Wednesday, October 14, 2015

Chronic Mercury Exposure in LN Perdigoes

This paper in Nature by Emslie et al (2015) piqued my interest having watched a documentary on sluicing in the developing world the other night ago.  So a paper about moderate to stratospheric mercury levels in ancient human remains naturally seems a little more interesting than it did last week. 

But first, let me delve into the paper and its conclusion before I get to my usual quackery.  A number of individuals from the Late Neolithic and Chalcolithic (pre-Beaker) of Southern Portugal were analyzed with those of Perdigoes (n=37) being found to have very, very high levels of mercury.  Mercury, or quicksilver, was historically extracted from cinnabar and Iberia exported it since prehistory.  Cinnabar was used in pigments and in burials in many places, but especially these places.

Tested Sites (Fig 1 from the paper)

The authors consider a number of reasonable options as to the mercury levels in the 37 souls of Perdigoes, eliminating the more topical and environmental possibilities.  Clearly, within the lifetime of these people, they were coming into prolonged contact with the element.

It's always possible that the people were doing something weird, like using vermillion as a food preservative or a medicine, but certainly not as an embalming agent, since it would only affect the flesh and the authors exclude various post-mortem uses like this.  For practical purposes, use of red body paint or tattoo ink is viewed by the authors as the most likely origin of prolonged contact and there is circumstantial evidence that a similar phenomenon may have affected Plains Indians with neuropathy or other peoples who used paints this way.  This is the conclusion of the paper and it seems the most plausible conclusion.

However, even young children had elevated levels which makes me suspicious.  The toxic levels of mercury and the importance of the Ossea Morena and the iron belt below it are just too tempting for the Beaker Blog.  The isotopic signature of the mercury for these sites appears to have originated two to three hundred miles away in Almaden, implying some degree of economic scarcity.  Scarcity necessarily creates inequality.  So while cinnabar may have been more common or attainable by average people than other commodities, it would require a level of use that is potentially far greater than individuals in other periods and places, like Çatalhöyük, Ancient Rome or their regional neighbors.

It doesn't appear that these tested individuals were responsible for mining or reducing cinnabar either, since they were the consumers of cinnabar from the mines at Almaden, a more central region of Iberia.

But, could there be other possibilities as well?

Recently, I blogged on a paper where the authors showed that most of the gold and copper of the British Early Bronze Age more likely came from sluicing the rivers in Wales and Cornwall, rather than excavation mining.  There were several suggestions as to the collection method, but this is a fairly recent hypothesis in the developing stage.

It has been shown that gold mining using the mercury amalgamation process was used by 1,000 B.C.  It's worth noting that Almaden (again) was the primary supplier of Carthaginian and Phoenician amalgamation mercury (Olaf Malm, 1998) and the same by Romans in a later period.  (de Lacerda and Salomon, 1997b) 

Amalgamation is basically 'panning', but using amalgamation as a more effective way to capture particles, example> [youtube].  Hydraulic mining has become a big issue in the developing world, search Lacerda and Salomon...

Prehistoric Gold in Europe: Mines, Metallurgy and Manufacture (Morteani, Northover 1993)

Perdigoes lies in a small geological zone called the Ossea Morena, a zone which appears to have been the main supplier for the earliest copper metallurgy at the Zambujal (at this time) and neighboring Atlantic fortresses (Müller, Goldenberg, Bartelheim et al., 2007)

Prehistoric Gold in Europe: Mines, Metallurgy and Manufacture (Morteani, Northover 1993)

Amalgamation can be used to extract gold, silver and copper and it's always possible that this process was known much earlier.  Maybe this would answer some of the puzzling questions about Perdigoes?

Opened and quickly filled ditches?  The location of the site?  Heavily vitrified crucibles?

But then again, people used to salt their food with lead, so a simple answer may be the best answer.
Interpretation LBK EN by Karol Schauer

Chronic mercury exposure in Late Neolithic/Chalcolithic populations in Portugal from the cultural use of cinnabar
Steven D. Emslie1, Rebecka Brasso2, William P. Patterson3, António Carlos Valera4,
Ashley McKenzie1, Ana Maria Silva5, James D. Gleason6 & Joel D. Blum6

Cinnabar is a natural mercury sulfide (HgS) mineral of volcanic or hydrothermal origin that is found worldwide. It has been mined prehistorically and historically in China, Japan, Europe, and the Americas to extract metallic mercury (Hg0) for use in metallurgy, as a medicinal, a preservative, and as a red pigment for body paint and ceramics. Processing cinnabar via combustion releases Hg0 vapor that can be toxic if inhaled. Mercury from cinnabar can also be absorbed through the gut and skin, where it can accumulate in organs and bone. Here, we report moderate to high levels of total mercury (THg) in human bone from three Late Neolithic/Chalcolithic (5400–4100 B.P.) sites in
southern Portugal that were likely caused by cultural use of cinnabar. We use light stable isotope and Hg stable isotope tracking to test three hypotheses on the origin of mercury in this prehistoric human bone. We traced Hg in two individuals to cinnabar deposits near Almadén, Spain, and conclude that use of this mineral likely caused mild to severe mercury poisoning in the prehistoric population. Our methods have applications to bioarchaeological investigations worldwide, and for tracking trade routes and mobility of prehistoric populations where cinnabar use is documented.

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