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IOWA CITY - New University of Iowa research out this week associates higher exposure to commonly used insecticides - including those in use across Iowa - with an increased risk of death from all causes, specifically cardiovascular disease - even as the market share of that potentially deadly pesticide grows.
That swell in use, according to UI assistant professor of epidemiology and study author Wei Bao, means the rate of deaths related to the chemical exposure likely has increased as well - although he urged more investigation.
Findings from the study on pyrethroid exposure were published Monday in the JAMA Internal Medicine journal and reported nationally in publications such as the New York Times.
The UI research suggests individuals with high levels of exposure to pyrethroid insecticides are three times more likely to die of cardiovascular disease than those with low or no exposure.
'You would think, normally, cancer is an important endpoint or the brain is an important endpoint for these kinds of chemicals,” UI occupational and environmental health professor Hans-Joachim Lehmler told The Gazette.
'So I have to admit, from my personal perspective, that looking at cardiovascular disease - that there is actually a link - was quite unexpected.”
And while the research established an association, both Lehmler and Bao cautioned the study hasn't established individuals died as a direct result of exposure to pyrethroids. Bao said the findings indicate a high likelihood of a link, but follow-up study is needed.
'It's really important to be cautious - we're looking at an association here,” Lehmler said.
Pyrethroids are among the most commonly used insecticides, dominating the market of commercial household insecticides, according to the UI Office of Strategic Communication.
Iowa State University's Extension and Outreach news service reports pyrethroids are a synthetic substitute for older products and are related to the naturally occurring botanical insecticide pyrethrin.
Pyrethroids, according to Iowa State, can remain in effect for days or weeks after application and can vary in their toxicity - although they've been deemed less toxic than some of the pesticides they've replaced.
They're most active against insects such as ants, cockroaches, fleas, beetles and wasps, and have become 'the insecticides of choice” in over-the-counter products - under brand names such as 'Bug-B-Gon,” 'Hot Shot” and 'Tempo.”
They're used widely in public and residential settings, and in Iowa agriculture, they're common in the form of Permethrin, according to Lehmler.
'Different farmers probably have different preferences, but it is my understanding that they're used in soybeans and corn, in part because they're fairly broad in what they're targeting,” Lehmler said.
Agriculture is tantamount to Iowa's existence, making it a logical setting for the research.
'Living in Iowa, looking at pesticides is certainly an important exposure that we need to be concerned about,” Lehmler said. 'Because we're in some ways ground zero for a lot of these pesticides that are being used in agriculture.”
UI researchers were able to assess human exposure because metabolites of pyrethroids can be measured in urine, and 2,116 adults over age 20 participated in a U.S. National Health and Nutrition Examination Survey from 1999 to 2002. That, among other factors, involved giving urine samples.
Researchers then cross-referenced those samples with mortality records to determine how many participants had died by 2015 and from what.
They found that those with the highest levels of a pyrethroids metabolite in their urine were 56 percent more likely to have died by 2015 - with heart disease cited as the leading cause with a three times greater likelihood, according to the study and the UI Office of Strategic Communication.
In that the analysis involved a nationally representative sample of American adults, and not just those working in agriculture, Boa said his group's findings have broader public health relevance, according to the university.
Although the UI research didn't determine how its subjects became exposed to the pesticides, other studies have found most exposure comes through food, such as fruits and vegetables sprayed in the field. Exposure also can come through residential use in gardens or in homes for pest control.
Bao reported the pyrethroid market share has increased since the data was collected from 1999 to 2002, meaning related heart disease deaths tied to exposure could be up as well.
'There is very little out there where people have actually looked at the cardiovascular system as a target of toxicity for these kind of compounds,” Lehmler said. 'And so I would expect that this study will incentivize not only us here in Iowa, but everywhere in the world where these pesticides are being used, in their studies to go back and look at it if they have the same findings.”
If, he said, the findings are confirmed and the wider science community establishes a direct link, 'It's probably a good idea to go back and look at how we're using these particular pesticides and the safest way possible - or if there are ways of improving this and maybe restricting them.”
Also contributing to the paper, 'Association Between Exposure to Pyrethroid Insecticides and Risk of All-Cause and Cause-Specific Mortality in the General US Adult Population,” was Buyun Liu, with the UI College of Public Health, and Derek Simonsen, a UI graduate student in human toxicology.
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