Pesticides may promote respiratory symptoms in farmers

Researchers have identified a number of commonly used pesticides that are associated with respiratory wheeze in farmers, according to a study published online in Environmental Health Perspectives.

Many of the chemicals in agricultural pesticides are also used in residential pesticides, the researchers warned.

“This is the most comprehensive list of pesticides in relation to wheeze that has been evaluated to date,” said lead author and environmental epidemiologist Jane Hoppin, ScD, Associate Professor of Biological Sciences and Deputy Director of the Center for Human Health and the Environment at North Carolina State University, in Raleigh, NC.

“Fifty-one of the pesticides we tested in this study had never been analyzed in terms of their effects on respiratory outcomes,” added Dr. Hoppin. “And some of them, like glyphosate, 2,4-D, and permethrin, aren’t just used on farms. They’re used residentially now to kill weeds or treat fleas on pets. We believe it’s important information that will help people make decisions about pesticides.”

Although little is known about the potential respiratory impact of most currently used pesticides, there’s increasing evidence that pesticide exposures contribute to respiratory symptoms and asthma, the researchers wrote.

For this study, Dr. Hoppin and colleagues used interview data obtained from the 2005-2010 Agricultural Health Study (AHS), which they analyzed for associations between allergic and non-allergic wheeze and the current use of 78 pesticides. Of the 22,134 male farmers who participated in AHS, 6% reported allergic wheeze (both wheeze and allergy), while 18% had non-allergic wheeze (wheeze only).

After adjusting for age, body-mass index, smoking, current asthma, and driving diesel tractors, the researchers found that younger farmers, smokers, individuals with higher BMIs, and current asthmatics were more likely to wheeze. While asthma was more common among those with wheeze, only 27% of those with allergic wheeze and 8% of those with non-allergic wheeze reported current asthma. Farmers who applied pesticides more often and those who drove diesel tractors were also more likely to wheeze.

The 78 pesticides in the study included 45 herbicides/plant growth regulators, 25 insecticides, 6 fungicides, 1 fumigant, and 1 rodenticide. Overall, 29 pesticides had some association with at least one type of wheeze. Of these, 19 were significantly associated with allergic wheeze, 21 with non-allergic wheeze, and 11 were significantly associated with both.

Of the herbicides associated with wheeze, the three most commonly used ones—atrazine, 2,4-D, and glyphosate (commonly sold under the trade name RoundUp)—showed evidence of an exposure-response relationship for at least one of the wheeze outcomes, the researchers found.

Of the insecticides, carbaryl (sold under the trade name Sevin) was significantly associated with allergic wheeze and showed strong evidence of an exposure-response relationship. Also, three of the 8 pyrethroid insecticides were associated with wheeze—as a group, the pyrethroids are among the most commonly used insecticides, particularly for residential use. Notably, the most frequent users of the pyrethroid permethrin were more likely to report wheeze, both allergic and non-allergic. However, the most commonly used pyrethroid in this study, cyfluthrin, was not associated with wheeze.

“Our analysis included the majority of pesticides used in agriculture, home and garden, and industrial/commercial/governmental uses in the United States,” the authors wrote. “The findings for chemicals like glyphosate, 2,4-D, carbaryl, and the pyrethroids are particularly relevant for consumers who would like to minimize their wheeze and allergy risk associated with the use of chemicals in their homes, gardens, and play areas.”

Future studies should focus on potential mechanisms and strategies to minimize exposure, the researchers advised.