Fig 1.
Geological map of the Mesoamerican region.
Samples from this study are denoted by colored circles. Sample numbers correlate with the samples described in Table 1. The Chicxulub crater basin is denoted by dashed lines. Map adapted from the U.S. Geological Survey Geologic Map of North America (public domain, http://ngmdb.usgs.gov/gmna/).
Table 1.
Lead and strontium results from the Mesoamerican samples used in this study.
Table 2.
Lead values from modern botanical and weak-acid soil leachate samples recovered from Yucatan, Mexico.
Fig 2.
Modern Yucatan botanical and soil lead isotopic ratios compared with anthropogenic lead from the Torreón smelter.
The Yucatan soil leachates show similar ratios to Torreón, Mexico, indicating they are likely contaminated by modern anthropogenic lead added to the local soils during the era of leaded gasoline usage. The plant samples form a trend from the soil leachates to higher 207Pb/204Pb and 206Pb/204Pb, indicating various degrees of anthropogenic lead contamination. The lead isotopic ratios for dust and blood samples from children in Torreón were previously reported by Soto-Jiménez MF, Flegal AR. Childhood lead poisoning from the smelter in Torreón, Mexico. Environ Res. 2011; 111: 590–596.
Fig 3.
Comparative results for the lead isotope ratios.
(A) 208Pb/204Pb and 206Pb/204Pb and (B) 207Pb/204Pb and 206Pb/204Pb. Outliers >24 for the 206Pb/204Pb are not shown as these highly radiogenic ratios are not likely to play a role in the overall bioavailable lead in the region because they exhibit low concentrations of lead (for more information, see text).
Table 3.
Comparison of lead ratios obtained from limestone leachates with residues.
Table 4.
Lead, thorium, and uranium concentrations (ppm) in selected samples from the study area.
Fig 4.
Ranges for the geographic regions, based on K-means cluster analyses.
(A) 208Pb/204Pb and 206Pb/204Pb; (B) 207Pb/204Pb and 206Pb/204Pb. Modern anthropogenic lead is represented by the soil leachate isotopic average based on the four Yucatan samples reported in this study. Although included in the cluster analysis, the 206Pb/204Pb outliers above 20 are not shown in this graph in order to more clearly see the distinction between the other clusters.
Fig 5.
Results for 207Pb/204Pb and 206Pb/204Pb overlaid on previous data reported from the Guatemalan Volcanic Highlands.
206Pb/204Pb values >20 are not shown in order to more clearly discern the Volcanic Highlands data in relation to data from the other sub-regions. Previous data reported in Bardintzeff JM, Deniel C. Magmatic evolution of Pacaya and Cerro Chiquito volcanological complex, Guatemala. Bull Volcanol. 1992; 54: 267–283; Feigenson MD, Carr MJ, Maharaj SV, Juliano S, Bolge LL. Lead isotope composition of Central American volcanoes: Influence of the Galapagos plume. Geochem Geophys Geosys. 2004; 5(6): 1–14; Singer BS, Smith KE, Jicha BR, Beard BL, Johnson CM, Rogers NW. Tracking open-system differentiation during growth of Santa María Volcano, Guatemala. J Petrol. 2011; 52(12): 2335–2363; Walker JA, Carr MJ, Patino LC, Johnson CM, Feigenson MD, Ward RL. Abrupt change in magma generation processes across the Central American Arc in southeastern Guatemala: Flux-dominated melting near the base of the wedge to decompression melting near the top of the wedge. Contrib Mineral Petrol. 1995; 120(3): 378–390.
Table 5.
Summary of statistics for the lead values.
Table 6.
Results of the Mann-Whitney U Test.
Fig 6.
Comparison of 87Sr/86Sr with 206Pb/204Pb.
206Pb/204Pb values >20 are not shown. Strontium values were previously reported in Hodell DA., Quinn RL, Brenner M, Kamenov G. Spatial variation of strontium isotopes (87Sr/86Sr) in the Maya region: A tool for tracking ancient human migration. J Archaeol Sci. 2004; 31: 585–601 and Gilli A, Hodell DA, Kamenov GD, Brenner M. Geological and archaeological implications of strontium isotope analysis of exposed bedrock in the Chicxulub crater basin, northwestern Yucatán, Mexico. Geol. 2009; 37: 723–726.