Toxic mercury, aquatic ecosystem collapse, and the ancient Lowland Maya

Environmental impacts endured by the Lowland Maya during the Classic Period (250 to 920 CE) included droughts, deforestation, and soil erosion. Recent studies on mercury (Hg) pollution and cyanotoxins suggest that degraded water quality was also a stressor for the Pre-Columbian Maya. Hg in the Maya region is related to use of both elemental mercury and mineral cinnabar (HgS), the latter used as a red pigment. Questions, however, remain concerning the toxicity of Hg or the consequences of prehistoric Hg exposure on ecosystem and human health. Here, we show that Classic Period Hg concentrations in sediment cores from two lakes on the Yucatán Peninsula exceeded modern sediment Hg toxicity thresholds by orders of magnitude for centuries during ancient Maya occupation. Sediments also have evidence of aquatic food web collapse (algae, bacteria, cyanobacteria, ostracods, snails, and nonbiting midges), coincident with the time of high Hg concentrations, confirming that Hg toxicity was an additional environmental stressor for Classic Maya populations.