首页|Soil phosphatase assay to evaluate arsenic toxicity should be performed at the soil's actual pH
Soil phosphatase assay to evaluate arsenic toxicity should be performed at the soil's actual pH
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NETL
NSTL
Elsevier
Soil phosphatase is considered an indicator to assess soil arsenic (As) pollution. In the phosphatase activity determination, a fixed buffer value (pH 5-10) is commonly used for all soils, ignoring the soil's actual pH. Here, we determined the soil phosphatase activity of 20 soils under As stress at the soils' pH, and the As inhibition mechanism was also explored by the enzyme kinetics. Our results show that soil phosphatase activity was significantly inhibited under As stress. The inhibition rate in acid soils (39.2 %) was considerably higher than in alkaline soils (25.4 %) when As concentration was 600 mg kg~(-1). For alkaline soils, As inhibited phosphatase by competitive inhibition or linear mixed inhibition, while for acid soils, it was more complex, including linear mixed inhibition, non-competitive inhibition, and anti-competitive inhibition. Simultaneously, our results showed that the ecological dose (ED10) described by the partial inhibition model was far below than the complete inhibition model. According to the partial inhibition model, the ED_(10) of As ranged from 2.66 to 164.07 mg kg~(-1) for alkaline soils and 0.11 to 89.95 mg kg~(-1) for acid soils. Moreover, V_(max)/K_m of phosphatase is a more sensitive index for evaluating As contamination than V_(max) in partial inhibition models. The ED_(10) obtained based on the relationship between V_(max)/K_m and As concentration was 0.64-34.75 mg kg~(-1) for acid soils and 8.48 to 20.16 mg kg ~(-1) for alkaline soils. This also confirms V_(max)/K_m as a sensitive and ideal index for assessing As pollution under soils' actual pH. Furthermore, soil pH and cation exchange capacity are dominant factors affecting As inhibition on soil phosphatase. The above kinetic studies indicate that performing the assay by adjusting the buffer pH to the soil pH is essential for more accurately evaluating arsenic toxicity.
Tiancong Gao、Haixia Tian、Huimin Niu、Ziqi Wang、Yunchao Dai、Mallavarapu Megharaj、Wenxiang He
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College of Natural Resources and Environment, Northwest A&F University, Key Laborztory of Plant Nutrition and Agro-environment in Northwest China,Ministry of Agriculture, Yangling 712100, Shaanxi, China
Global Centre for Environmental Remediation, College of Engineering, Science and Environment, University of Newcastle, Callaghan, NSW 2308, Australia
NETL
NSTL
Elsevier
