While it's not uncommon for individual agricultural employees to become ill from chemical exposure, the recent cases involving larger numbers of workers alarmed advocates.
"Anytime a group of people are poisoned, that's a concern," said Margaret Reeves, senior scientist at the Oakland-based Pesticide Action Network.
The chemicals that may have gotten workers sick in the Watsonville case were Pristine Fungicide, Rally 40WSP, DiPel-DF and Widespread Max.
Some of those chemicals can interfere with reproductive and endocrine systems and can irritate skin and eyes, according to Reeves.
"Pesticides travel far from where they're applied in concentrations that can cause people to get sick or even, over a long time, chronically ill permanently," said Mark Weller, co-director of Californians for Pesticide Reform. "The same kind of thing could have happened near a school."
"It's very sad," said Jeannie Economos, an activist at the Farmworker Association of Florida. "Some of these pesticides can cause long-term health consequences."
The incidents in Watsonville and Salinas are under investigation by the agricultural commissioners in Santa Cruz and Monterey counties.
In California, the state's division of Occupational Safety and Health (Cal/OSHA) does not investigate incidents in which farmworkers get sick from chemical releases.
A spokesman for the Department of Pesticide Regulation emphasizes that it's protocol for county agricultural commissioners, not state regulators, to lead investigations into such cases.
In the Watsonville incident, Santa Cruz County agricultural commissioner Juan Hidalgo, who's leading that county's probe, is refusing to release the name of the company under investigation.
Hidalgo said Wednesday that his office is conducting interviews into the incident.
"We hope to conclude interviews late next week, at which point I would be able to release the name of the operation under investigation," he said.
That lack of disclosure outraged activists and experts.
"That is a key piece of information that one would expect to be able to have access to," said Reeves of the Pesticide Action Network.
"I was surprised that an investigative agency was not providing the name of the firm," UC's Shaiken said. "Transparency is essential in any investigation of this type. Knowing the identity of the company is important."
"It shows that the growers are on the defensive," said Economos at the Farmworker Association of Florida.
In Monterey County the agricultural commissioner early on identified Tanimura & Antle as the company it's investigating in connection with the incident that hospitalized 18 celery workers on June 22.
A spokeswoman for the company said this week that the firm is eager to see the results of the investigation.
"The health and safety of our workers is our primary concern," said Samantha Cabaluna.
She noted that while 18 workers were hospitalized, not all of them showed symptoms of exposure.
The California Farm Bureau Federation, an industry group that represents farmers and ranchers in almost every county of the state, says it supports "prompt, consistent penalties for incidents in which pesticides are misused in ways that cause public or environmental injury," according to the organization's spokesman, Dave Kranz.
"Our organization also supports continuing education of pest control advisers and applicators in the safe and effective use of pesticides. Applicators and field employees currently undergo training on an annual basis," Kranz said.