Ecotoxicological Effects Of PAHs And SO₂Combined Pollution On Soil-plant System Of Wheat And Ryegrass In Shanxi Industrial And Mining Area

This study used wheat and ryegrass as experimental plants, and used freshly mixed loess born in Industrial and mining areas of Shanxi Province as tested soil to study the ecotoxical effects of combined pollution of polycyclic aromatic hydrocarbons (PAHs) and sulfur dioxide (SO2) on the soil-plant system. The experiments were conducted in green house, and the continuous extraction method, biochemical technique, denaturing gradient gel electrophoresis (PCR-DGGE), fluorescent quantitative PCR (RT-PCR) technique etc, were mainly carried out. PAHs and SO2are two typical environmental pollutants in Shanxi industrial and mining area. PAHs (represented by naphthalene, phenanthrene, pyrene) and SO2(sulfate and sulfite were used as SO2derivatives in soil) were applied in the soil either single or combined with different concentrations to study the effects on the seedling growth of wheat and ryegrass. Meanwhile, soil enzyme activity, plant antioxidant enzyme activity, the diversity of soil microbial community and soil microorganism quantity were also examed. The main results were summarized as follows:The rate of wheat seed germination was not sensitive to single and combined pollution of PAHs and SO2in the soil. The rate of the ryegrass seed germination was affected more than that of the wheat under the combined PAHs and SO2. Under the condition of single PAHs or SO2pollution, the plant height and root elongation of ryegrass and wheat seedlings were improved at lower concentrations, while inhibited at higher concentrations. The underground biomass of wheat was not significantly affected by PAHs, but the growth of ryegrass root was greatly affected by the single SO2than by PAHs, Under the combined pollution of PAHs and SO2, the plant height, root elongation, and underground biomass of wheat and ryegrass were all showed as synergistic stimulation effect at low concentration, but synergistic inhibition effect at high concentration. Under the single or combined pollution of PAHs and SO2, malondialdehyde (MDA) content in the leaves of ryegrass were all increased when compared with the control. Moreover, lipid peroxidation product was significantly increased with the increase of concentration, and the cell membrane damaged induced by combined pollution was significantly stronger than that that of single pollution. Oxidative stress damage caused to the plant tissue by single or combined pollution of PAHs and SO2. GPX is a sensitive index to high concentration of SO2(500-1000mg·kg-1), and GPX activity was significantly inhibited at higher concentration; CAT is a sensitive index to high concentration of PAHs (100mg·kg-1, and CAT activity was also significantly inhibited at higher concentration; POD was significantly induced under both single and combined pollution of PAHs and SO2. CAT was significantly induced under the lower concentration of combined pollution.Soil sucrase and soil dehydrogenase were showed the similar adaptability under the single or combined pollution of PAHs and SO2, and they were all increased at the middle and low concentration, but all inhibited at higher concentration. Soil dehydrogenase activity and sucrase activity had a significantly negative correlation with the concentration of PAHs respectively(r=0.893, r=-0.908,P<0.05). Under the condition of single and combined pollution of PAHs and SO2, soil urease activity was generally activated to a certain extent and had a significantly positive correlation (r=0.952, P<0.05) with the concentration of SO2, which indicated that soil urease activity was significantly affected by concentration of SO2.It was showed that soil microorganisms were inhibited by high concentration of PAHs or SO2, which lead to disappearance of some sensitive flora and the reduction of soil microbial communities and microbial quantity; however, soil microbial communities and microbial quantity were improved at lower concentration of PAHs or middle or lower concentration of SO2. The extent of variation of diversity index in combined pollution of PAHs and SO2were greater than those of single pollution. Compared with the control, biodiversity index was increased at the lower concentration of combined pollution (S1P1and S2P2), while was inhibited at the medium and higher concentrations (S3P3and S4P4). It was indicated that there were synergistic inhibition effects on soil bacterial species under the high concentration of combined pollution, and soil microbial species were more sensitive to combined pollution of PAHs and SO2.