In a national population-based study, researchers in the United States linked increased risk of cancer due to the use of agricultural pesticides with smoking, a better understood risk factor for cancer. The findings were published in Frontiers in Cancer Control and Society.
Pesticides cause cancer
In modern agriculture, pesticides are essential to ensure sufficiently high yields and food safety. However, these chemicals can have negative effects on plant and animal life, as well as on the people exposed to them.
“In our study, we found that for some types of cancer, the effect of agricultural pesticide use is comparable in magnitude to the effect of smoking,” said lead study author Dr. Isain Zapata, an associate professor at Rocky Vista University College of Osteopathic Medicine in Colorado.
“We accept that a person who is not a farmer and lives in a community with heavy agricultural production is exposed to many of the pesticides used in their vicinity. They become part of their environment,” Zapata said.
The researchers found that in such an environment, the impact of pesticide use on cancer incidence rivaled that of smoking. The strongest association was between non-Hopkins lymphoma, leukemia, and bladder cancer. In these cancers, the effects of pesticide exposure were more pronounced than the effects of smoking.
“We present a list of the main pesticides that contribute to some specific cancers, but we strongly emphasize that it is the combination of all these elements and not just one of them that makes the difference,” Zapata stressed.
Because pesticides are not used one at a time, researchers said it is unlikely that any one pesticide is to blame. While some pesticides are discussed more frequently than others, all of them, and especially combinations, can have an impact.
Accordingly, the researchers included 69 pesticides for which usage data is available through the United States Geological Survey. “In the real world, people are not likely to be exposed to a single pesticide, but rather to a cocktail of pesticides in their region,” Zapata said.
The researchers said their study is the first comprehensive assessment of cancer risk from a population-based perspective at the national level. Until now, no large-scale study has looked at the big picture and put pesticide use in context with a cancer risk factor that is no longer in question, in this case smoking.
“It’s hard to explain the extent of a problem without context, so we incorporated smoking data. We were surprised to see estimates in similar ranges,” Zapata said.
The researchers said that while their study adds to the knowledge about pesticide use in the United States, cancer risk factors are complicated, and assessing the big picture may not reflect individual outcomes. For example, geography has a strong impact. In regions that grow multiple crops, such as the Midwest, which is famous for its corn production, associations between pesticides and cancer rates were stronger.
One of the researchers’ goals is to get people, including those who are not frequently exposed to pesticides, to think about the problems that pesticide use poses in a broader context.
“Every time I go to the supermarket to buy food, I think of a farmer who contributed to the production of that product. These people often put their lives at risk for my convenience and that plays a role in my appreciation for that product. It has definitely had an impact on how I feel when that forgotten tomato in the fridge goes bad and I have to throw it in the trash,” Zapata said.
Pesticides may increase cancer risk in children
The study, published in the International Journal of Hygiene and Environmental Health, found that children exposed before birth to the chemicals acephate and bromacil had an increased risk of developing unilateral retinoblastoma, or cancer of one eye, and that exposure to pymetrozine and kresoxim-methyl increased the risk of all types of retinoblastoma.
“What matters is finding the specific perpetrators and identifying them,” said Julia Heck, an associate professor in the department of epidemiology at the UCLA Fielding School of Public Health who studies the environmental causes of childhood cancer.
Identifying specific pesticides linked to cancer is the first step toward banning them or replacing them with less harmful alternatives.
The researchers studied land-use data and pesticide use reports, which provide information about where, when, and in what quantities chemicals are applied, to determine locations of potential pesticide exposure. They considered 132 pesticides associated with cancer.
They compared children with retinoblastoma to randomly selected children with California birth certificates and found that those with cancer were more likely to have been born in neighborhoods near areas where specific pesticides were applied.
Pesticides can increase cancer risk by disrupting hormones, damaging DNA, and causing inflammation. Children are especially vulnerable because their organs are still developing, according to previous research.
Childhood cancer is a leading cause of death in children, but unlike adult cancers, there aren’t as many identified causes. Although retinoblastoma has high survival rates, children can suffer long-term effects from chemotherapy and radiation, Heck said, which is why it’s critical to identify the causes and prioritize prevention.
Other factors that increase the risk of retinoblastoma include air pollution, sunlight, X-rays, and workplace hazards.
At the industry level, farmers should be more aware of the potential health risks of pesticide application and consider alternative solutions, said lead author Shiraya Thompson, who conducted research during her graduate program in epidemiology at UCLA.
It is also important to consider health inequalities that may arise from different levels of pesticide exposure, she added.
Because it is difficult for parents to protect themselves and their families from pesticide exposure, regulatory agencies such as the Environmental Protection Agency should limit the use of harmful pesticides to reduce cancer risks, Heck said.
“You may have very little control over what happens in the cornfields near you,” he said. “And you may not even be aware of what the farmers near you are putting down.”
Thompson stresses that more research, such as animal studies, is needed to find out which pesticides are actually carcinogenic and what specific harms they cause.
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