( CNN ) A Delaware father is in stable condition and improving as his two boys remain in critical condition after they became sick -- perhaps from pesticide exposure , federal officials say -- during a trip to the U.S. Virgin Islands . Steve Esmond , his teenage sons and the teens ' mother fell ill more than two weeks ago in St. John , where they were renting a villa at the Sirenusa resort . The family has confidence in their medical professionals and is hopeful for a full recovery , according to a statement released Monday from the family 's attorney , James Maron . The teens ' mother , Theresa Devine , was treated at a hospital and released , and is in occupational therapy , Maron said . The U.S. Environmental Protection Agency said Friday that the presence of a pesticide at the rented villa in St. John may have caused the illnesses , which were reported to the EPA on March 20 . Paramedics were called to the villa , which the family was renting . Esmond was found unconscious ; the boys and their mother were having seizures , Maron said . The lawyer did not say who called the paramedics . Elias Rodriguez , an EPA spokesman , said the agency 's preliminary test results `` do show that there was a presence of methyl bromide in the unit where the family was staying . '' Exposure to methyl bromide can result in serious health effects , including central nervous system and respiratory system damage , according to the EPA . The use of the pesticide is restricted in the United States because of its acute toxicity . It 's not allowed to be used indoors . Only certified professionals are permitted to use it in certain agricultural settings . For example , the pesticide is injected into the soil of some U.S. strawberry fields , said Judith Enck , an EPA regional administrator . `` We trust that the strawberry producers are making sure that there 's not excess pesticide residue on strawberries , '' Enck said . `` You definitely want to wash them really good . `` This is a pesticide that 's been around for a long time , and ironically because of its impact and damage to the ozone layer , it 's being phased out because of the air impacts of this fumigant , '' Enck added . Field workers at a Connecticut nursery were poisoned by the chemical in 1990 , according to the Journal of Industrial Medicine . In 2011 , warehouse workers in California fell ill after exposed to grapes imported from Chile fumigated with methyl bromide , the U.S. Centers for Disease Control and Prevention said . Dr. Sanjay Gupta , CNN 's chief medical correspondent , said many parts of the world banned the chemical , a neurotoxin . The agent is to be used only outdoors . The chemical is also odorless and colorless , Gupta said . `` It 's not something that you would have any warning of , '' Gupta said . The chemical is often mixed with tear gas so people can be aware of its presence , he added . The EPA said it is working with local government agencies to investigate whether the family was made ill after a fumigation at the resort on March 18 and whether any environmental regulations or laws were violated . Enck , the EPA regional administrator , said paramedics were called early on March 20 . Sea Glass Vacations , which acts as a rental agent for several units at Sirenusa , said the unit directly below the one where the family stayed was recently treated for pests , but that the family 's unit was not treated . The company said it licensed an outside company , Terminix , for the pest control services . On Monday , it ended its contract with Terminix . In an email to CNN before the termination , a spokesman for Terminix wrote that the company is `` committed to performing all work ... in a manner that is safe for our customers , employees , the public and the environment '' and is `` looking into this matter internally , and cooperating with authorities . '' The U.S. Department of Justice has initiated a criminal investigation . `` Many questions remain why an odorless pesticide of this level of toxicity could be manufactured , distributed and applied in a residential area resulting in this family 's injuries , '' Maron said . The attorney added : `` The family is confident that the responsible parties will be brought to justice and held accountable . '' CNN 's Rob Frehse , Jean Casarez , Sara Ganim , Jason Hanna , Laura Ly and Michael Martinez contributed to this report .
Chemical damages ozone and is being phased out , though it 's used in strawberry fields , EPA says . A Delaware family becomes ill at a resort in the U.S. Virgin Islands . Preliminary EPA results find methyl bromide was present in the unit where they stayed .