Twenty farmworkers in Washington became ill after being exposed to new pesticides that drifted over from a neighboring field, the Centers for Disease Control announced in a new report. The pesticide mixture involved does not appear to have been associated with any reported illnesses before.

In April, cherry orchard workers in Douglas County were tying branches to trellises when workers at a neighboring pear orchard drove by on a tractor pulling pesticide sprayers. The sprayers contained a mixture of the pesticides novaluron, pyridaben and triflumizole. Within minutes, all 20 workers began feeling ill. Someone called 911. Emergency medical workers took five people to the hospital, and another 11 later sought medical care.

All 16 workers experienced neurological symptoms, including headache and paresthesia, a tingling, burning or prickling of the skin. Most of the workers also experienced stomach problems such as nausea, eye irritation and respiratory issues.

This incident brings up three issues, the CDC said:

  1. Off-target pesticide drift: Pesticide applicators can protect themselves, but those nearby didn’t. Pesticide drift is the most common cause of acute pesticide illness among farmworkers.
  2. Toxicity of new pesticides on the market: The CDC said previously published work on these pesticides indicated that they had not been associated with human illness before.
  3. Worker notification requirements: The cherry orchard was not notified that the pear orchard would be applying pesticides that day. Currently, federal guidelines require notification only to the workers on the farm where the pesticide will be applied.

The reported illnesses in this case are the first associated with pyridaben, novaluron and triflumizole. It is unclear if one pesticide is responsible or if the combination of the three is.

“The product label for pyridaben warns that it can be fatal if inhaled and that pesticide applicators and handlers are required to use extensive personal protective equipment, including air-purifying respirators,” the report says.

The National Academy of Sciences also released a new report that makes several recommendations to the California Department of Pesticide Regulation to improve its risk assessment process for pesticides to be registered in the state.

Reveal has been covering the effects of pesticides since November, including threats to farmworkers and the problem of pesticide drift.

This story was edited by 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.