Contamination of the Conchos River in Mexico: Does It Pose a Health Risk to Local Residents?

Presently, water contamination issues are of great concern worldwide. Mexico has not escaped this environmental problem, which negatively affects aquifers, water bodies and biodiversity; but most of all, public health. The objective was to determine the level of water contamination in six tributaries of the Conchos River and to relate their levels to human health risks. Bimonthly samples were obtained from each location during 2005 and 2006. Physical-chemical variables (temperature, pH, electrical conductivity (EC), Total solids and total nitrogen) as well as heavy metals (As, Cr, Cu, Fe, Mn, Ni, V, Zn, and Li) were determined. The statistical analysis considered yearly, monthly, and location effects, and their interactions. Temperatures differed only as a function of the sampling month (P < 0.001) and the pH was different for years (P = 0.006), months (P < 0.001) and the interaction years x months (P = 0.018). The EC was different for each location (P < 0.001), total solids did not change and total nitrogen was different for years (P < 0.001), months (P < 0.001) and the interaction years x months (P < 0.001). The As concentration was different for months (P = 0.008) and the highest concentration was detected in February samples with 0.11 mg L−1. The Cr was different for months (P < 0.001) and the interaction years x months (P < 0.001), noting the highest value of 0.25 mg L−1. The Cu, Fe, Mn, Va and Zn were different for years, months, and their interaction. The highest value of Cu was 2.50 mg L−1; for Fe, it was 16.36 mg L−1; for Mn it was 1.66 mg L−1; V was 0.55 mg L−1; and Zn was 0.53 mg L−1. For Ni, there were differences for years (P = 0.030), months (P < 0.001), and locations (P = 0.050), with the highest Ni value being 0.47 mg L−1. The Li level was the same for sampling month (P < 0.001). This information can help prevent potential health risks in the communities established along the river watershed who use this natural resource for swimming and fishing. Some of the contaminant concentrations found varied from year to year, from month to month and from location to location which necessitated a continued monitoring process to determine under which conditions the concentrations of toxic elements surpass existing norms for natural waters

Co-occurrence, possible origin, and health-risk assessment of arsenic and fluoride in drinking water sources in Mexico: Geographical data visualization

Arsenic and fluoride in drinking water present a significant challenge to public health worldwide. In this study, we analyze the results of one of the largest surveys of drinking water quality in Mexico: 14,058 samples from 3951 sites, collected between January and December 2017. We use these data to identify the distribution and possible origin of arsenic and fluoride in drinking water throughout the country, and to estimate the associated health burden. The highest concentrations appear in alluvial aquifers in arid northern Mexico, where high-silica volcanic rock likely releases both arsenic and fluoride to the groundwater. We find fluoride contamination to be significantly correlated with aridity (Pearson correlation = −0.45, p = 0.0105), and also find a significant difference in fluoride concentrations between arid and humid states (Welch's t-test, p = 0.004). We estimate population exposure by assigning to each town in Mexico the average concentration of any sampling sites within 5 km. Our results show that 56% of the Mexican population lives within 5 km of a sampling site, 3.05 million people are exposed to fluoride above the reference dosage of 0.06 mg/(kg ∗ day), 8.81 million people are exposed to arsenic above the limit of 10 μg/L, and an additional 13,070 lifetime cases of cancer are expected from this arsenic exposure alone. This burden of disease is concentrated in the arid states of north-central Mexico

Competitive adsorption interactions of strontium, cobalt and cesium in suspensions of calcium montmorillonite: Electrochemical behavior and modeling.

In this study, the capacity of calcium montmorillonite to adsorb stable Sr, Cs, and Co (analogs of typical low-level waste radionuclides), under a variety of operational conditions, was investigated. Specifically, the objectives of this study were to determine the factors governing adsorption, the reversibility of the adsorption process, and to model variations of adsorption with respect to pH, ionic strength and presence of competitive cations. The adsorption of Sr and Cs is insensitive to pH in a range of 4 to 9, while Co adsorption increases in alkaline conditions (pH $\u3e$ 8), suggesting that the complexating behavior of cobalt is reflected in its adsorption behavior. The adsorption was more reversible for Cs than for Sr and Co, implying that hydrated Sr and Co adsorb in the interlayer, while Cs probably adsorbs in the broken edges of the particles. The presence of competing cations causes a decrease in adsorption of Sr, Cs, and Co. Adsorption of these cations at intermediate concentrations was modeled using a logarithmic function, in both single-component and mixture systems. Deviations from the logarithmic behavior at low (C\sb{e}1000 $\mu$eq/L) concentrations suggest linear adsorption for the former and other reactions, such as precipitation and multiple-layer adsorption, for the latter. The comparable magnitude of the competition coefficients obtained for Sr, Cs and Co in binary mixtures implies that these cations exert similar degree of competiveness. Adsorption data was also modeled by surface complexation models (SCM), based on a hypothesis of four mechanisms: protonation and deprotonation of surface groups, adsorption of target cations in OH-sites, and ion-exchange of the targeted cation with Ca ions of the surface. Complete analysis of the chemical species present in the solution was found to be useful to determine the surface-solution interphase interactions occurring in a particular system, by allowing the calculation of mass- and charge-balances in each phase. Variations in adsorption results due to the type of electrolyte solution used as background suggests the use of a standardized procedure for adsorption batch experiments, so that results obtained by different researchers can be compared. A full description of the response of the system to parameters that affect adsorption is essential to predict contaminant transport, in case of soil contamination events. (Abstract shortened by UMI.

Making Connections to Real Data and Peer-Review Literature: A Short Soil Exercise in a Geochemistry Class

A class exercise was designed for a college-level geochemistry class to promote inquiry and student participation. In this exercise, real soil data available online was analyzed to evaluate geochemical associations among different soil orders and as a screening tool for anthropogenic metal contamination. Students were asked to read a peer-reviewed research article and use the methods in it as a model for analyzing their dataset. The exercise provided a setting to review and reflect on the changes that rocks undergo to produce soils, with ion substitution and formation of clay minerals as key steps in this process. Both active learning and cooperative learning were involved. Students made decisions about which path to take toward reaching a common goal; they first worked independently and later discussed the results as a group, comparing between three statistical methods applied with the data with respect to their advantages and limitations. The real-life dataset exposed students to the common shortcoming of having less-than-ideal coverage of data forced them to make decisions on how to proceed further with their analysis, and provided a good example of how scientific research is conducted. Our approach allowed students to actively engage in their learning and reach their goals, which were evidenced by their comments and their zeal to complete each part of the exercise; however, historic data collection is required to formalize these assertions

Heavy metal concentrations in drainage sediments possibly affected by landfill leachate

Leachate was observed outside the confines of the Stone County Landfill, Missouri. Ants Creek and South Ants Creek located in the vicinity of the landfill may have received leachate. Both streams drain into Table Rock Lake. Previous studies of other landfills in southwestern Missouri revealed the presence of enriched concentrations of some heavy metals in drainage sediments of streams affected by leachate. Sediments were collected from the same location sites along the two aforementioned streams in 1992 and 1995. The purpose of this research was to determine if the two streams were affected by leachate and if there was a change in metal content between 1992 and 1995. Samples were also collected in 1995 from a stream which acted as the control for the study. Two different sediment size fractions were used in the study. The concentrations of Cu, Pb, Zn, Cd, Co, Ni, Cr, Fe, Mn, Ba, Ca, and Ag were determined in some geochemical phases of the finer grain size fraction while the same metals were determined from a nitric acid extraction in the larger grain size fraction. Atomic absorption techniques were used in the study. More than 4,200 metal concentration determinations were made in this study. The results indicated no enrichment of metal concentrations in the sediments of Ants Creek and South Ants Creek. Also there was no significant difference in the content of each metal in the sediments of Ants Creek compared to the same in South Ants Creek. This result was the same in samples representing both years. It was concluded that leachate from the landfill had no noticeable affects on sediments in both streams. Therefore it appeared that waters and sediments in Table Rock Lake were not enriched in these metals from landfill activity.Project # G-2029-03 Agreement # 14-08-0001-G-2029-0

Watershed assessment along a segment of the Rio Conchos in Northern Mexico using satellite images

Satellite images were used to illustrate the usefulness of such data in evaluating the ecological impacts of precipitation and land use on selected segments of the lower Rio Conchos in northern Mexico. Variations in the size and turbidity of impounded reservoirs, riparian vegetation, soil salinity and land use within the Rio Conchos basin were analysed using four Landsat TM images over a period of 10 years. A variety of image enhancements were applied to determine subtle changes between the images. These, when combined with precipitation and historical land-use data as well as one time water quality and soil EC, provided useful interpretation of the images, and therefore, in the monitoring of the basin

Abandoned Pb-Zn mining wastes and their mobility as proxy to toxicity: A review

Lead and zinc (PbZn) mines are a common occurrence worldwide; and while approximately 240 mines are active, the vast majority have been abandoned for decades. Abandoned mining wastes represent a serious environmental hazard, as Pb, Zn and associated metals are continuously released into the environment, threatening the health of humans and affecting ecosystems. Iron sulfide minerals, when present, can form acid mine drainage and increase the toxicity by mobilizing the metals into more bioavailable forms. Remediation of the metal waste is costly and, in the case of abandoned wastes, the responsible party(ies) for the cleanup can be difficult to determine, which makes remediation a complex and lengthy process. In this review, we provide a common ground from a wide variety of investigations about concentrations, chemical associations, and potential mobility of Pb, Zn and cadmium (Cd) near abandoned PbZn mines. Comparing mobility results is a challenging task, as instead of one standard methodology, there are 4-5 different methods reported. Results show that, as a general consensus, the metal content of soils and sediments vary roughly around 1000 mg/kg for Zn, 100 for Pb and 10 for Cd, and mobilities of Cd \u3e Zn \u3e Pb. Also, mobility is a function of pH, particle size, and formation of secondary minerals. New and novel remediation techniques continue to be developed in laboratories but have seldom been applied to the field. Remediation at most of the sites has consisted of neutralization (e.g. lime,) for acid mine discharge, and leveling followed by phytostabilization. In the latter, amendments (e.g. biochar, fertilizers) are added to boost the efficiency of the treatment. Any remediation method has to be tested before being implemented as the best treatment is site-specific. Potential treatments are described and compared

Geochemical Fractionation of Stream Sediments Impacted by Pb-Zn Mining Wastes: Missouri, USA

Stream sediments affected by historic mining in Aurora, Missouri, were digested via sequential extraction to determine the amount of Zn, Pb, and Cd bound to each of five geochemical phases: exchangeable, carbonate, Fe-Mn oxides, organic matter, and residual. The metal bound to the exchangeable and carbonate phases represents an approximation of the metal that is bioavailable, and thus a source of toxicity to aquatic biota and a contamination risk to the aquifer underneath. The bioavailable fraction was found to increase with total metal content, comprising an average of 19% of the total Zn, 13% of the Pb, and 14% of the Cd. In general, Pb was preferentially bound to the residual fraction, Zn to the Fe-Mn oxides fraction, and Cd to the organic fraction. As a result of metals binding to different chemical fractions, each of these metals will mobilize differently if/as environmental conditions change and chemical weathering progresses. The most mobile of the three metals was Cd and the least mobile Pb. The concentration pattern for each metal downstream reflects their relative mobility

Geochemical mapping of Pb- and Zn-contaminated streambed sediments in southwest Missouri, USA

Purpose: Four locations in southwest Missouri, USA, purportedly contaminated with mining wastes, Joplin, Aurora, Springfield, and the James River, were investigated for lead and zinc content using spatial distribution and statistical analyses. Lead (Pb) and zinc (Zn) concentrations in streambed sediment samples were compared spatially against a regional background concentration map to determine both the contamination level and dispersion of these metals. Materials and methods: Streambed sediment data were retrieved from USGS Geochemical Databases (N = 1,019) with which sediment geochemical maps were constructed. Publically available metal content data for each of four historic mining sites were also retrieved from separate studies. The Pb and Zn concentrations at each of the historic mining sites were compared against background concentrations using geochemical mapping interpolation (inverse distance weighted (IDW) method), box plot diagrams, Pearson correlation, and rationing. Results and discussion: Pb and Zn were present in a large range of concentrations in the regional background concentration data (concentrations up to 3,460 mg kg-1 Pb and 14,027 mg kg-1 Zn) with a median of 22.0 and 53.0 mg kg-1, respectively. Concentrations of Pb and Zn in Joplin and Aurora were significantly higher, while the concentrations of Pb and Zn at the two sites near Springfield were closer to regional background concentrations. The metal content maps and association among metals both indicate that mining wastes are the main source of contamination. Conclusions: Even though mining ceased over 40 years ago and remediation has been applied to the area, some streambed sediments in the area contain potentially toxic concentrations of Pb and Zn, especially around the cities of Joplin and Aurora. The background geochemical maps of the area were instrumental for identifying the sources and extent of these metals in sediments in this area

State of remediation and metal toxicity in the Tri-State Mining District, USA

Mining operations in the Tri-State Mining District of Kansas, Missouri and Oklahoma (TSMD), once one of the major lead and zinc mining areas in the world, had completely ceased by 1970. As mining companies moved out, the land was left with underground tunnels and mine shafts and the surface with abandoned tailings piles, which progressively contaminated groundwater and soil. Despite remedial actions undertaken in the 1980\u27s, areas within the TSMD still contain Cd, Pb, and Zn concentrations exceeding safe levels. Because of the large area and highly dispersed occurrence of wastes, environmental studies generally have been confined either to a stream basin or to a single state. Studies also have differed in their approach and analytical methodologies. An overview of the totality of the TSMD and its present state of contamination is presented here. Data show that metal content in sediments have the following common features: (1) a wide range of Pb and Zn concentrations, up to three orders of magnitude, (2) median values for Cd, Pb and Zn content in sediments and soils were similar among studies, (3) median values for most studies were at or above the guidelines recommended for aquatic habitats, and (4) highest content of Pb and Zn were closely associated with the geographical location of former mining and smelting centers. The above observations imply that mine wastes remain a problem and further remediation is needed. Cost-effective remedial alternatives for this area\u27s geology, climate, and land use, are discussed