Historical Insights into Maya Mercury Contamination
The environmental pollution linked to human activities is not merely a modern phenomenon. Recent research has unveiled that during the Classic Period (250-920 AD), the Maya people contaminated Lake Cobá and the Xcach cenote, located in Mexico’s Yucatán Peninsula, with mercury. This finding highlights an environmental and health issue for ancient populations residing in these areas, as it resulted in the degradation of aquatic ecosystems and chronic exposure to this toxic metal through water and food sourced from these bodies of water.
Previous studies have documented that this ancient Mesoamerican civilisation used elemental mercury and cinnabar as a red pigment to adorn ceramics, buildings, and funerary objects. Continuous exposure to mercury poses serious risks to the human nervous system and disrupts ecosystems. In aquatic environments, certain bacteria can convert mercury into methylmercury, a particularly hazardous form that accumulates in organisms and is transferred through the food chain. While there had been records of mercury remnants in various Maya settlements, the extent of this contamination and its impact on ecosystems and human populations remained unclear until recent investigations.
Scientific Investigation and Findings
In 2023, a team of scientists led by Matthew Neal Waters from Auburn University in Alabama extracted sediment cores from four lakes in the Yucatán Peninsula. Through the application of paleolimnology and radiocarbon dating techniques, they discovered that mercury concentrations persisted over centuries in Lake Cobá and the Xcach cenote. Notably, levels at the latter site reached up to six times the severe effect threshold established by current toxicological standards.
The research, published in a recent issue of a scientific journal, indicated that the accumulation of this heavy metal commenced in both water bodies during the early centuries AD, albeit with varying intensities. In Lake Cobá, mercury concentrations began to rise around 40 AD, peaking at 2.3 micrograms per gram between 250 and 300 AD. Conversely, the Xcach cenote experienced three significant contamination episodes, the most notable occurring between approximately 535 and 820 AD, with an average concentration of 8.4 micrograms per gram and a peak of 18 micrograms per gram around 720 AD. The findings suggest that elevated mercury levels persisted at this site for nearly three centuries.
Human Activities as a Source of Contamination
The researchers ruled out atmospheric sources of contamination, as elevated mercury levels were not found in the sediments of Cenote Polol and Chichankanab lagoon. This distinction supports the hypothesis that human activities were the primary contributors to the problem. The scientists propose that the Maya may have transported mercury from other regions, which subsequently entered the water bodies through soil erosion.
The study also examined remains of algae, cyanobacteria, ostracods, snails, and aquatic insect larvae to assess the relationship between rising mercury levels and changes in ecosystem composition. The analysis revealed a significant decline in indicators of algae, cyanobacteria, and photosynthetic bacteria during periods of heightened mercury presence. A similar trend was observed among higher trophic level organisms, as the remains of ostracod shells disappeared from Lake Cobá, while insect larvae numbers decreased in the Xcach cenote.
Implications for Ancient Maya Populations
These outcomes suggest that elevated mercury concentrations disrupted food webs and degraded aquatic ecosystems, likely impacting the health of the populations inhabiting these regions. Fish and shellfish were integral to the diet of the ancient Maya, both of which are efficient bioaccumulators of mercury. Consequently, it is plausible that human populations in Cobá and Xcach experienced chronic mercury exposure over decades or even centuries, at levels deemed toxic by contemporary standards.
The research does not conclusively determine whether the ancient Maya in these areas developed mercury-related illnesses or precisely establish the level of risk they faced. However, it demonstrates that the environmental degradation they encountered was not solely attributable to natural phenomena such as drought, deforestation, or soil erosion. The authors assert that their findings provide circumstantial evidence of the Maya’s trade and use of mercury, alongside the potential toxicity associated with it in specific locations.