Farm Worker Safety

Farm workers come into daily contact with pesticides, often over periods of years. Their health and safety is of great importance not only to Dow AgroSciences and the Environmental Protection Agency (EPA) in the United States, but also to regulatory agencies and research organizations around the world, including the World Health Organization (WHO).

Farm workers can potentially have greater exposures to pesticides than the general population, and this can occur over periods of years.  Therefore, it is important to ensure that safe-use practices are established and monitored so that the amount of any given pesticide absorbed is too low to cause health issues. Requirements for personal protective equipment, field reentry intervals, and specific instructions for mixing loading and applying the products are required based on thorough review and evaluation by the EPA. Some states, where farm workers repeatedly handle cholinesterase inhibiting pesticides, such as chlorpyrifos, also require other methods for monitoring the health of the workers.

Biomonitoring Studies

One of the methods sometimes used for monitoring the health of farm and manufacturing plant workers is biomonitoring. Biomonitoring involves analyzing blood or urine samples for:

• Traces of TCPy¹, a by-product of chlorpyrifos breaking down in the body or in the environment.
• Biological changes from exposure (usually inhibition of the enzyme cholinesterase).

Government biomonitoring studies have reported the presence of trace levels of the chlorpyrifos breakdown product TCPy in most samples of human urine analyzed in the U.S. This is not surprising, given that the EPA does allow minute levels of chlorpyrifos to be present in food. (see Consumer Safety.)

Unfortunately, some pesticide critics misinterpret or misuse biomonitoring data and equate pesticide presence in the body at any level to an unacceptable health risk. This has generated controversy and public concern. Government researchers who conduct biomonitoring studies are generally quick to point out, however, that the detectable trace-level presence of pesticides, their breakdown products, or other trace contaminants in bodily fluids, such as urine, is no indication that these compounds are causing harm or that the levels found have any significance for human health. The Center for Disease Control (CDC) stated in a report published in 2005²:

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.

Protecting Workers

Biomonitoring can have a number of positive effects in the workplace, including increasing hazard awareness, identifying unsafe work practices, and preventing sustained excess exposures that could eventually result in adverse effects. One important biomonitoring test looks for cholinesterase inhibition, which is the most sensitive marker for chlorpyrifos levels in the body.

When the cholinesterase enzyme is inhibited in the brain or nerve tissue, the tissue can no longer regulate nerve function. Symptoms include nausea and flu-like responses. Cholinesterase Inhibition can, however, occur in blood plasma and red blood cells without measurable adverse effect. (Blood and plasma cholinesterases have no established function, in the body.) Chlorpyrifos substantially inhibits blood cholinesterases before brain cholinesterase is ever affected. Before inhibiting brain cholinesterase, chlorpyrifos exposure inhibits essentially all plasma cholinesterase and more than 30 percent of red blood cell cholinesterase, without provoking any signs or symptoms of toxicity. Therefore, biomonitoring of blood cholinesterases provides an effective “early warning” for chlorpyrifos exposure levels. (See scientific research.)

Workplaces monitoring worker cholinesterase levels typically have established protocols that designate specific levels of red blood cell inhibition that trigger evaluation of individual work practices and/or temporary reassignment to other duties while cholinesterase levels are replenished.

Extensive research and 40 years of experience demonstrate that employees who follow good work practices with chlorpyrifos do not receive measurable depressions of red blood cell cholinesterase.