Pesticides may cause NHL, other cancers
Photo by John Messina
The International Agency for Research on Cancer (IARC), the specialized cancer agency of the World Health Organization, has found evidence suggesting that 5 organophosphate pesticides may be carcinogenic.
The IARC classified the herbicide glyphosate and the insecticides malathion and diazinon as “probably carcinogenic” to humans and the insecticides tetrachlorvinphos and parathion as “possibly carcinogenic” to humans.
A summary of these findings has been published in The Lancet Oncology.
Glyphosate
For the herbicide glyphosate, the IARC found limited evidence of carcinogenicity in humans. Case-control studies of occupational exposure to glyphosate in the US, Canada, and Sweden showed increased risks for non-Hodgkin lymphoma (NHL).
However, the Agricultural Health Study (AHS) showed no significantly increased risk of NHL in subjects exposed to glyphosate.
A study of community residents showed increases in blood markers of chromosomal damage after glyphosate formulations were sprayed nearby. And glyphosate was shown to cause DNA and chromosomal damage in human cells, although bacterial mutagenesis tests were negative.
In studies of male mice, glyphosate increased the incidence of renal tubule carcinoma and hemangiosarcoma. Glyphosate also increased the incidence of pancreatic islet-cell adenoma in male rats, and a glyphosate formulation promoted skin tumors in mice.
The IARC said glyphosate has the highest global production volume of all herbicides. It is used in agriculture, forestry, urban, and home applications.
Glyphosate has been detected in the air during spraying, in water, and in food. The general population is exposed to the chemical primarily by living near sprayed areas, home use, and diet. But the IARC said the level of exposure observed is generally low.
Malathion
The IARC classified malathion as “probably carcinogenic” for humans based on limited evidence linking the insecticide to NHL and prostate cancer. Occupational use of malathion was associated with an increased risk of prostate cancer in a Canadian case-control study and in the AHS.
Studies of occupational exposures in the US, Canada, and Sweden revealed positive associations between malathion and NHL. However, results of the AHS did not show an association between the insecticide and NHL.
Studies showed that malathion induced DNA and chromosomal damage in humans and animals, although bacterial mutagenesis tests were negative. Results also suggested malathion disrupts hormone pathways.
Experiments in mice showed malathion increased the incidence of hepatocellular adenoma or carcinoma (combined). In rats, the insecticide increased the incidence of thyroid carcinoma in males, hepatocellular adenoma or carcinoma (combined) in females, and mammary gland adenocarcinoma after subcutaneous injection in females.
The IARC said malathion is used in “substantial volumes throughout the world” to control insects in agricultural and residential areas.
Workers may be exposed to malathion during the use and production of the product. The general population may be exposed if they live near sprayed areas, use the product at home, or consume food exposed to the chemical.
Diazinon
The IARC classified diazinon as “probably carcinogenic” for humans based on limited evidence linking the insecticide to NHL, leukemia, and lung cancer.
Two multicenter, case-control studies of agricultural exposures suggested a positive association between diazinon and NHL. The AHS showed positive associations with specific subtypes of NHL but no overall increased risk of NHL. The AHS also suggested an increased risk of leukemia and lung cancer in subjects exposed to diazinon.
Evidence suggested that diazinon induced DNA or chromosomal damage in human and mammalian cells in vitro. In vivo, diazinon increased the incidence of hepatocellular carcinoma in mice and leukemia or lymphoma (combined) in rats, but only in males receiving the low dose in each study.
