Dina L. Lopez

One century of arsenic exposure in Latin America: a review of history and occurrence from 14 countries.

The global impact on public health of elevated arsenic (As) in water supplies is highlighted by an increasing number of countries worldwide reporting high As concentrations in drinking water. In Latin America, the problem of As contamination in water is known in 14 out of 20 countries: Argentina, Bolivia, Brazil, Chile, Colombia, Cuba, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Peru and Uruguay. Considering the 10 μg/L limit for As in drinking water established by international and several national agencies, the number of exposed people is estimated to be about 14 million. Health effects of As exposure were identified for the first time already in the 1910s in Bellville (Córdoba province, Argentina). Nevertheless, contamination of As in waters has been detected in 10 Latin American countries only within the last 10 to 15 years. Arsenic is mobilized predominantly from young volcanic rocks and their weathering products. In alluvial aquifers, which are water sources frequently used for water supply, desorption of As from metal oxyhydroxides at high pH (>8) is the predominant mobility control; redox conditions are moderate reducing to oxidizing and As(V) is the predominant species. In the Andes, the Middle American cordillera and the Transmexican Volcanic Belt, oxidation of sulfide minerals is the primary As mobilization process. Rivers that originate in the Andean mountains, transport As to more densely populated areas in the lowlands (e.g. Rímac river in Peru, Pilcomayo river in Bolivia/Argentina/Paraguay). In many parts of Latin America, As often occurs together with F and B; in the Chaco-Pampean plain As is found additionally with V, Mo and U whereas in areas with sulfide ore deposits As often occurs together with heavy metals. These co-occurrences and the anthropogenic activities in mining areas that enhance the mobilization of As and other pollutants make more dramatic the environmental problem.

FLUID FLOW IN FAULT ZONES : INFLUENCE OF HYDRAULIC ANISOTROPY AND HETEROGENEITY ON THE FLUID FLOW AND HEAT TRANSFER REGIME

Fluid circulation, heat transfer, and the development of thermal springs are examined for vertical fault zones with anisotropic permeability and internal heterogeneity. Interactions between thermally driven convective circulation in the fault zone and topographically driven groundwater flow through the surrounding country rock are mapped in permeability space (permeability of the country rock versus fault zone permeability) and compared to earlier results for homogeneous, isotropic fault zones. Simulations with a fault zone 4–10 times more permeable in the strike than in the dip direction show that the field of steady convection expands in permeability space, promoting stable convection at both higher and lower flux rates. Higher groundwater discharge temperatures (by 12–18°C) are predicted relative to an isotropic fault because this anisotropy favors the formation of a smaller number of convection cells, creating a flow pattern that is more efficient in capturing heat from the country rock and transmitting it to a reduced number of discharge sites. Simulations with a fault zone 4–10 times less permeable in the strike than the dip direction indicate the regional flow from the country rock overrides buoyancy-driven convective circulation in the fault zone at lower values for the country-rock permeability. Heterogeneity internal to the fault creates complex patterns of flow and variations in the geothermal gradient that reflect the connections of higher-permeability regions interior to and along the surface trace of the fault. Channeling of the flow leads to minor differences in the maximum discharge temperature relative to the homogeneous case but creates significant enhancement in the local heat flux owing to the higher groundwater discharge rates.

Arsenic in the human food chain: the Latin American perspective

Many regions of Latin America are widely reported for the occurrence of high arsenic (As) in groundwater and surface water due to a combination of geological processes and/or anthropogenic activities. In this paper, we review the available literature (both in English and Spanish languages) to delineate human As exposure pathways through the food chain. Numerous studies show that As accumulations in edible plants and crops are mainly associated with the presence of high As in soils and irrigation waters. However, factors such as As speciation, type and composition of soil, and plant species have a major control on the amount of As uptake. Areas of high As concentrations in surface water and groundwater show high As accumulations in plants, fish/shellfish, livestock meat, milk and cheese. Such elevated As concentrations in food may result in widespread health risks to local inhabitants, including health of indigenous populations and residents living close to mining industries. Some studies show that As can be transferred from the water to prepared meals, thereby magnifying the As content in the human diet. Arsenic speciation might also change during food preparation, especially during high temperature cooking, such as grilling and frying. Finally, the review of the available literature demonstrates the necessity of more rigorous studies in evaluating pathways of As exposure through the human food chain in Latin America.

Arsenic in volcanic geothermal fluids of Latin America

Numerous volcanoes, hot springs, fumaroles, and geothermal wells occur in the Pacific region of Latin America. These systems are characterized by high As concentrations and other typical geothermal elements such as Li and B. This paper presents a review of the available data on As concentrations in geothermal systems and their surficial discharges and As data on volcanic gases of Latin America. Data for geothermal systems in Mexico, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, Ecuador, Bolivia, and Chile are presented. Two sources of As can be recognized in the investigated sites: Arsenic partitioned into volcanic gases and emitted in plumes and fumaroles, and arsenic in rocks of volcanic edifices that are leached by groundwaters enriched in volcanic gases. Water containing the most elevated concentrations of As are mature Na-Cl fluids with relatively low sulfate content and As concentrations reaching up to 73.6 mg L⁻¹ (Los Humeros geothermal field in Mexico), but more commonly ranging from a few mg L⁻¹ to tens of mg L⁻¹. Fluids derived from Na-Cl enriched waters formed through evaporation and condensation at shallower depths have As levels of only a few μg L⁻¹. Mixing of Na-Cl waters with shallower meteoric waters results in low to intermediate As concentrations (up to a few mg L⁻¹). After the waters are discharged at the ground surface, As(III) oxidizes to As(V) and attenuation of As concentration can occur due to sorption and co-precipitation processes with iron minerals and organic matter present in sediments. Understanding the mechanisms of As enrichment in geothermal waters and their fate upon mixing with shallower groundwater and surface waters is important for the protection of water resources in Latin America.

Precursory diffuse carbon dioxide degassing signature related to a 5.1 magnitude earthquake in El Salvador, Central America

Abstract Anomalous changes in the diffuse emission of carbon dioxide have been observed before some of the aftershocks of the 13 February 2001 El Salvador earthquake (magnitude 6.6). A significant increase in soil CO 2 efflux was detected 8 days before a 5.1 magnitude earthquake on 8 May 2001 25 km away from the observation site. In addition, pre- and co-seismic CO 2 efflux variations have also been observed related to the onset of a seismic swarm beneath San Vicente volcano on May 2001. Strain changes and/or fluid pressure fluctuations prior to earthquakes in the crust are hypothesized to be responsible for the observed variations in gas efflux at the surface environment of San Vicente volcano.

Effect of subsidence on recharge at abandoned coal mines generating acidic drainage: The Majestic Mine, Athens County, Ohio

This paper addresses the relationship between the geology, hydrology, and transient variations in discharge and water chemistry of acidic water discharged by an abandoned underground coal mine: the Majestic Mine in Athens County, Ohio, a partially-flooded, downdip, drift mine. The Middle Kittanning (No. 6) Coal (Allegheny Series, Pennsylvanian System) was mined room-and-pillar until 1921. Loss of support from mine collapse has created large vertical subsidence fractures along the naturally occurring joints within the brittle sandstone overburden. The mine discharge hydrograph, temperature, and pH of the mine discharge indicate that the hydrology of the Majestic Mine can be explained in terms of pseudokarst hydrology. During rainfall events, water is preferentially recharged through the subsidence features. Increased pressure from the mine inflow is transmitted through the flooded workings, causing a rapid increase in discharge, and forcing older mine water out of the mine. A stream draining an overlying watershed is captured by one of the subsidence features, contributing 60 to 80% of the mine water outflow. During the summer, recharge to the mine is negligible because potential evapotranspiration is higher than precipitation. During late summer and fall months, when the mine pool is at its lowest elevation, atmospheric oxygen penetrates back into the mine workings, enhancing the oxidation reactions. During the increased discharge of the spring months, washing of the reaction products from the mine walls produces the highest metals concentrations and chemical loads. *** DIRECT SUPPORT *** A03BX002 00004

Characterization and assessment of chemical modifications of metal-bearing sludges arising from unsuitable disposal

Ettringite-gypsum sludge, formed by neutralization of acid mine drainage with lime, has been stored temporarily in the open pit of a uranium mine that floods periodically. The present study characterized samples of this sludge, named according to the time of placement as Fresh, Intermediate, and Old. Standard leaching and sequential extraction procedures assessed the associations and stabilities of U, Zn, Fe, Mn, and other contaminants in the solid phases. Corresponding mineralogical transformations associated with sludge weathering were modeled using PHREEQC. The main crystalline phases were ettringite, gypsum and calcite; the minor constituents were fluorite and gibbsite. This mineral assemblage could be attributed to the incongruent dissolution of ettringite to form gibbsite, calcite, and gypsum. Sequential extractions indicated high contents of U, Ca, SO(4), and Zn in the water-soluble (exchangeable) and carbonate fractions. Thus, the analytical and modeling results indicated that despite being classified as non-toxic by standard leaching protocols, the minerals composing the sludge could be sources of dissolved F, SO(4), Fe, Zn, Mn, U, and Al under various environmental conditions. Decommissioning strategies intended to prevent contaminant migration will need to consider the chemical stability of the sludge in various environments.

Characterization and fate of polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in soils and sediments at the Portsmouth Gaseous Diffusion Plant, Ohio

The U.S. Department of Energy Portsmouth Gaseous Diffusion Plant is in the early stages of decommissioning and decontamination. During operations, the site drew a large amount of electric power and had multiple large switchyards on site. These are a source of polychlorinated biphenyls (PCB) contamination to both on-site and off-site streams. Some soil remediation has been completed in the main switchyard. During 2011 and 2012, fifteen sites were sampled at the surface (<10 cm) and subsurface (20-30 cm) to characterize the extent of PCB contamination, to identify weathering and migration of PCB contamination and to explore potential polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) contamination due to transformer fires and explosions in the 1950s and 1960s. Stagnant sites tended to exhibit more migration of contamination to deeper sediments than sites with fast-moving waters, and the highest concentrations were found at the bottom of a settling pond. A signature set of five dioxin-like PCBs were consistently found across the site with higher concentrations in carbon rich surface sediments. PCB concentrations had a significant inverse correlation with clay content, suggesting that PCBs did not bind to clays at this site. Remediation has reduced PCB concentrations throughout the site compared to levels found in previous studies and long-term upkeep of sediment lagoons is necessary to retain PCB and dioxin-rich sediments. The flow regimen, organic carbon and clay content play a very important role in the fate of PCBs in the environment at the surface as well as downward migration.

Solute Transport at Low Flow in an Acid Stream in Appalachian Ohio

The spatial variability in chemical composition of water and sediments along Snow Fork, a stream draining 70 km2 of southeastern Ohio, was investigated under low-flow conditions. The stream is affected by acid mine drainage (AMD) beginning atEssex Mine, an abandoned mine opening, and extending 23 km downstream to the confluence with Monday Creek. Volumetric discharge and changes in stream water and sediment metalconcentrations were examined to identify chemical interactionsand processes controlling the transport and fate of metalcontaminants. The stream loses water to the groundwater system insome sections. The water loss probably occurs through fracturesconnecting the stream to underlying underground coal mines. Massbalance (loading) and mineral saturation index calculations wereused to identify metal sources and sinks. Dissolved metal loadingincreases downstream along the length of Snow Fork, despite theprecipitation of metals as hydroxides in the streambed,indicating multiple groundwater sources of AMD along the flowpath. Relatively high dissolved metal concentrations and lowsediment metal concentrations occur where the pH is low,indicating that local sediment-water interaction dominates masstransfer between sediments and water. Calculated mineralsaturation indexes indicate that aluminum and iron hydroxidesprecipitate in some stream segments and dissolve in others. X-raydiffractograms of sediments show two distinct mineral groups.Amorphous or weakly crystalline minerals dominate one group foundnear the stream headwaters near the underground mine. Crystallinemineral phases dominate the sediments downstream. Thesediffractograms contain the primary peaks for quartz, kaoliniteand illite all of which constitute the local sandstones, shalesor underclay. Peaks of amorphous phases of iron and manganese,if present, are obscured. The implications of these findings arethat the transport of metals in sediments may be as important asdissolved metal transport in estimating the overall stream load,particularly if downstream sources of AMD may remobilize metalsfrom soluble precipitates.

Airborne castanea pollen forecasting model for ecological and allergological implementation.

Castanea sativa Miller belongs to the natural vegetation of many European deciduous forests prompting impacts in the forestry, ecology, allergological and chestnut food industry fields. The study of the Castanea flowering represents an important tool for evaluating the ecological conservation of North-Western Spain woodland and the possible changes in the chestnut distribution due to recent climatic change. The Castanea pollen production and dispersal capacity may cause hypersensitivity reactions in the sensitive human population due to the relationship between patients with chestnut pollen allergy and a potential cross reactivity risk with other pollens or plant foods. In addition to Castanea pollens importance as a pollinosis agent, its study is also essential in North-Western Spain due to the economic impact of the industry around the chestnut tree cultivation and its beekeeping interest. The aim of this research is to develop an Artificial Neural Networks for predict the Castanea pollen concentration in the atmosphere of the North-West Spain area by means a 20years data set. It was detected an increasing trend of the total annual Castanea pollen concentrations in the atmosphere during the study period. The Artificial Neural Networks (ANNs) implemented in this study show a great ability to predict Castanea pollen concentration one, two and three days ahead. The model to predict the Castanea pollen concentration one day ahead shows a high linear correlation coefficient of 0.784 (individual ANN) and 0.738 (multiple ANN). The results obtained improved those obtained by the classical methodology used to predict the airborne pollen concentrations such as time series analysis or other models based on the correlation of pollen levels with meteorological variables.