Soil pH alteration by chromium pollution compromises urease-based toxicity assessment

Area of Science:

• Environmental Chemistry
• Soil Science
• Biochemistry

Background:

• Industrial waste introduces chromium (Cr) into soils, altering pH and complicating contamination assessment.
• Chromium's impact on soil enzymes like urease is significant but influenced by environmental factors.

Purpose of the Study:

• Investigate Cr inhibition mechanisms on urease activity.
• Determine the role of Cr-induced pH changes in urease inhibition.
• Assess Cr toxicity in different soil environments.

Main Methods:

• Enzyme kinetics assays for urease activity.
• X-ray photoelectron spectroscopy (XPS), Raman, and Fourier-transform infrared spectroscopy (FTIR) for Cr-binding analysis.
• Structural equation modeling to evaluate Cr-induced pH effects.

Main Results:

• Cr3+ and Cr6+ significantly inhibited Jack bean urease activity.
• Cr binds to urease via carbonyl and amino groups.
• Soil mitigated Cr toxicity; Cr6+ enhanced urease in most soils.
• Cr3+ caused noncompetitive inhibition; Cr6+ caused noncompetitive inhibition in Jack bean urease.
• Cr-induced pH shifts strongly influenced urease activity and kinetics.

Conclusions:

• Cr contamination's impact on urease activity is pH-dependent.
• Accurate Cr toxicity assessment requires considering Cr-induced pH changes.
• Findings inform risk assessment and management of Cr-contaminated soils.