The Research On Soil Biochemical Activity Affected By PFOA And Mercury

With the rapid development of industrialization in China, a large number of industrial wastes used as irrigation and sludge were discharged into environment, leading to the severe destruction of soil ecosystem. Mercury is one of heavy metals causing soil pollution. PFOA is considered as a kind of persistent refractory organic pollutants recently. Both of them have significant effect on soil ecosystem. Therefore the eco-toxicological effects of the two pollutants became hot issues in areas of environment, soil and biology currently.As an important component of soil, soil enzymes play a key role in the nutrient cycle, energy metabolism and pollution monitoring. It has been widely used as soil eco-toxicological target by domestic and foreign scientists. However, few of them investigated the effect of PFOA on soil enzyme activities. Therefore it is necessary and important to study on the relationships among Hg, PFOA and soil enzyme activity in both theory and practice.Simulation method was adopted in this paper. We investigated the relationships among soil urease, alkaline-phosphatase, invertase, dehydrogenase and Hg, PFOA in several major soil types of China. The main conclusions were as follows:1. In the same type soil, there was a significantly positive correlation between soil urease, alkaline phosphatase, invertase, dehydrogenase activity, urease kinetic parameters(Vmax, Vmax / Km, k), the parameters of soil total enzyme activity(TEI) and the major soil fertility factor. So these can be used as indicators of soil fertility levels.2. PFOA can inhibit the activity of jackbean urease and soil dehydrogenase activity. As the PFOA concentration increased, there was significant regularity, while significant or highly significant negative correlation between soil dehydrogenase activity and PFOA concentrations. Therefore, soil dehydrogenase activity can be an index evaluating PFOA pollution levels. The critical value of ED10 and ED50 was 31 mg·kg-1 and 153 mg·kg-1. The minimum ED10 and ED50 value in the acid soil was 56.4 % and 55.2 % of that in the alkaline soil, concluding that the dehydrogenase activity in acidic soil was more sensitive to PFOA contamination than that in alkaline soil.3. Soil alkaline phosphatase and invertase activities were not sensitive to PFOA pollution. Soil urease activity was more sensitive to the PFOA, but as PFOA concentration increased, their relationships were not significantly correlated. The TEI of acidic soil and alkaline soil with low fertility was more sensitive to PFOA pollution. The TEI can be used as indicator to evaluate soil PFOA contamination.4. Hg in low concentrations can partly increased soil urease activity, while Hg in high concentrations inhibited soil urease activity. There was significantly or highly significantly negative correlation between Hg concentration and urease activity in most soils. This indicates that soil urease activity can be used as indicator to evaluate Hg pollution to a certain extent. The ecological dose value of ED10 of soil polluted slightly by Hg was 0.13 ~ 0.81 mg·kg-1 and urease activities in acidic soil and soils with low content of organic matter were more sensitive.5. The effect of Hg on urease enzymatic parameters in soil showed that Hg increased Km, but in general Km were in the same order of magnitude, so it can be regarded as a constant parameter. The kinetic parameters such as Vmax,Vmax/Km and k were reduced as a whole with the increase of Hg concentration, and their relationship was significantly or highly significantly negative correlation. It was proved that Hg reaction mechanism was non-competitive inhibition. And Vmax, Vmax/Km, k values, together with soil enzyme activity can be indexes to monitor Hg pollution in soil. Urease dynamic parameters such as Vmax/Km, k were more sensitive to the Hg pollution and Vmax/Km and k in acid soil were more sensitive to Hg contamination than that in alkaline soil. The critical values of ED10 in these two type soils were 0.16 mg·kg-1 and 1.82 mg·kg-1.6. Hg can inhibit soil alkaline phosphatase, invertase activity, but the relationships between them were not significantly negative correlation in all soil tested, so soil alkaline phosphatase and invertase activities can not be used as indicators of Hg pollution. Hg can significantly inhibit soil dehydrogenase activity, and there was significantly or highly significantly negative correlation between them. This indicates soil dehydrogenase activity can be an index used to evaluate Hg pollution in soil. The critical Hg concentrations in soil were 0.88 mg·kg-1 for moderately polluted.7. Hg decreased TEI in acid and alkaline soils with low soil fertility, and the relationships between them were highly significantly negative correlation only in four soils(No. 2, 5, 7,8).8. PFOA+Hg inhibited soil urease and dehydrogenase activities. We calculated the net variation(ΔU) of soil urease and dehydrogenase activities. The results indicated that there was interaction effect between PFOA and Hg and the effect differed in different soil types. The specific mechanism need to be studied further. PFOA+Hg in high concentrations can inhibit soil invertase activity, and there was interaction effect between them. And it showed antagonism effect in soils with high organic matter content, while synergistic effect in soils with low organic matter content. It can be concluded that there was stronger buffer ability to pollutants in soils with high organic matter content. Soil alkaline phosphatase activity was not sensitive to PFOA+Hg pollution.9. From the discussion of four kinds of activities above, we can conclude that soil dehydrogenase activity was more sensitive to PFOA pollution. The critical PFOA concentrations in soil were 31 mg·kg-1 for slightly polluted and 151 mg·kg-1 for moderately polluted. Soil urease and dehydrogenase activities were more sensitive to Hg pollution. The critical Hg concentrations in soil were 0.13 mg·kg-1 for slightly polluted soil and 0.88 mg·kg-1 for moderately polluted.