INFLUENCE OF HEAVY-METAL IONS IN DRINKING -WATER ON THE ACTIVITY OF THE ACHE-BIOSENSOR

Because of the specific inhibition of the enzyme acetylcholinesterase (AChE) by organophosphoric ester, -thioester and N-methylcarbamates an acetylcholinesterase biosensor can be used to screen drinking water f or the presence of compounds used as insecticides. The presence of hea vy metal ions may also lead to a decrease in catalytic activity of the enzyme, and in this way a misinterpretation of the results of the scr eening is possible. In this paper the effect of lead, iron, copper and zinc ions on the activity was examined, with the view to the concentr ation limit given by the decree for drinking water in the Federal Repu blic of Germany. Zinc and copper ions in drinking water produce a dete ctable inhibition (3 mg/L copper produced an inhibition of 10 to 20%, 5 mg/L zinc an inhibition of 10%), therefore the presence of copper, l ead and other heavy metal ions not tested in drinking water may produc e wrong results in pesticide screening. The coimmobilization of albumi n and enzyme was successfull in eliminating the inhibition caused by h eavy metal ions. Using this membrane for a 3 mg/L copper solution an i nhibition of only 0.3% higher was measured and for a 5 mg/L zinc solut ion an inhibition of 2.3% lower than the inhibition of TRIS-buffer its elf. This results were in the range of the standard deviation, which m eans that no inhibition could be measured with this metal ion solution using albumin containing AChE-membranes. The use of this modified mem brane in real drinking water samples shows clearly lower inhibition va lues than that of membranes without albumin.