The Maya used so much red paint that they accidentally poisoned lakes and waterways with mercury, a new study finds, Live Science reported. The pigment was cinnabar, a vivid-red mercury-sulfide mineral used as vermilion. Runoff can enter water, where anaerobic bacteria transform it into highly toxic methylmercury that accumulates up the food chain. The Maya, who lived in what is now southern Mexico and Central America, painted sculptures, monuments, walls, plazas, pottery, and the dead. Cinnabar was a common ingredient, along with red ocher made from nontoxic hematite. Red, to them, represented the sun, blood, and life. "They would have seen a strange color change in the water … and a drop in its productivity, such as fish for protein," said first author Matthew Waters, a paleolimnologist at Auburn University. The Maya depended heavily on freshwater fisheries, including shellfish.
Previous studies had found high mercury in the southern highlands and south-central lowlands, but not a full look at Mexico's Yucatán Peninsula. Waters and colleagues reported overwhelming signs of mercury poisoning, probably from cinnabar paint, in a study published Nov. 4 in Science Advances. They studied sediment cores from Cobá Lake, beside the Maya city of that name, and Cenote Xcach (also spelled X-Canché), a flooded sinkhole beside a little-excavated ruined city. The cores cover more than 2,000 years, and the periods of mercury poisoning coincide with several stretches of the Preclassic and Classic periods, from about A.D. 40 to 820. "We did not suspect [the Maya] used it in the quantities that we were seeing," Waters said.
The U.S. Environmental Protection Agency has determined it is unsafe to drink water with mercury above 2 parts per billion, Live Science noted, and the official limit for mercury in fish is 1 part per million. Severe poisoning can occur when mercury in human blood exceeds about 100 parts per billion. The most polluted parts of the Yucatán cores had a mercury level of 2.3 parts per million, the team found. "They experienced this for decades and, in one case, for centuries," Waters said. The cores lacked tiny fossils of freshwater shellfish, a sign that high mercury was killing aquatic life, and had hardly any traces of algal blooms that should have been common.
Scholars debate why Maya civilization collapsed in the eighth and ninth centuries, with disruption of food supplies by drought a leading suspect. Waters said that although mercury levels were high in the Preclassic and Classic periods, the environmental damage had been falling in many places for hundreds of years by the time of the collapse, though it may have been a contributing factor. Cinnabar does not occur naturally in the Yucatán and was probably imported from what is now Honduras. At Cobá Lake, those imports appear to have stopped, and poisoning there fell to a background level of about 20 parts per billion by A.D. 520. At Cenote Xcach, the cores showed the poisoning continued until the collapse. The study documents a long water-quality disaster from a prized pigment. It does not present mercury as the main explanation for the Maya collapse.