Why you should care about a chemical you’ve never heard of? The case to ban Chlorpyrifos

500 Women Scientists
6 min readAug 25, 2017

500WS Environmental Strike Team

Lead Authors: Dr. Judith Weis and Jewel Lipps

Have you heard of the pesticide chlorpyrifos? Whether you have or not, there is a good chance that you and your family have come in contact with this harmful chemical, as the residues of chlorpyrifos applied to crops contaminate our food and drinking water. The Environmental Protection Agency’s (EPA) risk assessors have determined that even low exposure to this toxic chemical can have negative neurodevelopmental effects [a], but the current administration and EPA head Scott Pruitt refuse to finalize its ban. Fortunately, congress introduced of a new bill in July, SB1624, The Protect Children, Farmers & Farmworkers from Nerve Agent Pesticides Act, which will ban chlorpyrifos use on food crops. This legislation would be a major step toward eliminating the use of a dangerous nerve agent in the agriculture industry. Here, we outline key human health and environmental issues with chlorpyrifos and make the case for why it should be eliminated.

Just what is Chlorpyrifos?

Chlorpyrifos is a pesticide sprayed on the surface of food crops — specifically, it is an organophosphate insecticide used to kill insect pests systemically and on contact. It inhibits the enzyme acetylcholinesterase (AchE), which means death for insects and thus the prevention of crop harm and loss that can be a hardship for farmers.

In the U.S., roughly 6 million pounds of this pesticide were used on around 10 million acres between 2009 and 2013. Soybeans, corn, alfalfa, oranges and almonds top the list in terms of pounds of chlorpyrifos applied. Farmers also applied chlorpyrifos to over 30 percent of their apple, asparagus, walnut, onion, grape, broccoli, cherry and cauliflower crops (FactCheck.org).

The Danger

Chlorpyrifos is a potent neurotoxic agent that does not only affect the insects it is intended for. In 2000, EPA banned all homeowner use because its application on lawns and termites posed unacceptable risk to humans. Now, EPA scientists [1,2] have determined that even the very low levels of dietary and drinking water exposure to chlorpyrifos can damage children’s developing brains. Their analysis shows that residues of chlorpyrifos at the levels present on food crops exceed the safety standard under the Federal Food, Drug, and Cosmetic Act (FFDCA). In addition, the estimated drinking water exposure, including from non-food uses, also exceeds safe levels.

Children with prenatal exposure to chlorpyrifos have shown signs of reduced IQ, loss of working memory, and attention deficit disorders [b]. Adults poisoned by chlorpyrifos experience vomiting, muscle cramps, twitching, tremors and weakness- the National Pesticide Information Center provides an online Chlorpyrifos general fact sheet with details on exposure scenarios and symptoms.

Animals are also susceptible to the poison, including fish, birds and mammals.Many reported incidents of wildlife mortality were related to its use on lawns and use on golf courses, but since these uses were restricted by EPA, the danger to wildlife has been reduced [c].

Who is at risk

People can be exposed to and harmed by chlorpyrifos by eating food containing the residue of the insecticide, drinking water containing the residue, inhaling volatiles after pesticide application to crops, or getting the pesticide on their skin. If a pregnant woman is exposed to the pesticide, her unborn child may be exposed as well.

Once sprayed, the neurotoxic pesticide enters the environment at the site it is used. People who live near farms are at risk from the chemical drift after its application to crop fields. Latino families in the Central Valley of California report smelling the pesticide drift in their homes and are petitioning the State of California to ban the pesticide [4]. Agricultural workers who mix, load and apply chlorpyrifos are at risk- even with the maximum amount of personal protective equipment [d].

The EPA assessment demonstrates that the long-term risk from dietary exposure and drinking water exposure of chlorpyrifos residue put children and female adults at risk [e]. This toxicant causes permanent damage to unborn children (embryos and fetuses), thus the children experience neurological problems throughout their life.

What should be done

This dangerous chemical should be banned from being used on crops and our food. Banning chlorpyrifos is an essential step to ensuring full protection of children’s neurological health, the wellbeing of pregnant women and mothers, and the safety of farm communities.

Additionally, banning chlorpyrifos, one of the most common agricultural pesticides, throws open the door of opportunity for scientists to develop safe, environmentally responsible solutions to pest management on food crops. One of the leading innovators is Dr. Pam Marrone. In 2006, she founded Marrone Bio Innovations, a research and development company that has successfully developed effective pesticides from naturally occurring materials like plants and microorganisms [3]. In this short video, she explains her mission and shows her laboratory.

When scientific innovation is paired with a commitment to people’s safety and environmental responsibility, safe pest management options that work for farmers can be discovered. Chlorpyrifos should be banned- its use on food crops exposes people to a harmful nerve agent, and as Dr. Marrone shows us, using chlorpyrifos is a risk we don’t need to take.


a EPA risk assessments used a physiologically-based pharmacokinetic-pharmacodynamic (PBPK-PD) model to consider variations in a chemical’s effects on a person based on age and genetics and to predict how the same dose may affect various members of a large population differently. The human health risk assessment used dose-response data on acetylcholinesterase inhibition (AChE) in laboratory animals and also evidence from epidemiology that indicates effects may occur at lower exposures than indicated by the toxicology database. The 2016 revised human health risk assessment uses neurodevelopmental effects as the critical effect.

b In humans, neurotoxic effects of prenatal exposure to chlorpyrifos were evaluated in 228 children through the first 5 years of life. Previous reports showed widespread prenatal exposure, and significant adverse impact of high prenatal exposure on birth weight and birth length (Whyatt et al, 2004), and increased risk of developmental delay and symptoms of ADHD-like problems at three years of age (Rauh et al., 2006). Neuropsychological functioning at 5 and 7 years of age was evaluated in this same cohort (Rauh 2008). After adjustment for race/ethnicity, sex, maternal education, maternal IQ, prenatal secondhand smoke exposure, and measures of poverty, chlorpyrifos was significantly and positively related to attentional problems (distractibility and concentration difficulties) and hyperactivity (restlessness, fidgeting, and difficulty sitting still).

c EPA also examined effects on wildlife. The effects of chlorpyrifos have been studied extensively in many taxa, particularly fish and aquatic and terrestrial invertebrates. They considered over 1,400 ecotoxicity studies, including ~180 fish studies, 26 amphibian studies, ~ 330 aquatic invertebrate studies, 32 aquatic plant studies, 58 bird studies, 1 reptile study, ~160 mammalian studies, ~500 terrestrial invertebrate studies, and ~125 terrestrial plant studies. The residential uses have been eliminated; termiticide uses have been restricted; and the application rate on golf courses was reduced. Additionally, no-spray buffers around surface water bodies, as well as rate reductions for agricultural uses, further reduced the environmental burden of chlorpyrifos.

d EPA risk assessment used the PBPK-PD model to predict occupational exposure, that is, risk to people who live and work closest to the chemical. The results indicated that all occupational scenarios led to health risks of concern.

e EPA relied on USDA’s Pesticide Data Program monitoring data to determine how much chlorpyrifos residue remains on the food crops that women and children eat. EPA then input this data in the PBPK-PD model to predict the steady-state chlorpyrifos consumption of children and women who eat one meal a day of food that has low chlorpyrifos residue on it.


  1. Environmental Protection Agency, Revised Human Health Risk Assessment on Chlorpyrifos, https://www.epa.gov/ingredients-used-pesticide-products/revised-human-health-risk-assessment-chlorpyrifos
  2. Environmental Protection Agency, Biological Evaluation Chapters for Chlorpyrifos ESA Assessment, https://www.epa.gov/endangered-species/biological-evaluation-chapters-chlorpyrifos-esa-assessment#executivesummary
  3. Environmental Protection Agency, Review of Chlorpyrifos Poisoning Data, https://www3.epa.gov/pesticides/chem_search/cleared_reviews/csr_PC-059101_14-Jan-97_410.pdf
  4. Marrone Bio Innovations. 2011. Pam Marrone Recognized for Leadership & Innovation by NRDC. https://marronebioinnovations.com/wp-content/uploads/2012/10/110426.pdf
  5. McQuate, Sarah. California’s Farm Communities Mobilize to Ban Pesticide. The Mercury News, 20 Aug. 2017, www.mercurynews.com/2017/08/19/4725501/.
  6. Rauh, VA, R. Garfinkel, FP Pereira, HF Andres.et al. 2006. Impact of prenatal chlorpyrifos exposure on neurodevelopment in the first 3 years of life among inner city children. Pediatrics 118:
  7. Rauh, V.A. 2008. Effects of prenatal chlorpyrifos exposure on 5 and 7-year neuropsychological functioning. Epidemiology 19: S39-#40.
  8. Whyatt RM, V. Rauh, DB Barr, DE Camann et al. 2004 Prenatal insecticide exposures and birth weight and length among an urban minority cohort. Environ. Health Persp. 112: 1125–1132