Mercury contamination in ancient water reservoirs at the Maya city of Ucanal, Guatemala

Abstract

Although the use of mercury in the form of cinnabar (HgS) by the ancient Maya has been widely documented, there are few datasets available to understand potential exposure to mercury from ancient Maya reservoirs. This study analyzed the chemical composition of stratigraphically excavated dried sediments from 3 ancient water reservoirs located in different zones and social contexts at the site of Ucanal, Guatemala, to determine how potential contamination of water reservoirs varied through space and time. High levels of mercury, relative to natural concentrations in soils, were identified throughout the complete temporal sequence and were omnipresent in all three water reservoirs, indicating that mercury contamination may have affected both elite and non-elite sectors of the population. Average total mercury concentrations in the reservoirs’ sediments were above 1 $\mu$g/g, the toxic effect threshold above which freshwater ecosystem sediments are deemed to be heavily polluted. A sharp increase in mercury was recorded for the Terminal Classic period, when the city reached its apogee, with average concentrations of 3.08 $\mu$g/g for Aguada 2, 11.88 $\mu$g/g for Aguada 3 and 3.17 $\mu$g/g for Piscina 2. Non-reservoir soil samples also show mercury contamination throughout the city core, a situation which would have led to the accumulation of mercury in water reservoirs through its mobilization within the various drainage areas.