Thursday, March 8, 2012

Lead-poisoning in Rome: The skeletal evidence

A recent article in the online publication io9, “The First Artificial Sweetener Poisoned Lots of Romans“ provided a (very) brief look at some of the uses of lead (Pb) in the Roman world, including the tired old hypothesis that it was rampant lead poisoning that led to the downfall of Rome - along with gonorrhoea, Christianity, slavery, and the kitchen sink.

The fact the Romans loved their lead is not in question, with plenty of textual and archaeological sources that inform us of the uses of lead – as cosmetics, ballistics, sarcophagi, pipes, jewellery, curse tablets, utensils and cooking pots, and, of course sapa and defrutum (wine boiled down in lead pots) – but what almost all news articles regarding the use of lead in ancient Rome seem to ignore is data from osteological evidence.

Contemporary medical knowledge allows us to understand that metabolic disorders can be caused by a lack of nutrients: a lack of vitamin C causes scurvy; and a lack of vitamin D can lead to 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 is not required by the human body for metabolic functions, unlike vitamins C or D. This element is found naturally in the environment, so it can be expected to find trace levels of lead in the skeleton of every individual, both ancient or modern. However, because of the physical properties of lead being malleable and easily worked people have been using it to create a large range of items and thus have been exposed to heavy metal toxicity for millennia. The dangers of lead were not full appreciated until the second half of the 20th century, which was why lead began to be taken out of household goods such as paints and fuels.

The main danger of lead – the reason that it is toxic – is due to the way it interferes with the normal enzyme reactions within the human body. Lead actually mimics the properties of other metals that are essential to biological functioning. But as lead does not 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 haemoglobin, or red blood cell production, which can cause anaemia. So doctors in modern times often find anaemia in a person with lead poisoning. Lead is also particularly problematic because it stays in the body for a long time once it has been absorbed, inhaled, or ingested. Most of the lead is deposited in our bones and teeth. However it can be removed from the body by excretion through the kidneys and urine, but it is a very slow process without modern chelation therapy.

A measure of lead

In modern society, lead poisoning is diagnosed through a blood test to determine the level of lead in the body. With ancient remains however there is no blood to sample and so it is necessary to investigate lead levels in what can be measured in bone and enamel. Probably the first and only study to actually measure levels of lead in skeletons from Rome is the one that involved samples provided by the author from two cemeteries at Casal Bertone and Castellaccio Europarco (1st-3rd c AD) near Rome itself.* 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 (Montgomery et al. 2010).

One of the charts (Figure 11.1) from that article has the Roman samples highlighted 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 (Figure 11.3) shows my Roman samples separated from the British samples. These are all median human lead concentrations. There is a visible 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 means though, other than that some people likely had lead poisoning and others didn’t. The sample size is fairly small, and more importantly, it is unclear 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 involved in these industrial processes. 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 behaviour, loss of short-term memory, and slurred speech – and a host of other problems, like anaemia and constipation.

End of Empire?

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), artefacts, and now skeletons. But the data – as it currently stands – simply does not support a conclusion of high lead concentration in the population as a whole. More research of this sort is required 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 further biochemical analysis of those skeletons takes place later this year, so stay tuned!

Killgrove, Kristina. 2012. "Lead-poisoning in Rome: The skeletal evidence". Past Horizons. Posted: February 24, 2012. Available online:

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