A prized red pigment used by the ancient Maya did more than brighten murals, pottery, temples and burials. Sediment cores from two lakes on Mexico’s Yucatán Peninsula show that mercury linked to cinnabar accumulated at concentrations above modern toxicity thresholds for centuries—and the peaks arrived alongside a collapse across several layers of the aquatic food web.
The strongest evidence comes from Lago Cobá and Cenote Xcach, where researchers reconstructed a long environmental timeline from lake-bottom mud. At Cobá, mercury remained above a benchmark associated with probable harm to sediment-dwelling organisms for more than 200 years, including nearly a century above the severe-effect level. At Xcach, the peak reached roughly six times that severe-effect threshold and persisted for about 300 years before falling sharply around 850 CE.
Ancient mud preserved a chemical timeline
The research team, led by Auburn University paleolimnologist Matthew Waters, published its results in Science Advances. Long cylinders of lake sediment work like environmental history books: deeper layers are older, and each layer can retain chemical and biological evidence of what was happening when it formed.
The study’s mercury spikes occurred during the Classic Maya Period, broadly dated from 250 to 920 CE. Cinnabar—mercury sulfide—was valued for its vivid color and used across Maya material culture. The researchers argue that its intensive use is the most plausible source of the concentrated contamination around Cobá and Xcach, rather than a broad natural event such as mercury arriving uniformly from the atmosphere.
That distinction matters. Cobá was a major city connected by an extensive network of raised stone roads known as sacbeob. The team’s interpretation raises the possibility that cinnabar was not merely an occasional luxury but a traded commodity moving through established routes. The study does not identify the precise mines that supplied it, so that part of the story remains open.
The lake communities changed at the same time
Mercury alone would be an alarming discovery, but the biological record makes the result far more consequential. During the periods of highest contamination, the cores show declines in markers associated with algae, cyanobacteria and purple sulfur bacteria—organisms near the base of an aquatic food web.
The team also revisited a puzzle preserved in older Cobá cores. Researchers in the 1990s had found a section where shells from ostracods, tiny aquatic crustaceans, disappeared. Testing archived material showed high mercury in the same interval. New cores likewise recorded missing ostracods, while specialists studying nonbiting midge larvae found major changes among the dominant species.
That pattern stretches from microscopic producers to small animals that depend on them. It does not demonstrate that every organism died directly from mercury, but it does show a broad ecological disruption coinciding with concentrations that modern sediment guidelines classify as harmful. According to Auburn University’s account of the research, the biological community eventually recovered as mercury levels declined.
What the study can—and cannot—tell us about people
The findings add water quality to the environmental pressures faced by Classic Maya communities, alongside drought, deforestation, erosion and the challenge of supporting large urban populations. They do not prove that mercury poisoned residents, caused illness or drove the decline of Maya cities. The sediment cores contain no direct measure of human exposure, and the study does not establish a simple line from contaminated lakes to political collapse.
Exposure was possible, however. People could have encountered mercury through water, fish or work involving cinnabar, and mercury can accumulate through food webs. Reuters’ report on the study notes that Cobá may have supported 60,000 to 90,000 people during the Classic Period, while Xcach remains much less studied. Those population estimates make the water-quality question impossible to shrug off, even while the human-health evidence remains indirect.
A beautiful color with an environmental cost
The payoff here is not a sensational claim that cinnabar “ended” Maya civilization. It is a clearer, stranger and more tangible story: a coveted color left a chemical signature in two lakes, that signature rose far beyond modern toxicity thresholds, and the living communities preserved in the mud changed with it.
For archaeologists, the mercury peaks may become another way to trace how widely cinnabar circulated and how intensively it was used. For environmental scientists, the cores show how a culturally valuable material can create long-lived pollution without factories, engines or modern industry. Ancient history did not lack environmental contamination; it simply wrote the evidence in different places.
Featured image credit: Map of Mesoamerica and the Lago Cobá and Cenote Xcach study sites from Waters et al., Science Advances (2026), DOI 10.1126/sciadv.aeh3280, licensed under CC BY 4.0. Image retrieved from the study figure reproduced by Phys.org.
