Studies to evaluate the effects on the activity of acid and alkaline phosphatases of 20 trace elements showed that all trace elements inhibit the activity of phosphatases in soils. Results showed that the relative effectiveness of the trace elements in inhibition of phosphatase activity depends on the soil. When the trace elements were compared by using 25 µmole/g soil, the average inhibition of acid phosphatase in three soils showed that Hg(II), As (V), W(VI), and Mo(VI) were the most effective (average inhibition >50%) and that Ba(II), Co(II), and As(III) were the least effective (average inhibition <10%) inhibitors. Other elements that inhibited acid phosphatase activity in soils were: Cu(I), Ag(I), Cd(II), Cu(II), Zn(II), Mn(II), Sn(II), Ni(II), Pb(II), Fe(II), Cr(III), Fe(III), B(III), Al(III), V(IV), and Se(IV); their degrees of effectiveness varied in the three soils used.The most effective inhibitors of alkaline phosphatase activity in soils were Ag(I), Cd(II), V(IV), and As(V). All the trace elements that inhibited acid phosphatase activity also inhibited alkaline phosphatase activity. The order of effectiveness of the trace elements in inhibition of acid phosphatase activity was different from that of inhibition of alkaline phosphatase activity. Generally, the inhibitory effect of trace elements was less in the presence of 2.5 µmole/g soil than in the presence of 25 µmole/g soil. In addition to the effect of trace elements, phosphate ion inhibited acid and alkaline phosphatase activities in soils. Related anions such as NO2‐, NO3‐, Cl‐, and SO42‐ were not inhibitory in the presence and absence of buffer.
