GEOCHEMICAL AND BIOLOGICAL ENRICHMENTS OF MERCURY: HOLOCENE AND PALEOCENE EXAMPLES COMPARED

Anthropogenic enrichments of soils, human archeological remains and geochemical enrichment have been well documented. Here, we report on geochemical and biological enrichments with heavy metals in Holocene Peru and compared this to enrichment in Holocene and Paleocene settings in New Mexico (NM), USA. We also speculate that human adaptation to mercury toxicity may have taken place in remarkably short time spans of a few thousand years or less during the Holocene. We found mercury concentrations in pigeon feathers and llama wool from free ranging birds and animals, proxies for biologic enrichments, in Albuquerque, NM, ranging from 0.006 to 0.019 mg/Kg of tissue. The values for Peru range from 22.0 to 556 mg/Kg for the same tissues. We discovered, in 64-million-year-old fossilized plants from New Mexico (Puercan interval of Nacimiento Formation, San Juan Basin), a mercury concentration of 1.11 mg/Kg of fossil, whereas contemporaneous plant material from the Rio Grande Basin, also in New Mexico, contained no mercury. Additionally, we searched for overt signs of mercury toxicity in contemporaneous human inhabitants of Huancavelica, Peru, one of the ten most polluted places in the world. The mercury concentration in their hair was well below the admissible levels, whereas assessment of their annual scalp hair growth-rate showed marked reduction in growth (~ 5cm/yr) versus ~ 16cm/year for normal scalp hair from other continents. This is consistent with a toxic effect of heavy metals on human metabolism in Huancavelica, Peru. Contemporaneous anthropogenic activities are known to increase heavy metal accumulation in the biosphere with potentially devastating effects on humans. However, signs of relatively rapid human evolutionary adaptation to such toxins might already be evident in some parts of Peru.