Ten of the 29 pesticides tested by experts, including some of the most commonly used in the United States, were associated with thyroid cancer in a single pollutant model over a 20-year period.
These included oxyfluorphane, glyphosate and paraquat dichloride.
Additionally, in the 20 years before diagnosis or study interview, the risk of thyroid cancer increased according to the total amount of pesticides exposed to patients.
According to the authors, this study provides the first evidence in favor of the theory that exposure to residential pesticides from agricultural use increases the risk of thyroid cancer.
The incidence of thyroid cancer in the United States has increased significantly during the past 30 years, increasing by approximately 3% annually.
While some experts blame the increase on improved detection techniques, other publications argue that environmental, genetic and lifestyle risk factors may also be to blame.
Except for studies that focused on radiation exposure, few studies have looked at the effect of environmental exposure on the incidence of thyroid cancer.
According to earlier research, people working in the leather, wood and paper industries, as well as those exposed to pesticides, flame retardants and environmental solvents, are at greater risk.
Some insecticides are known to be mutagenic or have been proven to cause tumor growth and chromosomal abnormalities in cultured cells.
These include 19 insecticides that cause DNA cell damage in vitro, including the active ingredient in the popular herbicide, glyphosate.
Pesticides can also change how thyroid hormone is produced, which has been linked to a higher risk of developing thyroid cancer.
Previous research on the relationship between pesticides and thyroid cancer has been inconsistent or had methodological flaws, such as self-reporting of exposures, lack of details on particular pesticides, and small sample numbers.
California produces the most agricultural output of any state in the United States.
In addition, California used 162 million pounds of agricultural pesticides in 2008, or about 25% of the total amount used in the United States.
Meanwhile, the cases of advanced thyroid cancer are increasing in the state.
This study looks at the relationship between thyroid cancer risk and exposure to pesticides, including 19 that damage DNA cells.
The researchers proposed that pesticide exposure may be an important missing piece that requires further research.
Using thyroid cancer cases from the California Cancer Registry (1999–2012) and controls drawn from a population-based sample, the authors performed a case-controlled analysis.
Trial participants were 35 years of age or older, patients with thyroid cancer, and residents of the study area at the time of their diagnosis.
Individuals who were 35 years of age or older and had lived in California for at least five years prior to the research interview were eligible to be recruited from the same geographic area as controls.
pesticides and cancer
According to the US research National Institutes of Health (NIH), Beyond Pesticides, exposure to lindane and metalaxyl pesticides increases the risk of thyroid cancer.
Thyroid cancer is in its advanced stages and cases of non-invasive thyroid tumors are both on the rise.
However, given how common pesticide exposure is among the general population, experts speculate that environmental contaminants such as pesticides may be part of this increase.
More than 8 million people die from cancer each year, making it one of the top causes of mortality worldwide.
Specifically, the International Agency for Cancer Research (IARC) forecasts a 67.4% increase in new cancer cases by 2030.
There are more cases of thyroid and reproductive malformations as a result of endocrine (hormone) disruption due to various environmental contaminants such as pesticides.
Therefore, research like this emphasizes how important it is to understand how pesticide use can increase the risk of latent diseases (such as cancer), which do not manifest themselves immediately after exposure.
“More work is needed to understand the potential function of these compounds in thyroid carcinogenesis,” the researchers wrote.
The Agricultural Health Study, a group of certified pesticide applicators between 1993 and 1997 and 1999 to 2005, provided data on pesticide use and exposure.
The exposure records covered 50 different pesticides, and for 44 of them, the researchers looked at thyroid cancer risk.
The cumulative intensity-weighted lifetime exposure method was used by the scientists to identify factors that affect the risk expressed over days.
The incidence of thyroid cancer in male participants was evaluated by researchers in 2014 to 2015, and they used Cox regression to calculate hazard ratios and confidence intervals.