UC finds ancient Maya reservoirs contained toxic pollution

Researchers from the University of Cincinnati found toxic levels of pollution in four central reservoirs in Tikal, an ancient Maya city that dates back to the third century B.C. in what is now northern Guatemala.

UC's findings suggest droughts in the ninth century likely contributed to the depopulation and eventual abandonment of the city.

"The conversion of Tikal's central reservoirs from life-sustaining to sickness-inducing places would have both practically and symbolically helped to bring about the abandonment of this magnificent city," the study concluded.

A geochemical analysis found that two reservoirs nearest the city palace and temple contained extremely high and toxic levels of mercury that UC researchers traced back to a pigment the Maya used to adorn buildings, clayware and other goods. During rainstorms, mercury in the pigment leached into the reservoirs where it settled in layers of sediment over the years.

The study was published in the Nature journal Scientific Reports.

UC’s diverse team was composed of anthropologists, geographers, botanists, biologists and chemists. They examined layers of sediment dating back to the ninth century when Tikal was a flourishing city.

Previously, UC researchers found that the soils around Tikal during the ninth century were extremely fertile and traced the source to frequent volcanic eruptions that enriched the soil of the Yucatan Peninsula.

“Archaeologists and anthropologists have been trying to figure out what happened to the Maya for 100 years,” said David Lentz, a UC professor of biological sciences and lead author of the study.

For the latest study, UC researchers sampled sediment at 10 reservoirs within the city and conducted an analysis on ancient DNA found in the stratified sediment of four of them.

Sediment from the reservoirs nearest Tikal’s central temple and palace showed evidence of cyanobacteria. Consuming this water, particularly during droughts, would have made people sick even if the water were boiled, Lentz said.

“We found two types of blue-green algae that produce toxic chemicals. The bad thing about these is they’re resistant to boiling. It made water in these reservoirs toxic to drink,” Lentz said.

UC researchers said it is possible but unlikely the Maya used these reservoirs for drinking, cooking or irrigation.

“The water would have looked nasty. It would have tasted nasty,” said Kenneth Tankersley, an associate professor of anthropology in UC’s College of Arts and Sciences. “There would have been these big blue-green algae blooms. Nobody would have wanted to drink that water.”

Researchers found lower but still toxic levels of mercury in sediments from more distant reservoirs called Perdido and Corriental, which also would have provided drinking water for city residents during the ninth century.

Reservoirs near the temple and palace likely would have been impressive landmarks, much like the reflecting pool at the National Mall is today.

“It would have been a magnificent sight to see these brightly painted buildings reflected off the surface of these reservoirs,” said co-author Nicholas Dunning, head of geography in UC’s College of Arts and Sciences.

With its bright red color, cinnabar was commonly used as a paint or pigment across Central America at the time.

“Color was important in the ancient Maya world. They used it in their murals. They painted the plaster red. They used it in burials and combined it with iron oxide to get different shades,” Tankersley said.

Featured image at top: UC researchers Nicholas Dunning, left, Vernon Scarborough and David Lentz set up equipment to take sediment samples during their field research at Tikal. Photo/Liwy Grazioso Sierra