EPA believes that the children are the future, at least according to the new chlorpyrifos assessment

By Savannah Volkoff and Eileen Thorsos

In December 2014, EPA released an updated health risk assessment for the chemical pesticide chlorpyrifos. Chlorpyrifos has been on the EPA’s radar since 2000, when the EPA began taking action to limit the use of and human exposure to chlorpyrifos. The new assessment considers exposure via multiple sources as well as exposure to vulnerable populations and highlights potential risks to workers who use chlorpyrifos or work in greenhouses or fields after chlorpyrifos is applied. The new assessment kept the Food Quality Protection Act’s 10x safety factor that is used to protect children and sensitive populations.

What is chlorpyrifos?

Chlorpyrifos is a type of organophosphate insecticide that can also be used to treat ticks, mites, and nematodes. You can learn more about chlorpyrifos by reading the National Pesticide Information Center’s fact sheet.

Why is chlorpyrifos a health concern?

Scientists in our own Duke Superfund Research Center have found chlorpyrifos to be risky to brain development in infant animals. Let’s dive right into some of that science, with the disclaimer that it might get a bit confusing. Stick with me!

Acetylcholine is a major neurotransmitter vital to the proper functioning of our nervous system. It also plays a role in our ability to see, hear, and focus our attention. Chlorpyrifos prevents the enzyme acetylcholinesterase from doing its job – clearing acetylcholine from the synapses between two nerve cells. When chlorpyrifos or other organophosphate insecticides prevent this enzyme from functioning properly, the nerve cells become overloaded with acetylcholine. High doses of chlorpyrifos can poison people, leading to confusion, sweating, muscle twitching, trouble breathing, and other neurological problems due to the buildup of acetylcholine between neurons.

These scientists, Dr. Ted Slotkin, Fred Seidler, and Dr. Ed Levin, have investigated what happens when young animals, whose brains are still forming, are exposed to much lower doses of chlorpyrifos (doses that are lower than what is normally used in toxicology studies) at sensitive times for brain development. Our research has demonstrated that at these low doses, chlorpyrifos may also affect other neurotransmitters, including serotonin, another neurotransmitter. Such exposures seem to change how the nerve systems in these animals form connections. As the exposed animals grow older, they have poorer memory, may be more depressed, and may be hyperactive.

How does the EPA determine risk?

According to the webpage explaining the updated chlorpyrifos risk assessment, EPA assesses exposure “from multiple sources including those from food, drinking water, pesticide inhalation and absorption of the pesticide through the skin for all populations, including infants, children and women of childbearing age.” EPA uses the results from the exposure studies in a mathematical model that predicts the chemical’s effect on a wide range of people with different traits (sex, age, genetics, etc.).

From these models, EPA determines an exposure level considered low enough that it does not cause harmful symptoms in people. Then, EPA sets standards for different routes of exposure (such as pesticide application, re-entry to an area after an application, or food residue), including a safety buffer beyond the estimated acceptable exposures.

How is the December 2014 assessment different from previous assessments?

This update responds to public comments received from a risk assessment completed in June 2011 and  considers exposure via multiple sources as well as exposure to vulnerable populations. In addition, the new assessment highlights potential risks to those who directly handle chlorpyrifos, such as pesticide applicators, or those who work in greenhouses or fields after chlorpyrifos is applied.

In 2011, EPA considered relaxing the standards for the amount of chlorpyrifos residue allowed to remain on food. Based on recent studies on the effects of chlorpyrifos exposure during brain development, including multiple studies by Duke researchers, EPA found enough potential for neurological effects from low exposure to chlorpyrifos to keep the current, stricter standards. These stricter standards are specifically designed to protect developing infants and children.

Timeline of EPA action on chlorpyrifos:

  • In June 2000, the Agency eliminated all homeowner uses, except ant and roach baits in child resistant packaging.
  • In 2000, EPA required that all use of chlorpyrifos products in the United States be discontinued on tomatoes. The use on apple trees was restricted to pre-bloom and dormant applications. The grape tolerance was lowered to reflect the labeled dormant application.
  • In 2002, EPA restricted the use of chlorpyrifos on citrus and tree nuts as well other crops.
  • In 2012, EPA further limited the use of chlorpyrifos by significantly lowering pesticide application rates and creating “no-spray” buffer zones around public spaces, including recreational areas and homes.

(Taken directly from the EPA webpage, “Revised Human Health Risk Assessment on Chlorpyrifos”)


Public comments on the December 2014 revisions have been open since January 14, 2014 and will remain open until March 16, 2015. To submit a comment, follow this link.