Chlorpyrifos: A Persistent Pesticide Threat to Health and the Environment

Chlorpyrifos, a potent organophosphate insecticide, has long been used across the world for pest control in agriculture, households, and livestock management. While it helped increase food productivity, mounting scientific evidence over the past few decades has exposed its severe health and environmental risks. In 2025, the global community, under the Stockholm Convention on Persistent Organic Pollutants, is pushing for a complete ban on this toxic chemical due to its far-reaching consequences.

Chemical Identity and Properties

• Chemical Name: O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate

• Common Name: Chlorpyrifos

• CAS Number: 2921-88-2

• Molecular Formula: C₉H₁₁Cl₃NO₃PS

• Type: Broad-spectrum chlorinated organophosphate

• Physical Properties:

  • White, crystalline solid with a strong, unpleasant odor

  • Poorly soluble in water

  • Can persist in the environment for extended periods

• Mode of Action:
  Chlorpyrifos is a cholinesterase inhibitor that disrupts the nervous system of insects by preventing the breakdown of acetylcholine. This can also affect humans and other animals, causing neurotoxicity and developmental disorders.

Origin and Development

Chlorpyrifos was initially developed in Nazi Germany for use in chemical warfare. After the war, it was repurposed for agricultural use and later patented by Dow Chemical Company in 1966. It was first commercially introduced in 1965 as a pesticide for use in both agricultural and domestic settings. Over the decades, it became one of the most widely used insecticides globally due to its effectiveness against pests in crops like rice, maize, cotton, vegetables, and fruits.

Major Uses

• Agricultural Crops: Used to control a wide range of pests in rice, maize, cotton, sugarcane, and vegetables.

• Domestic Use: Previously used in termite control, household insect sprays, and mosquito repellents.

• Veterinary Products: Included in tick and flea collars for pets.

• Public Health Programs: Used for mosquito and vector control.

Although many developed countries have banned or restricted its use, chlorpyrifos continues to be used in many developing nations, including India, for crop protection and vector control.

Health Hazards and Human Exposure

Acute Effects

• Headaches, dizziness, blurred vision

• Nausea, vomiting, sweating

• Muscle twitching, respiratory distress

• In extreme cases, convulsions and death

Chronic Exposure and Developmental Risks

• Neurodevelopmental damage in children, including:

  • Reduced IQ

  • Memory impairment

  • Attention disorders (ADHD)

• Endocrine disruption

• Reproductive and fetal toxicity

• Potential links to certain cancers

The 2003 Indian Study on Breast Milk Contamination

One of the most alarming findings came from a 2003 study in Bhopal, India, where breast milk samples from mothers of infants under one month old contained chlorpyrifos levels of 230 µg/L. This was 41 times higher than the average levels reported in other global studies. This revelation sparked public health concerns about infant exposure to neurotoxins through breastfeeding, especially in vulnerable populations.

In addition to breast milk, chlorpyrifos residues were also found in:

• Human blood samples

• Water bodies

• Agricultural produce (vegetables and fruits)

These findings underscored the widespread environmental contamination and human exposure, particularly in India, where the pesticide remains in use despite documented harm.

Environmental Impact

Chlorpyrifos is now recognized as a Persistent Organic Pollutant (POP) due to its:

• Long half-life in soil and water

• Bioaccumulation in the food chain

• Toxicity to non-target species, including bees, fish, amphibians, birds, and soil organisms

It is frequently detected in rivers, lakes, and even remote ecosystems like the Arctic, demonstrating its ability to travel long distances through air and water. Chlorpyrifos also contributes to soil degradation and loss of biodiversity in agroecosystems.

Resistance and Misuse

Overuse of chlorpyrifos has led to pest resistance, particularly in species like:

• Diamondback moth

• Brown planthopper

• Aphids

• Mosquitoes

This resistance has prompted farmers to use higher-than-recommended doses, further aggravating the risks to human health and the environment.

Global Regulatory Status

Countries That Have Banned or Restricted Chlorpyrifos

• European Union: Fully banned in 2020 based on EFSA findings

• United States: Banned food uses in 2021; California banned all uses

• Canada, China, South Korea, UAE: Implemented bans or phase-outs

• Colombia, Kenya, New Zealand, and Vietnam: Prohibited import or domestic use

Countries Still Using It

• India: Though a 2020 draft order proposed a ban on 27 pesticides including chlorpyrifos, no official ban has been implemented. It remains one of India’s top-used pesticides on crops like paddy and cotton.

• Australia and parts of Africa and Southeast Asia: Still permit limited usage with varying regulatory frameworks.

The Stockholm Convention and Global Ban Proposal

In 2025, chlorpyrifos was proposed for inclusion in Annex A of the Stockholm Convention. Chemicals listed in Annex A are subject to a global ban without exemptions.

Key advocates during the 2025 Geneva meeting included:

• Dr. Emily Marquez (PAN International): Emphasized the link between chlorpyrifos and brain damage in children

• Alia Dianah (PAN Asia Pacific): Called for justice for vulnerable communities

• AD Dileep Kumar (PAN India): Shared findings on contamination across India

These experts urged countries to stop supporting exemptions and join the call for a complete, global prohibition of chlorpyrifos to protect human health, ecosystems, and the rights of future generations.

Safer Alternatives Exist

Numerous cost-effective and eco-friendly alternatives to chlorpyrifos are available, including:

• Biopesticides and botanical extracts

• Integrated Pest Management (IPM)

• Agroecological farming methods

• Mechanical and biological pest control techniques

Transitioning to these alternatives can protect farmers’ health, reduce soil and water contamination, and foster sustainable agriculture.

The Urgent Need for a Global Ban

Chlorpyrifos exemplifies how a chemical once hailed as a solution can become a widespread health and environmental threat. The neurotoxic impacts on children, the contamination of breast milk in India, and its persistence in ecosystems paint a compelling case for immediate global action.

A total ban under the Stockholm Convention, without exemptions, is not just scientifically justified, but morally imperative. As we confront overlapping crises of public health, environmental degradation, and climate change, eliminating legacy pollutants like chlorpyrifos is a step toward a safer, more equitable world.