EPA Allowable Exposure for Consumers

For more than 40 years, government authorities worldwide have regulated chlorpyrifos for the protection of human health by restricting authorized uses so that non-occupational exposures to the chemical would be too low to cause even a non-toxic change in particular blood enzymes. These enzymes (cholinesterases) are the most sensitive biological indicators of exposure to chlorpyrifos.

Cholinesterases are enzymes naturally produced by the body. In the brain or other nerve tissues, these enzymes are essential for proper nerve function. Cholinesterases are also found in red blood cells and in blood plasma, where they have no established bodily function. Cholinesterase in blood, however, is the first and most sensitive indicator of chlorpyrifos exposure — and it is the measure by which the EPA sets its exposure limits.

The following summarizes extensive evaluations of scientific data that the EPA undertook prior to renewing registrations of chlorpyrifos for continued use in 2000. Their regulatory review spanned 17 years of studies and indicated that exposures from authorized agricultural uses of chlorpyrifos — including exposures to children and pregnant women — offered a “reasonable certainty of no harm.”

This decision was reaffirmed by the EPA in 2006.

Allowable Exposure

Cholinesterases become inhibited (or inactivated) when they are exposed to a variety of naturally-occurring and manmade substances, including organophosphate insecticides like chlorpyrifos. When they are inhibited, these enzymes no longer regulate nerve function. Because the body is continually making these enzymes, cholinesterase inhibition occurs without signs or symptoms of toxicity unless exposures become too great.

Researchers generally agree that the inhibition of brain cholinesterase is the primary means by which chlorpyrifos exposure results in adverse effects.

However, inhibition of blood cholinesterase causes no signs or symptoms of adverse effect and occurs before brain cholinesterase is ever affected. Moreover, chlorpyrifos inhibits essentially all plasma cholinesterase and more than 30% of red blood cell cholinesterase before ever affecting brain cholinesterase and causing any signs or symptoms of toxicity.

Based on these findings, regulators have thus far concurred that restricting authorized uses to keep chlorpyrifos exposures too low to inhibit even blood cholinesterases provides an effective safeguard against the potential for toxic effects.

Standards vs. Exposures

How do the limits set by the EPA for chlorpyrifos exposure compare with actual exposures?

Based on a review of government and independent laboratory monitoring of thousands of people for the presence of the chlorpyrifos breakdown product, TCPy, in their urine, researchers have estimated that current U.S. non-occupational exposures to chlorpyrifos are less than 10 nanograms per kilograms of body weight (ng/kg/BW) per day. (Eaton et al., 2008)

The EPA set its health-based standard for acceptable chronic exposure to chlorpyrifos at 30 ng/kg/BW. The daily non-occupational exposures measured in volunteer subjects fell below 10 ng/kg/BW. This means that chronic, non-occupational chlorpyrifos exposures fall well within the EPA’s health-based standards.

Moreover, laboratory studies found that doses of up to 500,000 ng/kg/BW had no measurable effect. Even at exposures of 1,000,000 ng/kg/BW chlorpyrifos produced only non-toxic changes in the nerve enzymes typically tested for chlorpyrifos sensitivity.

The following graphic helps put the EPA’s safety requirements regarding chlorpyrifos exposure into perspective:

At the very top of the tower (320 meters high) would be the dose of chlorpyrifos needed to cause a non-adverse effect in an enzyme measurable in laboratory tests.

Halfway down the tower (160 meters high) would be the level shown to have no effect.

Only one centimeter from the base of the tower would be the EPA’s maximum allowable daily exposure from labeled use.

From this illustration, it is clear that the margin of protection available for the EPA’s registered uses of chlorpyrifos is very large.

These margins have been established by the EPA based on extensive research and testing and are intended to provide ample protection not only for the population at large but also for potentially sensitive subgroups such as women and children. Read more about how the EPA sets its standards.

Five years after agreeing to a voluntary phase-out of the residential uses of chlorpyrifos in the U.S., Dow AgroSciences announced that it was discontinuing its regulatory support for the registration of chlorpyrifos for residential uses in all nations around the world.

Today, Dow AgroSciences focuses its chlorpyrifos business on agricultural uses of the product. These uses were found by EPA to meet the U.S. legislative standard of posing “a reasonable certainty of no harm,” and the product remains registered for agricultural uses in more than 100 nations, where it continues to offer significant value to growers.

Widely used and extensively studied for decades, chlorpyrifos has registrations worldwide supported by an extensive proprietary and published database. More than 5,000 studies and reports have been conducted evaluating chlorpyrifos in terms of human health and the environment.

No other pest control product has been researched more thoroughly.

U.S. vs. Other Nations

The EPA’s standards for acceptable chlorpyrifos exposure are the most stringent of any nation registering the product. The EPA’s standard is 300 times more restrictive than the one set by the World Health Organization and 100 times more restrictive than the standard set by Australian regulators.