Toxic levels of a pollutant usually associated with waste from modern industry have been revealed among the most unlikely of archaeological sites.
Long before conquerors from distant lands introduced the ravages of war and disease, Mayan civilizations dusted the soils of their urban centers with the heavy metal mercury.
Levels of the element are so high in some areas that researchers are advised to prepare to save their health.
“Environmental mercury pollution is commonly found in modern urban and industrial landscapes,” says Duncan Cook, a geoarchaeologist at the Australian Catholic University and lead author of a review of the Maya environmental legacy.
Along with a team of researchers from the US and the UK, Cook examined datasets collected from 10 Classic Period Maya excavation sites and their environs, which included environmental measurements of mercury levels.
A comparison of measurements from across the region found seven of the sites reported at least one area contaminated with a mercury concentration that exceeds or equals modern benchmarks for toxic levels.
“The discovery of mercury buried deep in soils and sediments in ancient Maya cities is hard to explain until we start looking at the archeology of the area that tells us the Maya used mercury for centuries.”
In its pure form, mercury is a shiny gray metal that melts at a relatively low temperature, turning it into a viscous fluid once commonly referred to as quicksilver.
However, throughout much of history, mercury-containing compounds have had a variety of uses in industry and culture. Among the most famous is mercuric nitrate, a substance used to harden felt for hats that was claimed to poison the nervous systems of 19th-century artisans who worked with it.
Perhaps the most widely used form of mercury over the centuries is crystalline mercury sulfide, a mineral also known as cinnabar.
Commonly found near hot springs and areas of volcanic activity, mercury pigment has been used as a crimson coloring agent in works of art around the world since time immemorial.
To the blood-obsessed Maya, cinnabar was more than just a pretty shade of red.
“For the Maya, objects could contain ch’ulelor soul power, which resided in the blood,” says University of Cincinnati geoarchaeologist Nicholas Dunning.
“Thus, the bright red pigment of cinnabar was a priceless and sacred substance, but unbeknownst to them it was also deadly, and its legacy remains in the soils and sediments around ancient Maya sites.”
Curiously, the limestone foundations upon which the ancient Maya infrastructure was built do not provide the kind of geology ripe for cinnabar production. To find a good source of the mineral, you’ll need to travel to the edge of the Mayan world.
Archaeological studies indicate, in fact, that cinnabar was mined in Central America as early as the second to first millennium BC, a time when the Olmec civilization flourished.
By the time the Maya were erecting monuments to their gods across the land around the third century CE, cinnabar was already in common use, mostly in powdered form to add color to decorative pieces or even burials.
In rare cases, the refined metal itself has been uncovered, usually in association with ritual crypts or elite burials. How the Maya got their hands on this pure form of the element – either through trade or their own alchemical methods – is still something of a mystery.
To what extent this liberal dusting of mercury sulfide affected the health of the Maya is also not entirely clear, although a growing body of research suggests that the toxic metal had at least seeped deep into their bones.
One of the last rulers of the Mayan city of Tikal, a king named Dark Sun, was particularly obese, a possible indication of a metabolic disease usually caused by mercury poisoning.
Beyond past health concerns, the researchers highlight the need for today’s archaeologists to take precautions to protect themselves from the toxic metal as they dig into the multi-layered history of the Mayan civilization.
“This result is yet more evidence that just as we are living in the Anthropocene today, there was also a ‘Mayan Anthropocene’ or ‘Mayaken,'” says Tim Beach, a geoarchaeologist from the University of Texas.
“Metal contamination appears to have been [an] effect of human activity on history’.
This research was published in Frontiers in Environmental Science.