硫丹及其主要代谢产物对紫色土中酶活性的影响

Abstract

采用室内避光培养,研究了硫丹及其主要代谢产物(硫丹硫酸盐和硫丹二醇)在紫色土中的质量浓度变化及其对土壤酶活性的影响。结果表明,<em>α</em>-、<em>β</em>-硫丹在紫色土中的消解过程符合一级反应动力学方程,半衰期分别为32-99d和69-116 d。代谢产物硫丹硫酸盐浓度在前20 d增加较快,30 d后基本趋于稳定;硫丹二醇浓度先增加后减小,15 d时达到最大。5 mg/kg的硫丹处理5 d时对脲酶和硝酸还原酶活性起激活作用,随着培养时间的增加,硫丹处理对脲酶活性从无显著影响逐渐转向抑制,第60天时抑制作用达到最大;高浓度处理(100 mg/kg)强烈抑制脲酶活性,最大降幅达到94.5%。硫丹处理(除5 mg/kg外)对硝酸还原酶活性起抑制作用,浓度越大,抑制作用越强,最大降幅达到89.9%。5 mg/kg的处理抑制多酚氧化酶活性,10-20 mg/kg的处理30 d后由激活逐渐转向抑制;100 mg/kg的处理起激活作用,第15天时酶活性达到最大,随后持续下降,第60天时恢复到对照水平。偏相关分析表明,脲酶、硝酸还原酶活性与硫丹硫酸盐浓度呈显著负相关,硫丹硫酸盐抑制这两种酶的活性;多酚氧化酶活性与<em>α</em>-、<em>β</em>-硫丹、硫丹硫酸盐和硫丹二醇浓度的偏相关性不显著。;Purple soil samples were treated with technical grade endosulfan at 5 concentration levels (0, 5, 10, 20 and 100 mg/kg), and incubated in glass flask in dark environment for 60 d so as to study the effect of endosulfan and its main metabolites on soil enzyme activities, such as urease, nitrate reductase and polyphenol oxidase. Meanwhile, the mass concentrations of <em>α</em>-, <em>β</em>-endosulfan, endosulfan sulfate and endosulfan diol in the soil were determined. The results showed that both of the degradation processes of <em>α</em>- and <em>β</em>-endosulfan accorded with the first-order reaction kinetic equation, and the half-times were obtained as 32-99d and 69-116 d, respectively. The half-time increased with the amount of endosulfan spiked in the soil. The concentration of endosulfan sulfate increased continuously in the first 20 d, and kept basically stable after incubation for 30 d. While the concentration of endosulfan diol first increased and reached maximum at the 15th day, and then decreased gradually. Compared with CK (without endosulfan), urease activity in the soil spiked with 5 mg/kg of endosulfan at the 5th day increased 20.0%. Besides this, urease activity in the soil spiked with 5-20 mg/kg of endosulfan gradually turned from no significant change to inhibition with time, and the inhibition reached maximum at the 60th day. Urease activity was significantly inhibited and the highest decrease percent reached 94.5% at the 5th day in the soil spiked with 100 mg/kg of endosulfan. Pearson correlation analysis indicated that there was significantly negative correlation between urease activity and the concentration of <em>α</em>-, <em>β</em>-endosulfan, endosulfan sulfate, and endosulfan diol, while that was negatively related to the concentration of endosulfan sulfate at the confidence level of 0.05 based on partial correlation analysis. The partial correlation between urease activity and the concentration of <em>α</em>-, <em>β</em>-endosulfan, and endosulfan diol was not significant. It revealed that endosulfan sulfate was an inhibitor to urease. Nitrate reductase activity in the soil spiked with 5 mg/kg of endosulfan increased significantly at the 5th day, and was inhibited with the increases of endosulfan concentration and incubated time, and the highest decrease percent in the soil spiked with 100 mg/kg of endosulfan reached 89.9% at the 60th day. Pearson correlation analysis indicated that there was significantly negative correlation between nitrate reductase activity and the concentration of <em>α</em>-, <em>β</em>-endosulfan, endosulfan sulfate, and endosulfan diol at the confidence level of 0.01, while that was negatively related to the concentration of endosulfan sulfate at the confidence level of 0.01 based on partial correlation analysis. The partial correlation between nitrate reductase activity and the concentration of <em>α</em>-, <em>β</em>-endosulfan, and endosulfan diol was not significant. It revealed that endosulfan sulfate was an inhibitor to nitrate reductase. Polyphenol oxidase activity in the soil spiked with endosulfan changed greatly with time. In general, polyphenol oxidase activity in the soil spiked with 5 mg/kg of endosulfan was inhibited, and that spiked with 10 mg/kg of endosulfan was similar to that of CK, whereas that was significantly lower than that of CK at the 60th day. Compared with CK, polyphenol oxidase activity in the soil spiked with 20 mg/kg of endosulfan had no significant change at the 5th and 30th day, and significantly increased at the 10th and 15th day, and then reached maximum at the 20th day, which was significantly lower at the 60th day, and that in the soil spiked with 100 mg/kg of endosulfan was much higher before the 60th day, and the increase percent reached maximum (139.9%) at the 15th day, and then decreased continuously, finally reached CK level at the 60th day. Pearson correlation analysis indicated that there was significantly positive correlation between polyphenol oxidase activity and the concentration of <em>α</em>-, <em>β</em>-endosulfan, endosulfan sulfate, and endosulfan diol at the confidence level of 0.01, while the partial correlation between polyphenol oxidase activity and their concentration was not significant. These results indicated that the concentrations of <em>α</em>-, <em>β</em>-endosulfan, endosulfan sulfate, and endosulfan diol have little effect on polyphenol oxidase when they exist alone in the soil.