Environmental Factor

November 2011


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High pesticide exposure associated with cognitive decline

By Robin Arnette
November 2011

Jane Hoppin, Sc.D.

Hoppin said, “I was surprised that we could see any difference with HPEEs, because they're very non-specific and it's a self-reported exposure. If we had better detail, such as whether they got it on their clothing, on their skin or in their lungs, and knew what pesticides were involved, we may be able to find a larger neurological difference.” (Photo courtesy of Steve McCaw)

Fred Gerr, M.D.

Gerr said that the research collaboration created a synergy that was based upon the strength of the AHS, Hoppin's epidemiological expertise, and his group's experience with the administration of neurobehavioral tests. (Photo courtesy of the University of Iowa College of Public Health)

Farmers routinely apply pesticides to crops, but this common occurrence can sometimes result in farmers being exposed to the chemicals. Although these accidental exposures don't propel farmers to seek medical attention, they still may have long-term health consequences. That's why researchers are now focusing on these high pesticide exposure events or HPEEs to better understand how they impact human health.

According to new research from scientists at NIEHS, the University of Iowa, and the National Cancer Institute, HPEEs may be a cause for concern. In a paper published online(http://www.ncbi.nlm.nih.gov/pubmed/21927986) Exit NIEHS in the International Archives of Occupational and Environmental Health, agricultural workers who had at least one HPEE involving pesticides that contain organophosphate scored lower on cognitive tests compared to agricultural workers who never had an HPEE.

“We know that if a person suffers pesticide poisoning there may be long-term cognitive consequences, but our study shows that you don't need to be poisoned to have effects,” said Jane Hoppin, Sc.D.(http://www.niehs.nih.gov/research/atniehs/labs/epi/chronic/staff/hoppin/), a staff scientist in the NIEHS Epidemiology Branch and co-author of the study. “About 23 percent of these farmers in the Agricultural Health Study reported having an HPEE in their lifetime, so HPEEs are important exposures that haven't been considered.”

Brain games

Hoppin said she and her colleagues recruited 693 men out of approximately 52,000 pesticide applicators who were enrolled in the Agricultural Health Study (AHS)(http://www.niehs.nih.gov/research/atniehs/labs/epi/studies/ahs/index.cfm), a study sponsored by several federal agencies to examine health changes in licensed pesticide applicators and their spouses from North Carolina and Iowa. To evaluate central nervous system (CNS) function, trained technicians administered nine neurobehavioral tests to the men to assess memory, motor speed, sustained attention, verbal learning, and visual scanning and processing.

Participants with an HPEE and those without had similar scores on seven of the nine tests, but subtle differences on two tests got the researchers' attention. Participants who had reported an HPEE were 4.2 seconds slower on the Digit-Symbol Test and 2.5 seconds slower on the Sequences A test (see text box for more information).

Fred Gerr, M.D. (http://www.public-health.uiowa.edu/faculty-staff/faculty/directory/faculty-detail.asp?emailAddress=fred-gerr@uiowa.edu) Exit NIEHS, a professor in the Department of Occupational and Environmental Health at the University of Iowa College of Public Health and a co-author on the paper, was responsible for conducting the neurobehavioral tests. He said the tests the researchers used measured a wide range of distinct mental abilities and, in the absence of severe brain injury, it is uncommon to see lower scores on all tests administered. 

He added, “Broadly speaking, the two tests affected by HPEEs both assess visual scanning and mental processing of information.”

Pesticides and human health

Hoppin admits, however, that the research had several limitations. With 693 participants, the study was fairly small. Also, these volunteers were exposed to a broad range of pesticides and exposure levels, making it difficult to determine what aspect of the HPEE actually contributed to lower test scores. It could have been the active ingredient in the pesticide or one of the many other chemicals that comprise the 95 percent of inert material. Nevertheless, the findings indicated that HPEEs sped up the cognitive decline that humans experience, equivalent to the effect of being 3.9 years older.

Although the results are of vital importance to agricultural workers who handle pesticides, Hoppin stressed that people who use over-the-counter pesticides in their homes shouldn't extrapolate the study's findings to residential use. This research was specific to licensed pesticide applicators working with organophosphate pesticides. However, all individuals should use care and read the label when handling and working with pesticides.

In future work, the research team will investigate how exposure to specific pesticides impacts neurobehavioral function, and whether these exposures affect human disease. For instance, Hoppin said, additional studies from the AHS revealed that people with HPEEs are more likely to have asthma.

“This current work adds to our body of knowledge about the effects of pesticides,” Hoppin said.

Citation: Starks SE, Gerr F, Kamel F, Lynch CF, Alavanja MC, Sandler DP, Hoppin JA(http://www.ncbi.nlm.nih.gov/pubmed/21927986) Exit NIEHS. 2011. High pesticide exposure events and central nervous system function among pesticide applicators in the Agricultural Health Study. Int Arch Occup Environ Health; doi: 10.1007/s00420-011-0694-8 [Online 7 September 2011].

Neurobehavioral testing

The nine examinations included the Continuous Performance Test, Digit-Symbol Test, Finger Tapping, Grooved Pegboard, Auditory Verbal Learning Test (AVLT) Total Recall, AVLT Delayed Recall, AVLT Recognition, Sequences A, and Sequences B. The tests took place in private rooms and were timed. The two tests in which agricultural workers with an HPEE scored lower are described below.

Digit-Symbol Test

Designed to measure visual scanning and processing, the test used a code of nine symbols, for example, $, %, @, with a number underneath each symbol. When volunteers saw a symbol-number combination flash on their computer monitor, they were supposed to type the number on the keyboard.

Sequences A

Designed to measure visual scanning and motor speed, the test consisted of a map that had the letters of the alphabet randomly dispersed throughout. The volunteers were supposed to find the letters in order, starting with the letter A.



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