Researchers from McMaster University and the Royal Ontario Museum studying a 160-year-old soup can found in the Canadian Arctic have detected lead levels that are off the scale further proof, they say, of the lead poisoning believed to have doomed the 19th-century Franklin Expedition during its quest to transit the Northwest Passage. Photograph by: Handout , CNS

Scientists studying a 160-year-old can of soup found in the Canadian Arctic have detected lead levels in its broth and sealant that are "off the scale" — further evidence, they say, of the lead poisoning believed to have doomed the 19th-century Franklin Expedition during its quest to transit the Northwest Passage.

Researchers from McMaster University in Hamilton and Toronto's Royal Ontario Museum — which had the historic tin of ox-cheek soup in its collection — performed tests on the can and its contents to try to confirm a controversial theory about the ill-fated polar voyage of the British ships Terror and Erebus in the late 1840s.

Franklin and 129 of his crew died during the journey across Canada's forbidding northern sea route after the ships became irretrievably locked in ice near King William Island in 1847.

A Canadian government-sponsored search for the famously elusive shipwrecks — widely considered the Holy Grail of marine archeology — was conducted in 2008 and is scheduled to resume next summer.

Previous research — including tests at McMaster in the 1990s on bones of Franklin crewmen recovered from Arctic gravesites — has shown dangerously high levels of lead suspected of having leached from solder used to weld lids on the expedition's supplies of tinned food.

Lead poisoning from the food — or possibly from pipes used in the ships' freshwater systems, according to a more recent theory — has been blamed for damaging the health of Franklin and his men and impairing the judgment they required to survive being stranded for years in the harsh Arctic environment.

The can of soup tested at McMaster was left on Dealey Island in 1852 by crewmen from a rescue mission sent to search for the Terror and Erebus. Scientists believe the provisions from the two rescue ships — HMS Resolute commanded by Henry Kellett, and HMS Intrepid captained by Francis M'Clintock — were identical to those supplied for Franklin's expedition, and therefore shed fresh light on a prime suspect from that ill-fated voyage.

High lead levels in both the soup and its container were detected by McMaster experts in experiments using X-ray fluorescence, a non-destructive method of analyzing objects that's available at only two laboratories in Canada.

"The numbers showed us lead levels that were pretty much off the scale," Fiona McNeill, a medical science and radiation expert, said in a statement after tests Tuesday on the can's lid.

"It was an instantaneous test. We had already tested the soup found in the can and found high levels of lead, so we were certain we were going to find similar levels in the sealing solder."

Fellow researcher David Chettle, a McMaster medical physicist, told Canwest News Service on Tuesday that the latest tests are not conclusive, but added that "it certainly makes it difficult to imagine any other source of lead" sufficient to harm Franklin and his crew.

"I think it begins to close the circle of evidence around the role for lead," he said. "What we can't be sure of is how quickly that lead went from the solder to the soup."

McMaster anthropologists are planning to continue the probe by making their own supply of ox-cheek soup and canning it using Victorian-era methods. The cans will be opened and tested at intervals over the next year to record how much and how quickly the lead is leaching into the soup.