Abstract: The responses of invertase and urease reaction kinetics to phthalate esters (PAEs) were assessed in the northeastern black soil by the indoor simulation method. The enzymatic activities of invertase and urease were measured by 3,5-dinitrosalicylic acid method and indophenol blue colorimetric method, respectively, when dimethyl phthalate (DMP) and dibutyl phthalate (DBP) were used as the test materials. The results suggested that the enzyme activities of invertase and urease were inhibited by PAEs in black soil. Based on the linear regression equation of soil enzyme activities and PAEs concentrations, the critical indicators of the slight contamination (ED₁₀) in black soil were obtained. The ED₁₀ values of invertase and urease for DMP contamination in black soil were 24.352 mg·kg^-1 and 5.015 mg·kg^-1, respectively, and the ED₁₀ values of invertase and urease for DBP contamination in black soil were 16.911 mg·kg^-1 and 8.677 mg·kg^-1, respectively. According to the principle that the smaller ED₁₀ the more sensitive, the results indicated that urease was sensitive to PAEs pollution in black soil and could be used as the biochemical index of PAEs contamination. The kinetic parameters of invertase and urease were decreased by DMP and DBP in black soil, which belonged to the anti-competitive inhibition mechanism. PAEs contamination in black soil might change carbon, nitrogen cycle and the ecosystematic function of black soil, and then affect the sustainable development of black soil.

Key words: soil biochemistry, soil contamination, enviromental toxicology