(JTA) — Two Jerusalem girls died after inhaling the fumes of a powerful pesticide.

Avigayil and Yael Gross, two and four years old respectively, died Wednesday from breathing in the fumes of a pesticide which an exterminator had left inside a room in their home.

The room was supposed to be sealed but fumes may have leaked, according to a report on the news site Ynet. They were buried Thursday.

The toxin, phosphine, also affected the girls’ two brothers, Michael and Yitzchak, five and seven years old, who are still in critical condition at the cardio medicine department of the Schneider Children’s Medical Center near Tel Aviv, according to Channel 2 news.

The parents of the children brought them to a doctor Tuesday because of diarrhea and vomiting but medical staff failed to diagnose their condition as poisoning and prescribed paracetamol to reduce pain and fever, Channel 2 reported. The parents called an ambulance the following day when one of the girls stopped breathing in their apartment in Givat Mordechai, a neighborhood of Jerusalem.

Doctors at the Schneider medical center have no prior experience with phosphine and cannot offer any specific antidote, according to Dr.Efrat Baron-Harlev, the center’s deputy director.

The exterminator, a man with 30 years of professional experience, is being held by police pending an investigation to determine whether there is grounds to for prosecution on criminal negligence, according to Channel 2’s website.