The state Department of Agriculture has turned over to the federal government its report on workers sent to a Kauai hospital after entering a Syngenta Inc. cornfield sprayed with a powerful pesticide.

While the results of its investigation were not disclosed, the department said it was taking the incident “very seriously” as a possible violation of workplace protection standards.

Dean Higuchi, spokesman for the Hawaii office of the U.S. Environmental Protection Agency, confirmed that the agency received the results of the state investigation.

“It is an open investigation with us,” Higuchi said Tuesday by email. “We cannot comment any further.”

The last time the agency received an investigation from the state was in 2011, when Kamaaina Termite & Pest Control was fined $17,000 for misusing a fumigant called Vikane, he said.

The state Department of Agriculture’s Pesticide Branch has been the lead investigator in the Kauai incident, with state health and labor safety officials providing technical advice and help.

Syngenta sent 10 farmworkers to a hospital Jan. 20 after they entered a cornfield that had been sprayed with the pesticide chlorpyrifos. Syngenta station manager Josh Uyehara said some employees returned to work the next day and that all 10 workers were back to work five days following the incident.

“All were cleared by physicians to return to work with no medical follow-up required,” Uyehara said.

Uyehara said the workers were in the field for a short period, less than 15 minutes, based on their statements.

He said chlorpyrifos was applied to the cornfield to control insects.

Uyehara said workers are supposed to wait 24 hours before entering a field that has been sprayed with chlorpyrifos but that they entered the field after 20 hours.

He said that after the incident, management instituted a review of field re-entry procedures and were awaiting a final report on the investigation by the state.

“We will take into account any recommendations and observations, when we receive the final HDOA (Hawaii Department of Agriculture) report,” Uyehara said.

The restrictions imposed on the use of chlorpyrifos, registered by Dow Chemical in 1965, have tightened over the 16 years. The EPA said chlorpyrifos can overstimulate the nervous system, causing nausea, dizziness, confusion and, at high exposure, respiratory paralysis and death.

The pesticide is a gray powder that is mixed with other chemicals, including calcium polysilicate, Kaolin, titanium dioxide and silica.

Both titanium dioxide and silica are listed as carcinogenic to humans.

Chlorpyrifos also can be acutely toxic to fish, depending on the dose.

The EPA banned residential use and use on tomatoes in June 2000. In 2002 the agency restricted the use of chlorpyrifos on citrus and tree nuts as well as other crops.

Agency officials in 2012 further limited chlorpyrifos’ use by lowering pesticide application rates and creating “no-spray” buffer zones around public places, including recreational areas and homes.

Fenix Grange of the state Hazard Evaluation and Emergency Response Office said chlorpyrifos is under EPA review with the possibility that it might no longer be allowed on any produce. Officials said they are worried about people drinking water from small water systems in heavily farmed areas where chlorpyrifos is used.

Dow Chemical spokesman Garry Hamlin, noting that the proposed ban was prompted by a 9th Circuit Court case, said Dow disagrees with the EPA’s proposal and remains confident that all issues related to the use of chlorpyrifos can be resolved with a more refined analysis.

“EPA’s drinking water assessments … are based on hypothetical, worst-case-scenario modeling of surface water runoff,” Hamlin said, adding that the EPA’s projections run contrary to real water monitoring data.

Fear of the impact of agricultural pesticides near residential areas has prompted some Hawaii residents to favor establishing a minimum buffer zone between pesticide-treated fields and residential areas and schools.

The state Department of Agriculture has opposed establishing buffer zones, saying pesticide use is based on scientific testing through the EPA’s pesticide registration review process.

Department officials say the buffer zone restrictions are already addressed by the EPA.

Earlier this year a state House bill calling for buffer zones was deferred by two committees.

According to EPA, an estimated 8 million pounds of chlorpyrifos is used annually in agriculture, notably on apples, broccoli, onions and cauliflower. Corn accounts for 1 million pounds a year, while soybeans account for nearly 2 million pounds.

It’s also used in nonagricultural settings such as nurseries and Christmas tree plantations, and on golf course turf.