In March, a new study came out in PNAS discussing "Lead in ancient Rome's city waters" (Delile et al. 2014). It was quickly covered by major science news outlets, largely because of a mention of lead poisoning in Rome on the new Neil deGrasse Tyson-helmed Cosmos, with venues like TIME stating, "Lead didn't bring down ancient Rome," but others like Discover inaccurately commenting that "Lead in ancient Rome's water was 100 times natural level." Now that I've gotten through the SAA conference and submitted final semester grades, I wanted to take a close look at the paper in advance of talking about lead poisoning in a talk I'm giving in San Antonio on Monday.
|Lead pipe from Ostia Antica.|
(photo credit: Chris 73 CC BY-SA 3.0)
This project involves Pb isotope values (not concentrations) to test whether the Pb present in the cores was naturally occurring or the result of anthropogenic (man-made) Pb use. Pb isotopes, like Sr, O, and S, can actually be used to investigate mobility and migration of humans and animals. We all ingest at least trace amounts of these elements because they occur normally and naturally in our environment. Different ratios of these elements give us information, therefore, into the kind of environment in which a person grew up, allowing us to see if people or animals changed locations after they were born. But testing the soil for Pb isotopes gave these researchers information into whether the soil's Pb was from the local environment or from imported Pb (and therefore anthropogenically-caused introduction of Pb).
Using the Pb isotopes, the authors found two major components when they tested the soil: first, there was naturally-occurring Pb likely from the Alban Hills (volcanic rock) and from Mediterranean seawater as a result of erosion of Apenninic limestone. But second, there was a component that could not be explained using the local geology. Specifically, the Pb component they found is called Hercynian Pb, which is not found in the Italian peninsula. It's normally found in SW Spain, parts of France, Germany, England, Greece, and the Alps. This anthropogenic or human-introduced Pb component is also, they say, consistent with four of the five fistulae they tested.
So what does this mean for the levels of Pb pollution in the Roman water system? Here's where some of the news coverage gets some of the interpretations wrong. Delile and colleagues (2014:4, emphasis mine) calculate that, given an estimate of Tiber River water running through fistulae at the height of the Roman Empire:
It can therefore be deduced that fistulae increased Pb in the water distributed in Rome over the natural level by a factor of about 40, 14, and 105 for the Early Empire, Late Empire, and High Middle Ages, respectively. [...] These levels are maximum values because they characterize the final output of the water system to the Tiber, while most Roman citizens would have used drinking water that was tapped, whether legally or illegally, all along the water distribution system. The inferred increases of Pb in the water of the Roman distribution system unquestionably attest to general lead pollution of Roman drinking water, but the Pb concentrations at issue are unlikely to have represented a major health risk.Now, go back and read the Discover story if you're so inclined. I'll wait. Did you notice how the author cherry-picked the largest number, which represents the High Middle Ages (whereas "ancient Rome" generally means the Roman Empire when talking about lead poisoning)? See how the author cherry-picks a quote about lead being a major public health issue, only to admit at the end that the authors of the study don't discuss health problems (except that they do in the sentence I've highlighted above)? Lead is present in our environment, of course, and although 14 and 40 times sound scary, those numbers may not mean much if the natural level of lead is very low. That's basic math. Definitely the worst coverage of this article I've seen.
Getting back to the elegant study, though, the authors further show (Delile et al. 2014:5) using the chronology of the sediment cores and the fluctuating Pb isotope values that their data line up with written history:
The isotopic contrast between the fractions rapidly diminishes, although quite smoothly, from the Early to the Late Roman Imperial periods. This change is largely accounted for by the dramatically smaller contribution of anthropogenic Pb to leachates and therefore by a lesser pollution of Tiber water. One interpretation of this may be a redirection of spring water away from the lead pipes of Rome, in some way related to the controversial decline of the population or to a poorly documented deterioration of the water distribution system.
The later fifth and sixth century transition is coevel with Belisarius' fixing of the decommissioned aqueducts of Rome at the end of the Gothic Wars (535-554 AD). Byzantine repairs of the water distribution system may have remobilized massive amounts of corrosion products from abandoned lead pipes in which water may have stagnated for protracted lengths of time. Although a causal relationship cannot be formally demonstrated, the discontinuities in the cores at Portus seem contemporaneous with historically documented events such as the struggle for the control of the port between Gothic and Byzantine forces (536-552 AD) and the damages inflicted to the water distribution system during the Arab sack of Rome in the mid-ninth century.Really, really good stuff!
This paper, of course, makes me think of the Pb concentration (and isotope) data from my Romans buried at Casal Bertone and Castellaccio Europarco, just outside of Rome, in the 1st-3rd centuries. Here's a chart of Pb concentration data from Britain and Rome, with data coming from Montgomery et al. 2010:
|Lead concentration from skeletons from Britain and Rome.|
(Raw data from Montgomery et al. 2010, Tables 11.2, 11.3, 11.4.)
If we could take the pre-Roman Britain lead level (0.08 median) as possibly analogous to pre-anthropogenic-Pb Rome, then you could have a 40-fold increase and not have widespread lead poisoning. 105 times (the possible level above natural Pb levels in the High Middle Ages for the Tiber basin), however, is pretty darned high. Medieval Europe clearly liked their lead.
The most fascinating thing to come out of the Delile et al. paper for me is the idea that the Tiber was the source of the Pb pollution. This isn't particularly surprising, since waste from the various industries within the urbs and the suburbium would flow into the Tiber. And the Romans knew not to drink Tiber water or eat fish out of it; they were well aware of pollution, even if they didn't quite understand the mechanisms. But these results give me pause because they could indicate that Romans whose skeletons held high levels of lead grew up playing and possibly drinking and eating close to the Tiber. Since we have little information that links dead bodies buried in the suburbium with living quarters in the urbs, knowing that proximity to Tiber waters could result in high Pb values is a good bit of data to store away for when Sr/O analysis can give me a finer resolution for residence and mobility in the Empire. That is, I hope that someday I can figure out where in Rome people lived by looking at their skeletons, historical information, geological data, and other contextual factors. Skeletons are all well and good, but being able to understand living communities in Rome has always been my goal.
The Delile et al. article represents a massive step forward in helping all of us who research the ancient world understand more about the variation in environment and health in the Roman Empire.
Delile H, Blichert-Toft J, Goiran JP, Keay S, & Albarède F (2014). Lead in ancient Rome's city waters. Proceedings of the National Academy of Sciences of the United States of America, 111 (18), 6594-9. PMID: 24753588.
Killgrove K (2012). Lead poisoning in Rome - the skeletal evidence. Powered by Osteons.
Montgomery J, Evans J, Chenery S, Pashley V, & Killgrove K (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.