Risk Factors for Cholinesterase Depression among Pesticide Handlers

Principal Investigator: Matt Keifer, MD, MPH
Adjunct Professor, Env. and Occ. Health Sciences
University of Washington

NIOSH 2006-2011 

In 2004, the Washington State Department of Labor and Industries (WADL&I), under mandate from the Washington State Supreme Court, initiated a new cholinesterase (ChE) monitoring program for agricultural workers who handle toxicity class I or II organophosphate (OP) or N-methyl-carbamate (CB) pesticides. Although these investigations have revealed several potential risk factors, none of these factors have been confirmed through a comparison against work practices and conditions among a reference group of handlers who did not have depressed ChE activity. These characteristics of the newly established ChE monitoring program offer researchers an unprecedented opportunity to investigate determinants of overexposure to OP and CB pesticides. In this study, we identified and characterized risk factors for ChE depression among handlers participating in the Washington State ChE monitoring program.

In collaboration with local occupational medicine clinics in rural regions, 265 agricultural pesticide handlers were enrolled in this study. For each participant, the risk of ChE depression was evaluated with respect to workplace, behavioral, and genetic characteristics (paraoxonase or PON1 status). Findings identified the following risk factors being associated with BuChE inhibition: cleaning spray equipment, mixing/loading pesticides and not using a locker to store PPE. Protective factors were: wearing a full-face respirator and wearing chemical-resistant footwear. Identification of genetic susceptibility (PON1 status) in farm workers exposed to organophosphate pesticides. This is the first time that a study of a working population has demonstrated the validity of the assumptions behind PON1’s effect on pesticide overexposure susceptibility.

In 2009, the Committee on Pesticide Exposure Reduction (COPER) was founded to bring together representatives from the three state agencies with responsibilities related to occupational exposure to agricultural pesticides including the WA State Department of Agriculture, WA State Department of Health, WA State Department of Labor and Industries, and the PNASH Center.

Specific Aims

Aim 1. Enroll 50% of Washington State pesticide handlers who undergo repeat ChE testing in an ongoing crosssectional
Aim 2. Collect information about likely key risk factors for pesticide over-exposure from participating handlers.
Aim 3. Characterize PON1 status in blood specimens from each participant.
Aim 4. Determine which risk factors are associated with ChE inhibition, including workplace conditions, behavioral
factors, and PON1 status.
Aim 5. Evaluate the impact of educating workers and growers about risk factors for ChE depression.
Partners and Advisories
Central Washington Occupational Medicine
Department of Entomology and Environmental Toxicology, Washington State University
Farmworker Education Program, Washington State Department of Agriculture
Lourdes Clinic
Pesticide Incident Reporting and Tracking Panel, Washington State Department of Health
Scientific Advisory Committee, Washington State Cholinesterase Monitoring Program
WA Department of Labor and Industries
WorkCare, PLLC
Yakima Worker Care and Sunnyside Worker Care
UW Department of Epidemiology and Medical Genetics

Cholinesterase Inhibition | Buena Salud La Inhibicion del Colinesteraza
Good Fruit Grower, March 2009

Hofmann, J. N., Keifer, M. C., De Roos, A. J., Fenske, R. A., Furlong, C. E., van Belle, G., & Checkoway, H. Occupational determinants of serum cholinesterase inhibition among organophosphate-exposed agricultural pesticide handlers in Washington State. Occupational and Environmental Medicine. 2011 June 1;67(6), 375–386. http://doi.org/10.1136/oem.2009.046391. PubMedPMID: 19819864; PMCID: PMC2908529. 

Hofmann, J. N., Keifer, M. C., Checkoway, H., De Roos, A. J., Farin, F. M., Fenske, R. A., and Furlong, C. E. Biomarkers of Sensitivity and Exposure in Washington State Pesticide Handlers. Advances in Experimental Medicine and Biology. 2011 Feb 18;660, 19–27. http://doi.org/10.1007/978-1-60761-350-3_3. PubMedPMID: 20221867; PMCID: PMC3041670.

Hofmann-JN, Checkoway-H, Borges-O, Servin-F, Fenske-RA, Keifer-MC. Development of a computer-based survey instrument for Organophospohate and N-methyl-carbamate exposure assessment among agricultural pesticide handlers. Ann. Occup. Hyg. epub April 2010; Vol 54, No 6: 640-50. PubMedPMID: 20413416; PMC2918489.

Hofmann, J. N., Keifer, M. C., Furlong, C. E., De Roos, A. J., Farin, F. M., Fenske, R. A., Checkoway, H. Serum Cholinesterase Inhibition in Relation to Paraoxonase-1 (PON1) Status among Organophosphate-Exposed Agricultural Pesticide Handlers. Environmental Health Perspectives. 2009 June 9;117(9), 1402–1408. http://doi.org/10.1289/ehp.0900682. PubMedPMID: 19750105; PMCID: PMC2737017.