Sanchez-Hernandez Juan C, Sandoval Marco
Ecotoxicology Lab, Fac. Environmental Science and Biochemistry, University of Castilla-La Mancha, Toledo, Spain.
Department of Soil and Natural Resources, Fac. Agronomy, University of Concepcion, Chillán, Chile.
Ecotoxicol Environ Saf. 2017 Aug;142:303-311. doi: 10.1016/j.ecoenv.2017.04.032. Epub 2017 Apr 28.
The impact of pesticides on extracellular enzyme activity has been mostly studied on the bulk soil scale, and our understanding of the impact on an aggregate-size scale remains limited. Because microbial processes, and their extracellular enzyme production, are dependent on the size of soil aggregates, we hypothesized that the effect of pesticides on enzyme activities is aggregate-size specific. We performed three experiments using an Andisol to test the interaction between carboxylesterase (CbE) activity and the organophosphorus (OP) chlorpyrifos. First, we compared esterase activity among aggregates of different size spiked with chlorpyrifos (10mgkg wet soil). Next, we examined the inhibition of CbE activity by chlorpyrifos and its metabolite chlorpyrifos-oxon in vitro to explore the aggregate size-dependent affinity of the pesticides for the active site of the enzyme. Lastly, we assessed the capability of CbEs to alleviate chlorpyrifos toxicity upon soil microorganisms. Our principal findings were: 1) CbE activity was significantly inhibited (30-67% of controls) in the microaggregates (<0.25mm size) and smallest macroaggregates (<1.0 - 0.25mm), but did not change in the largest macroaggregates (>1.0mm) compared with the corresponding controls (i.e., pesticide-free aggregates), 2) chlorpyrifos-oxon was a more potent CbE inhibitor than chlorpyrifos; however, no significant differences in the CbE inhibition were found between micro- and macroaggregates, and 3) dose-response relationships between CbE activity and chlorpyrifos concentrations revealed the capability of the enzyme to bind chlorpyrifos-oxon, which was dependent on the time of exposure. This chemical interaction resulted in a safeguarding mechanism against chlorpyrifos-oxon toxicity on soil microbial activity, as evidenced by the unchanged activity of dehydrogenase and related extracellular enzymes in the pesticide-treated aggregates. Taken together, these results suggest that environmental risk assessments of OP-polluted soils should consider the fractionation of soil in aggregates of different size to measure the CbE activity, and other potential soil enzyme activities.
农药对胞外酶活性的影响大多是在土壤整体尺度上进行研究的，而我们对其在团聚体粒径尺度上的影响的了解仍然有限。由于微生物过程及其胞外酶的产生取决于土壤团聚体的大小，我们推测农药对酶活性的影响具有团聚体粒径特异性。我们使用一种火山灰土壤进行了三项实验，以测试羧酸酯酶（CbE）活性与有机磷（OP）毒死蜱之间的相互作用。首先，我们比较了添加毒死蜱（10mg/kg湿土）的不同大小团聚体之间的酯酶活性。接下来，我们在体外研究了毒死蜱及其代谢产物毒死蜱氧磷对CbE活性的抑制作用，以探索农药对酶活性位点的团聚体粒径依赖性亲和力。最后，我们评估了CbE减轻毒死蜱对土壤微生物毒性的能力。我们的主要发现如下：1）与相应对照（即无农药团聚体）相比，微团聚体（<0.25mm粒径）和最小的大团聚体（<1.0 - 0.25mm）中的CbE活性显著受到抑制（为对照的30 - 67%），但最大的大团聚体（>1.0mm）中的CbE活性没有变化；2）毒死蜱氧磷是比毒死蜱更有效的CbE抑制剂；然而，在微团聚体和大团聚体之间未发现CbE抑制存在显著差异；3）CbE活性与毒死蜱浓度之间的剂量反应关系表明，该酶具有结合毒死蜱氧磷的能力，这取决于暴露时间。这种化学相互作用导致了一种针对毒死蜱氧磷对土壤微生物活性毒性的保护机制，农药处理后的团聚体中脱氢酶和相关胞外酶的活性未发生变化就证明了这一点。综上所述，这些结果表明，对有机磷污染土壤的环境风险评估应考虑将土壤按不同大小的团聚体进行分级，以测量CbE活性以及其他潜在的土壤酶活性。
