Soil pollution by heavy metals and other trace elements is one of the major environmental problems associated with some industries. Studies to evaluate the effects on the activity of acid and alkaline phosphatases of 20 trace elements showed that all the trace elements inhibited the activity of phosphatases in soils. The relative effectiveness of the trace elements in inhibition of phosphatase activity depended on the soil. When the trace elements were compared by using 25 .mu.mol/g soil, the average inhibition of acid phosphatase in 3 soils showed that Hg(II), As (V), W (VI) were the most effective (average inhibition > 50%), and Ba(II), Co(II) and As(III) were the least effective (average inhibition < 10%) inhibitors. Other elements that inhibited soils acid phosphatase activity 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 3 soils used. The most effective inhibitors of alkaline phosphatase activity in soils were Ag(I), Cd(II), V(IV) and As(V). All 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. The inhibitory effect of trace elements was less in the presence of 2.5 .mu.mol/g soil than in the presence of 25 .mu.mol/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.
