The water in some reservoirs of Tikal city of the Maya civilization in the ninth century of our era contained so much mercury, phosphates and metabolic products of cyanobacteria that was hardly drinkable, it is reported in Scientific Reports. This, coupled with frequent droughts, most likely, led to the fact that people left the settlement.
The reasons for the rise and fall of ancient civilizations are now being investigated in order to understand how modern people to farm and not spend all available resources — i.e. how to achieve sustainable development. In this respect, particularly interesting Maya: they have managed to build a developed society in the tropical rainforest, and their civilization existed for about 3500 years, from about 2000 BC until the arrival of Europeans in the XIV century (a separate city held to 1697).
However, the decline of the Maya began before the advent of foreigners to be clear of the age of the abandoned buildings of this civilization. So, one of the key cities, Tikal (the ruins located in Northern Guatemala in the Department of El petén), the people left in the middle of the ninth century of our era. Before that, apparently, the population of Tikal fell for a long time. Why the city is empty, is not precisely known, although the causes are actively seeking for more than 60 years.
Chemists, microbiologists, archaeologists and specialists from other areas (all employees of the University of Cincinnati), headed by David Lenz (David A. Lentz) studied the composition of sediments on the bottom four tikalsky water tanks. In samples of material from different layers of palynology analyzed species composition and condition of the pollen, paleoethnobotany was looking for 16S ribosomal RNA of bacteria and archaea, as well as DNA of other organisms (the species of origin of genetic material was found out by a quantitative polymerase chain reaction), geochemists atomic absorption spectrometry and other methods determined the content of mercury and phosphate, capable of large amounts of harm to human health.
In samples from two reservoirs nearby to the main temple and the Palace, the mercury content exceeded the threshold value, after which begins to show a toxic effect (1 microgram per gram of sediment). Apparently, most of the metal accumulated in tanks in the late classic period of Maya civilization (600-900 ad), that is, shortly before Tikal were deserted. The Maya used a paint on the basis of mercury in rituals, in particular in the burials, and this likely contributed to the contamination of drinking water by this metal.
Also in those vessels was increased concentration of phosphates (PO43−). In the late classic period, it was 0,80—0,92 micrograms per gram of sediment, which is 4 times more than in the pre-classical period (0.2 micrograms per gram of sediment). Traditionally phosphates associated with organic pollution, and here they could serve as a kitchen for residents of the Central Acropolis (that is, the rulers and nobility), which was located close to one of the tanks. Waste from the cooking poured almost the threshold of the kitchen, and in the rainy season they could drain the potable water tank.
DNA and RNA reservoir suggests that in the last century of life of Tikal in drinking water had a lot of cyanobacteria (also called blue-green algae) genera Planktothrix and Microcystis. Most likely, their abundance contributed to the high phosphate concentration. Cyanobacteria cause “water bloom”: that is painted in different colors products of microorganisms, though many of these chemicals are toxic. Microcystin — compound secreted by cyanobacteria of the genus Microcystisis toxic to humans already in a nanomolar concentrations and are resistant to boiling, so the water from the tanks with them were hardly fit to drink.