Fate of Complex Pollutants of Lead and Benzoapyrene in Soil-Plant System

An indoor pot experiment was conducted to study fate of complex pollutants of Lead (Pb) and Benzoa pyrene (Bap), low and moderate in concentration, in the soil-plant system and interaction between the two pollutants. The experiment was designed to 4 factors and 6 levels with Pb concentration varying in the range of of 0-1 120 mg·kg^-1 and Bap concentrations in the range of 0-6.4 mg·kg^-1 in the soil. Results show that in bulk soil, Pb, regardless of forms, was not affected by the coexisting Bap and the natural degradation of Bap was also not either by the coexisting Pb. In the rhizosphere soil of ryegrass, the contents of exchangeable and carbonate bound Pb and Fe-Mn bound Pb were obviously lower than in the non-rhizosphere soils, while the contents of organic and sulfide bound Pb significantly higher, which may be attributed to exudation and Pb absorption of the ryegrass roots. Pb concentrations in shoots and roots of corn and ryegrass were found significantly and positively related to the total content of Pb in the soil, but not to content of the coexisting Bap. The degradation rates of Bap were increased significantly in the corn and ryegrass rhizopheres compared to that in non-rhizosphere soil. The effect of ryegrass is much higher than that of corn. The coexisting Pb in the rhizosphere soils had some inhibiting effect on Bap degradation, which may be related to the effect of the rhizosphere environment activating Pb and hence increasing microbial availability of Pb in the rhizosphere soil. Pb also had some effect on absorption of Bap by roots. In short, it can be concluded that the coexistence of Pb and Bap does not have any effects on the fate of Pb in both rhizosphere and non-rhizosphere environment and Pb has no effect either on the fate of Bap in non-rhizosphere environment. However, in rhizosphere environment, Pb does affects the degradation of Bap as well as the absorption of Bap by roots.