California regulators have ruled that farmers must restrict their use of chloropicrin, a toxic pesticide widely used to prepare soil for planting.

Credit: Sam Hodgson for CIR

This week, California regulators ruled that the state’s farmers must restrict their use of chloropicrin, a toxic pesticide widely used to prepare soil for planting.

The new controls set by the California Department of Pesticide Regulation are intended to protect farmworkers and pesticide applicators who work closely with the tear-gas-like chemical, as well as people who live and work nearby. The state is imposing wider buffer zones around fields where the chemical is applied and smaller restrictions on how many acres can be fumigated at once. Growers also will be required to give 48 hours’ notice, instead of the usual 24 hours.

Chloropicrin is injected into soil as a gas, and it has the potential to drift off-site. Exposure can cause eye irritation and watering and respiratory trouble. It was used during World War I as “vomiting gas” because it could penetrate gas masks and force soldiers to pull them off to throw up and expose themselves to other toxic chemicals.

After the war, America had a surplus of chloropicrin. That’s when farmers realized it made a great pesticide.

To get an idea of how reliant farmers are on this pesticide, we analyzed the state’s Pesticide Use Reporting data. And the numbers are striking: California’s use of chloropicrin increased 650 percent from 1991 to 2012.

How did this happen? The spike in chloropicrin use came as the U.S. phased out methyl bromide, a fumigant that contributes to depletion of the ozone layer.

Chloropicrin applied in California |Crear infográficos

In 2012, the most recent data available, California growers used 8.7 million pounds of chloropicrin on fields. The bulk of it went to strawberry crops, but it also is commonly used for growing raspberries, peppers, tomatoes and lettuce.

Ventura County accounts for almost one-third of all chloropicrin applied in the state. Monterey County is the next biggest user, followed by Santa Barbara. Fumigant use in California overall is on the rise. In November, The Center for Investigative Reporting revealed how California’s strawberry industry is hooked on fumigants such as chloropicrin, 1,3-Dichloropropene and others.

This story was edited Robert Salladay and copy edited by Nikki Frick.

Rachael Bale can be reached at Follow her on Twitter: @Rachael_Bale.

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Rachael Bale is a reporter and researcher for The Center for Investigative Reporting. Previously, she worked at KQED in San Francisco and The Center for Public Integrity, an investigative journalism nonprofit in Washington, D.C., where she covered campaign finance in the 2012 election. A California native, she has a bachelor's degree in political science from Reed College and a master's degree in journalism from American University.