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Hospital officials say a Texas woman is in critical condition a day after four of her children died and five other family members were sickened by an accidental poisoning under her home. Police officials in Texas say a criminal investigation is underway.

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A spokesman for University Medical Center in Lubbock says 45-year-old Martha Balderas of Amarillo is in critical condition Tuesday, a day after fire officials responded to the accidental poisoning.

BSA Health System in Amarillo says five patients are in stable condition at its hospital. Fire officials say they are Balderas' husband and four of their children. Fire officials said the three boys, ages, 7, 9 and 11, and a girl age 17, died Monday.

Amarillo Fire Capt. Larry Davis said Tuesday that the father told first responders he had spread a professional grade pest control pellet under the family's mobile home. Authorities later determined that phosphine gas was likely released when the father used a garden hose on Sunday to try to wash away the pesticide.

Davis says a professional certification or license is required to purchase the product, called Weevil-Cide. He says the father does not have that license. The father told first responders through an interpreter that he obtained the pesticide from a friend.

Police spokesman Officer Jeb Hilton says the department's special crimes unit is investigating because children were involved.

Chip Orton, emergency management coordinator for the city of Amarillo and Potter and Randall counties, says his staff is working with a number of state and federal agencies to decontaminate the home. The Texas Commission on Environmental Quality has hired a private contractor to help.

Fire officials say the father spread a commercial grade pest control pellet under the house and tried to wash some of it away with a garden hose. Poisonous phosphine gas was released as a result.

Orton says the gas typically casts off in about eight to 12 hours after it's been in contact with water, but personnel close to the home are wearing protective breathing equipment and hazmat suits as a precaution.

Medical experts who specialize in poison control say accidental poisonings from the active ingredient in the pest control substance that led to the death of four Amarillo children are not uncommon, but deaths from aluminum phosphide are rare.

Cynthia Aaron, the medical director for the Michigan Regional Poison Control Center at Children's Hospital of Michigan, says the doctors at the center see mostly adults with exposure issues to phosphine gas from aluminum phosphide because the pesticide is used in industrial shipping.

The American Association of Poison Control Centers reported 82 exposures to aluminum phosphide in 2015 with two deaths.