(Beyond Pesticides, June 24, 2015) The International Agency for Research on Cancer (IARC) has found that there is some evidence in experimental animals that the popular herbicide, 2,4-D, is linked to cancer and now classifies it as a Group 2B, ‚Äúpossibly carcinogenic to humans.‚ÄĚ IARC also classified lindane, used commonly in the U.S. as a topical lice treatment, in Group 1,‚Äúcarcinogenic to humans‚ÄĚ based on sufficient evidence in humans with the onset of non-Hodgkin lymphoma (NHL). These latest cancer findings come just months after the agency classified the world‚Äôs most widely used herbicide, glyphosate (Roundup), as ‚Äúprobably carcinogenic to humans,‚ÄĚ raising public concerns on the lack of action from U.S. regulators.
This month, 26 experts from 13 countries met at the World Health Organization‚Äôs (WHO) IARC in Lyon, France to assess the carcinogenicity of the insecticide lindane, the herbicide 2,4-D, and insecticide DDT. The findings are published in the Lancet. The new IARC findings come months after the agency classified glyphosate, the ingredient in the popular Roundup weed killer, as a Group 2A ‚Äúprobable‚ÄĚ carcinogen, citing sufficient evidence of carcinogenicity based on laboratory studies. This decision sparked renewed calls for the U.S. Environmental Protection Agency (EPA) to take action on the herbicide and remove it from the market. However, EPA has stated that it does not agree with the recent IARC finding and continues to ignore questions about glyphosate‚Äôs hazards and questions of ¬†its necessity in crop production. Meanwhile, France has moved forward to ban glyphosate sale in garden centers citing IARC‚Äôs findings.
2,4-D was classified as possibly carcinogenic to humans (Group 2B), based on¬†limited evidence in experimental animals and inadequate evidence in humans. According to IARC, ‚ÄúThere is strong evidence that 2,4-D induces oxidative stress, a mechanism that can operate in humans, and moderate evidence that 2,4-D causes immunosuppression, based on in vivo and in vitro studies. However, epidemiological studies did not find strong or consistent increases in risk of NHL or other cancers in relation to 2,4-D exposure.‚ÄĚ
In the review conducted by IARC experts, population-based case-control studies of 2,4-D exposure in relation to lymphoma and leukemia were found to provide mixed results. The working group conducted a meta-analysis of 11 studies that shows no association of non-Hodgkin lymphoma with over-exposure to 2,4-D. The consensus of the working group was that there is inadequate evidence in humans for the carcinogenicity of 2,4-D. But in animal studies, the group finds that there was limited evidence in experimental animals for the carcinogenicity of 2,4-D. Many of the studies under review observed increased incidence of reticulum-cell sarcoma in laboratory mice. In male rats, 2,4-D in the diet induced a positive trend in the incidence of rare brain cancer tumors (astrocytomas). However, other studies provided strong evidence that 2,4-D induces oxidative stress that can operate in humans and moderate evidence that 2,4-D causes immunosuppression, based on in-vivo and in-vitro studies.
2,4-D, one half of chemical makeup of Agent Orange, is highly toxic as it is linked to numerous adverse health effects, including increased risk of birth defects, reduced sperm counts, Parkinson‚Äôs disease, and endocrine disruption. Previous studies looking at 2,4-D and cancer found high incidence of NHL reported among farmers and other occupational groups working with 2,4-D. According to a study from researchers at the National Cancer Institute, frequent use of 2,4-D, has been associated with 2- to 8-fold increases of NHL in studies conducted in Sweden, Kansas, Nebraska, Canada, and elsewhere. Farmers using 2,4-D have been associated with an increased risk of NHL in 131 lymphohematopoietic cancers (LHC) in a case-control study embedded in a cohort of 139,000 members of United Farm Workers of America (UFW) diagnosed in California between 1988 and 2001. Additionally, studies from the National Cancer Institute and other sources have reported an association between exposure to lawn chemicals, like 2,4-D, and adverse impacts in dogs. One study by Glickman et al. (2004) reported that exposure to lawns or gardens treated with phenoxy herbicides was associated with an increased risk of transitional cell carcinoma of the urinary bladder in Scottish Terriers, compared with exposure to untreated lawns or gardens. For more read Beyond Pesticides’ ChemWatch factsheet.
2,4-D is also an endocrine disruptor and is known to interfere with the thyroid hormone. Laboratory studies have observed the hormone effects of 2,4-D exposure, including estrogenic activity in various organisms exposed to 2,4-D, decreases in the thyroid gland transport and production functions, and impairment of hormone iodination in the thyroid glands of laboratory rats. According to EPA’s registration documents for 2,4-D, current data demonstrate effects on the thyroid and gonads following exposure to 2,4-D, and there is concern regarding its endocrine disruption potential.
Unfortunately, its use is predicted to increase due to the deregulation and expected proliferation of 2,4-D tolerant genetically engineered (GE) crops. Concerns around increased 2,4-D use on GE crops revolves around increasing the onset of 2,4-D-resistant weeds, direct and indirect adverse impacts on human health, increased in drift to non-target sites, and the contamination of food and water. Earlier this year, several conservation, food safety, and public health groups filed a motion challenging the EPA‚Äôs decision to expand the use of a new 2,4-D product to be used on GE crops citing serious impacts the powerful new herbicide cocktail will have on farmworkers, neighboring farms, and ground and surface water, as well as endangered species.
The use of 2,4-D also comes with the possibility for dioxin contamination, which has been a long part of 2,4-D‚Äôs history. Expected increases in 2,4-D use means that the frequency of low level dioxin residues entering the environment may also increase. Dioxins are a carcinogenic class of chemicals that have left a toxic legacy for human health and environmental protection across the U.S due to their persistence and toxicity. Dioxins have notoriously long half-lives, are bioaccumulative, and present broadly significant health risks developmentally and postnatally.
See Beyond Pesticides’ 2,4-D page on the Gateway on Pesticide Hazards and Safe Pest Management for a comprehensive scientific and regulatory review of 2,4-D, including references to epidemiological studies that link the chemical’s use to elevated rates of cancer in humans.
Lindane was classified in the highest cancer category as ‚Äúcarcinogenic to humans‚ÄĚ (Group 1) based on epidemiological cohort and case-control studies of non-Hodgkin lymphoma in several countries which provided sufficient evidence in humans of carcinogenicity. According to IARC, information from the U.S. Agricultural Health Study, a large prospective cohort study with detailed exposure assessment, reported statistically significant increases in non-Hodgkin lymphoma risk with increasing occupational exposure to lindane. Population-based case-control studies in the mid-western USA and Canada also reported consistently positive associations. In animal studies, lindane was observed to consistently increase the incidence of benign or malignant liver tumors. The agency finds that there is strong evidence that lindane causes immunosuppressive effects that can operate in humans.
Although banned in several other countries, lindane is still used in the U.S. as lice treatment, regulated by the U.S. Food and Drug Administration (FDA). Lindane was formerly used in agricultural insecticides until it was banned by EPA for use on crops in 2006. Additionally, lindane was added to the Stockholm Convention on Persistent Organic Pollutants (POPs) list of chemicals to be eliminated or restricted globally, but the treaty still allows for pharmaceutical use until the existing stocks are depleted. The dangers of lindane are well documented. Lindane is an organochlorine class pesticide, similar in structure to DDT, and a known neurotoxicant and endocrine disruptor. In addition to being a carcinogen, perhaps the most startling health effect associated with the use of lindane is seizures in young children and adults at doses of 1.6 and 45 grams, respectively. Attempts to pressure the FDA to ban lindane have failed, as the agency still allows lindane as the active ingredient in lice shampoos and lotions.
See Beyond Pesticides’ lindane page on the Gateway on Pesticide Hazards and Safe Pest Management.
The long banned insecticide DDT was classified as Group 2A ‚Äúprobably carcinogenic to humans.‚ÄĚ DDT was widely used during World War II and subsequently it was widely applied to eradicate malaria and also used in agriculture. DDT is banned for use in the U.S. even though other developing countries may still use the chemical. Despite the fact that DDT is banned in the U.S. concentrations of this toxic chemical‚Äôs major metabolite, DDE, have remained alarmingly high in many ecosystems, including¬†surface waters, the Arctic, and even¬†U.S. national parks. The legacy of DDT is still being felt in communities across the U.S. as contaminated soil leads to the continued poisonings of birds and fish. DDT and its metabolites persist in the environment and are capable of long-range transport, bioaccumulate in human and animal tissue, and up the food chain. A recent study finds that exposures to DDT in utero can lead to the development of breast cancer later in life. The study reports that elevated levels of DDT in the mother‚Äôs blood led to a four-fold increase in the daughter‚Äôs risk of developing breast cancer. DDE has been linked to an early start to menopause and potentially harmful effects on ovarian function. People with high levels of exposure to DDT are also four times more likely to have Alzheimer‚Äôs disease than people with low levels.
According to IARC, there is sufficient evidence in experimental animals for the carcinogenicity of DDT and its metabolites DDE and DDD. In mice, studies gave positive results for multiple tumor sites, with DDT consistently increasing the incidence of benign and malignant liver tumors; lymphoma incidence was also increased in some studies. Further, there is strong evidence that DDT affects several mechanisms that can operate in humans. The experts also report that estrogenic effects and androgen-receptor antagonism were consistently observed in numerous experimental systems including human cells in vitro.
In light of federal inaction on glyphosate, 2,4-D and other toxic pesticides, it is up to local grassroots action to increase environmental awareness in communities across the country. Beyond Pesticides has the tools necessary for local activists to increase environmental awareness in schools and communities through our¬†Databases that Support Action. We promote getting active to safeguard your community and the surrounding environment from toxic insults: teach your neighbors how to¬†maintain their land without toxic pesticides,¬†protect honeybees from neonicotinoids insecticides,¬†aquatic species from endocrine disrupting chemicals, and the¬†streams, lakes, and rivers we all depend on from the widespread use of harmful synthetic pesticides and fertilizers.¬†To make your community sustainable and take it off the pesticide treadmill, join Beyond Pesticides‚Äôcommunity-based campaigns through our website, or contact us directly at [email protected].
Source: The Lancet, Reuters
All unattributed positions and opinions in this piece are those of Beyond Pesticides.