Ramiro Rodríguez

Arsenic distribution in mesquite (Prosopis laevigata) and huizache (Acacia farnesiana) in the Zimapán mining area, México

Arsenic concentrations have been determined in mesquite (Prosopis laevigata) and huizache (Acacia farnesiana) growing on As-rich soils in the semi-arid mining area of Zimapán, México. The elevated As contents in the substrates (up to 32 000 mg/kg) were reflected in the dry weight concentrations of twigs (up to 82.7 mg/kg in mesquite and 225 mg/kg in huizache), and leaves (up to 78.2 mg/kg in mesquite and 67.0 mg/kg in huizache). Arsenic concentrations in twigs and leaves collected in less impacted soils (containing up to 110 mg/kg of As) reached a maximum of 20.8 mg/kg in mesquite twigs and 27.8 mg/kg in mesquite leaves. Differences of several orders of magnitude in surface substrate As concentrations were not reflected in plant As contents. A low proportion of available As in substrates, as well as deep plant roots which may reach less contaminated sediments, explains this behaviour. The pod As concentrations from tailings-affected sites were not significantly different from background samples. Nearly all mesquites and huizaches from the high-As substrates were above standards for foodstuffs. The As concentration in vegetation growing on soils affected by tailings and smelter/slags points to a potential contamination of the food chain, mainly through goats, the most common mammals in the area. Mesquites and huizaches are not hyperaccumulators but are As-tolerant plants and can therefore be considered as an option for a remediation programme to stabilize eroding tailings.

Evaluation of hydrochemical changes due to intensive aquifer exploitation: case studies from Mexico

The impact of intensive aquifer exploitation has been observed in numerous places around the world. Mexico is a representative example of this problem. In 2010, 101 out of the 653 aquifers recognized in the country, showed negative social, economic, and environmental effects related to intensive exploitation. The environmental effects include, among others, groundwater level decline, subsidence, attenuation, and drying up of springs, decreased river flow, and deterioration of water quality. This study aimed at determining the hydrochemical changes produced by intensive aquifer exploitation and highlighting water quality modifications, taking as example the Valle de Toluca, Salamanca, and San Luis Potosi aquifers in Mexico’s highlands. There, elements such as fluoride, arsenic, iron, and manganese have been detected, resulting from the introduction of older groundwater with longer residence times and distinctive chemical composition (regional flows). High concentrations of other elements such as chloride, sulfate, nitrate, and vanadium, as well as pathogens, all related to anthropogenic pollution sources (wastewater infiltration, irrigation return flow, and atmospheric pollutants, among others) were also observed. Some of these elements (nitrate, fluoride, arsenic, iron, and manganese) have shown concentrations above Mexican and World Health Organization drinking water standards.

Geological, hydrogeological, and geothermal factors associated to the origin of arsenic, fluoride, and groundwater temperature in a volcanic environment El Bajío Guanajuatense, Mexico

Arsenic and fluoride groundwater concentrations over national standards for drinking water were measured in the regional aquifer of Juventino Rosas, Guanajuato State, Central Mexico. Also anomalous temperature occurs in groundwater wells of the area. Concentrations of total dissolved solids, silica, and chloride are too low to indicate a geothermal heat source. Additionally, isotopic evidence indicates that groundwater from the studied wells is subject to an evaporation process affected by the humid weather of the zone. The chemical characteristics of the water indicate a deep circulation warm water system in normal geothermal gradient. The warm waters of Juventino Rosas are mainly of three types: Water type I: (Na–HCO3), represented by the highest temperature wells and presence of fluoride and arsenic; water type II (Na–Ca–HCO3) that represents a mixing process between water types I and III. In this group, the sample 13JR contained high concentration of F−; water type III (Ca–HCO3), represented only by one sample (Cen 2) located over the outcrop of shales, limestones, and metamorphic rocks. This sample contains the highest concentrations of sulfate, manganese, and iron. All the geological and geochemical evidences indicate that rhyolite units are the most probable source of As and F−. The area corresponds to a low-temperature and low-enthalpy system and not to a well defined geothermal system.

The origin of groundwater arsenic and fluorine in a volcanic sedimentary basin in central Mexico: a hydrochemistry hypothesis

A groundwater sampling campaign was carried out in the summer of 2013 in a low-temperature geothermal system located in Juventino Rosas (JR) municipality, Guanajuato State, Mexico. This groundwater presents high concentrations of As and F− and high Rn counts, mainly in wells with relatively higher temperature. The chemistry of major elements was interpreted with different methods, like Piper and D’Amore diagrams. These diagrams allowed for classification of four groundwater types located in three hydrogeological environments. The aquifers are hosted mainly in alluvial-lacustrine sediments and volcanic rocks in interaction with fault and fracture systems. The subsidence, faults and fractures observed in the study area can act as preferential channels for recharge and also for the transport of deep fluids to the surface, especially in the basin plain. The formation of a piezometric dome and the observed hydrochemical behavior of groundwater suggest a possible origin of the As and F−. Geochemical processes occurring during water–rock interaction are related to high concentrations of As and F−. High temperatures and alteration processes (like rock weathering) induce dissolution of As and F−-bearing minerals, increasing the content of these elements in groundwater.RésuméUne campagne d’échantillonnage des eaux souterraines a été menée durant l’été 2013 dans un système géothermal basse-température situé dans la municipalité de Juventino Rosas (JR), Etat du Guanajuato, Mexique. L’eau souterraine présente de fortes concentrations en As et F− et des teneurs élevées en Rn, surtout dans les puits à température relativement élevée. La chimie des majeurs a été interprétée par différentes méthodes, comme les diagrammes de Piper et D’Amore. Ces diagrammes tiennent compte du classement des 4 types d’eau souterraine, situés dans trois contextes hydrogéologiques. Les aquifères sont contenus principalement dans des sédiments fluvio-lacutres et des roches volcaniques connectées à des systèmes de failles et de fractures. La subsidence, les failles et les fractures observées dans l’aire d’étude peuvent agir comme des chenaux préférentiels pour la recharge ainsi que pour le transfert de fluides profonds vers la surface, particulièrement dans la plaine du bassin. La formation d’un dôme piézométrique et le comportement hyrogéochimique observé de l’eau souterraine suggèrent une origine possible de As et F−. Les processus géochimiques qui se produisent pendant l’interaction eau–roche sont associés aux fortes concentrations en As et F−. Les hautes températures et les processus d’altération (comme l’altération des roches) provoquent une dissolution des minéraux contenant As et F−, augmentant la concentration de ces éléments dans l’eau souterraine.ResumenSe llevó a cabo una campaña de muestreo de aguas subterráneas en el verano de 2013 en un sistema geotérmico de baja temperatura situado en el municipio de Juventino Rosas (JR), Estado de Guanajuato, México. Esta agua subterránea presenta altas concentraciones de As y F− y altos contenidos de Rn, principalmente en pozos con temperatura relativamente alta. Se interpreta la química de los principales elementos con diferentes métodos, como diagramas de Piper y de D’Amore. Estos diagramas permitieron clasificar cuatro tipos de aguas subterráneas ubicadas en tres ambientes hidrogeológicos. Los acuíferos se alojan principalmente en sedimentos aluviales, lacustres y rocas volcánicas en interacción con los sistemas de fallas y fracturas. La subsidencia, fallas y fracturas observadas en el área de estudio pueden actuar como canales preferenciales para la recarga y también para el transporte de fluidos profundos hacia la superficie, especialmente en la llanura de la cuenca. La formación de un domo piezométrico y el comportamiento hidroquímico observado en el agua subterránea sugieren un posible origen del F− y del As. Los procesos geoquímicos que ocurren durante la interacción agua–roca son relacionados con altas concentraciones de As y F−. Las altas temperaturas y los procesos de alteración (como meteorización de las rocas) inducen la disolución los minerales que llevan As y F−, aumentando el contenido de estos elementos en el agua subterránea.摘要2013年夏季在位于墨西哥瓜纳华托州Juventino Rosas市的低温地热系统中进行了地下水采样。地下水中砷、氟和氡的含量很高,主要是在相对较高温度的井中。采用不同的方法如Piper和 D’Amore图标法解译了主要元素的化学成分。这些图表可以对位于三个水文地质环境中的四种地下水类型进行分类。含水层主要赋存于冲积—湖湘沉积物中及具有断层和断裂系统的火山岩中。研究区观测到的沉降、断层和断裂可以充当补给的优先通道,也可以充当深层流体到地表的传输优先通道,特别是在盆地平原更是如此。测压丘的形成及地下水观测到的水文化学特征显示出了砷和氟的可能来源。水岩相互作用期间的地球化学过程与砷和氟的含量高有关。高温度和更替过程(如岩石风化)引起了含砷和含氟矿物的溶解,增加了这些元素在地下水中的含量。ResumoUma campanha de amostragem de águas subterrâneas foi realizada no verão de 2013 em um sistema de baixo gradiente de temperatura geotermal, localizado no município de Juventino Rosas (JR), Estado do Guanajuato, México. As águas do aquífero apresentam alta concentração de As e F− e alta contagem de Rn, principalmente em poços com temperatura relativamente mais elevada. A química dos elementos maiores dissolvidos foi interpretada em diferentes métodos, como diagramas de Piper e D’Amore. Estes diagramas permitiram a classificação de quatro tipos de águas subterrâneas localizadas em três ambientes hidrogeológicos. Os aquíferos estão hospedados principalmente em sedimentos aluvionares-lacustres e rochas vulcânicas de interação com sistemas de falhas e fraturas. A subsidência, falhas e fraturas observadas na área de estudo podem agir como canais preferenciais de recarga e também para o transporte de fluidos profundos para a superfície, especialmente na planície da bacia. A formação de domos piezométricos e o comportamento hidroquímico observado nas águas subterrâneas sugerem uma possível origem de As e F−. Os processos geoquímicos que ocorrem durante a interação água–rocha estão relacionados com a alta concentração de As e F−. Altas temperaturas e processos de alteração (como intemperismo) induzem a dissolução de minerais contendo As e F−, aumentando o teor desses elementos nas águas subterrâneas.

Methodological approach for the analysis of groundwater quality in the framework of the Groundwater Directive

All countries of the European Union are required to determine the evolution of groundwater quality, including trend assessment. With this aim, the Water Framework Directive advises using standardized statistical analysis, like least squares regression. But this methodology is not applicable to all situations and what’s more, does not offer a sound methodological framework. There are many statistical procedures to evaluate temporal behaviour of environmental data but, when applied unconnectedly, erroneous conclusions can be reached due to bias of assuming partial or particular conducts. In this paper, a methodology for studying such information is proposed, integrating most common methods for time series analysis. To provide a sound scientific basis to the methodology, statistic intervals combined with trend assessment are proposed, after adjusting a regression curve and applying smoothing techniques to select the baseline level. Confidence intervals have been used when a threshold value does exist. Whether it is not fixed or the baseline level exceeds the standard, prediction intervals were employed. The approach has been analysed at Plana de Vinaroz Groundwater Body (PV). As a result, PV is classed of poor chemical status in regard to diffuse pollution and sea water intrusion, and consequently a programme of measures is necessary. In relation with marine intrusion, a regional downward trend has been found, showing no further deterioration. An additional outcome of the procedure is a methodological framework for the systematic review of the relevant information for evaluation of Groundwater Body chemical status, which includes additional steps to check the effectiveness of the programme of measures and update the baseline level periodically. The proposed methodology, based on procedures usually applied separately, provides a comprehensive framework for groundwater quality data analysis. It will allow more rigorous implementation objectives of the Directive. Results obtained for the developed case are more robust from the statistical point of view, because all hypotheses have been contemplated.

Medical Geology in Mexico, Central America and the Caribbean

An overview of the occurrence, concentrations, and possible sources of toxic elements released by geogenic processes that may threat the health of millions of people of Mexico, Central America, and the Caribbean is presented. The geology and tectonic characteristics of Mexico and Central America constitute an appropriate environment for the presence of arsenic and fluoride in groundwater of many zones of the area. Health problems linked with As-tainted water consumption have been documented in Mexico and Nicaragua where epidemiological and toxicological studies have been developed. Fluorosis has been recognized mainly in the central and northern part of Mexico and also in Antigua, Puerto Rico, and Trinidad. Specific health effects resulting from exposure to natural dust transported from Africa have been identified in the Caribbean. Radon exposure may also affect the population living in volcanic and active tectonic environments. However, this problem has only been studied by some researchers, mainly in Mexico and Nicaragua. Collaboration among research groups and authorities has been scarce. The review presented here, although not exhaustive, shows the urgency for increasing that collaboration specially to identify polluted areas, sources, and health effects, of the routine collection and analysis of arsenic and fluoride in all potable water sources of the area, and of developing short-term measures to decrease their concentrations to safe levels.

Analysis of Groundwater Monitoring Data Sets with Non-Detect Observations: Application to the Plana de Sagunto (Valencia, Spain) Groundwater Body

Under article 17 of the Water Framework Directive the European Union was required to establish a framework to prevent and control groundwater pollution. Taking into consideration distinctive characteristics of groundwater concentration data, appropriate statistical tests are required. In this regard, Annex IV of the Groundwater Directive sets that all measurements below the quantification limit have to be substituted by half of the value of the highest quantification limit, except for total pesticides. To set a methodological approach to evaluate censored data, the Plana de Sagunto Ground Water Body has been chosen. Several methods have been tested based upon application to different degrees of censoring to the available sample data. Censored estimation techniques, like Kaplan-Meier or Robust Regression have proved to be helpful in checking compliance with threshold values.

Interdisciplinary hydrogeological investigations

Traditionally, the responsibility for hydrogeological investigations in developing countries falls on governmental institutions, accustomed more to the management and handling of the resource rather than to its research. At the present time, the characteristics of developing countries restrict the possibility of applying and developing contemporary techniques and methodologies in the field of hydrogeology to universities or high‐level educational institutions, which do not necessarily maintain communication with the authorities in charge of the supply and administration of water. As an example of this research policy the Aquifer Development Project, carried out by the Geophysics Institute of the National University of Mexico (UNAM), is presented.