Researchers working in Guatemala have discovered high levels of mercury contamination at the ancient Maya city of Ucanal, 280km north-east of Guatemala City. Identified in soil samples taken from across the city’s core and its water reservoirs, the toxic metal may have caused Ucanal’s inhabitants serious health problems.
“The discovery of mercury in the soil and reservoirs was expected, but the extent of it was a surprise,” says Jean Tremblay, a PhD student in anthropology at the Université de Montréal in Canada and lead author of the research paper published in the Journal of Archaeological Science: Reports. “What is particular to our study is that we systematically detected mercury throughout the city core (near both elite and non-elite residential zones) and through the entire occupation history of the site. Everyone was exposed to mercury, regardless of social status.”
Tremblay and his colleagues identified mercury in dried sediments from three of Ucanal’s ancient reservoirs, which collected water that drained from the parts of the city surrounding them. The average mercury concentration in each was at a level classified as heavily polluted. Beyond the reservoirs, the team found the highest concentration of mercury in a ceremonial zone at the city’s core, with lower but still significant amounts in samples taken from other locations, including residential zones.
“Our study shows that mercury dispersed into the environment was mobilised during precipitation events and found its way into the reservoirs as particles which accumulated at the bottom of the reservoirs,” Tremblay says.
Ucanal’s dangerous levels of mercury contamination probably results from the Maya’s extensive use of cinnabar, a bright red ore of mercury and sulphur. “Cinnabar was used in burial rituals, employed as pigments used to paint buildings and as decorative colouring for luxury ceramics, engraved bone objects, carved stone ornaments and figurines, and as ritual offerings in themselves,” Tremblay explains.
“It is believed that the Maya used this inorganic substance due to its intense red colour associated with blood and therefore to death and rebirth, an important part of Maya cosmology,” he adds. “It differs from other red mineral pigments, such as those deriving from iron oxides, in its bright purplish shades of red.”
The team found mercury contamination throughout the city’s history—a period roughly from 800 BCE to 1521 CE—and noticed that its levels sharply increased during the 9th century, when Ucanal reached its peak. This may have been due to Ucanal having increased access to long-distance trade, Tremblay says, which would have brought more mercury to the city.
With mercury such a prominent feature of everyday life, the people of Ucanal could have been exposed to the toxic metal by drinking water, accidentally inhaling or ingesting it when grinding cinnabar, or when touching cinnabar during rituals. Nonetheless, it is difficult for researchers to know whether mercury found in skeletal remains results from environmental exposure during life or happened after death because of the funerary rituals.
Over recent years, it has become clear that mercury contamination was a widespread problem for the Maya. “Cinnabar was used throughout the ancient Maya world and mercury has been measured in soils at numerous ancient Maya sites,” Tremblay says. One study, published in the journal Frontiers in Environmental Science in 2022, lists nine Maya archaeological sites where elemental mercury and cinnabar have been found. Among them was the important site of Copan in Honduras, where mercury was identified in ten contexts.
The team will continue its archaeological work at Ucanal, Tremblay says. “This particular research highlights the possibility that ancient Maya peoples were living in environments that could pose adverse health effects,” he says. “We intend to investigate further the geochemistry of the site to further document the ancient local environment.”
