Chlorpyrifos is an insecticide that is a white crystal-like solid with a strong odor. It does not mix well with water, so it is usually mixed with oily liquids before it is applied to crops or animals. It may also be applied to crops in a capsule form. Chlorpyrifos is widely used in homes and on farms. In the home, it is used to control cockroaches, fleas, and termites; it is also used in some pet flea and tick collars. On the farm, it is used to control ticks on cattle and as a spray to control crop pests.

Structural diagram: National Institutes of Health

Fate & Transport

Chlorpyrifos enters the environment through direct application to crops, lawns, and pets

It may enter the environment in the home and workplace

It may also enter the environment through volatilization, spills, and the disposal of chlorpyrifos waste

Chlorpyrifos sticks tightly to soil particles

It does not mix well with water, so it rarely enters local water systems

Once in the environment, it is broken down by sunlight, bacteria, or other chemical processes

Exposure Pathways

Using it to control household pests such as fleas or cockroaches

Breathing air outside of homes where chlorpyrifos was applied to the ground around the foundation to control termites

Breathing air in a field where chlorpyrifos was sprayed on to crops

Touching soil in a field where it was sprayed

Breathing air near a waste disposal site which contains chlorpyrifos

Health Effects

Breathing high levels of chlorpyrifos results primarily on nervous system effects, such as headaches, blurred vision, and salivation. It has also resulted in unstable blood pressure, diarrhea, nausea, and muscle cramps. Ingesting very high concentrations of chlorpyrifos can cause paralysis, seizures, loss of consciousness, and death, while high concentrations can cause dizziness, runny nose, confusion, salivation, and rapid heart rate. It can also cause muscle weakness after the original symptoms have disappeared. It is not known whether chlorpyrifos can affect reproduction or cause birth defects in people. One animal study reported a decrease in the movement of sperm following exposure to chlorpyrifos, but it is not known if people would experience similar effects.

It is not known whether chlorpyrifos causes cancer in people. Animal studies have not shown that chlorpyrifos causes cancer. The EPA has determined that chlorpyrifos is a possible human carcinogen.

There is a general test that can be used to determine if you have been exposed to a group of insecticides, including chlorpyrifos. This test measures the activity of an enzyme called acetylcholinesterase in the blood. There is also a test which measures a metabolite, or breakdown product, of chlorpyrifos in the urine. This test is accurate for several days after the exposure to chlorpyrifos occurred.

Information excerpted from:

Toxicological Profile for Chlorpyrifos 1996

Agency for Toxic Substances and Disease Registry
U.S. Dept. of Health and Human Services