Sunday, 24 July 2011

Time we put the tinned food back in the cupboard: Busting the Franklin Expedition myth of 'lead poisoning from tinned food'.


The idea that Franklin's men were poisoned by lead from tinned food has reached almost the status of dogma. For many members of the public it seems to be almost the only 'fact' they know about the expedition.

Owen Beattie and John Geiger's bestselling book 'Frozen in Time' (2004 edition) includes the statement "There is no question of the source of the lead found in the bodies of Franklin's men: it came from the tinned foods". This claim is supported by a paper by Walt Kowal and others published in the Journal of Archaeological Science in March 1991, but, contrary to that claim, the source of the lead was questioned from the very first.

ISOTOPES:

Kowal and his co-authors found that the ratios of the several isotopes of lead in solder from cans found on Beechey Island matched the ratios measured in human remains from Beechey and King William Islands. They concluded from this that the lead in both cases came from the same source. That seems reasonable - indeed it's likely that all the lead on the ships came from the same source.

No measurements were made on contemporary British samples of lead, instead the authors referred to a database of isotope ratios of 98 samples of lead ore from the British Isles published by Stephen Moorbath in 1962.

Having found no credible match, they speculated that:
"...since the isotopic ratio for the Franklin materials is so different from most lead sources in the British Isles, it is quite possible that the lead used in the solder manufacture came from some other nation".
Their argument seems to be, that because all of the other sources of lead which the members of the expedition would have been exposed would have come from British mines, then the only possible explanation for the presence of the unusual exotic lead in the human remains was that it had come from the solder of the tin cans.

Unfortunately mass-spectrometry was still in its infancy in the early sixties, and the isotope measurements published in Moorbath's paper do not bear direct comparison with those made thirty years later. In 1996 Brenda Rohl published isotope ratios of 383 samples of lead ore from the British Isles. Her introduction states:
"The data in pioneering papers such as Moorbath (1962) and Brown (1966) are now too inaccurate to be compared with modern lead isotope data".
MINING:

It is implausable that isotope data could be used to trace the origin of any industrial era lead back to a single mine. Even connecting a sample with a single mining region presents difficulties.

Veins of ore with distinct isotope ratios can occur in close proximity. Equally, veins with indistinuishable isotope signatures can occur many miles apart. A small number of smelters would serve numerous mines within a region, producing metallic lead with an isotope signature averaged from the constituent ores.

Lead is probably the most easily recycled material known to man. At the lead mills ingots of newly smelted lead would be melted together with old lead scrap to manufacture whichever products the market required, such as sheet or pipe or solder.

The isotope signature of a typical sample of manufactured lead would therefore represent an amalgam of both contemporary and previously active mining regions. The average composition of the mixture would change only gradually as established mining regions declined and new ore provinces were exploited.

In 1839, Andrew Ure published statistics showing the relative productivity of the different Lead mining regions at that time. The North Pennines (Durham, Cumberland, and Yorkshire) being the dominant region.


Click on image for source document

The following chart compares the Franklin project data with geological data from Rohl, chosen with reference to the above table, and data from 36 samples from the Northern Pennines, from a 2001 paper by Brett Scaife and others.

Click to enlarge.

Data points from the two Welsh counties are represented by the larger circles to make up for their small number. Derbyshire had been of greater significance in the preceding century hence may deserve greater prominence than Ure's figures suggest due to recycling of old lead. There has been no attempt to distinguish the relative productivity of individual mines within a region, nor to represent measurement confidence intervals.

The main feature to note in the above chart is that all the data points for the Franklin samples are within the locus of the data points for the Northern Pennines.

CONCLUSION:

It is plausible that the isotope signature shared by both the solder and the human remains is simply that of common English lead of the period and that the high levels of lead detected in the human remains could have resulted from exposure to any of a myriad of contemporary sources and certainly not uniquely to the solder of the tin cans.

That members of the expedition suffered from lead exposure is not disputed, but there is no evidence to suggest that "it was the reliance of Franklin's expedition on tinned food that was the root cause".

The supplier of the tinned food, the much vilified Stefan Goldner, is exonerated of any blame in connection with the demise of the Franklin Expedition.

The eminent Food Scientist and Science historian Keith Farrer, OBE (who even has an award named after him) was among the first to question the 'lead poisoning from tin cans' hypothesis.

In a paper published in the Journal of Archaeological Science in 1993, Farrer pointed out, among other things, that only acidic foods such as tomatoes can defeat the cathodic protection conferred on lead by the more reactive tin and iron and that the canned provisions supplied to the expedition included no acidic component. It appears that all published reports of canned food being been found with a high lead content have involved acidic foodstuffs.

Farrer's conclusion regarding the canned food was that "their contribution to the body loads of lead or to any incipient ill health in Franklin's crewmen was trivial".

However no scholarly article in a scientific journal can compete for the public consciousness with a bestseller like 'Frozen in Time'.

So I hope this small effort does something to redress the balance.
01-Aug-2011

11 comments:

  1. Peter,

    Fascinating post as ever! But although the idea that lead poisoning entirely explains the failure of the Franklin expedition is clearly specious, I don't think we can completely rule out lead from the tins as a contributing source to the crew's declining health.

    For one, spikes in the lead level of soft bone, as documented by Keenleyside et. al., certainly indicate an increase -- or at the very least, continuing exposure -- to lead during the expedition; this can't have been lead from exposure back in England. It's possible that Battersby's thesis that the on-board water supply was a culprit, but lead from the tins can't be ruled out.

    The point about food acidity is accurate -- but it should be noted that a significant proportion of Goldner's tins contained soup. Depending on its contents, this soup likely had a much higher acidity than, say, tinned beef -- and the largest soup tins were the size of buckets! I have always suspected that the soup in these tins might indeed have been heated in the tins, which would certainly bring out more lead, given the low melting point of the metal.

    The other thing yet to be explained is the high variation in lead levels -- the 11 individuals at NgLj-2 had levels varying from mild to extremely acute lead poisoning -- why this degree of variation? Clearly, some crew members were getting much more lead input than others; to my mind this could only be correlated with something like tinned food, as the amount of it dispensed to officers and seamen was very different, and many seamen hated tinned food and preferred salt pork, even as their scurvy-loosened teeth made it harder and harder to chew!

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  2. Thanks for that contribution Russell.

    Agreed that Keenleyside's work shows that there was a major source of lead contamination onboard ship. We can't rule out the tins as a contributing source but the food science evidence does seem to rule them out as the predominant source. In fact I'd be very surprised if it could be shown possible that they would have contributed more than 5%.

    The instructions on the printed labels on some of the surviving cans say that they should be put in boiling water to loosen their contents before opening so some sort of heating in the can is probable - a very good point. It should be easy enough to reproduce some soup from contempory recipes for testing. In fact I'm seriously looking at a replication attempt to compare the canned food with the snow melter as possible lead sources.

    Variation in lead level is often a feature of water borne lead contamination. The 'first draw' concentration in a house with lead plumbing is much greater than when the tap has been running for a few minutes. Farrer recounts a case of lead poisoning in a man who was always first into a pub when it opened and who's first pint had been lying in the pipe all night. The exceptional values reported for vertebral lead at NgLj-2 may reflect the ones who were routinely first in the queue!

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  3. Peter,

    Agree with you all round, and the 'first draw' idea is intriguing -- were officers, as it were, first to the (water) trough at mealtimes?

    Checking the ships' manifests again, I see "preserved soup" -- but this I think was more likely the "portable soup" made by boiling beef legs and onions until it congealed into a solid block, rather than tinned stuff. Quite a few tinned veggies, though -- wonder how they'd rank in acidity.

    It would be a great idea to reproduce some of these provisions -- and NMM has, or had, some tins as well as an infamous block of that soup -- worth trying, at least.

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  4. Peter,

    Interesting post. (See Russell's December, 2009 blog post: http://visionsnorth.blogspot.com/2009/12/franklin-era-tin-tests-positive-for.html) A team at McMaster University has already produced replicas of Goldner's tins and the first can should have been opened by now. I haven't heard about the results yet.

    Also, Google Books has an article about tests conducted on three old tins of food. (See: New Scientist, May 5, 1960, page 1138 it's availble on Google Books for free). One of these is a 7-pound tin of veal from 1823. It was from Parry's expedition. The veal had a Lead content of 18-parts-per-million and a Tin content of 2000-parts-per-million. The Tin level is high enough to cause illness to anyone eating enough of it. A taste test was also conducted.

    I've wondered about making a replica of Goldner's cans myself. The one thing I don't understand is how the Lead was applied to the joints? Today we have torches and rolls of lead solder but back then I'm imagining they might have poured molten Lead over the joints. Another important aspect to consider is what, if any, flux did they use to get the solder to flow into the joints?

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  5. Thanks Chris, I have emailed McMaster for more information on their press release. There have been several proposals for replication experiments but I'm not aware of any results published.
    Thanks for bringing the 1960 paper to my attention. Having read it now I see the results are quite similar for some cans opened in 1939, published under the title 'Historic Tinned Foods' which is available in full at http://www.itri.co.uk/pooled/articles/BF_TECHART/view.asp?Q=BF_TECHART_295491
    That includes details of the cans and Frozen in Time also has a good section on how they were made. If I recall correctly tallow was used as flux. Regards, Peter

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  6. Here's a recipe for a contemporary version of "portable soup" from a woman named Hannah Glasse:

    "Take two Legs of Beef, about fifty Pounds Weight, eight or nine gallons of water, twelve anchovies,large helpings of herbs and spices, six large onions, and a dry hard crust of a Two-penny loaf" and boil for at least eight to nine hours."

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  7. Indeed tallow was a common source of flux. The cans most likely would have soldered with the fire heated hand irons common until the 1910's. For simple or short term work at home string, wire or tongs would hold the metal together, likewise in small shops. In larger more industrial operations a bench frame would have used, some 19th frames had a form with openings for the solder, others used vices, clamps or their hands. Rosin was also used, as was solder fluid, which was an early form of flux.

    There are illustrations of the lamps, pre-runners of the early 20th century torches, as well as other tools and the recipes for making solder fluid, nasty stuff, one wonders if it was in the food as well.

    Here is some instructions circa 1861:
    http://books.google.com/books?id=S5YAAAAAMAAJ&pg=PA51&dq=soldering&hl=en&ei=w21FTsz_EuX10gHWtLmSCA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CDYQ6AEwAA#v=onepage&q=soldering&f=false

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  8. Russell: I've hauled the bathtub into the yard to use as a saucepan, now I'm off to the supermarket to get two cows legs...
    EW: Thanks for the fascinating and useful link.

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  9. There was lead in the pipes during my childhood. Likewise in housepaints, i was always 'helping' to scrape/sand/paint. I played with die-cast cars which were also part lead, and i played with them in the dirt on a little hill beside our house where there was undoubtedly a fair amount of lead paint chips. My Aunt's husband was a plumber, and while fixing something at our house, gave me a 7 in wide roll of sheet lead 1/8" thick and several feet long to play with. (superman could bend metal,too!) i played with that for years. Grandpa Braine work at American Tinning and their house was probably full of the stuff. I still have a lead ingot i use for a doorstop. I work in the Electronics industry, and for years, held the lead string in my mouth to join wires to parts with a soldering iron, inhaling the smoke. I know lead is suppposed to have a deleterious effect on cognition and cause stomache cramps. I must have been born a genius, because i am 54, and still just a bit smarter than the average bear... So how much lead is too much?

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  10. Oh, forgot to mention the pewter flask...

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  11. I used to play with lead too - melting it and casting it into shapes. Perhaps that's why I'm far short of being a genius. Seriously though, the doses which might affect a child's development are much lower than what would poison an adult. I have yet to fully analyse the figures but it looks like the Beechey Island bodies had lead exposure comparable to workers in white-lead manufactories without modern safety precautions. It's a good question and I hope to give a better answer in the future.

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