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Amidase Activity in Soils: IV. Effects of Trace Elements and Pesticides¹

ABSTRACT

Amidase was recently detected in soils, and this study was carried out to assess the effects of 21 trace elements, 12 herbicides, 2 fungicides, and 2 insecticides on the activity of this enzyme. Results showed that most of the trace elements and pesticides studied inhibited amidase activity in soils. The degree of inhibition varied among the soils used. When the trace elements were compared by using 5 µmol/g of soil, the average inhibition of amidase in three soils showed that Ag(I), Hg(II), As(III), and Se(IV) were the most effective Inhibitors, but only Ag(I) and As(III) showed average inhibition > 50%. The least effective inhibitors (average inhibition < 3%) included Cu(I), Ba(II), Cu(II), Fe(II), Ni(II), Al(III), Fe(III), Ti(IV), V(IV), As(V), Mo(VI), and W(VI). Other elements that inhibited amidase activity in soils were Cd(II), Co(II), Mn(II), Pb(II), Sn(II), Zn(II), B(III), and Cr(III). Enzyme kinetic studies showed that As(III) was a competitive Inhibitor of amidase, whereas Ag(I), Hg(II), and Se(IV) were noncompetitive inhibitors.

When the pesticldes studied were compared by using 10µg of active ingredlent per gram of soil, the average inhibition of amidase in three soils ranged from 2% with dinitroamine, EPTC plus R-25788, and captan to 10% with butylate. Other pesticides that inhibited amidase activity in soils were atrazine, naptalam, cbloramben, dicamba, cyanazine, 2,4-D, alachlor, paraquat, trifluralin, maneb, diazinon, and malathion. The inhibition of amidase by diazinon, alachlor, and butylate followed noncompetitive kinetics.

¹ Journal Paper no. J-10186 of the Iowa Agric. & Home Econ. Exp. Stn., Ames. Project nos. 2082 and 2112. Presented before Div. S-3, Soil Sci. Soc. Am., Detroit Mich. 3 Dec. 1980.

² Graduate Research Assistant and Professor of Soil Biochemistry, respectively. Dep. of Agron., Iowa State Univ., Ames, IA 50011. Dr. Frankenberger currently is Assistant Professor, Dep. of Soil and Environ. Sciences, Univ. of Calif., Riverside, CA 92521.

Received for publication February 17, 1981. Accepted for publication July 8, 1981.