After nearly 30 years of mystery, government scientists believe they have found four rail-car tankers that vanished into coastal waters near Vancouver carrying a lethal load of chlorine.
''We found two blobs that are fairly substantial. They could well be the long-lost rail cars,'' said Robie Macdonald, a research scientist at the Department of Fisheries and Oceans' Institute of Ocean Sciences in Sidney, B.C., who has been on the case of the missing chlorine tanks since they vanished in 1975.
Last month, as part of a long-term program to map the earthquake-prone ocean floor off the B.C. coast, the Canadian Hydrographic Service found something it is calling a "target of interest" deep in the mud of the Malaspina Strait. The finding came after a spate of searches using less-sophisticated equipment failed to find the massive metal tank cars in the late 1970s.
While Rob Hare, manager of hydrographic surveys for the service, cautions that the find "could be nothing, it could be a bed of gravel," it has stirred hopes that at last scientists will be able to find out whether the missing chlorine poses any health risks.
The problem started late in the evening of Feb. 18, 1975, during a fierce storm. The towboat Chieftain III had been commissioned to tow four pressurized metal railway tankers, filled with a total of 374 tonnes of liquid chlorine, from Gower Point, just 30 kilometres up the coast from Vancouver, to the Powell River Pulp Mill on northern Vancouver Island.
At 6:10 the following morning -- 94 kilometres up the Sunshine Coast -- the crew of the Chieftain III noticed that the tanks had vanished.
It was a potential catastrophe. Chlorine is corrosive as a liquid, but lethal when it's a gas. First used as a weapon of war at Ypres, Belgium, by the German army, it stalked soldiers in yellow-green clouds, killing them by destroying their respiratory organs.
An urgent search for the missing chlorine tanks followed in the days after they vanished in the ocean. Although the hunt was orchestrated by the federal government with the best technology of the day, it was no use.
Meanwhile, the maker of the tanks, each crafted from about 40 tonnes of steel and double-hulled, estimated that as long as the tanks hadn't broken open when they fell, their seals would eventually rust through by, say, the mid-1990s.
Mr. Macdonald of Fisheries and Oceans conducted a study to find out what would happen if the chlorine leaked slowly out of a corroded seal. He found that as long as the tanks were below about 30 metres of water, and the water stayed cold, and as long as the leaks were slow, the chlorine would probably just turn to bleach in the water and damage only the surrounding marine life, not human or animal life on land.
But marine toxicologist Shannon Bard of Dalhousie University in Halifax has a different view of the matter. Although she has been conducting research along the B.C. coast for years, she only heard about the missing chlorine tanks last summer, when she was billeted at the home of Esther Dyck in Powell River, the town of 22,000 that was the tanks' ultimate destination.
Ms. Dyck is one of the Powell River residents who are concerned about the chlorine. "It just seems we've been sitting on a bomb and no one is talking about it," she said in an interview.
Dr. Bard started asking some questions. What would happen if the leak were not slow? What if an earthquake hit, followed by a tsunami, and that drove the chlorine to the surface, turning the liquid into deadly gas?
She ran some mathematical models, looking at the whole 94-kilometre route that the Chieftain III took. No matter where along the route the tankers landed, if even one-quarter of 1 per cent of the original chlorine were released at once (less than a tonne, in other words), the odds are 2 to 1 that a dangerous concentration would hit land, causing irreversible health effects such as blindness and lung damage among humans and animals.
If fewer than 20 tonnes were released at one go, or 5 per cent of the original amount, the odds are 2 to 1 that a fatal concentration of the gas would hit land.
"The probability of this scenario occurring is low, though plausible," Dr. Bard writes in a scientific discussion of the issue she presented at a symposium at Dalhousie this month.
What if even more of the chlorine were released and hit the air at once? Could the Vancouver area, with its two million residents, be at risk? Dr. Bard's model doesn't examine that scenario, but she said the more chlorine released in a bubble, the further the health-risk zone would range.
She argues that if the tanks can be found, it is worth investigating the possibility of removing the chlorine, possibly salvaging the tanks and diminishing the risk.
But Mr. Macdonald is not convinced.
The new findings suggest that the tanks are at least 300 metres below the surface of the ocean, a depth that would keep the chlorine liquid. As a liquid, it would bleach the surroundings and eventually seep away. Disturbing the tanks could unleash the very scenario people want to avoid.
"We might be making a bad situation worse," he said.