Ecotoxicity of soil Pb pollution reflected by soil β-glucosidase: Comparison of extracellular and intracellular enzyme pool

Abstract

Lead (Pb) is a major environmental pollutant that threatens the soil environment and human health. Monitoring and assessing Pb toxicity on soil health are of paramount importance to the public. To use soil enzymes as biological indicators of Pb contamination, herein, the responses of soil β-glucosidase (BG) in different pools of soil (total, intracellular and extracellular enzyme) to Pb contamination were investigated. The results indicated that the intra-BG (intracellular BG) and extra-BG (extracellular BG) responded differently to Pb contamination. While the addition of Pb caused a significant inhibition of the intra-BG activities, the extra-BG activities were only slightly inhibited. Pb showed a non-competitive inhibition to extra-BG, while both non-competitive and uncompetitive inhibition were observed for intra-BG in the tested soils. The dose-response modeling was used to calculate ecological dose ED₁₀, which represents the concentration of Pb pollutant that causes a 10 % reduction in V_max, to express the ecological consequences of Pb contamination. A positive correlation was found between ecological dose ED₁₀ values of intra-BG and soil total nitrogen (p < 0.05), which suggests soil properties may influence Pb toxicity to soil BG. Based on the differences in ED₁₀ and inhibition rate among different enzyme pools, this study suggests that the intra-BG is more sensitive for Pb contamination assessment. From this, we propose that intra-BG should be considered when evaluating Pb contamination using soil enzymes as indicators.

Keywords: Ecotoxicological evaluation; Enzyme kinetics; Pb; Soil β-glucosidase.