Ofelia Morton-Bermea

Assessment of Atmospheric Metal Pollution in the Urban Area of Mexico City, Using Ficus benjamina as Biomonitor

Concentrations of vanadium, chromium, cobalt, nickel, copper, zinc, antimony, and lead were measured in Ficus benjamina leaves from the Mexico City urban area in order to assess their enrichment against background values. The instrumental analysis was performed using inductively coupled plasma mass spectrometry and the analytical method was tested using two certified reference materials from the National Institute of Standards and Technology (1547 Peach Leaves and 1573a Tomato Leaves). Enrichment factors were calculated, i.e., total to background concentration ratio, for each metal. Low enrichments of vanadium, cobalt, nickel, and copper (≈2), and mild enrichments of chromium and zinc (4.4, 4.5 respectively) were found in the entire area; oppositely, high enrichments were assessed for antimony (28.6) and lead (17.2). However, results indicate that metal concentrations strongly depend on the specific urban sub-area. Increments of metals were attributed to natural, vehicular, and industrial sources.

Heavy Minerals and Rare Earth Elements in Coastal and Inland Dune Sands of El Vizcaino Desert, Baja California Peninsula, Mexico

A heavy mineral (HM) study and light and heavy rare earth elements (LREE and HREE) analysis were performed in coastal and inland dune sands, El Vizcaino Desert, Central Baja California Peninsula, Mexico. Our study shows high abundances of hornblende and apatite in the El Vizcaino dune sands, suggesting a dominance of granodiorites/intermediate plutonic rocks and marine authigenic phosphorite in the dune sands. There is a relationship between unstable heavy minerals like hornblende, pyroxenes, and sphene, and heavy rare earth elements (HREE) that suggests that unstable heavy minerals are potential carriers of HREE in the dune fields. However, there is a slight depletion of HREE in relation to LREE, especially in one locality of the inland dunes probably associated with the wind regime and weathering of unstable heavy minerals in the sands. Inland, transitional, and coastal dune fields can be observed as different dune provinces by means of grouping HM and REE data in two separate dendograms. It seems that HREE are correlated with fine-grained sand sizes and correlated with high CIA values linked to slightly weathered sands.

RADIOCARBON LABORATORY AT THE NATIONAL AUTONOMOUS UNIVERSITY OF MEXICO: FIRST SET OF SAMPLES AND NEW 14C INTERNAL REFERENCE MATERIAL

This contribution reports the first set of samples and the creation of an internal reference material at the recently opened Radiocarbon Laboratory at the National Autonomous University of Mexico (UNAM). Samples for the initial measurements were selected from archaeological and dating projects on Teotihuacn, one of the largest and best-studied Mesoamerican urban and ceremonial centers. The 14C dates were compared to results obtained by 2 other laboratories in order to assess the results obtained at UNAM and validate the adopted methodology. As part of the quality assurance protocol, an internal reference material was created that consists of charred wood from the Teotihuacn site with a 14C activity in the value range expected for samples from Mesoamerican archaeological sites. Results from 7 analyses have a mean of 1750 16 BP (80.43 0.16 pMC).

Metal accumulation by plant species growing on a mine contaminated site in Mexico

The present work aims to assess the efficiency of heavy metal accumulation of native species growing in contaminated soils in the mining district of Taxco, Mexico. Soil and tailing sampling was conducted in three study sites: La Concha, El Fraile, and a control site. The study localities present diverse metal concentrations with significant differences in their proportion in the geochemical fractions. Results show that species Cupressus lindleyi and Juniperus deppeana accumulate Zn and Mn in anomalous concentrations at La Concha, where Zn is present in soluble fractions. Manganese, despite not being present mostly in the soluble fraction in soils and tailings, seems to have been increased in the soluble fraction after the plant growth. In contrast, samples of the same species taken at El Fraile and in the control site, where Zn and Mn are mainly contained in the residual fraction, do not show an anomalous enrichment. Other analyzed species growing under the same contamination conditions in La Concha (Jacaranda mimosifolia and Psidium guajava) do not show anomalous concentrations. These facts confirm the Zn and Mn accumulation capacity of C. lindleyi and Ju. deppeana, which depends on their accumulation ability and on the concentration of these elements in the soluble fraction.

Increase of the Environmental Pt Concentration in the Metropolitan Area of Mexico City Associated to the Use of Automobile Catalytic Converters

This work shows the results of de investigations concerning Pt concentration in the environment of Mexico City, product of the impact of the use of catalytic converters in the urban area. This research was carried out by assessing Pt concentration in dust samples and PM2.5 collected in the metropolitan area of Mexico City. Dust samples were divided in “road dust” and “urban dust” according to vehicle traffic exposure. Pt concentration in road dust samples, exposed to high traffic density, range from 37.7 to 231 µg kg−1 (mean 112 µg kg−1), whereas Pt concentration found in urban dust, collected in areas with low traffic density, varied between 26.4 and 86.6 µg kg−1 (mean 57 µg kg−1). PM2.5 samples were collected in five sites of the urban area during three different seasons (dry-warm, rainy, dry-cold). Results do not show significant spatial or temporal variation. Pt concentration ranges from 1 to 79 pg m−3. The comparison of Pt concentration in dust and PM2.5 samples presented here, with data reported for other urban areas, as well as with data previously reported for PM10 collected in 1991 and 2003 for the metropolitan area of Mexico City, allows to conclude a significant increase of Pt in this urban environment.

Changes in CO2 Emission Sources in Mexico City Metropolitan Area Deduced from Radiocarbon Concentrations in Tree Rings

We present radiocarbon ( 14 C) in tree rings from Mexico City and a reconstruction of fossil CO 2 concentrations for the last five decades, as part of a research program to understand the 14 C dynamics in this complex urban area. Background values were established by 14 C concentrations in tree rings from a nearby clean area. Agreement between background and NH-zone 2 values indicate Taxodium mucronatum is a good biomonitor for annual atmospheric 14 C variations. Values for the urban tree rings were significantly lower than background values, indicating a 14 C depletion from fossil CO 2 emissions. There is an increasing trend of fossil CO 2 between 1960 and 1990, in agreement with the population growth and the increasing demand for fossil fuels in Mexico City. Between 1990 and 2000, there is an apparent decrease in fossil CO 2 concentration, increasing again after 2000. The decrease in 2000, despite being of the same magnitude as the overall uncertainty, may reflect environmental policies that improved the energy efficiency and reduced CO 2 emissions in the area. The increase in fossil CO 2 concentration between 2000 and 2010 may be attributable to the significant growth of motor vehicle usage in Mexico City, which made transportation the main energy-demanding and -emitting sector.