Farm workers, including growers and custom applicators, may routinely come into contact with pesticides through handling during pest management operations as well as during crop husbandry and harvesting activities. Due to this routine contact with pesticides that may occur over an entire season or across many years for such workers, it is important to ensure that safe-use practices are established so that exposure to any given pesticide is lower than allowable regulatory limits protective of human health.

Exposure Assessment and Protection

Establishment of safe work practices for handling of pesticides during agricultural operations is based on consideration of health standards for allowable exposures and determination of pesticide levels to which workers may be exposed. Current regulations, including the Worker Protection Standard , mandate that pesticide product labels include requirements for personal protective equipment (e.g., gloves, goggles, long-sleeved shirts), field reentry intervals, and specific instructions for mixing, loading and applying the products. These requirements are based on thorough review and evaluation of both exposure and effects data by the EPA.

In support of safe worker protection practices and the EPA assessments on which they are based, Dow AgroSciences has actively partnered with other companies in generating generic data for estimating exposures to pesticide handlers, applicators, and workers reentering treated fields. Through organizations such as the Agricultural Handlers Exposure Task Force and Agricultural Reentry Task Force , a rich database of worker exposure studies related to common agricultural operations for pesticide products (e.g., airblast spraying, aircraft spray loading, granular application via tractor, hand-pruning following application) has been generated and supplied to the EPA. In addition, Dow AgroSciences has conducted chlorpyrifos product-specific exposure studies for several common crop uses, and has also conducted surveys of farm practices to support EPA’s human health evaluation (e.g., how many pounds of product most typically applied, number of acres treated per day, type of spray equipment used). As a result, chlorpyrifos product labels include only use practices and worker protection requirements that have passed EPA’s rigorous assessment process. Examples of worker protection practices required for use of chlorpyrifos, as excerpted from the approved Lorsban® Advanced2 product label are shown below:

  • Mixers, loaders, handlers and applicators must wear coveralls over long-sleeved shirt and long pants and chemical-resistant gloves.
  • Users must not allow worker entry into treated areas during the crop-specific restricted entry interval (from 24 hours to several days) unless personal protective equipment required for early entry is worn.
  • Users must respect the preharvest interval, and may not apply the product within (from 1 to 21 or more depending on crop) days before harvest.

Exposure Monitoring

Biomonitoring methods offer means of determining the actual pesticide exposure levels of farm and manufacturing plant workers. The two most common forms of biomonitoring for chlorpyrifos exposures include analyzing:

  • Urine samples for traces of TCPy1, a by-product of chlorpyrifos metabolism in the body.
  • Blood samples for biomarkers of exposure (e.g., inhibition of the enzyme cholinesterase).

Biomonitoring can be used to assess exposure in worker populations to increase hazard awareness, identify unsafe work practices, and prevent sustained excess exposures that could potentially result in adverse effects. By itself, biomonitoring only provides a snapshot of a given chemical's presence or absence in the body at a single point in time. Therefore, it is an important part of the process to establish personal baselines for these workers, against which these “snapshots” can be compared.

The most commonly employed biomonitoring approach for chlorpyrifos among farm and manufacturing workers looks for cholinesterase inhibition, which is the most sensitive marker of exposure. For example, some state agencies or institutions, where farm workers repeatedly handle cholinesterase inhibiting pesticides such as chlorpyrifos, may require blood cholinesterase monitoring as a check of adherence to label precautions and good hygiene practices. Workplaces monitoring worker cholinesterase levels typically have established protocols that designate specific levels of plasma or red blood cell cholinesterase inhibition that trigger evaluation of individual work practices and/or temporary reassignment to other duties while cholinesterase levels are replenished. Extensive research and 45 years of experience demonstrate that employees who follow label precautions and observe good work practices with chlorpyrifos do not receive measurable depressions of red blood cell cholinesterase.

Further Resources – Worker Protection

EPA Worker Protection Standards:

CropLife Worker Protection:

State Pesticide Safety Programs:

Agricultural Handlers Exposure Task Force:

Agricultural Reentry Task Force:

Further Resources – Biomonitoring

Washington State Dept. of Labor and Industries – Cholinesterase Monitoring

North Carolina State University – Cholinesterase Monitoring

Cholinesterase Inhibition and Biomonitoring, Extension Toxicology Network

Garabrant, D.H. et al. “Cholinesterase inhibition in chlorpyrifos workers: Characterization of biomarkers of exposure and response in relation to urinary TCPy.” Journal of Exposure Science and Environmental Epidemiology, 2009, Volume 19(7):634-42.

1 TCPy or TCP (3,5,6-trichloro-2-pyridinol) is a product resulting from the breakdown of chlorpyrifos in soil, water, or the human body.
2 Lorsban® Advanced is a Restricted Use Product, for sale to and use only by Certified Applicators or persons under their direct supervision.