Study links specific pesticides to increased risk of over 6 types of cancers

• Agricultural pesticide use in the U.S. is linked to various cancers as strongly as smoking cigarettes, a new population-based study shows.
• The study analyzed local records throughout the country to make the first national map of cancer risks associated with pesticide use.
• The authors note that as potentially toxic as individual pesticides may be, most often they are deployed in combination, and the study’s findings document the resulting enhanced risks of cancer.
• Given the importance of food security, the study recognizes the tradeoff between having enough food and an increased risk of cancers.

In areas near agricultural production, pesticides increase the risk of developing cancer as much as smoking, according to a new nationwide study.

Its authors found strong links between environmental pesticides and leukemia, non-Hodgkin’s lymphoma, bladder, colon, lung, and pancreatic cancers, as well as cancer combinations.

The researchers compared the risks of pesticides to the known cancer risk associated with smoking cigarettes to provide an easily understood measure of risk.

While the authors assert that “pesticides are an essential feature of modern-day agriculture” — resulting in robust crop yields on which the planet’s food security depends — it spotlights the inherent danger in relying on them.

“There are few innovations as significant in agriculture as the development and use of pesticides,” they write.

To assess associations between pesticides tracked by the United States Geological Survey and cancers, the researchers analyzed county-level data from across the U.S. They identified pesticides reported in each area, and cancer cases, as well as the incidence of cigarette smoking and other possible factors.

Though individual pesticides have been linked to cancers, the study emphasizes that mixtures of pesticides — the manner in which they’re typically delivered to crops — significantly multiply their carcinogenic risk.

This risk is not confined to areas where agriculture actually occurs. Many communities under the greatest threat are visited by hazardous air- and water-borne pesticides that emanate from neighboring farms.

States such as Iowa, Illinois, Nebraska, and Missouri exemplified the strongest pesticide/cancer links, suggesting a connection between the corn grown in the area and the carcinogenic risk in its production. The study also spotlights fruit production in California and Florida.

The study is published in Frontiers in Cancer Control and Society .

Pesticides vs. cancer risk

Senior author of the study Isain Zapata, PhD , assistant professor of research and statistics in the Department of Biomedical Sciences of Rocky Vista University, Englewood, CO, described the importance of maintaining agricultural productivity, which currently means living with pesticide use.

Unfortunately, Zapata said, “Organic farming does not have the output necessary to feed in an economically sustainable way our population. It is not a simple solution.”

“There is no magic bullet,” said Zapata.

“We need agricultural products, and we need to produce them in an affordable way, so everyone has access to them. There is no way around it,” he said.

The value of the study

Wael Harb, MD , board certified hematologist and medical oncologist at MemorialCare Cancer Institute at Orange Coast and Saddleback Medical Centers in Orange County, CA, who was not involved in the study, considered the findings valuable.

“It identifies significant associations between the pesticides and several cancers like leukemia, Hodgkin’s lymphoma, bladder, colon, lung, and pancreatic cancers,” he said. “In that sense, it’s a comprehensive holistic analysis to understand how the widespread exposure of pesticides contribute to cancer risk.”

“Establishing pesticide usage patterns fine-tunes the environment of usage in those communities,” said Zapata.

How specific pesticides are linked to cancer

Until this study, investigations of the pesticide/cancer connection have primarily focused on subsets of community populations, such as farmers and their spouses. This is the first comprehensive look at pesticides’ effect on the health of entire communities.

Perhaps the best-known pesticide considered in the study is Glyphosate, which is marketed as Roundup, and has been linked in some studies to lymphoma .

The International Agency for Research on Cancer (IARC) has classified Glyphosate as a probable carcinogen and $11 billion was awarded to plaintiffs suing over its use.

However, the U.S. National Institutes of Health’s Agricultural Health Study of 88,000 farmers and their spouses found no link between Glyphosphate and cancers .

The new study concluded that the frequent use of Glyphosate was associated with a higher risk of all cancers, colon cancer, and pancreatic cancer.

Similarly, all cancers, colon cancer, and lung cancer were linked to the use of Imazethapyr. Metolachlor, Metolachlor-S, and the combination of both were consistently associated with all cancers, colon cancer, and pancreatic cancer.

Other associations between the heavy use of specific pesticides and cancers were:

• Atrazine was frequently deployed in areas with an elevated risk for all cancers and colon cancers.
• Boscalid was heavily used in regions that had higher incidences of leukemia, non-Hodgkin’s lymphoma, and pancreatic cancer, as well as low added-risk regions for lung cancer.
• Dimethomorph was associated with a high added risk of leukemia and non-Hodgkin’s lymphoma, as well as a lower additional risk of colon cancer.
• Dicamba was consistently used in areas with a high added risk of colon cancer and pancreatic cancer.
• Dinotefuran was commonly used in counties with high rates of leukemia and non-Hodgkin’s lymphoma.
• While Dimethenamid was associated in the study only with a low added risk of bladder cancer, when it was used in combination with Dimethenamid-P, it was linked to a high added risk of pancreatic cancer.

Does combining pesticides increase cancer risk?

The study underscores the multiplying effects of pesticide combinations in potential carcinogenesis.

Said Harb, “[When] there’s more exposure to chemicals, there’s a higher risk of cancer because all of these pesticides are potential carcinogens.”

“The more exposure, the length of exposure, and the different chemicals combined can increase the risk of damage to the DNA or similar signal pathways,” he said.

“Cancer is a multi-step process. Sometimes it takes multiple hits,” said Harb. “Not everybody gets cancer, but some people might be more vulnerable than others.”

How pesticides trigger cancers

Harb explained, “It’s oxidative stress [from pesticides] that causes DNA damage and disruption in cellular signaling pathways.”

“As an example,” he said, “certain pesticides can lead to the formation of reactive oxygen species (ROS), and this reactive oxygen causes damage to the DNA, protein, and lipids.”

“This basically leads to mutations, alteration, gene expression, and ultimately carcinogenesis. We know the problem with cancer is developing mutations in the genome which lead to abnormal protein and carcinogenesis,” said Harb.

The future of pesticides

Zapata hoped that the study might move forward a considered conversation regarding pesticides.

For now, he suggested: “Bring awareness, special healthcare initiatives, and education on the risk and management of exposures.”

“This is very important, although easier said than done,” he noted, especially since “Rural areas where most agricultural production happens tend to be most deprived of these resources.”

In the longer term, he called for “continuing research and the development of less harmful chemicals or usage strategies.”