Polycyclic Aromatic Hydrocarbons (PAHS) are ubiquitous and persisted organic pollutants in environment. They attract extensive attentions since they are teratogenetic, carcinogenic and mutagenic. Some of them are available to organisms and the bioavailability is an important parameter for the biohazard to the non target organisms.

Plant- Microbe associated remediation is an effective manage method for PAHS polluted soils. Plant root exudates promote the ability of microbes to degrade soil pollutants. But inhibition of microbe PAHS removal by root exudates was also reported. So it is important to illustrate and use the rhizo-sphere effect for the plat-microbe associated remedy of polluted soil. 

Prof. GONG Zongqiang, Dr. GUO Meixia and colleagues in Soil Pollution Ecology Research Group from Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences evaluated the bioavailability of PASHs in polluted soils in agricultural soil and area around manufactured gas plant (MGP) by chemical method and bioassay and analyzed the feasibility of the methods.  

They added root exudates of maize (Zea mays) and soy (Glycine max L) into polluted microcosm and analyzed the effects of exudates with various plant species and TOC concentrations on PAHs degradation rate and microbe community structure. 

The results show that earthworm (Elsenia fetida) accumulation is unsuitable as an indicator to PAHs bioavailability of soil around MGP. Solid-phase micro-extraction (SPME) and Tenax-TA extraction both predicted the bioavailability to earthworm, but the later was more precise and sensitive.  

The interaction of mycobacteria (Mycobacterium sp) and root exudates promoted PAHs degradation by changing the microbe community structure and enhanced the PAHs bioavailability to earthworm. 

Different plant species and different exudates concentrations showed different effect. In agricultural soil, the PAHs removal rate (69.2-78.4%) of maize exudates was higher than that of soy exudates (66.8-74,5). But the Shannon diversity indexes (H’) for soil bacterial diversity in the former were lower than those in the latter.  

This indicates that it is microbial community functions but not biodiversity that plays an important role in PAHs degradation. 

The results were published entitled "Polycyclic aromatic hydrocarbons bioavailability in industrial and agricultural soils: Linking SPME and Tenax extraction with bioassays“ and "The influence of root exudates of maize and soybean on polycyclic aromatic hydrocarbons degradation and soil bacterial community structure in Ecotoxicology and Environmental Safety and Ecological Engineering” in Science Direct.  

The work was supported by NNSFC and the CAS project of Pollution Ecology and Environmental Engineering Key Laboratory.