College of Natural Resources and Environment, Northwest A&F University, Key Laboratory of Plant Nutrition and Agro-environment in Northwest China, Ministry of Agriculture, Yangling 712100, Shaanxi, China.
Global Centre for Environmental Remediation, Faculty of Science, University of Newcastle, Callaghan, NSW 2308, Australia.
Sci Total Environ. 2021 Jun 1;771:144835. doi: 10.1016/j.scitotenv.2020.144835. Epub 2021 Jan 23.
Fluorescein diacetate hydrolase (FDA-H) is an accurate biochemical method measuring the total microbial activity in soil, which indicates soil quality under ambient environmental changes such as pesticide parathion (PTH). However, the influence of PTH on the kinetics of FDA-H is still unknown. In this study, fifteen farmland soils were exposed to acute PTH pollution to investigate how the kinetic characteristics of FDA-H change with PTH concentration. Results showed that PTH strongly inhibited the FDA-H activities. The values of maximum reaction velocity (V) ranged from 0.29 to 2.18 × 10 mM g soil h and declined by 42.30%-71.01% under PTH stress. The Michaelis constant (K) values ranged between 2.90 and 14.17 × 10 mM and exhibited three forms including unchanged, increased (38.16-242.65%) and decreased (13.41-39.23%) when exposed to PTH. Based on the changes in two kinetic parameters, the inhibition of PTH on FDA-H was classified as three types, i.e., noncompetitive, linear mixed and uncompetitive inhibition. The competitive inhibition constant (K) and noncompetitive constant (K) ranged from 0.064 to 0.447 mM and 0.209 to 0.723 mM, respectively, which were larger than the K in values. The catalytic efficiency (V/K) of FDA-H is a sensitive integrated parameter to evaluate the PTH toxicity due to the higher inhibition ratio than the V. The PTH toxicity to FDA-H decreased with increase of soil organic matter and total nitrogen contents. This implied that the PTH toxicity could be alleviated by an increasing content of soil organic matter due to its buffering capacity to PTH. Besides, soils with a higher content of total nitrogen could provide stable environment for FDA-H to maintain its functionality under PTH pollution. Thus, the results of this study have great implications to the risk assessment of parathion in soils.
荧光素二乙酸酯水解酶（FDA-H）是一种准确的生化方法，用于测量土壤中的总微生物活性，它可以指示环境变化（如农药对硫磷（PTH））下的土壤质量。然而，PTH 对 FDA-H 动力学的影响尚不清楚。本研究中，将 15 种农田土壤暴露于急性 PTH 污染中，以研究 PTH 浓度如何改变 FDA-H 的动力学特征。结果表明，PTH 强烈抑制了 FDA-H 的活性。在 PTH 胁迫下，最大反应速度（V）值范围为 0.29-2.18×10mM g 土壤 h，下降了 42.30%-71.01%。米氏常数（K）值在 2.90-14.17×10mM 之间，当暴露于 PTH 时，表现出不变、增加（38.16-242.65%）和减少（13.41-39.23%）三种形式。基于两个动力学参数的变化，PTH 对 FDA-H 的抑制作用分为三种类型，即非竞争性、线性混合和非竞争性抑制。竞争抑制常数（K）和非竞争常数（K）范围分别为 0.064-0.447mM 和 0.209-0.723mM，均大于 K 值。由于比 V 具有更高的抑制率，FDA-H 的催化效率（V/K）是评估 PTH 毒性的敏感综合参数。由于土壤有机质和总氮含量的增加，PTH 对 FDA-H 的毒性降低。这表明由于对 PTH 的缓冲能力，土壤有机质含量的增加可以减轻 PTH 的毒性。此外，总氮含量较高的土壤可以为 FDA-H 提供稳定的环境，使其在 PTH 污染下保持功能。因此，本研究结果对土壤中对硫磷的风险评估具有重要意义。
