A Quebec coroner could not formally identify the toxic substance that killed two sisters vacationing in Thailand more than two years ago, but in a report released Monday the coroner said the cause was likely accidental poisoning by phosphine gas.

The two sisters, 26-year-old Noemi Belanger and 20-year-old Audrey, were on vacation in Thailand in June 2012. Only 48 hours after they arrived, they were found dead in their hotel room on Phi Phi Island. At the time, local police said the sisters did not appear to have been murdered or robbed.

Hotel workers checked in on the sisters after not seeing them for two days, and found them dead in their beds with vomit all over themselves inside the room.

Quebec coroner Renee Roussel said that circumstantial evidence and toxicology expertise determined their deaths were most likely due to phosphine poisoning. Phosphine is a toxic gas often used as an insecticide. It’s the same substance responsible for the poisoning deaths of two young children in Fort McMurray, Alta. in February, after their family brought the pesticide back from Pakistan to kill bedbugs in their apartment.

“Phosphine is a cheap and effective pesticide, largely available in Asia,” said the coroner in her report. “And it kills anything that breathes.”

Roussel explained the substance leaves no traces, which is why it is so difficult to pinpoint it as the exact cause. Roussel also said it’s a banned substance for fumigating hotel rooms in Thailand, but it appears it might still be used.

Over 20 Western tourists have died in similar circumstances since 2009, said Roussel, with the same signs and symptoms. These deaths have never been explained, she said, although many countries are pointing to phosphine as the culprit.

A Thai medical examiner had previously said the sisters died of DEET poisoning. But Roussel said in her report that the Quebec coroner’s office concluded the DEET in the sisters’ bodies was not in high enough concentrations to kill them.

The coroner recommended that the Quebec Health Institute make travellers more aware of the deadly dangers of certain pesticides which can be found in hotels. Roussel also wants more education for travellers on how to prevent and deal with accidental poisonings.

The Quebec Health Institute said they are taking the recommendations into consideration and will create an awareness campaign specifically targeted at warning travelers about dangers from pesticides.

Roussel said phosphine is a restricted product and only allowed for use by accredited experts in Canada.

Health Canada issued a warning in February of what it calls the “extreme danger” of using unregistered pesticide products to kill bedbugs.

The sisters grew up in Pohenegamook, a town in eastern Quebec near the Maine border.

The two had meticulously planned their vacation in Thailand. Noemi was widely travelled, having studied in China, France and had also visited Vancouver, Toronto and London among other places. Audrey had been taking a year off from her studies to travel.

They were on a month-long trip and on their last leg of their tour in East Asia before they died shortly after arriving in Thailand on June 12, 2012.

Their father, Carl Belanger, said not a day goes by that he doesn’t think of his daughters.

“They were two girls that were full of life. They were hard workers and we miss them,” he said, adding that he hopes other travellers listen to the warnings in the coroner’s report and watch out for the use of pesticides in hotel rooms.

Coroner report on deaths of Belanger sisters