On the anti‐cholinesterase activity of benomyl

The fungicide benomyl, previously reported to be an anti‐cholinesterase and toxic to earthworms, has now been shown to have little or no effect on cholinesterase. However, it breaks down to form two products: butyl isocyanate. which is an irreversible inhibitor of the enzyme of comparable potency to organophosphates; and methyl benzimidazol‐2‐ylcarbamate (MBC, carbendazim), which does not inhibit at all. The reported inhibitory power of benomyl is therefore likely to be due to formation of small quantities of the former. It is also concluded that toxicity of benomyl and MBC to earthworms cannot be due to inactivation of cholinesterase.