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Abstract: The explosive activity of Popocatépetl Volcano is a threat to the surrounding densely populated areas and it is therefore important to recognize indicators of change in eruptive style (explosive to dome building) within a short period of time. In this study we present results of vesicle size distributions (VSDs) and compositional analysis of matrix glass from juvenile clasts from five of the main plinian eruptions of Popocatépetl (ca. 23–1.2ka), the 2001 small eruption during partial dome collapse and four eruptions during 1997 (May 11th and June 14th, 15th and 30th). Major element analysis of matrix glass (WDS-EPMA) allows the estimation of the depth from which the erupted magma went into disequilibrium (between crystals and melt), by calculating the equilibrium pressure using the quartz–albite–orthoclase ternary system of Blundy and Cashman (2001). Quantitative interpretation of texture in juvenile (pumice or scoria) clasts via VSD analysis using CSD software was used to link physical changes experienced by magma during ascent, with conditions responsible for eruptions. The extent and style of vesiculation in juvenile clasts is also related to eruption style and duration and has specifically allowed the recognition of changes in vesicular texture that represent variations from explosive to dome building activity (Mangan and Sisson, 2000; Adams et al., 2006). This study highlights a more complicated story in terms of magma storage, than that previously accepted for the Popocatépetl volcanic system and is an important contribution to ongoing research at the volcano. [Copyright &y& Elsevier]

The provenance and nature of palygorskite clay used by Mayas for the creation of the outstanding Maya Blue pigment and pottery in the Yucatán peninsula has not been analyzed thoroughly. Especially the hypothesis of palygorskite being a diagenetic product of volcanic glass has remained uncertain. Here, we present a detailed study of zircon extracted from palygorskite-rich materials (sak lu'um) collected in the interior of the Sacalum cenote and near Chapab village, to evaluate the potential of zircon as an indicator mineral for tephra-derived palygorskite or clay-rich deposits intercalated with carbonate rocks. U-Pb zircon geochronology and correlative trace element analyses from stratigraphically different palygorskite-rich horizons indicate a restricted Eocene age range, which is coeval to the deposition of the host carbonates, and discrete airborne emplacement events of silicic tephra into warm and shallow waters at ca. 50 Ma and 41 Ma, likely derived from volcanoes in a continental magmatic arc. Our findings also indicate that palygorskite deposits in the Yucatán peninsula are not inherited from continental sources but rather formed in-situ partly from weathering of volcanic glass that sourced Si and Al required for palygorskite formation. • Silicic tephra is a precursor component for palygorskite in Yucatán, Mexico. • Eocene zircon in palygorskite deposits are coeval to carbonate formation. • Trace elements in zircon suggest ash derivation from a continental arc setting. • Tephra origin as fall-out from western Central American or Caribbean arcs. [ABSTRACT FROM AUTHOR]

The Binational Arsenic Exposure Survey (BAsES) was designed to evaluate probable arsenic exposures in selected areas of southern Arizona and northern Mexico, two regions with known elevated levels of arsenic in groundwater reserves. This paper describes the methodology of BAsES and the relationship between estimated arsenic intake from beverages and arsenic output in urine. Households from eight communities were selected for their varying groundwater arsenic concentrations in Arizona, USA and Sonora, Mexico. Adults responded to questionnaires and provided dietary information. A first morning urine void and water from all household drinking sources were collected. Associations between urinary arsenic concentration (total, organic, inorganic) and estimated level of arsenic consumed from water and other beverages were evaluated through crude associations and by random effects models. Median estimated total arsenic intake from beverages among participants from Arizona communities ranged from 1.7 to 14.1 µg/day compared to 0.6 to 3.4 µg/day among those from Mexico communities. In contrast, median urinary inorganic arsenic concentrations were greatest among participants from Hermosillo, Mexico (6.2 µg/L) whereas a high of 2.0 µg/L was found among participants from Ajo, Arizona. Estimated arsenic intake from drinking water was associated with urinary total arsenic concentration (p < 0.001), urinary inorganic arsenic concentration (p < 0.001), and urinary sum of species (p < 0.001). Urinary arsenic concentrations increased between 7% and 12% for each one percent increase in arsenic consumed from drinking water. Variability in arsenic intake from beverages and urinary arsenic output yielded counter intuitive results. Estimated intake of arsenic from all beverages was greatest among Arizonans yet participants in Mexico had higher urinary total and inorganic arsenic concentrations. Other contributors to urinary arsenic concentrations should be evaluated.

Human arsenic methylation efficiency has been consistently associated with arsenic-induced disease risk. Interindividual variation in arsenic methylation profiles is commonly observed in exposed populations, and great effort has been put into the study of potential determinants of this variability. Among the factors that have been evaluated, body mass index (BMI) has not been consistently associated with arsenic methylation efficiency; however, an underrepresentation of the upper BMI distribution was commonly observed in these studies. This study investigated potential factors contributing to variations in the metabolism of arsenic, with specific interest in the effect of BMI where more than half of the population was overweight or obese. We studied 624 adult women exposed to arsenic in drinking water from three independent populations. Multivariate regression models showed that higher BMI, arsenic (+3 oxidation state) methyltransferase (AS3MT) genetic variant 7388, and higher total urinary arsenic were significantly associated with low percentage of urinary arsenic excreted as monomethylarsonic acid (%uMMA) or high ratio between urinary dimethylarsinic acid and uMMA (uDMA/uMMA), while AS3MT genetic variant M287T was associated with high %uMMA and low uDMA/uMMA. The association between BMI and arsenic methylation efficiency was also evident in each of the three populations when studied separately. This strong association observed between high BMI and low %uMMA and high uDMA/uMMA underscores the importance of BMI as a potential arsenic-associated disease risk factor, and should be carefully considered in future studies associating human arsenic metabolism and toxicity., (Copyright © 2011 Elsevier Inc. All rights reserved.)