Degradation of Polycyclic Aromatic Hydrocarbons in Paddy Soils From Different Regions in China

Polycyclic aromatic hydrocarbons (PAHs) belong to an important class of persistent organic contaminants ubiquitously found in soils. Their fate in soil varies depending on both soil properties and their chemical structure. It is therefore important to understand the factors that control PAHs biodegradation in different soil environments. A study was conducted on eight paddy soils which are geographically distributed in different region of China. Time-course laboratory incubation was employed coupled with GC-MS analysis to explore the effects of variable soil properties on PAHs degradation, and evaluate the correlation between them. It was found that the capacities of PAHs degradation of different paddy soils were as follows:Sichuan (calcareous purple soil) > Heilongjiang (black soil) > Chongqing (neutral purple soil) > Shanxi (cinnamon soil) > Beijing (fluvo-aquic soil) > Anhui(yellow-cinnamon soil) > Henan (fluvo-aquic soil) > Hunan (yellow earth). The degradability of three PAHs was as follow:phenanthrene > fluoranthene> benzoa anthracene. Real-time quantitative polymerase chain reaction (qPCR) of 16S rRNA genes and phenanthrene dioxygenase functional gene phnAc demonstrate that the abundance of bacteria and phnAc gene was significantly stimulated by the addition of PAHs in these soil except the soils from Sichuan and Chongqing. Redundancy analysis indicate that the degradation pattern of phenanthrene and fluoranthene was positively associated with the content of NH₄⁺-N and soil organic matter significantly (P < 0.05), and negatively correlated with soil pH and water content. The degradation of benzoa anthracene was not significantly correlated with all the environmental parameters in this study (P> 0.05). Overall, results show that the fate of PAHs varies in different paddy soils, and the application of nitrogen and organic fertilizers could potentially stimulate the PAHs degradation rate in soils. The results of the study could provide basic information for evaluating the mechanism of PAHs degradation in natural soils and developing remediation strategy in China paddy soils.