Ancient Maya Red Paint Polluted Lakes With Mercury for Centuries

The ancient Maya may have poisoned their own lakes and sinkholes with mercury from red paint, according to a study published Nov. 4 in the journal Science Advances. Mud cores from two sites in Mexico's Yucatán Peninsula contain extreme mercury levels and show signs that aquatic life collapsed, Live Science reported.

The likely source was cinnabar, a bright-red mercury-sulfide mineral used to make the pigment vermilion. The researchers say runoff carried it into the water, where it turned toxic.

How red paint became a water pollutant

The Maya lived in what is now southern Mexico and Central America, and their descendants live there today. According to Live Science, they painted sculptures, monuments, walls, plazas and pottery red, and also colored the bodies of the dead during ceremonial funerals. Red represented the sun, blood and life to them.

Cinnabar was a common ingredient in the paint, alongside red ocher, which gets its color from hematite, a nontoxic iron mineral. When cinnabar runoff reaches lakes, bacteria that thrive without oxygen convert it into methylmercury in the sediments, the report explained. Methylmercury is highly toxic and builds up to higher levels as it moves up the food chain.

What the mud cores showed

A team led by Matthew Waters, a paleolimnologist at Auburn University in Alabama, studied sediment cores from Cobá Lake, a shallow lake beside the Maya city of Cobá, and from Cenote Xcach, a flooded sinkhole beside a little-excavated ruined city in the jungle. Earlier studies had found high mercury in the Maya southern highlands and south-central lowlands, but the Yucatán had not been fully examined.

The cores span more than 2,000 years. The periods of mercury contamination fall within the Preclassic and Classic periods, from about A.D. 40 to 820. The most polluted layers reached 2.3 parts per million of mercury. Waters said the Maya lived with such conditions for decades and, in one case, for centuries.

The cores also lacked tiny fossils of freshwater shellfish, which the researchers read as a sign that mercury was killing aquatic life. They also held few traces of algal blooms, which Waters said should have been frequent. The team suggests algae could not survive in the contaminated water.

Why it matters: a possible hit to food and water

Waters told Live Science that the Maya relied heavily on freshwater fisheries, including freshwater shellfish. In his view, people would have noticed an odd color change in the water and a decline in productivity, such as fewer fish for protein.

For context, Waters said the U.S. Environmental Protection Agency considers drinking water unsafe above 2 parts per billion of mercury. He said the U.S. limit for fish is 1 part per million, above which authorities can seize the catch. Severe poisoning in people occurs when blood levels exceed about 100 parts per billion, he said. Symptoms can include permanent lung damage, brain damage and death. The study measured sediments, and the report does not describe testing of Maya remains for mercury poisoning.

Waters said the team did not expect the Maya to have used cinnabar in the quantities the cores indicate.

Where the cinnabar came from, and what it says about the collapse

Cinnabar does not occur naturally in the Yucatán, so the researchers say it had to be imported, probably from what is now Honduras. At Cobá Lake, the imports appear to have stopped, and contamination there dropped to a background level of about 20 parts per billion by A.D. 520. At Cenote Xcach, the sediments show the poisoning continued until the Maya collapse.

Scholars still debate why the Maya civilization collapsed in the eighth and ninth centuries. Drought-driven disruption of food supplies is a leading suspect. Waters said that in many places the environmental damage from mercury had been easing for hundreds of years before the collapse. He added that mercury may still have been a contributing factor.

The findings come from sediment records at two sites, and the mercury is attributed to cinnabar paint as a probable source rather than a confirmed one.

Read next
Ancient Rain on Mars May Have Left Life's Building Block in Certain Spots
Andean Villagers Drank Arsenic-Laced Water for Millennia, and Their Genes May Show It
Rare Blue-Tailed Damselfly Returns to a Rebuilt Chalk River Near Hertford

Around Prague, based on reporting by Live Science