Metal effects on phenol oxidase activities of soils.

This study evaluates the effects of various metals, in concentrations ranging from 0 to 800 mM, on the phenol oxidase (PO) activities of three Mediterranean soils. Dose-response curves (DRC) were established for each metal and were divided into four groups according to metal effects on PO activity: inhibition, stimulation followed by inhibition, stimulation, and no effect. The area under dose-response curves (AUDRC) allowed metal effects on PO activities to be ranked. Results of statistical analyses of variance show that metals had more pronounced effects than soil or metal salt form (i.e., chloride or sulfate) on PO activities. Hence, according to the mean values of the AUDRC for each metal tested, PO activities were preferentially stimulated by Mg(II), Mn(II), Zn(II) and were inhibited in order by Cd(II)<Ni(II)<Cu(II)<Pb(II)<Al(III)<Co(II)<Ba(II)<Sn(II)<Fe(II).