A federal investigation into the recent sickening with a toxic pesticide of a U.S. family vacationing in the Virgin Islands found that the chemical has also been improperly used in Puerto Rico, the U.S. Environmental Protection Agency said Thursday.

Officials said documents suggest methyl bromide may have been improperly applied in various locations in Puerto Rico. EPA regional administrator Judith Enck said the agency and Puerto Rico's Department of Agriculture are investigating where and when the pesticide was used and how much was applied.

"The EPA is taking this very seriously," she said in a phone interview. "I can't tell you how widespread this is. ... We're very early in our investigation."

Enck said she is not aware of anyone sickened by methyl bromide in Puerto Rico. The EPA banned the chemical for residential use in 1984, primarily for health concerns.

Nancy Feliciano, agriculture department spokeswoman, said Puerto Rico officials would comment soon.

The chemical sickened a family of four from Wilmington, Delaware, last month in the U.S. Virgin Islands. Two teenage boys went into comas after being exposed at the Sirenusa Condominium Resort in Cruz Bay, St. John. The family was staying in the second floor of a unit whose first floor was sprayed with the pesticide to eradicate an indoor beetle that eats wood, officials have said. The family began having seizures and was flown to hospitals in the U.S.

Family spokesman James Maron did not immediately respond to a message for comment. He said in a statement last week that the boys remained in critical condition while their mother had been discharged and their father was recuperating.

The EPA has said a certified applicator working for Tennessee-based Terminix used the pesticide at the Virgin Islands resort. Sea Glass Vacations LLC, which rents units at Sirenusa, terminated its contract with Terminix last week. Terminix has said it is conducting its own investigation and is cooperating with the EPA.

EPA officials said Thursday the pesticide used in the Virgin Islands came from licensed distributors in Puerto Rico, where inspectors are visiting pesticide applicator companies, including Terminix.

"This has been prohibited since the 1980s," Enck said. "There should be no confusion."