Degradation Characteristics of DEHP Added into Mollisols at Different Concentrations and Its Effect on Enzyme Activities

  Objective  The degradation process of Di-(2-Ethylhexyl) phthalate (DEHP) and its effects on soil enzyme activities were investigated in a lab incubation experiment.

  Method  DEHP was added into mollisols at 0, 5, 10, 20, and 40 mg kg⁻¹ with three replications. Soil samples were collected at the 3^rd, 7^th, 14^th, 21^st, 28^th and 35^th days of incubation, and the concentrations of DEHP, Mono -(2-ethylhexyl) phthalate (MEHP), and phthalic acid (PA) were analyzed by gas chromatography-mass spectrometry (GC-MS). In the experiment of soil enzyme activities, DEHP was added to mollisols at 0, 30, 50, 100, 300, and 500 mg kg⁻¹ with three replications. Methods of indigo colorimetry, 3,5-dinitrosalicylic acid colorimetry, and potassium permanganate titration were used to determine the activities of urease, sucrase, and catalase.

  Result  On the 35^th day, the average degradation rate of DEHP was 39.95 %, the average accumulation rate of MEHP was 89.25 % and PA was not found. The activities of urease and sucrase were inhibited with the increase in the concentration of DEHP and their inhibition percentages were 22.6% and 33.5%.

  Conclusion  The concentration of DEHP and its toxicity could decrease in a short time incubation experiment of DEHP added to mollisols (at least 35 days). However, MEHP as degradation product of DEHP was still ecologically toxic or even more toxic, means that the overall environmental toxicity was not decreased. In addition, the activities of urease and sucrase would be inhibited in mollisols contaminated by DEHP.