[Effects of mercury and cadmium on the activity of urease in soils. I. Urea concentration].

Relationship between urease activity and heavy metals(Hg and Cd) under the condition of different urea concentration was studied. The results showed that the added urea concentration had an obvious positive effect on urease activity. Line and Langmuir models could be well described the relationship within the urea concentration tested. The calculation of urease parameters such as urea percent, urea-varying percent, and the maximum superficial urease activity reflected that Hg and Cd could remarkably reduce the positive effect from added urea, combined pollution of Hg + Cd displayed the most inhibition of the positive effect, and Hg produced the most ecological toxicity acting on soil urease activity. There was an adsorption mechanism in the enzyme reaction.