VOL.: 41 (1986) (p. 357)
During occupational exposure, such as ground spraying and other manual application of these herbicides, dermal absorption is a major route of entry into the body.
In manufacturing plants, exposures occur during the handling of raw materials, intermediates, finished products and process wastes. High-level short-term occupational exposures have also been caused by industrial accidents.
No study was available of pregnancy outcomes of women exposed occupationally to chlorophenoxy herbicides.
In one study of persons exposed to chlorophenoxy herbicides during military operations in Viet Nam, conducted ten years after exposure, no increase in the incidence of chromosomal aberrations or sister chromatid exchanges was observed.
Cytogenetic studies have been carried out on workers occupationally exposed to chlorophenoxy herbicides during spraying. In three of the studies, there was also exposure to other herbicides and the effect of chlorophenoxy herbicides could not be assessed. Studies in which occupational exposure was only to chlorophenoxy herbicides showed no increased incidence of chromosomal aberrations or sister chromatid exchanges.
In a large Danish cohort study of chemical workers exposed to chlorophenoxy herbicides [particularly (4-chloro-2-methylphenoxy)acetic acid (MCPA), 2-(4-chloro-2-methylphenoxy)propanoic acid (mecoprop), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-(2,4-dichlorophenoxy)propanoic acid (dichlorprop)], as well as other chemicals, no overall increase in cancer incidence rate was observed, but there were significantly increased risks of soft-tissue sarcoma and lung cancer in different subcohorts, which were not necessarily those with the highest exposures to chlorophenoxy herbicide preparations. A Finnish cohort study of brush control workers with short follow-up time showed no increased risk. A small Swedish cohort study of railroad workers who sprayed herbicides showed an increased risk of cancers at all sites combined for those exposed to both chlorophenoxy harbicide preparations and other herbicides. An excess incidence of all cancers was also reported from a very small cohort of Swedish forestry foremen exposed to chlorophenoxy herbicide preparations and other herbicides. A study of long-term pesticide applicators in the German Democratic Republic, heavily exposed to a number of chemicals, including 2,4-D and MCPA, demonstrated an increased risk of bronchial carcinoma.
A population-based case-control study conducted in northern Sweden showed a statistically significant association between exposure to chlorophenoxy herbicides, especially in forestry, and the occurrence of soft-tissue sarcomas. A second study on this type of tumour was conducted in southern Sweden, where a significant increase in the risk of developing soft-tissue sarcomas was associated with previous exposures to chlorophenoxy herbicides, mainly in agriculture. An increased risk of soft-tissue sarcoma was described among highly exposed Italian rice weeders in a population-based case-control study. A case-control study from New Zealand did not demonstrate an increased risk of soft-tissue sarcoma in people exposed to chlorophenoxy herbicides.
A statistically significant association between malignant lymphoma and exposure to chlorophenoxy herbicides was found in a Swedish case-control study; however, no such association was seen in a case-control study of these tumours from New Zealand. In a Danish cohort of chemical workers exposed to chlorophenoxy herbicides, there was also no increased risk of malignant lymphoma.
Three Swedish case-control studies of colon, liver and nasal cancer, respectively, which used the same study design and methods as in the studies on soft-tissue sarcoma and malignant lymphoma, did not demonstrate significantly increased risks. Exposure recall bias of cancer patients thus does not seem to explain the differences between the results of the Swedish and the New Zealand case-control studies of soft-tissue tumours and lymphomas.
In summary, well-conducted case-control studies have provided the most information on the association between cancer and occupational exposure to chlorophenoxy herbicides. Statistically significant elevated odds ratios have been observed for cancers at some sites, but not consistently, independent studies. The results of one cohort study on the incidence of soft-tissue sarcoma support the finding in case-control studies of an increased relative risk for these tumours. Other cohort studies have added little information. No consistent exposure-response relationship emerged from the different studies, and, in the studies that found an association, exposures were shorter than those usually associated with occupation-related cancers.
For definition of the italicized terms, see Preamble Evaluation.
Subsequent evaluation: Suppl. 7 (1987)
See Also: Toxicological Abbreviations