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.

Phytoremediation of copper-contaminated soils by drip or sprinkling irrigation coupled with intercropping.

Intercropping improves the phytoremediation of soil trace metal contamination. Dripping irrigation could further promote the phytoremediation of trace metals by influencing their speciation and total amount in soil. However, there is currently insufficient information elucidating this synergistic effect. In this study, the combined effect of drip irrigation and intercropping on the phytoremediation of Cu-contaminated soil was testified by investigating the changes of Cu spatial distribution and speciation in soil irrigated by dripping or sprinkling methods, as well as Cu bioconcentration factor and translocation factor by plants. Results showed that after a 30-day drip irrigation, the Cu level in soils near the drip outlet decreased by 4.7% and that in Triticum aestivum L. (T. aestivum) roots intercropped with Helianthus annuus L. (H. annuus) and Zea mays L. (Z. mays) dropped by 53.2% and 25.1%, respectively, relative to sprinkler irrigation. Meanwhile, the total Cu and exchangeable Cu levels in soils 6 cm away from the drip outlet increased by 10.8% and 20.4% after 30 days of drip irrigation, leading to 41.1% and 40.0% increases of Cu content in remediation plants H. annuus and Z. mays seedlings as compared to the values by sprinkler irrigation. Therefore, the drip irrigation enhanced the effect of intercropping on Cu phytoremediation.