Detection of organophosphorous pesticides with an immobilized cholinesterase electrode.

TLDR: Under controlled laboratory conditions, it was possible to correlate inhibition of cholinesterase activity with intramembranal pH shifts induced by substrate hydrolysis and this type of sensor could be used for screening purposes in the detection of pesticides in water pollution control.

Abstract: A simple and reliable method based on cholinsetersee inhibition Is proposed to detect organophosphate pesticides in water. The potenflometrlc method to measure enzymatic activity was applied to an immobilized chollneeteraae film coupled directly to a flat glass pH electrode. Under controlled laboratory conditions, It was possible to correlate inhibition of chollnseterese activity with intramembranal pH shifts Induced by subetrate hydrolysis. Measurements can be performed with such an enzyme electrode system In real time by monitoring the inhibition process, or after Incubation of the enzymatic film. Technical grade compounds of methylparathlon, azinphosethyl, and mevinphos were used as examples, and detected from ppm to several ppb after oxidative treatment. The sensitivity of the enzyme sensor depends on the Inhibitory power of the pesticide molecules, and therefore determines additional toxicity Information unavailable from other physico-chemlcal methods. This type of sensor could be used for screening purposes in the detection of pesticides in water pollution control and Is intended to be complementary to existing analytical methods. methods by developing automatic systems (6) and rapid determination (7), or by testing different cholinesterase sources to enhance selectivity and sensitivity to pesticides (8). This is because cholinesterases possess some unique characteristics: a relative specificity for pesticides and a great amplifying capacity related to the high enzyme turnover. The cholinesterase inhibition method can be considered an indirect biological assay in which it is not the pesticide itself that is detected (as in the other physicochemical methods), but rather the toxicological effect through the inhibitory power of the pesticide. The cholinesterase inhibition method can be related to, as well as complement, toxicological tests such as the LD,o or CL~0. The purpose of this study was to develop a simple and reliable method of pesticide detection that could be used for quality control tests in water treatment processes. The objective was to place an easily operated device for pesticide monitoring at the disposal of water distributors. This work was made possible by the availability of an acetylcholine electrode described previously (9), which consisted of an immobilized cholinesterase membrane coupled to a pH sensor.