A Quebec coroner is challenging the autopsy findings of Thai officials that ruled two Quebec sisters found dead in their hotel room in June were accidentally poisoned.

Coroner Renée Roussel told Radio-Canada the concentration of the chemical DEET in the sisters' systems wasn't enough to be fatal.

That contradicts the conclusion of Thai authorities, who performed post-mortems on the bodies of Noémi Bélanger, 25, and Audrey Bélanger, 20, shortly after the sisters were found on June 15 by hotel staff.

A pathologist determined the women likely ingested DEET, a principal ingredient in bug repellant, in a euphoria-inducing cocktail that is popular among youth in Thailand.

The sisters from Pohénégamook, Que., had just arrived on Thailand's Phi Phi Island and were last seen partying with two Brazilian friends in the early morning of June 13.

Investigators said there were no signs of foul play in their hotel room, but there was evidence that the women may have suffered some kind of toxic reaction.

DEET levels not fatal

Dr. René Blais of Quebec's poison control centre said the DEET concentration reported by the Thai pathologist doesn't correspond to a concentration that would be toxic, "let alone a concentration that would be fatal."

It's still unclear what caused their deaths if it wasn't DEET poisoning.

Secondary autopsies were conducted in Montreal, but the results haven't been released.

Thai investigators haven't closed the case. They submitted their investigation report to the Canadian Embassy in Thailand without making the findings public.

Other mysterious deaths

In the last three years, a dozen vacationers have died under suspicious circumstances in tourist areas of Thailand and Vietnam.

In 2009, two young tourists, one from the United States and the other from Norway, who were staying at a guest house near the hotel where the Bélanger sisters were found, also died under mysterious circumstances.

Their deaths remain unsolved, but there was speculation the women had been poisoned.

Earlier on HuffPost:

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  • Phra Nang

    Near the holiday center of Krabi, the stunning Phra Nang beach is presided over by the massive limestone karst that stands in the shallow blue water just offshore. Because it is only accessible by boat, this bay stands out as one of Thailand's least crowded swimming spots. When not enjoying the gorgeous view, wander over and visit the Tham Phra Nang Nok or "Princess Cave," which local fisherman claim the cave houses, well, a sea princess. Makes sense. <strong>Where to stay</strong>: There is a large selection of resorts both cheap and expensive near the beach that offer easy transport and travel guides for exploring the Krabi islands. A good bet is the <a href="http://www.krabi-hotels.com/phrananginn/" target="_hplink">Phra Nang Inn</a>, which has an attached spa and rooms from $70. The only drawback is Ao nang is commercialized, so it make an excellent base for exploring but a poor "secluded getaway." <strong>Getting There</strong>: For those coming from the USA, book a flight from <a href="http://www.bangkokairportonline.com/" target="_hplink">Bangkok's Suvarnabhumi International Airport</a> to Krabi Airport, then hop on a local shuttle bus to Ao Nang. The ride takes about two hours. Photo: <a href="http://www.flickr.com/photos/bjvs/4528779911/" target="_hplink">plusgood</a>/Flickr

  • Ao Phang Nga Marine Park

    Ao Phang Nga Marine Park stretches over 150 square miles, encompassing a crowd of karsts and not a few tiny, gem-like beaches. You'll need a boat to get in, but the trip--reminiscent of a voyage to Vietnam's famed Ha Long Bay is more than worth it. Would-be spelunkers and SCUBA divers will also find themselves with option aplenty as toothy, stalactite filled caves and healthy reefs are common here. <strong>Where to Stay</strong>: Most of the non-camping options are on the mainland, where <a href="http://www.starwoodhotels.com/lemeridien/index.html" target="_hplink">Le Meridien Khao Lak</a> offers the most complete package for $150 plus. The crazy expensive option is the <a href="http://www.sixsenses.com/SixSensesYaoNoi/" target="_hplink">Six Senses Yao Noi</a>, the local offering of one of the world's great luxury hotel chains. (If you have to ask, it is too expensive.) Layered in bamboo, mosquito nettings and pressed sheets, this island paradise delivers the sort of pampering it is impossible to deserve. <strong>Getting There</strong>: Buses and Taxis service Ao Phang Nga from Krabi via Thailand's Highway 4. <a href="http://www.krabiairportonline.com/" target="_hplink">Krabi's airport</a> hosts frequent flights to and from Bangkok and several other regional hubs. Photo: <a href="http://www.flickr.com/photos/feserc/3214963854/" target="_hplink">feserc</a>/Flickr

  • Chaweng, Koh Samui

    One of Thailand's most popular beaches, Chaweng is very big and very busy. Sunbathers will be offered drinks and foods by wandering vendors, providing vacationers with a perfect opportunity to become totally inanimate. For those that save their energy during the day, there is always plenty to do at night. The town is renowned for its bustling main strip. What visitors here call a Tuesday night, most people would call a bender. <strong>Where to Stay</strong>: With its playful kindergarten meets pop art stylings, the <a href="http://www.akwaguesthouse.com/" target="_hplink">Akwa Guesthouse</a> offers sun seekers a playful and very cheap option for $25. The Anantara Lawana Resort and Spa, with its clear pool and shaded pavilions, offers a more traditionally lovely oasis for over $300. <strong>Getting There</strong>: Fly into <a href="http://www.samuiairportonline.com/" target="_hplink">Koh Samui</a> and grab a taxi for the short ride south. Photo: <a href="http://www.flickr.com/photos/14324493@N08/1452430688/" target="_hplink">royster00</a>/Flickr

  • Railay

    The sand is soft, the beach is wide and the locals are friendly. The only complication here, other than finding a boat to bring you, is a total lack of good reasons to leave. For those that manage to pull themselves off the beach, Railay is also famous for rock climbing and there are day kayak tours and full-day boat and snorkeling trips to Koh Poda available. <strong>Where to stay</strong>: Visitors can stay in Krabi and head out to Railay for a day at the beaches and rock climbing, or choose from an excellent assortment of resorts including the <a href="http://www.railaybayresort.com/" target="_hplink"><a href="http://www.railayvillagekrabi.com/" target="_hplink">Railay Village Resort</a></a>, the <a href="http://www.krabisandsea.com/" target="_hplink">Sand Sea Resort</a> and the recently renovated <a href="http://www.railaybayresort.com/" target="_hplink">Railay Bay Resort</a> (from $120, 100 and $90 respectively). <strong>Getting There</strong>: Regular long tail boat service from Ao Nang and Krabi makes this area quite accessible for those who don't mind a brisk motorboat ride. Photo: <a href="http://www.flickr.com/photos/argenberg/648596433/" target="_hplink">Argenberg</a>/Flickr

  • Haad Rin Beach, Koh Pha Ngan

    This heavily trafficked half-moon bay is famous (read: infamous) for its full moon parties, when thousands of revelers descend on the beach to dance to house music and alter their states. The monthly party attracts mostly a younger crowd that unfortunately leaves garbage cairns to mark their path. Nonetheless, the beach is located near a beautiful headland and makes for a relaxing stop so long as long as there is some waxing or waning going on. <strong>Where to Stay</strong>: There are tons of hostels of highly varying quality near the beach and hotels will fill up prior to the party so booking a room here can be a little tricky. A good bet is the<a href="http://www.bestwesternphanganburi.com/" target="_hplink"> Best Western Phanganburi Resort </a>($150), which is located in a quiet area and offers a quiet place to relax, or detox -- whatever you need. <strong>Getting There</strong>: There is a <a href="http://www.haadrin.info/ferry.php" target="_hplink">ferry service</a> between Haad Rin and Koh Samui as well as frequent pick-up taxis. Koh Samui has an airport that is serviced predominantly by flights from Bangkok and occasionally by flight from various cities in Malaysia. Photo: <a href="http://www.flickr.com/photos/togawanderings/4842371697/" target="_hplink">ToGa Wanderings</a>/Flickr

  • Kata Beach, Phuket

    This 12.5 mile gem provides an option for travelers eager to hit the beach, but less than thrilled about rubbing tribal-tattooed shoulders with the backpacker tribe that can dominate the southern island of Phuket. The nearby towns are not nightlife centers, but they have plenty of shopping for the whole family and even a <a href="http://www.dinopark.com/" target="_hplink">dinosaur-themed miniature golf course</a>. Where to Stay: The <a href="http://www.katagroup.com/katabeach/index.htm" target="_hplink">Kata Beach Resort and Spa</a> offers all the amenities of a Club Med, in a shiny gold-leafed package starting at $180 while the <a href="http://www.sugarpalmgrand.com/" target="_hplink">Sugar Palm Grand</a> nearby offers clean, modern lines in contrast to the verdant shore for a little less, $60 and above. Getting There: Flights from Bangkok, Kuala Lumpur and Singapore regularly land at <a href="http://www.phuketairportonline.com/" target="_hplink">Phuket's international airport</a>. Take a taxi to the beach. Photos: <a href="http://www.flickr.com/photos/edwin11/5730364074/" target="_hplink">edwin. 11</a>/Flickr

  • Koh Lanta

    Off Thailand's Andaman coast, in waters renowned for strange creatures and empty horizons, Koh Lanta has become a popular playground for Europeans looking to get beyond the backpacker scene. The larger of the two islands that share the name Koh Lanta is where the vast majority of visitors head to take advantage of broad white sand beaches, excellent diving and a picturesque coastline dotted with mangrove forest and backed by waves of forested hills. Visitors here can also witness the Sea Gypsy communities that still subsist just off the coast. <strong>Where to Stay</strong>: The <a href="http://www.thehouben.com/" target="_hplink">Houben Hotel</a> is an architectural marvel, with cantilevered pools sticking out over a modernist shell and over a neatly kept palm grove ($115). Another excellent option is the <a href="http://www.lantasand.com/" target="_hplink">Lanta Sand Resort and Spa</a> ($100 to $200 depending on room size and season). Request a room on the bottom floor so you can roll out of your bed and into the pool. <strong>Getting There</strong>: Use the express transfer, a boat and minivan service that runs from <a href="http://www.krabiairportonline.com/" target="_hplink">Krabi</a> and <a href="http://www.phuketairportonline.com/" target="_hplink">Phuket</a> airports and you'll make it to the island in a little less than two hours and probably be only a little worse for the wear. Photo: <a href="http://www.flickr.com/photos/pretre/1581410108/" target="_hplink">Pretre</a>/Flickr

  • Maya Bay

    Maya Bay is just far enough out of the way--a boat ride or roughly 20-minute walk through the woods--that it feels secluded even though it really isn't. This beach has been attracting a bigger and bigger audience since it served as the backdrop for the Leonardo DiCaprio movie The Beach in 2000. (The set was finally washed away in 2004 by the Indonesian tsunami. Swimmers here can lay on their backs and look up across plains of limestone and scrub that almost always give way to clear skies. <strong>Where to Stay</strong>: Koh Phi Phi island has lots of options for the crowds of tourists it attracts. The <a href="http://www.zeavola.com/" target="_hplink">Zeavola Phi Phi</a> Resort (from $250) is a good bet for those looking to salt an authentic Thai vibe with touches of luxury. A nice option further downmarket at $180 is the <a href="http://www.phiphivilla360.com/" target="_hplink">Villa 360 Resort</a>, which overlooks the ocean and, beyond that, the mainland. <strong>Getting There</strong>: Boats are available in Phi Phi Don, where you can choose by variety, speed, and apparent seaworthiness. Photo: <a href="http://www.flickr.com/photos/tinabasgen/3384013332/" target="_hplink">tinabasgen</a>/Flickr