Comparison of methods for measuring cholinesterase inhibition by carbamates

The Acholest and tintometric methods are used widely for measuring blood cholinesterase activity after exposure to organophosphorus compounds. However, if applied for measuring blood cholinesterase activity in persons exposed to carbamates, the accuracy of the methods requires verification since carbamylated cholinesterases are unstable. The spectrophotometric method was used as a reference method and the two field methods were employed under controlled conditions. Human blood cholinesterases were inhibited in vitro by four methylcarbamates that are used as insecticides. When plasma cholinesterase activity was measured by the Acholest and spectrophotometric methods, no difference was found. The enzyme activity in whole blood determined by the tintometric method was </= 11% higher than when the same sample was measured by the spectrophotometric method.

Effect of sample storage on human blood cholinesterase activity after inhibition by carbamates

During an operational field trial with propoxur it was observed that the inhibition of whole blood cholinesterase was greater when samples were stored before the assay. Since measurement of cholinesterase activity is not always possible immediately after sampling, the effects of different storage conditions were evaluated. Human blood cholinesterases were inhibited in vitro by methylcarbamates and stored at different pH values, temperatures, and sample dilutions. The results showed that the degree of cholinesterase inhibition does not change if samples are diluted 300-fold with buffer at pH 5.0 at 4 degrees C and the enzyme activity measured within 4 hours after dilution. These conditions of storage were equally satisfactory for each of the three methylcarbamates studied and are therefore likely to apply to other carbamates as well.

Toxicity of carbamates for mammals

Toxicity studies have been carried out with a number of monomethylcarbamates, most of which reached an advanced stage in the World Health Organization insecticide evaluation programme. Both quantitative and qualitative distinctions have been found between the carbamates studied, and certain common characteristics that distinguish them in several important aspects from organophosphorus insecticides have been demonstrated.