A West Kauai agribusiness operation sent 10 farmworkers to the hospital Wednesday after they were exposed to a pesticide that the U.S. Environmental Protection Agency is considering banning.

Josh Uyehara, Syngenta station manager on Kauai, said some workers on Wednesday entered a cornfield that had been sprayed 20 hours earlier with the pesticide. The recommended wait period for the pesticide is 24 hours.

The field had been sprayed with chlorpyrifos, which goes by the brand name Lorsban. Within a few minutes of being on site, a manager informed the farmworkers that they should not have entered the area, ushered them out and offered immediate access to medical care, Uyehara said.

Ten workers were taken by company vehicles to Kauai Veterans Memorial Hospital in Waimea, where some were treated and released that day. Others were kept overnight for observation, Uyehara said. Some have since returned to work, but others are expected to return Monday. He would disclose information about any symptoms they experienced, citing health privacy laws.

Chlorpyrifos can overstimulate the nervous system, causing nausea, dizziness, confusion and, at very high exposures, respiratory paralysis and death, the EPA says.

“Safety really is a priority for us,” Uyehara said, adding action was taken immediately.

The EPA eliminated all homeowner use chlorpyrifos in 2000 except for ant and roach bait traps in child-resistant packaging and fire-ant mound treatment. Its use as a termiticide was phased out. It was discontinued on tomatoes, and its use was later restricted on other crops. In 2012, it was significantly lowered for pesticide use and no-spray buffer zones were created around homes and public spaces.

The EPA has proposed revoking all uses of chlorpyrifos by Oct. 30. The matter is now undergoing registration review, which is a program that re-evaluates all pesticides on a 15-year cycle.

If revoked, EPA would have to cancel the registration for associated food uses, including crops such as corn, soy, broccoli, cauliflower, cabbage and citrus.

“Based on EPA’s current analysis, there do not appear to be risks from exposure to chlorpyrifos from food, but when that exposure is combined with estimated exposure from drinking water in certain watersheds, EPA cannot conclude that the risk from the potential aggregate exposure meets the (Federal Food, Drug, and Cosmetic Act) safety standard,” the EPA says on its website.

“EPA’s 2014 revised human health risk assessment showed the potential for risks in small watersheds with high concentrations of farming where chlorpyrifos may be widely used,” the EPA said. The agency has assessed two regions — the Pacific Northwest and the Southeast areas. Hawaii has yet to be assessed.

Syngenta is one of several large agribusinesses operating on Kauai that have been criticized by some residents for their use of pesticides and their cultivation of genetically modified crops.

Uyehara said he notified the Hawaii Occupational Safety and Health Office and the Agriculture Department about Wednesday’s incident.

An Agriculture Department official said the department was notified Thursday and is conducting an investigation to help determine what pesticide label violation(s) may have occurred. The department reported it to the Environmental Protection Agency Region 9.

Kauai County Councilman Gary Hooser said, “It is truly unfortunate that Syngenta continues to use this chemical even though the EPA has raised so many red flags.”

He said chlorpyrifos has been found in small amounts in the air at Waimea Canyon Middle School and in water in Kekaha Ditch.

Hooser asked whether the Kauai County Department of Water Supply will test the drinking water for chlorpyrifos, and the agency said it “will wait for the EPA to complete a drinking water analysis for the entire country,” as well as wait for the EPA to finalize its ruling on the chemical.

A joint fact-finding report, ordered January 2015 by the Agriculture Department and the Kauai mayor, is due out this month.

The field where the workers were exposed is on several hundred acres cultivated by Syngenta in an area called Mana Plains, which is 2 miles from the westernmost homes in Kekaha, Uyehara said.

The company grows a mix of conventional and genetically modified corn and soybeans, and that particular field grows seed corn, both conventional and GMO. Their fields are not involved in testing or developing pesticides.

“For us the bottom line is it is still registered in the state,” and making sure the company follows the product label, according to the federal guidelines, Uyehara said.

He said the EPA has a standard process and, at any given time, the EPA is reviewing many products.

Hooser said he has concerns that if migrant workers are used, they may leave after three months, and there is no monitoring of their health, and may not have the same protection as regular employees.

Uyehara said the company follows all labor requirements and are concerned for their workers’ welfare. The workers are contracted by a third-party company that provides farm laborers, most of whom are local. The agency exhausts local options before looking to migrant workers, typically from the West Coast, he said.

Uyehara said the company has 108 regular employees and anywhere from five to 200 third-party agency employees to perform seasonal fieldwork on Kauai.