International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 2A)

For definition of Groups, see Preamble Evaluation.

VOL.: 53 (1991) (p. 45)

5. Summary of Data Reported and Evaluation

5.1 Exposure data

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.

Insecticides are applied by aerial spraying and by various ground-based techniques, ranging from hand-held sprayers and dusters to vehicle-mounted hydraulic sprayers, air sprayers, foggers and power dusters.

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. Similarly, in a cohort of licensed pest control workers from Florida, there was significantly increased mortality from lung cancer, which was particularly high among workers licensed for 20 years or more; a nonsignificant excess risk for brain cancer was also seen. A follow-up of deaths among plant protection workers and agronomists in eastern Germany showed an increased risk of lung cancer which also increased with length of exposure; survey data indicated that the smoking habits of these pesticide workers were similar to those of the general population.

Among farmers licensed for pesticide use in the Piedmont region of Italy, increased risks for skin cancer and malignant lymphomas were reported; lung cancer incidence was not studied.

A cohort of licensed pesticide applicators in Sweden showed excess risks for cancers of the lip and testis, a slight excess risk for Hodgkin's disease, and risks similar to those of the general population for non-Hodgkin's lymphoma and soft-tissue sarcoma. Overall, there was a deficit of lung cancer risk that was probably related to the lower smoking rates of the applicators.

In a study of a large cohort of grain millers in the USA, flour-mill workers had excess risks for non-Hodgkin's lymphoma and pancreatic cancer; the risk for lung cancer was not increased.

5.2.3 Case-control studies

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. In Kansas, the risk increased slightly with frequency of use of insecticides as a group. In a study in Washington State, non-Hodgkin's lymphoma was associated with potential contact with chlordane and DDT. DDT use was also associated with non-Hodgkin's lymphoma in one of two studies in Sweden.

Multiple myeloma was associated with use of pesticides (particularly organochlorine insecticides) in a study in the USA. The risk for multiple myeloma was also elevated among farmers in the USA exposed to unspecified herbicides and pesticides.

The results of six studies in Sweden and the USA on soft-tissue sarcoma in association with exposure to insecticides were inconsistent.

Chronic lymphocytic leukaemia has been associated with use of insecticides in the USA and with use of DDT in Sweden.

The risk for brain cancer was associated with exposure to insecticides and fungicides in farmers in Italy.

Overall, the strongest evidence that exposure to nonarsenical insecticides causes cancer in humans comes from the cohort studies of applicators. Two of these studies showed significant excesses of lung cancer. Two showed rising risks with duration of exposure, whereas the third showed an inverse association. These findings were based on small numbers in the subgroups with the longest exposure, and applicators in some of these studies had potential contact with arsenical insecticides. Some case-control studies of multiple myeloma and other tumours of B-cell origin show small excesses among people exposed to insecticides. In most studies, however, potential confounding by other agricultural exposures had not been fully explored.

5.3 Other relevant data

In a study in India, an excess of spontaneous abortions was reported among couples exposed to several pesticides in grape gardens. In a population in Colombia, where exposure to many different pesticides occurred, increased risks for spontaneous abortion and decreased birth weight were reported.

Several studies on the cytogenetic effects of work with pesticide formulations are described. Only in the case of ethylene dibromide and phosphine was exposure to a single, identified insecticide. No cytogenetic effect was observed with exposure to ethylene dibromide, while a significant excess of chromosomal aberrations was observed among the phosphine fumigators. All other studies were of workers handling not only a mixture of insecticide formulations but also other pesticide formulations. The majority of these studies reported increases in the frequency of chromosomal aberrations and/or sister chromatid exchange among the exposed workers. With the exceptions noted above, in no instance, however, could the involvement of non-insecticides be eliminated.

5.4 Evaluation

There is limited evidence that occupational exposures in spraying and application of nonarsenical insecticides entail a carcinogenic risk.

Overall evaluation

Spraying and application of nonarsenical insecticides entail exposures that are probably carcinogenic to humans (Group 2A).

For definition of the italicized terms, see Preamble Evaluation.

N.B.: Arsenic and arsenic compounds are carcinogenic to humans (IARC,1987). This evaluation applies to the group of chemicals as a whole and not necessarily to all individual chemicals within the group.

Last updated: 20 November 1997

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