More than a half a century ago when Lyndon Johnson was President and telephones were stationary rotary devices, the pesticide chlorpyrifos was introduced into the market.

Chlorpyrifos seemed like an effective improvement over the existing chemistry and it quickly became one of the most widely used pesticides in the world.

It was extensively applied in California on farms and in homes until the early 2000's when the U.S. Environmental Protection Agency banned indoor applications due mostly to concerns about potential harmful effects on infants and children.

Today, while the use of chlorpyrifos on California farms has greatly diminished, slightly more than one million pounds are still applied annually on over two million acres, much of it by airplanes and air blasters.

We now understand that the use of chlorpyrifos can pose a potential threat to both human health and wildlife. It inhibits the activity of cholinesterase, an enzyme necessary for proper functioning of the nervous system. Chlorpyrifos is also highly toxic to fish and invertebrate species that are important to a healthy ecosystem. 

Several years ago, the Department of Pesticide Regulation’s air monitoring and surface water monitoring indicated that chlorpyrifos is moving off targeted crops. The Department decided in 2014 to make improvements in how chlorpyrifos is regulated and applied.

An important initial measure was to make chlorpyrifos a restricted use material which limits its purchase and application to those holding a restricted material permit. This greatly increases the oversight of its use by County Agricultural Commissioners, who enforce pesticide regulations at the local level.   

More recently, DPR medical toxicologists have completed a human health risk assessment for chlorpyrifos. The assessment builds on work done by the U.S. EPA and will guide DPR scientists as they develop additional protective methods to reduce off-site movement of chlorpyrifos.  

DPR understands that chlorpyrifos can be an important tool when reserved for especially challenging pest outbreaks. Unfortunately, however, it seems it is often used on a regular basis because it is inexpensive, powerful, and familiar.

Given the risks posed by chlorpyrifos use this should not be the norm. For most insect control, there are newer, safer alternatives that are just as effective as chlorpyrifos.

While DPR is working to make improvements in the use of chlorpyrifos, U.S. EPA is also scrutinizing how this pesticide is used. What is certain and what matters most is that DPR will continue to craft new policy based on the best available science to protect Californians and their environment as chlorpyrifos is applied.

In the meantime, I ask growers that currently use chlorpyrifos to ask themselves this question – Is there an alternative pesticide that will do the job?

Times change, technology changes, and our understanding of chemicals and their effects changes. On the other hand, pest pressures are constant and the importance of keeping people and our environment safe will always be a certainty.

All pesticides must be applied with thought and care, especially one such as chlorpyrifos where the negative consequences are so well understood.

(Note: This is an opinion-editorial submitted by California Department of Pesticide Regulation Director Brian Leahy).