Wednesday, January 25, 2012

Lead Poisoning in Rome - The Skeletal Evidence

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A friend alerted me to today's IO9 post, "The First Artificial Sweetener Poisoned Lots of Romans."  It's a (very) brief look at some of the uses of lead (Pb) in the Roman world, including the hoary hypothesis that rampant lead poisoning led to the downfall of Rome - you know, along with gonorrhea, Christianity, slavery, and the kitchen sink. 

curse tablet, shot, pipe, ingots, jewelry The fact the Romans loved their lead isn't in question.  We have plenty of textual and archaeological sources that inform us of the use of lead - as cosmetics, ballistics, sarcophagi, pipes, jewelry, curse tablets, utensils and cooking pots, and, of course sapa and defrutum (wine boiled down in lead pots) - but what almost all stories about the use of lead in ancient Rome miss is the osteological evidence.

But let's start with some contemporary medical knowledge.  Metabolic disorders can be caused by a lack of nutrients - a lack of vitamin C gives you scurvy, and a lack of vitamin D gives you rickets - but they can also be caused by an abundance of something, like too much fluoride, too much mercury, too much arsenic, or too much lead.

Lead is a heavy metal, one that isn't needed by the human body, unlike vitamins C or D.  This element is found in the environment naturally, so we do expect to find some amount of lead in the skeleton of every person, ancient or modern.  But, because of the physical properties of lead - it can be made into hard, sharp things - people have been using it for millennia and thus have been exposed to heavy metal toxicity for millennia as well. The dangers of lead actually weren't well known until the second half of the 20th century, which was when lead was taken out of things like paint and gasoline.

The main problem with lead - the reason that it's toxic - is that it interferes with normal enzyme reactions within the human body.  Lead can actually mimic other metals that are essential to biological functioning.  But since lead doesn't work the same way as those metals, the enzymatic reactions that depend on things like calcium, iron, and zinc are disrupted.  The most damaging enzymatic reaction that lead affects is the production of hemoglobin, or red blood cell production, which can cause anemia.  So doctors in modern times often find anemia in a person with lead poisoning.  Lead is also particularly problematic because it stays in the body for a very long time once it's absorbed, inhaled, or ingested.  Most of it gets deposited in the bones and teeth.  Lead can be removed from the body, excreted through the kidneys and urine, but it's a very slow process without modern chelation therapy.

We don't have blood in ancient remains, of course, so we have to investigate lead through the levels we can measure in bone and enamel.  As far as I know, the first and only study to actually measure levels of lead in skeletons from Rome is the one that involved my samples from the two cemeteries of Casal Bertone and Castellaccio Europarco (1st-3rd c AD).*  The analysis was led by Janet Montgomery, now at Durham University, and also involved around 200 samples from Britain from the Neolithic to the Late Medieval periods (see below, Montgomery et al. 2010).

One of the charts from that article is below.  The Romans are there in the middle.  What you can see is that there are fairly low levels of lead in the earlier periods in Britain (Neolithic to Iron Age) and in the post-fall of the Roman Empire (5th-7th c AD).  So what do those numbers mean on a scale of Normal to Lead Poisoned?  Well, the modern recommendation by the World Health Organization and the Centers for Disease Control is that children should not have more than 1 mg/kg of lead in their bones (or 10 ug/dL measured in blood).  Back to the chart, and no one in the Neolithic is getting poisoned.  By the Iron Age, some people are above that level.  The Imperial period is pretty special - we've got people with lead levels up to 30 mg/kg, which is 30 times higher than modern recommendations!  In fact, this level is three times higher than the level the WHO considers "very severe lead poisoning."

The chart below shows my Roman samples separate from the British samples.  These are all median human lead concentrations.  You can see a spike in the British samples during the Roman period, but the Romans themselves are so much higher, at least until the Medieval period, when people started working with lead again. 

It's not yet clear what the data mean, though, other than that some people likely had lead poisoning and others didn't.  The sample size is fairly small, and more importantly, I don't know where people were living.  That is, if the people buried at Casal Bertone and Castellaccio Europarco were living in an industrial area or were metalworkers, then they were more at risk for high levels of lead than were people not living in those areas and not doing those jobs.  What is clear, though, is that lead poisoning is not something you'd want to have.  People with very severe lead poisoning tend to have major neurological changes - brain swelling leading to seizures and headaches, aggressive behavior, loss of short-term memory, and slurred speech - and a host of other problems, like anemia and constipation.

Did lead poisoning cause the fall of the Roman Empire?  Probably not.  Yes, there was increased lead production in the Roman Empire, which we know from histories, ecological sources (like ice cores from Greenland and peat bogs in Europe), artifacts, and now skeletons.  But the data - few as they are - simply don't support a conclusion of high lead concentration in the entire population.  More research of this sort is needed, of course, to examine the potential effects that anthropogenic lead had on the population of Rome and the Empire.  Fortunately, more will be forthcoming from Gabii as I start biochemical analyses of those skeletons this year, so stay tuned!


* Aufderheide and colleagues (cited below) did test 20 skeletons from Italy, including a few from the greater Rome area.  However, this was not an in-depth study, in that the skeletons were from various places.  They further note that they could not control for lead diagenesis, which may (or may not) have thrown off their measurements.  Twenty years later, the technology for identifying lead concentration in skeletons is greatly improved.  Aufderheide and colleagues found that skeletons from the Roman period (by which they mean the Imperial period) had much higher lead levels than in the previous centuries, which is consistent with our study and the understanding that lead working increased in this time period.

Further Reading:


A. Aufderheide, G. Rapp, L. Wittmers, J. Wallgren, R. Macchiarelli, G. Fornaciari, F. Mallegni, & R. Corruccini (1992). Lead exposure in Italy: 800 BC-700 AD. International Journal of Anthropology, 7 (2), 9-15 DOI: 10.1007/BF02444992.

J. Montgomery, J. Evans, S. Chenery, V. Pashley, & K. Killgrove (2010). 'Gleaming, white, and deadly': using lead to track human exposure and geographic origins in the Roman period in Britain. Roman Diasporas, Journal of Roman Archaeology, Suppl 78, 199-226.

C. Roberts and K. Manchester. 2007. The Archaeology of Disease. Cornell University Press.

T. Waldron.  2009.  Palaeopathology.  Cambridge University Press.