Chemicals have been used to control insects for centuries but have come into widespread use only within the past century, with the development of a variety of synthetic insecticides. Of the several hundred chemicals that have been applied for insecticidal purposes, fewer than one hundred have been used extensively. The principal classes of compounds that have been used as insecticides are organochlorine, organophosphorus, carbamate and pyrethroid compounds and various inorganic compounds. Insecticides comprise a higher proportion of the total pesticide usage in developing countries than in developed countries. Occupational exposures occur in the mixing and loading of equipment and in the spraying and application of insecticides.
Absorption resulting from dermal exposure is the most important route of uptake for exposed workers.
5.2 Carcinogenicity in humans 5.2.1 Descriptive and ecological studies Several death certificate case-control studies in the USA evaluated cancer risks in association with ecological measures of insecticide exposure. The risk for multiple myeloma tended to be greater for farmers residing in counties where insecticides were more heavily used, but that for leukaemia did not. 5.2.2 Cohort studies A cohort of workers from a large pest control company in the USA had an excess lung cancer risk. Overall, there was a deficit of lung cancer risk that was probably related to the lower smoking rates of the applicators. The risk for non-Hodgkin's lymphoma rose with frequency of use of organophosphorus insecticides among farmers in Nebraska, an association that could not be accounted for by use of phenoxyacetic acid herbicides.