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Release: Oct. 6, 2000

EDITORS: This study in the American Journal of Industrial Medicine is available online at

UI study finds link between livestock insecticide application and lung disease symptoms

IOWA CITY, Iowa -- Farmers who apply insecticides to their livestock are nearly four times more likely to have symptoms of lung disease than farmers who don't apply insecticides to their farm animals, according to a study by researchers at the University of Iowa College of Public Health.

This new finding, in a study published in the October issue of the American Journal of Industrial Medicine, is consistent with results of other studies involving pesticide usage, said Nancy L. Sprince, M.D., UI professor of occupational and environmental health and lead author of the study.

"Other studies have shown that exposure to heavy grain dust in grain elevators or exposures to organic dusts in animal confinement facilities can lead to asthma-like symptoms such as wheezing in the chest," Sprince said. "Ours is the first study to show that this specific type of insecticide application to livestock causes any health effects."

The results were based on responses from 385 Iowa farmers enrolled in the Iowa Farm Family Health and Hazard Surveillance Project, a population-based study that assessed diseases and injuries in relation to farm exposures. This part of the Farm Family Study examined the association between airway disease symptoms and farm exposures, including those from pesticides, grain dust, animal confinements and silos. The data were collected in 1994 from farm families in 18 Iowa counties, two counties from each of the state's nine crop and livestock reporting regions. A cooperative agreement with the National Institute for Occupational Safety and Health funded the study.

After adjusting for factors such as age and smoking, UI researchers found that the likelihood of asthma-like symptoms for farmers who personally apply insecticides to their livestock nearly quadrupled. In addition, these farmers were nearly three times as likely to experience flu-like symptoms called organic dust toxic syndrome (ODTS). The procedure itself involves pouring or

spraying insecticide directly over the animal, creating the potential for skin and inhalation exposure for the farmer.

Stephen Reynolds, Ph.D., UI professor of occupational and environmental health and a
co-investigator on the study, noted that since the survey was done in 1994, more farmers have switched to "ear-tagging" their livestock -- attaching a clip containing insecticide to the animal's ear. The chemical is spread among the livestock as the animals come into contact with each other. The procedure requires less direct human handling of insecticides and is less toxic than pouring or spraying.

"A number of farmers still do the hand-pouring," Reynolds said. "We think this is an area that needs further study."

Sprince, Reynolds and their colleagues are planning to develop a grant proposal for a follow-up study to gauge firsthand the exposures farmers face when applying insecticides to their livestock.

"The information we had for this study was self-reported from questionnaires," she said. "We need to measure farmers' symptoms and lung function, and measure dust and pesticide concentrations in the air, to get a better idea of what's going on in the body and in the environment where these farmers do this type of work."

The UI researchers also reported other findings from the study:

  • Farmers who had conventional vertical silos (storage units for hay and silage used for animal feed) were almost three times more likely to have asthma-related symptoms and 2.4 times more likely to have the flu-like symptoms of ODTS than farmers without vertical silos. Sprince said that this finding confirmed previous studies done in this area.
  • Farmers with animal confinement buildings were three times as likely to report having a cough, four times as likely to have chest tightness while at work and twice as likely to have the
    flu-like symptoms of ODTS.
  • Unlike results of most studies of grain elevator workers, the UI study results in Iowa farmers did not show an association between respiratory symptoms and grain production. This suggested that exposures of Iowa grain farmers may be different from those of grain elevator workers, Sprince said.

Around 13 percent of the farmers included in the study identified themselves as smokers, which is about half the national average, Sprince said. She added that newer data from 1999 suggest that smoking rates among Iowa farmers have fallen even further.

"We're seeing some healthy behaviors among farmers, in terms of not smoking," Sprince said. "It's the occupational exposures and the related health symptoms that we need to examine more closely."

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