They know lead poisoning was an issue; they were optimistic that canned food, which wasn’t available before, would get them through rough spots. All it did was sicken them and prolong their agony (they were stranded for a couple of years).
I saw a special on this; it was very depressing. Inuits were the last to see them alive, and talked to one group (which had separated from a nearby group when they began eating their dead).
I'm pretty sure lead helped screw up Robert Falcon Scott's ill-fated South Pole expedition.
The tins of fuel staged along the way were soldered with lead, and they leaked/evaporated.