Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are widespread environmental contaminants and their fate in nature is of great environmental concern because of their persistence, toxic, and carcinogenic properties.These pollutants are gradually accumulating in wastewater-irrigated soils, and lead to the contamination of food plants.Consumption of PAH and HM contaminated food plants is the major food chain route for human exposure and poses health risks.In this study, soil and food contamination with PAHs and HMs, bioaccessibility of PAHs, plant uptake mechanisms,and bioremediation of contaminated soils were investigated, including several green house experiments and field surveys.Field survey results indicated that there was a substantial build-up of PAHs and HMs (Cd, Cu, Pb and Zn) in wastewater-irrigated soils.Regarding the pollution load index, the values indicated that the wastewater-irrigated soils were low-to-moderately enriched with Cr, Cu, Ni, Pb and Zn, while strongly enriched with Cd.Concentrations of Cd, Cr, Ni, and Pb in all sampled plant species,while Ni in Raphanus sativus L., Zea mays, Brassica juncea L., Brassica oleracea L,Brassica napus, and Lactuca sativa L have exceeded the permissible limits set by State Environmental Protection Agency (SEPA) in China, and World Health Organization (WHO).A greenhouse pot experiment, using lettuce (Lactuca satuva L) as a representative leafy vegetable was conducted to assess the concentrations of PAHs and HMs in vegetables grown in wastewater-contaminated soils.PAH concentrations in plant tissues increased with increasing soil PAH concentrations.Linear regression analyses showed that the relationships between soil and shoot PAH concentrations were stronger for low molecular weight (LMW) PAHs (R2 between 0.51 and 0.92) than for high molecular weight (HMW) PAHs (R2 0.02 and 0.60), suggesting that the translocation for LMW-PAHs is faster than HMW-PAHs.Plants were also highly contaminated with HMs,particularly Cd, Cr, Pb and Ni, totally or partially exceeding the SEPA and/or WHO limits set for vegetables.A field survey was conducted to assess health risk from PAHs in soils due to soil ingestion, one of the potentially important pathways of exposure to environmental pollutants.Oral bioaccessiblity of PAHs in surface soils was assessed using physiologically based in vitro gastro-intestinal tests regarding both gastric and small intestinal conditions.Results indicated that the oral bioaccessibility of PAHs in small intestinal condition was significantly higher (from P＜0.05 to P＜0.001) than gastric condition.The bioaccessibility of individual PAHs in soils generally decreased with increasing ring number of PAHs in both gastric and small intestinal conditions.It is suggested that care should be given while establishing reliable soil criteria for PAHs,especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-to-mouth activities.Similarly, another pot experiment was conducted in green house to assess the effects of humic acids (HAs) on phytoavailability of HMs in soil, plant growth and HM uptake, using wheat (Triticum aestivum) as a test plant.Results indicated that HAs present in sewage water increased both the availability and transfer of HMs in the soil-plant continuum and subsequently may increase human exposure to HMs in polluted soil.These results suggested that, when assessing the effect of sewage irrigation on soil quality, HAs contained in sewage water should be taken into consideration.Furthermore, soil enzymatic activities play important roles in nutrient cycling and have been used as biological indicators for assessing the impacts of soil contamination with HMs.A green house study was conducted focusing on soil microbial community change and potential inhibitory effects of HMs on soil enzymatic activities at different application rates of Cd and Pb.Results showed that the HMs slightly inhibited the enzymatic activities in all HMs amended samples, and the extent of inhibition increased significantly with increasing level of HMs and varied with the incubation periods.The soil bacterial community structure, as determined by polymerase chain reaction-denaturing gradient gel electrophoresis techniques (PCRDGGE), was different in the contaminated samples as compared to the control.The highest community change was observed in the samples amended with high level of Cd.Furthermore, bioremediation is a more cost effective, noninvasive, and publicly acceptable way to remediate contaminated soils, therefore, a green house study was conducted to investigate the fate of pyrene in the rhizosphere of rye grass (Lolium multifiorum L).Pyrene removal efficiency for rhizospheric soils was 59.12％ and 68.72％in pyrene and Pb/pyrene amended soils, respectively.Bacterial community structure, asdetermined by PCR-DGGE, was different in the contaminated samples as compared to the control.Pyrene addition showed a dramatic effect on the numbers ofpyrene degraders and their numbers were higher in rhizospheric soil than non-rhizospherie soil.In both rhizospheric and non-rhizospheric soils, the increased potential for pyrene degradation was observed at several levels such as slow diminishing ofpyrene, enhancing numbers of pyrene degraders and increased prevalence of nahAc and pdo1 dioxygenase genes.Our findings suggest that the interaction between bacterial species and plant roots is very complex and influence the pyrene degradation capacity of bacterial community.