The FQPA attempts to safeguard both workers and consumers from excessive pesticide exposure.

Pest problems and management vary widely throughout the country based on climate, soil types, and other conditions. One element of pest management is chemical pest control, which has a central place in modern agriculture.

Chemical pest control has contributed to the dramatic increase in crop yields in recent decades for most major field, fruit, and vegetable crops. The use of pesticides has allowed growers to produce crops profitably in otherwise unsuitable locations, extend the growing season, maintain product quality, and extend product shelf life.

Over the past few years, however, new regulations have been introduced in an attempt to safeguard the health of those who work regularly with various pesticides. Specifically, a landmark regulation signed on August 3, 1996, the Food Quality Protection Act (FQPA), amends, updates, and resolves inconsistencies between the two major, previously existing, pesticide laws, the Federal Insecticide, Fungicide, and Rodenticide Act (1972) and the Federal Food, Drug, and Cosmetic Act (1938).

Risk Assessment
The FQPA establishes a safety standard for pesticide residues in raw and processed foods that requires the Environmental Protection Agency (EPA) to consider aggregate exposure in its decision-making processes. Additionally, the FQPA requires periodic reevaluation of pesticide registrations and tolerances to help ensure that the scientific data supporting these licenses remain up-to-date. The simple assessment schemes that were previously used to make these determinations are no longer adequate. With the FQPA, new models for cumulative risk assessment have been introduced, and considering how assessments are performed provides clues to the new methodology behind the registration process.

Pesticides are composed of a broad class of crop protection chemicals that include insecticides, herbicides, rodenticides, and fungicides. A risk assessment must be performed for each pesticide before registration. Risk assessment calculates the likelihood that an adverse health effect will result from exposure to a given concentration level of a particular chemical. The assessment includes four parts: hazard identification, dose–response assessment, exposure assessment, and risk characterization.

Hazards
Hazard identification involves the review and evaluation of a chemical’s toxic properties through the use of laboratory studies on animals by correlating exposure levels with observed health effects. Because the goal is to determine how much of a chemical causes a toxic reaction, laboratory animals receive a wide range of exposures, including doses higher than those to which people might be exposed. The highest single dose that will cause adverse effects, but not death, is called the “maximum tolerated dose”. The highest single pesticide dose that does not cause any observable harm or side effect is known as the No Observable Adverse Effect Level (NOAEL).

Once a NOAEL is determined, an additional safety factor known as a Margin of Exposure (MOE) is added to compensate for uncertainties in the process. Typically, a MOE of 100 is used; this number is based on the assumption that one safety factor of 10 will account for the differences between how humans and animals react to various chemicals, and subsequent multiplication of that factor by an additional 10 will take into consideration different human sensitivities to chemical irritants. Dividing the NOAEL by the MOE determines the “reference dose”—a number normally used to estimate the human toxicity of a pesticide that is defined as the amount of a pesticide residue that could be ingested daily over a 70-year lifetime without causing any cumulative ill effects.

Dose Responses
Dose–response assessments examine a chemical’s toxic properties and estimate the amount of the specific compound that could potentially cause an adverse effect. The analysis of a noncarcinogen, for instance, is analyzed with a dose–response curve. In the case of known carcinogens, however, it is assumed that an effect at any dose is possible and has the potential to develop into cancer.

Exposures
Exposure assessment uses toxicological studies to estimate an individual’s potential exposure to a pesticide at work, at home, or in food. These studies gauge exposure on an acute (one time), subchronic (one to three months), and chronic (long-term and lifetime) basis for each of the three main routes of exposure: oral, dermal, and inhaled.

Risks
Risk characterization combines all other assessments to determine the probability of an adverse effect resulting from pesticide exposure and ultimately determines the permissible exposure levels from which standards are derived. Once a pesticide is marketed, the EPA continues to monitor the health records of professional pesticide users and those working in pesticide production facilities.

Pesticide Handler Exposure
The EPA’s Agricultural Worker Protection Standard (WPS), 40 CFR Parts 156 and 170, is designed to protect workers from pesticide exposure. Criteria for handler activities, field re-entry restrictions, pesticide labeling, and more are specified by this standard.

Pesticide users are required by law to follow the instructions on pesticide labels. Certain pesticides can only be legally applied by certified and licensed applicators that risk fines and other penalties if they do not adhere to application instructions. WPS and FQPA also require pesticide users to be trained in mixing, loading, handling, and applying pesticides; the proper use of equipment and protective clothing; and workplace hygiene.

Occupational exposure levels are typically estimated using surrogate exposure data from the EPA’s Pesticide Handler’s Exposure Database, a listing that contains several measured dermal and inhalation exposure values. According to the EPA, it is the formulation, the method and rate of application, the percent of active ingredient, and the number of acres treated—not the chemical properties of the pesticide—that determine the dermal and inhalation exposure levels. Yet even when a worker is exposed, the NOAEL for a given pesticide is typically much higher than the actual exposure level. So how relevant are the established exposure levels?

In his presentation at the 2001 ACS Regional Meeting in San Diego, Robert Krieger of the Department of Entomology at the University of California, Riverside, stated that it is riskier “to set a pheromone trap [in a tree] than it is to pick the apple [from that tree]—but that’s not the perception. Risk assessment starts with a hazard assessment by toxicologists who determine the level at which there is no observed effect, but the public assigns a biological risk to this nothing number.”

At the same meeting, H. Erdal Ozkan of the Food, Agricultural, and Biological Engineering Department at Ohio State University added that another problem with worker exposure is the application equipment. “Many highly effective pesticides are disappearing from the market due to stringent regulations, which usually result from application and handling mistakes. For example, labels on pesticide containers indicate the proper application rates. However, these rates can be achieved only if the application equipment is suitable for the job, calibrated frequently, and operated properly.

“Regulatory guidelines in the U.S. indicate that the application should be within 5% of the recommended label rate,” he continued. “Evaluation of hundreds of sprayers in several states indicates that pesticide accuracy continues to be a problem in the U.S. and new strategies to educate pesticide applicators should be discovered.” Ozkan observed that the part of the pesticide applicator education program associated specifically with selection, operation, and calibration of application equipment receives inadequate attention. “While some states address the topic adequately, most others allocate only 30 minutes to cover application equipment.”

Solving the Problem
If the regulatory goals are improved risk mitigation for workers and sound science, is the FQPA solving the problem? Not according to Krieger. “Absorbed dosage is the chemical part of the risk,” he states. “What does it mean? What is exposed risk? Contact?”

Krieger stresses that there is a difference between available residue and biologically available residue. Currently, risk assessments are based on calculations derived from environmental factors only. Krieger suggests, however, that the risk assessment should be calculated using biological indices. “Exposure estimates [that] are not based upon biological monitoring tend to overestimate the magnitude of worker exposure, prolonging the perception that workers are doing their jobs under harmful conditions,” he summarizes. “This perception is incorrect based upon our previous monitoring experience . . . [and] gives workers, the public, insurance carriers, and the regulatory community a very negatively biased view of what happens when pesticides are used.”

Concerns about worker exposure center not only on whether training and equipment are adequate, but also on whether the reference dose level is based on appropriate scientific calculations. Without the substantiation of long-term results, it is difficult to know whether exposure levels are relevant. Thus, several of the assumptions involved in the mitigation of pesticide risk to workers have been questioned. Although pesticides have been shown to cause adverse health effects, for the risk assessment to be valid, the science behind the risk assessment must be sound and Krieger, among others, believes that the present worker exposure levels based on passive dosimetry are too high.

Standards and regulations are in place to protect the pesticide worker as much as possible. The weakness in pesticide risk mitigation centers on the validity of the measurements used in hazard identification. Yet there is no risk-free future, no matter what the technology or the means of measuring exposure. The best future will be one in which an informed and prudent risk-assessment process prevails.