It remains one of the greatest mysteries of polar exploration. In 1845, a well-provisioned Royal Navy expedition commanded by Sir John Franklin embarked to find the North-West Passage between the North Atlantic and Pacific Oceans. A total of 129 officers and men set sail on Franklin’s two ships, the Erebus and Terror. None returned.

The disaster was the greatest single loss of life inflicted upon any polar expedition. Only a few scattered remains – papers and bones – have since been found of Franklin’s men on north Canada’s frozen islands. These testify that at some point, some crewmen resorted to cannibalism in a bid to survive, a revelation that horrified Victorian Britain. As Andrew Lambert states in his biography, Franklin: Tragic Hero of Polar Navigation, the story is “a unique, unquiet compound of mystery, horror and magic”.

In the intervening years, there have been many attempts to explain why Franklin’s well-provisioned expedition failed, with one recent idea finding particular popularity. According to Owen Beattie and John Geiger, in their bookFrozen in Time: The Fate of the Franklin Expedition, analyses of the skeletons of three Franklin crew members, whose graves were found on Beechey Island in northern Canada, showed they had suffered from severe lead poisoning that would have had “catastrophic” consequences for themselves and for their fellow crewmen.

Lead poisoning causes abdominal pain, confusion, headache, anaemia and, in severe cases, seizures, coma and death. And, according to Beattie and Geiger, it could be traced to their ships’ canned food. (The expedition carried provisions for three years.) Poorly soldered, the authors argued, the tins’ food contents would have been contaminated with lead and would have poisoned the crewmen, an idea that has since achieved widespread acceptance.

Not every scientist agrees, however, and several studies have since argued that the support for the idea is poor, culminating in a paper, written by Keith Millar, Adrian Bowman and William Battersby, that is published in the current issue of the journal Polar Record. It argues that the evidence for widespread lead poisoning in the crew is questionable. “We looked at two key pieces of evidence,” says Millar, of the Institute of Health and Wellbeing at Glasgow University. “The analyses of the bones of the three crew men – John Torrington, John Hartnell and William Braine – who died in 1846 and who were buried on Beechey Island and a statistical study of how lead might have affected the entire crew.” Beattie and Geiger found very high levels of lead in the body of Torrington, a stoker on the expedition: 226 parts per million (ppm), which was 10 times higher than samples taken from Inuit skeletons found in the area. The discovery formed a key part of Beattie and Geiger’s theory.

But as Millar points out, high levels of lead were common in men and women in Victorian times. “Drinking water and food were often contaminated and some medicines also contained lead. The lead found in the men’s bones could easily have been acquired at home. More to the point, there was wide variation in lead levels between the three men. It is not at all clear that it killed them, certainly not all of them”

A similar analysis of seven other skeletons of men from the Franklin expedition who died a couple of years later also found wide variations in lead in their bones. In some cases, these were well above standards that are now considered safe. Others were not, however. “There is not enough evidence to support the idea the Franklin expedition was solely wiped out by lead-contaminated food,” adds Millar.

As to the real cause of the loss of the expedition, that remains open to speculation. “However, it was probably ice, not lead, that killed them,” he argues. Extreme cold trapped the expedition for two winters near King William Island in northern Canada. “By the following year, provisions would have been running short. By then, Franklin and 23 others had died. We don’t know why. The surviving men had no option but to desert the ships and trek south to the mainland. But they were ill-equipped, and probably in poor health, so escape was beyond them. Their plight was desperate and all died in the attempt.”