Tropical high mountain lakes as indicators of airborne trace element contamination: El Sol and La Luna lakes, Central Mexico

High-mountain lakes (HMLs) are relevant indicators of global change due to their capacity to reflect environmental shifts. Temporal changes of concentrations, enrichment factors and fluxes of eleven trace elements (Ag, As, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, and Zn) were assessed in ²¹⁰Pb-dated sediment cores collected at El Sol and La Luna lakes, the only Mexican HMLs, in the crater of the Nevado de Toluca Volcano (NTV). This study examines the factors contributing to the recent (post-1900) rise in trace element inputs to the lakes, exploring whether this rise is related to soil erosion in NTV hillslopes due to nearby anthropogenic activities. Background (pre-1900) and recent concentrations of most trace elements, along with the magnitude and temporal variations of their fluxes, were similar between lakes. Also, the background values for most elements in the lacustrine sediments were similar to those found in soils surrounding the lakes. The enrichment factors indicated minimal contamination by most trace elements, excepting for the moderate enrichment by Pb in both lakes and by Hg in La Luna Lake. Based on a factor analysis, that evidenced the resemblance in the trace element composition between the soils and solely the oldest lake sediments (undated segment of the cores), this study demonstrates that soil erosion can explain the sediment chemistry for the oldest lake sediments, but not for the recent ones. Given the lakes' remote location, minimally influenced by human activities, Pb and Hg contamination was attributed to aeolian transport, mainly originating from surrounding urban areas (e.g., Toluca City). This research underscores the importance of environmental management to safeguard high-mountain ecosystems, especially in regions threatened by air pollution from nearby industrial cities, but also from rural areas where burning of coal for cooking and heating is still relevant.