Year of Publication

2016

College

Public Health

Degree Name

Dr. of Public Health (Dr.P.H.)

Committee Chair

Wayne Sanderson, PhD, MS

Committee Member

Steven Browning, PhD

Committee Member

Bin Huang, DrPH

Abstract

Background: Pesticides and organic solvents are two classes of neurotoxic substances regularly used in agriculture. Pesticides have been studied in relation to a range of nervous system effects, and have been repeatedly shown to relate to depression in agricultural workers. Likewise, occupational solvent exposure is recognized as a risk factor for central nervous system effects, including mood disturbances and cognitive impairment, across various industries. Many gaps in knowledge regarding the effects of chronic exposure to these substances on mental/neurological health in agricultural workers still exist. The specific aims of the current analysis were to 1.) Estimate associations between metrics of a.) pesticide exposure and b.) organic solvent exposure and results from the Center for Epidemiologic Studies Depression Scale of depressed mood; and 2.) Estimate associations between questionnaire-based organic solvent exposure metrics and measures of central nervous system function assessed from a battery of nine neurobehavioral tests.

Methods: This was a cross-sectional analysis of a subsample of 701 licensed pesticide applicators (i.e., the Neurobehavioral Testing Study add-on) that participated in the Agricultural Health Study (AHS) in Iowa and North Carolina and were evaluated for neurobehavioral (NB) performance between 2006 and 2008. Participants eligible for the NB Study were male farmers that completed all phases of AHS questionnaires. Further exclusion criteria excluded AHS participants with a diagnosis of various medical conditions, as well as those who reported drinking >42 alcoholic beverages/week, reported pesticide poisoning at AHS Phase 3, or lived >150 miles away from testing facilities. Stratified random sampling was conducted among eligible participants to provide adequate representation of individuals with higher lifetime use of selected organophosphate pesticides. A total of 1,807 AHS participants were subsequently eligible for the NB Study, of which 39% participated. Ever-use and cumulative use of pesticide information was compiled from all phases of the AHS for 16 specific organophosphates, 4 specific carbamates, all-organophosphate pesticide use, all-pesticide use, and high pesticide exposure events (HPEEs). At the time of neurobehavioral evaluation, solvent exposure was assessed in a questionnaire. An ever-use and categorical years of use variable based on the median years of exposure for each measure were derived for gasoline, paint/lacquer thinner, petroleum distillates, and use of any solvent (sample sizes for benzene, toluene, and turpentine were not large enough to evaluate). Three solvent-based activity variables ascertained at enrollment were also evaluated (ever-use of solvent additives in mixing pesticides, ever-use of gasoline to clean hands or equipment, and ever-use of other solvents for cleaning). Depressive symptoms were measured using the Center for Epidemiologic Studies Depression Scale (CES-D). Various neurobehavioral functions, including attention, visual scanning/processing, motor speed, motor coordination, learning, memory, and motor speed/scanning were evaluated using a battery of nine tests administered by trained professionals. Multivariable linear regression was employed to estimate the association between each measure of pesticide exposure and solvent exposure and CES-D score; as well as each measure of solvent exposure and performance on each neurobehavioral test.

Results: Direction of associations between pesticide exposure measures and CES-D score were inconsistently positive and negative. However, few specific pesticide measures were found to be significantly associated with CES-D score (p

Conclusions: Results from the current study may suggest relationships between neurotoxic chemicals, such as some pesticides and organic solvents, and mental/neurobehavioral health outcomes that exist on a linear scale. This study serves as a justification for further research as well as early behavioral interventions in agricultural workers. That is, because subtle changes in central nervous system function can occur with exposures that may exist on a sub-clinical level, efforts should be taken to minimize exposure and prevent further progression that could eventually lead to clinical disorders.

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