The ruins of Tikal in Guatemala were abandoned more than 1,000 years ago, and were rediscovered by a gum sapper in 1853.
But scientists might be closer to understanding why its inhabitants abandoned the city, the capital of a warring state that became one of the most powerful kingdoms of the Maya.
Research found toxic levels of pollution in reservoirs in the heart of the city, hinting that the water had become undrinkable after droughts in the ninth century.
This contributed to the decline and eventual abandonment of the city, according to researchers from the University of Cincinnati.
The city flourished between 300 and 850AD, and was known to the Maya themselves as Mutul.
Researchers found toxic levels of mercury and algae in four central reservoirs in Tikal, an ancient Maya city that dates back to the third century C in what is now northern Guatemala.
“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 said.
Geochemical analysis found that two reservoirs nearest the city palace and temple contained extremely high and toxic levels of mercury.
The researchers traced the contamination 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.
“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.
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.
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,” he 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.
They believe a combination of economic, political and social factors prompted people to leave the city and its adjacent farms. But the climate no doubt played a role, too, Lentz said.
“They have a prolonged dry season. For part of the year, it’s rainy and wet. The rest of the year, it’s really dry with almost no rainfall. So they had a problem finding water.”
The researchers say that one popular pigment used on plaster walls and in ceremonial burials was derived from cinnabar, a red-coloured mineral composed of mercury sulfide that the Maya mined from a nearby volcanic feature known as the Todos Santos Formation.
A close examination of the reservoir sediment using a technique called energy dispersive X-ray fluorescence spectrometry found that this pigment was the source of the mercury in the water.