Before chemist Ron Martin took a close look at the bones of the British sailors who died during the 19th-century Franklin expedition to find the Northwest Passage, he figured their demise was the result of the widely circulated theory that they died of lead poisoning from the soldering on the tins that held their food.

Then, with help from other scientists using high-tech laser and X-ray imagery to look deep inside bits of tibia and vertebra from the few corpses that have been found, the professor from Western University in London, Ont., discovered the new scientific data couldn't support that older hypothesis.

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Fragments of vertebra from a Franklin expedition sailor thought to have died in 1846 were found on Beechy Island. (Keith Jones/Brookhaven national Laboratory)

Sure, the bones of the men who set out with Sir John Franklin in 1845 were riddled with lead, but Martin's research  suggested it had been in the bones so long it couldn't all have come from the canned food.

"To me it just becomes more and more puzzling," says Martin.

"They had a lot of lead in them, but they had a lot of lead in them when they arrived. It's a mystery within a mystery within a mystery. What I want to know is where all the lead came from in the first place."

In the overall Franklin mystery, the role of lead is just one of many intruiguing questions surrounding the sad fate of the 129 sailors, including Franklin, who set out from England on the ships Erebus and Terror.

Parks Canada marine archeologists hope to return to the frigid waters off the coast of Nunavut this summer to resume their three-year search for the ships that were, according to Inuit testimony, beset by ice in 1846 and deserted by their crews off King William Island two years later.

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Skulls of members of the Franklin expedition were discovered and buried by William Skinner and Paddy Gibson in 1945 on King William Island. (National Archives of Canada/Canadian Press)

But they are still waiting on a final OK for this summer's efforts, and the search so far has proved elusive, while the questions only keep growing.

If lead in the tins wasn't the prime factor in the sailors' demise, what was? Where might more human remains be found? And, more than 170 years after the ships disappeared, what realistically might remain of the wooden vessels, even though they had been reinforced to try to counter the harsh Arctic conditions?

Those questions, however, rise from what is known about the mission, and there is so much that isn't.

"When Franklin received his orders from the Admiralty," says Ryan Harris, the Parks Canada marine archeologist leading the efforts to find the ships, "those directed him to proceed from Parry Channel, Cape Walker, southwest towards the mainland, to other stretches of the shoreline that had been surveyed previously by Franklin himself.

"That really sealed the fate of those 129 individuals. Because essentially they were directed into the grip of one of the most difficult ice choke points in the Canadian Arctic archipelago. They couldn't have found themselves in a more difficult spot."

Still, what exactly happened after they hit that tough spot is anything but clear. As part of their ongoing efforts, Harris and others at Parks Canada will review the latest research by Martin and his colleagues.

"If lead contaimination was an issue, and it certainly has been subject to much debate, maybe it made their final pangs that much more unbearable, I don't know," Harris says. "But the fact of the matter is that scurvy was probably the more pernicious influence."

Franklin artifacts to Canada?

Plans are under discussion to have some of the artifacts previously recovered from the Franklin expedition in the 19th century come temporarily to Canada from their home at the National Maritime Museum in London, England.

"It hasn't been formalized yet," says Ryan Harris, the Parks Canada marine archeologist leading the quest to find Franklin's lost ships.

The artifacts — everything from tinted spectacles to cutlery and a pocket watch — were returned to England by some of the many 19th-century search parties sent out to try to discover the fate of Franklin's expedition.

"I think Canadians would really appreciate the opportunity to see them first-hand," says Harris, who along with other Parks Canada staff visited England on a research trip in January.

"We're a bit impoverished in terms of Franklin material remains. If we are so lucky to locate one of the two ships in the coming year or years, we hope to change that."

While in England, Harris gave several lectures on the Franklin search and did interviews with journalists across the U.K.

That disease tended to afflict mid-19th-century maritime missions at about the three-year point, when supplies of lemon and lime juice would start to lose their potency, especially after going through several freeze-thaw cycles.

"Malnutrition and just incredible fatigue is really what would eventually break these men down," says Harris.

Still, he says, there are "many aspects that we don’t know." The main one being where the ships ended up.

"There have been always theories that at least one of the ships was re-manned by a small contingent of the crew after the initial retreat and that, in fact, one ship may have been navigated further south into the Queen Maud Gulf where we've been looking for it.

"Potentially locating one of these wrecks would shed light on some of these questions. What were their final days like? What were the thought processes, what were the difficult decisions that they were making?"

In Ron Martin's case, he started asking his questions about lead after a scientific friend — Keith Jones of Brookhaven National Laboratory on New York's Long Island — told him he had some Franklin bone samples. Jones had examined the fragments in the lab's synchrotron and wanted Martin to take a look at the results.

Jones had received the fragments more than 20 years ago from Owen Beattie, the University of Alberta anthropologist whose 1980s research had concluded that, while the Franklin sailors had most likely died of tuberculosis and pneumonia, lead poisoning from the badly soldered tins was a contributing factor.

Jones says the bones had been sitting around the Brookhaven lab for quite a while when "we just decided in thinking about the Franklin expedition that we could go back and do a better job with current instrumentation."

Lead in bone is "very complex," says Jones, and he doesn’t think it could be the "sole source" of the problem faced by Franklin's men.

"It may have come in, but I just think there are other factors that are probably more important."

Jones sent bone fragments and his results to Martin, who eventually wrote a paper incorporating work by other scientists from Western and the University of Windsor.

"When I looked at the images [Jones] presented, the one thing that struck me was that there was lead present everywhere in the bone," says Martin.

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HMS Erebus and HMS Terror, shown in an illustration from the Illustrated London News published on May 24, 1845, set sail from Greenhithe, England. (Illustrated London News/Getty Images)

"The one thing we're really confident of is, in the densest part of the bone, any lead in there has been there for about 20 years. Remember, the expedition only lasted for three or four."

Martin is quick to point out the scientists didn't "disprove" Beattie's hypothesis, just that they failed to support it.

"It does raise a very interesting problem. Where did all the lead come from and I don't know. I would love to know."

The scientific probings of the bone samples may not be over. After Martin gave a talk at a conference in Quebec this spring, representatives of Canadian Light Source in Saskatoon approached him suggesting the samples are worth a look with their synchrotron.

"I've got to think of what might reasonably be done," says Martin. "I don’t just start looking at things for the fun of it so I've got to think of something that would extend my existing research."

At Brookhaven, a new synchrotron, National Synchrotron Light Source II, is in the works, and Jones said it would be interesting to use the improved technology — it will produce X-rays that are 10,000 times brighter than NLSE I — to look at the Franklin bones again.

Harris says Parks Canada hopes to return to the Arctic this summer to continue the search for Erebus and Terror. Efforts so far have covered about 800 square kilometres, or half the "higher-priority" search areas. A review of last summer's sonar scanning efforts turned up no further details or hints of where the ships might be.

"We have a pretty good idea of exactly what we see in real time. We just double check everything when we get back to Ottawa," says Harris. "There were ... no surprises."

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Sir John Franklin's expedition set out to find and traverse the cold waters of the fabled Northwest Passage. (Evan Mitsui/CBC)

He acknowledges that the search is a "long row to hoe," and that "we're confronted with an incredible expanse of ocean to systematically sift through."

The enormity of the task is not lost on Harris, but he remains hopeful the search efforts will pay off.

"It's really hard to escape the idea you couldn't possibly make a dent, but hour after hour and week after week, year after survey year, you see the aggregate coverage build up and yes … we're making steady headway toward eventually locating one of these ships.

"On any given day it's maybe not terribly exciting, but it will be a life-changing experience when it does happen, if it does."