Kd) of 1,2-dichlorobenzene (DCB) from water to soils containing different petroleum levels. The sorption isotherm of dichlorobenzene in several petroleum-contaminated soils with different organic matter content and the microbial toxicity test of several petroleum-contaminated soils were determined. It is found that when the petroleum content is about 5% of the soil organic matter content, the sorption of petroleum to organic matter reached saturation limit. When organic matter reaches petroleum saturation limit, the sorption coefficient of DCB by soil particles increased linearly with the increase of petroleum content (R2 > 0.991). The results provided important insights into the understanding the fate of petroleum pollutants in soil and the analysis of soil toxicity.

[Chemical fixation of metals in soil using bone char and assessment of the soil genotoxicity].

We evaluate the effects of soil in situ remediation by application of bone char as a soil amendment based on chemical and biological assessment. The application of bone char decreased the Pb in the in the water soluble (WS), exchangeable (EX), carbonate-bound (CAR) and Fe-Mn oxides-Bound (Fe-Mn) fraction but increased the Pb in organic-bound (ORG) fraction indicating the decreased bioavailability of Pb. The application of bone char decreased the Cd, Cu and Zn in water soluble, exchangeable, carbonate-bound fraction by increasing substantial amounts of heavy metals in the ORG fraction or Residual (RES) fraction. The soil genotoxicity was evaluated using plant comet assay of root tip cells of Allium cepa L. and the results indicated that bone char application reduced genotoxcity of heavy metals, decreasing the DNA damages in plants which was consistent with the changes of the chemical forms of Pb, Cd, Cu and Zn indicating the changes of the chemical forms of heavy metals may be one of the reasons for decreased soil genotoxicity.