Effect of phosphorus addition on the reductive transformation of pentachlorophenol (PCP) and iron reduction with microorganism involvement.

The transformation of phosphorus added to the soil environment has been proven to be influenced by the Fe biochemical process, which thereby may affect the transformation of organic chlorinated contaminants. However, the amount of related literatures regarding this topic is limited. This study aimed to determine the effects of phosphorus addition on pentachlorophenol (PCP) anaerobic transformation, iron reduction, and paddy soil microbial community structure. Results showed that the transformation of phosphorus, iron, and PCP were closely related to the microorganisms. Moreover, phosphorus addition significantly influenced PCP transformation and iron reduction, which promoted and inhibited these processes at low and high concentrations, respectively. Both the maximum reaction rate of PCP transformation and the maximum Fe(II) amount produced were obtained at 1 mmol/L phosphorus concentration. Among the various phosphorus species, dissolved P and NaOH-P considerably changed, whereas only slight changes were observed for the remaining phosphorus species. Microbial community structure analysis demonstrated that adding low concentration of phosphorus promoted the growth of Clostridium bowmanii, Clostridium hungatei, and Clostridium intestinale and Pseudomonas veronii. By contrast, high-concentration phosphorus inhibited growth of these microorganisms, similar to the curves of PCP transformation and iron reduction. These observations indicated that Clostridium and P. veronii, especially Clostridium, played a vital role in the transformation of related substances in the system. All these findings may serve as a reference for the complicated reactions among the multiple components of soils.

Polycyclic aromatic hydrocarbons in soils in the vicinity of Nanjing, China.

The occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in vegetable soils from five vegetable fields (including: Liuhe, Xixia, Pukou, Jianye and Yuhua districts) in Nanjing outskirt were investigated with high performance liquid chromatography (HPLC) equipped with fluorescence detector. The total concentrations of 15 priority PAHs in 126 soil samples ranged from 21.91 to 533.84ng g(-1) dry weight, and the sum of seven carcinogenic PAHs concentrations varied from 1.48 to 236.19ng g(-1) dry weight. Statistical analysis of the PAHs concentrations showed that the highest PAHs concentration was observed in Liuhe, and the lowest PAHs concentrations were found in Xixia among the five districts. The ratios of fluoranthene to sum of fluoranthene and pyrene concentrations (Flt/(Flt+Pyr)) were more than 0.5 in 99% of vegetable soil samples, showing that the PAHs in soils were generally derived from straw and coal combustion sources. The results from principal component analysis (PCA) further indicated that extensive combustion activities affected the PAHs distribution in Nanjing vegetable soils.