A long-standing Arctic mystery has become even more baffling with research that appears to debunk a common theory about the demise of the Franklin expedition.

Chemists at the University of Western Ontario used an array of the latest analytic techniques to conclude that poorly made cans of food were not responsible for the lead that poisoned the officers and crew of the doomed 19th-century voyage to explore the Arctic.

"We'll probably never know what happened to the crew of the Franklin [expedition], so it will remain one of the great mysteries of Canadian history," said Prof. Ron Martin.

"Our resources fail to support the hypothesis that the lead in the bones came from tins, and I certainly believe it didn't."

SPECIAL REPORT: Searching for Franklin

The Franklin expedition headed north, never to return, in 1845. Although some remains of the 129 crew have been discovered, along with ghastly evidence of cannibalism, the two ships Erebus and Terror have never been found despite a century and a half of searching.

Their mystery and legend remain to this day.

Bones reveal high levels of lead

Three graves of Franklin crew members discovered on Beechey Island were exhumed in 1984 and their corpses analyzed in an attempt to shed light on the disaster.

While diseases, including pneumonia and tuberculosis, are believed to have been the immediate causes of death, high levels of lead found in the sailors' bones are thought to have weakened the men and clouded their judgment. Looking for a source of the lead, scientists concluded it probably came from the solder used to seal the cans of food in the ships' stores.

Martin's work, published in February in Applied Physics A, re-examined some of the bones using techniques developed since the original analysis. Martin and his colleagues concluded there was so much lead in the bones, and it was distributed so widely, that it couldn't have accumulated during the few months the men were at sea before they died.

Nor did he find areas where lead was concentrated, as there would be if the potent toxin had only recently been ingested.

"The wide distribution and high concentrations of lead in the measured bones is indicative of long-term exposure before the start of the expedition," says the paper.

"The lead distribution is essentially uniform as might be expected from lifetime lead ingestion. There is no evidence for a sudden massive increase in lead during the latter part of any individual's life."

Source of lead uncertain

Martin's work would also appear to exonerate other sources of lead that some researchers have proposed as a source, including the ship's water system. Water pipes on Franklin's vessels were made of lead.

Lead is toxic to the heart, bones, intestines, kidneys and reproductive and nervous systems. Symptoms of lead poisoning include confusion, which makes it an attractive explanation for some of the decisions made by Franklin and his crew after their ships were stuck in the ice, such as dragging heavy lifeboats over the tundra laden with non-essentials such as silverware.

Martin's team concludes that if Franklin and his men were poisoned by lead, it probably began long before they set sail for what is now the Canadian Arctic.

The mystery, which has inspired Canadian artists from folksinger Stan Rogers to novelist Mordecai Richler, persists.