H42A-01 INVITED
Water, Water Everywhere but is it Safe to Drink? Some Detrimental Health Effects Associated with Consumption of Groundwater Enriched in Naturally-Occurring Contaminants
Drinking water represents a major pathway of trace elements into the human body. As such, groundwaters, the chemistry of which reflect water/rock interaction, can be a source of trace elements which will have a marked health effect on humans consuming them. Health problems associated with the consumption of groundwater enriched in various elements and compounds have been recorded for many years. For example, high-arsenic groundwaters used for public water supply were first associated with harmful health effects as early as 1917 in Córdoba Province in Argentina, where the local population suffered from skin disorders. Subsequently, in the 1960s consumption of high-arsenic groundwaters was identified as a factor in the aetiology of "black foot disease", an endemic vascular disease, in Taiwan. However, it is problems associated with the very high-arsenic groundwaters of the highly populous Ganges delta area of Bangladesh and West Bengal that has more recently highlighted the health problem of consuming high-arsenic waters. The most obvious problems of excess arsenic consumption through drinking water are arsenical skin lesions, the severity of which being generally correlated with arsenic content of the water. A high incidence of cancers of the skin, bladder and other organs has been recorded in the high-arsenic drinking water areas of the world. A high incidence of vascular disease, found in the arsenic-rich area of Taiwan, has also been shown to occur in Bangladesh. In addition, it has been suggested that high arsenic in drinking water results in increased incidence of diabetes mellitus. Fluorine is another element long recognised as having a major effect on the well-being of humans. Consumption of high-fluorine waters were first identified as having a detrimental effect on teeth in the 1920s and 30s. It was subsequently shown that where fluorine is present in drinking waters at concentrations of around 0.5 to 1 mg/L it can have beneficial effects on humans, resulting in healthy teeth and bones. However, several areas of the world where potable waters derive from the ground, very high concentrations of fluorine, generally in excess of 4 mg/L have resulted in dental fluorosis and, at very high concentrations, crippling skeletal fluorosis. The detrimental effects of consuming elevated amounts of fluorine-rich drinking water are exacerbated by a poor, low-protein diet. Radioactive elements such as radon and uranium can be transported in groundwater. Domestic water supplies enriched in radon can in some areas represent a major pathway into humans, being released during showering etc, it can be inhaled and as such contributes to the incidence of lung cancer. In addition to the potential health problems of its radioactivity, uranium has been shown to be a nephrotoxin. High-uranium groundwaters consumed by humans over the short term can result in kidney damage.
H42A-02
Using U/Th Series Nuclide Systematics for Modelling Subsurface Radionuclide Transport
U- and Th- series nuclides have provided essential tools for studying weathering and subsurface element transport processes. The radionuclides U, Th, Ra, Rn, and Pb have a range of half-lives and contrasting chemical behaviours, and their distribution between subsurface solids and water can be used to quantify rates of soil formation, chemical and mechanical weathering of watersheds, and potentially, subsurface water flow rates. Decay systematics clearly connect the different isotopes, although transfer between different phases and through subsurface systems are generally defined through a series of assumptions that have not been experimentally substantiated. Modification of these assumptions may have significant effects on the choice of models and the conclusions of U/Th series studies. Two key areas of uncertainty are: Nuclide inputs. Comparing the different isotopes requires relating the input rates from recoil and weathering. The common assumption is that nuclides are released at similar rates by recoil and congruently by weathering. Various theories have been proposed for preferential release of Rn and leaching of radionuclides, although such effects, as well as possible radionuclide fractionation during weathering release, have not been substantiated. Surface interaction mechanisms. It is generally assumed that radionuclides are removed from water onto surfaces only by reversible adsorption. However, coprecipitation, incorporation into aging secondary mineral structures, and different binding mechanisms can inhibit isotope exchange with nuclides in solution. Data from the unconfined Mojave River Basin aquifer, with a reasonably well-defined flow pattern and groundwater ages of up to ~40,000 years illustrates the response of the U/Th series nuclides to extended water- rock interaction. Measurements of 222Rn find relatively uniform recoil rates throughout the aquifer. If this rate is applied to other daughter nuclides, then the rate of 234Th release can be obtained This then defines the input of 234U, which is expected to increase with groundwater age, regardless of the extent of reversible adsorption. The narrow range of 234U/238U ratios implies that there is continuing weathering release of 238U as well. However, measured U concentrations are actually relatively constant, indicating that either the recoil of 222Rn is actually much higher than that of other elements, or U is irreversibly incorporated into the aquifer solids at the same rate as it is released. Sequential leaching experiments with aquifer materials suggests that released daughter nuclides are produced within Fe oxyhydroxides surface coatings, compatible with similar loss rates for recoiled daughter nuclides. Mechanisms for incorporation of U are therefore required here, and may be important elsewhere for greatly limiting trace elements, including low level contaminants, in the environment. Incorporation of such processes in radionuclide transport models will strongly affect inferred transport rates.
H42A-03
Mechanisms of Radium Mobilization for Radium-Rich Groundwater from the Nubian Sandstone and Carbonate Aquifers in the Negev, Israel: Implications for Fossil Groundwater Resources in the Middle East
The radium isotope quartet (226-Ra, 228-Ra, 224-Ra, 223-Ra), radon, and uranium (238-U, 234-U) isotopes were investigated in brackish to saline groundwater from the Nubian sandstone and Lower Cretaceous carbonate aquifers in the Negev, Israel. Our data show that Ra activity in both aquifers are high and far exceeds international drinking water threshold levels. The 228-Ra/226-Ra and 224-Ra/223-Ra ratios in the groundwater from the two aquifers are closely associated with the measured of 232-Th/226-Ra and predicted 224-Ra/223-Ra ratios in the respective aquifers rocks. This indicating that Ra in the Nubian sandstone is derived from interactions with rocks hosting nuclides from both Th- and U-decay series, whereas the carbonate aquifer contributes nuclides exclusively from the U-decay series. In the sandstone aquifer we found that Ra activity is strongly correlated with temperature. The high 224-Ra/228-Ra, d223Ra (defined as 223-Ra/226-Ra/0.046) (>1) and 234-U/238-U (3.3) ratios in the Nubian groundwater suggest that Ra is primarily derived from recoil process on the aquifer solids. We quantified the Ra recoil and retention by normalizing the 224-Ra to 222-Rn activities in the water, taking into account the 232-Th/226-ra ratios in the aquifer rocks. Given that a large fraction of Ra is in the form of RaSO4 species (a range of 0.15 to 0.5) and the correlation of RaSO4 species with Ba content we propose that Ra recoil is retained by co-precipitation onto secondary barite mineral and/or exchange with surface coating. In the carbonate aquifer we show that Ra activity is strongly correlate with both salinity and dissolved oxygen content. Groundwater with high 226-Ra activity has typically low d223Ra ratios and 222-Rn/226-Ra ratios, which suggests that Ra mobilization is controlled by desorption from surface coating that is enhanced under conditions of high salinity and reduced groundwater. Our findings indicate that under stagnant groundwater conditions, Ra can be mobilized from aquifer rocks with common Ra activities, without significant Ra removal (e.g., adsorption). The lack of significant Ra sinks is due to combination of factors including reducing conditions, lack of available adsorption sites, high temperature (that inhibit both barite saturation and adsorption), and groundwater chemistry (e.g., formation of RaSO4 species). These findings could have implications for possible high Ra anomalies in many other similar groundwater basins in the Middle East.
H42A-04
Natural Arsenic Pollution of Groundwater in Mining Zones of Mexico
Arsenic concentrations exceeding drinking-water standards have been measured in groundwater of various areas of Mexico. This is a relevant public health problem since groundwater supplies most drinking water of the country. Although a natural source has been proposed as the cause of water contamination at most sites, the specific processes releasing As have only been identified in a few aquifers. The geological characteristics of Mexico including volcanic, geothermal, and highly mineralized zones constitute favorable environments for As occurrence. Furthermore, As-abundance in bedrock has lead Mexico to be one of the major world As-producers. As-bearing minerals like arsenopyrite, scorodite, mimetite, adamite, tennantite and nickeline can be found in several zones. Besides, arsenic may be a minor component of Fe, Ag, Cu, Pb, Zn, and Au ores. While thousands of people have been chronically exposed to As, arsenic-related health effects have been documented only for residents at some Mexican locations, like Comarca Lagunera, Zimapan, and Acambaro. Water-rock interactions may release As to water in mining areas, but ore extraction and processing produce surface wastes that can also release As to groundwater. Investigations developed in two historical mining zones revealed different As contents in groundwater. At Zimapan, a semi-arid area about 250 km NE of Mexico City, abundant arsenopyrite and hydrogeological conditions produced high As concentrations in deep wells exploited for drinking water supply. Oxidation and dissolution of As-bearing minerals mainly arsenopyrite, scorodite and tennantite released As to the fractured deep limestone aquifer. In addition, mining operations polluted shallow wells. In contrast, low levels of As were detected in wells near mine tailings in the warm sub-humid zone of Taxco, Guerrero. To explain those differences, the mineralogy and the geochemical processes occurring in tailings at both areas were studied. Results showed that besides As levels in processed ore, mineralogy of the ore deposits is one of the main causes of different degrees of As release. Precipitation of secondary minerals like gypsum, goethite, K-jarosite and hematite produced a cemented layer that retains As in the active oxidation zone of the tailings at Taxco. Formation of beundantite also reduces As dispersion. At Zimapan, the relative proportion of pyrite and calcite leads to differences on As mobility, evidenced by mineralogy and geochemical fractionation of As in tailings. Geology of the substrate under the tailings also affects the pollution levels of shallow wells. Granular alluvial material permits a greater mobilization of As at Zimapan than in Taxco, where presence of limonites and calcareous lutites results in low As groundwater contents. Economically and technical affordable treatment methods have been tested to clean the water. At Zimapan, addition of local limestone proved to remove a high proportion of As; flocculation with iron salts was also suitable to treat polluted water.
H42A-05
Management of the Arsenic Groundwater System Lagunera - MEXICO
Arsenic in drinking water is considered one of the most important environmental causes of cancer mortality in the world. Groundwater resources of the Comarca Lagunera region (Northern Mexico), which represents the main source of drinking water for more than 2 million people in the area, show arsenic concentrations ranging from 5 to 750 micro g/l. Large areas have concentrations quite above the Mexican standard of 25 micro g/l for human use and consumption. The aquifer is overexploited and the groundwater levels at the central part of the aquifer are drawn down more than 100 m in less than 50 years. The drawdown provoked the dissolution and migration of the geogenic existing arsenic within the aquifer. The presence of arsenic has been related to several potential sources. It was found out, that the main source is geothermal activity, less mining and the use of arsenical pesticides. The process of the geneses of the arsenic pollution implicates, that the highest content is on the bottom of the aquifer. Data analysis showed, that arsenic concentration is correlated to the age of the groundwater. "Older" water has higher arsenic content than "younger" water and the oldest water can be found at the bottom of the aquifer. Before 1950 the groundwater level in the Comarca Lagunera was close to the surface and there were only dug and shallow wells with low groundwater abstraction. The water was pumped from the upper parts of the aquifer and because this was "young" water it had low arsenic content. Then after 1950 a lot of wells, mainly for irrigation, were built and in 2002 there were 2350 active wells with an abstraction of about 1088 Mio cbm/year. In consequence to this the groundwater level decreased extraordinary. More and more "older" water was pumped and the arsenic content increased. Furthermore at the beginning of 1960 the river Nazas was canalized and lined, so that the natural groundwater recharge by infiltration from the river was stopped. By this way, the mixing of "young" water with less arsenic and "old" water with high arsenic was excluded, which results in the long term to higher arsenic concentrations in the groundwater. In order to understand the actual situation and to prognosticate the further development of the arsenic concentration in the Comarca Lagunera region, it was necessary to reproduce the historical development with a simulation model which includes the different anthropogenic impacts. For this purpose the groundwater model MODFLOW was used and the investigation area of about 7000 sq km was divided by a regular square grid with a mesh size of 1 km. The calibration of the model started with steady state conditions, using an assumed, uninfluenced "original status" of 1900. Subsequently, the influence of the immensely rising groundwater discharge beginning 1950 and the canalization of the river Nazas were simulated and the results were compared with measurements at selected times. The prognostic calculations showed, that the increase of the arsenic concentration will go on in the future under the present conditions of overpumping. Therefore, it has to be reduced. To control the arsenic migration towards the urban wells for dringking water supply artificial recharge can be done. Another possibility is a treatment, especially subterranean, of arsenic or to use surface water for drinking water purposes.
H42A-06
Presence of Fungicides Used to Control Asian Soybean Rust in Streams in Agricultural Areas in the United States
Concentrations of 11 fungicides were measured in stream samples during 2 years in agricultural areas in the United States that grow predominantly corn and soybean. The fungicides are registered for control of Asian Soybean Rust (ASR), which entered the United States in 2004. Many of these fungicides were registered under an emergency exemption because evaluation of environmental risks related to their widespread use on soybeans had not been completed. Some of these fungicides are considered moderately to highly toxic to fish and aquatic invertebrates. We developed a solid-phase extraction and gas chromatography/mass spectrometry method for determining the fungicides at low concentrations (ng/L). Stream samples were collected 2 to 4 times at study areas during the late spring through fall season when fungicides are applied. Six fungicides registered for control of ASR (Phakospora pachyrhizi) in 2005 were measured in streams in Alabama, Georgia, North Carolina, South Carolina, and Mississippi during August-November, 2005. One or more fungicides were detected in 8 of the 12 streams sampled. Azoxystrobin, pyraclostrobin, propiconazole, tebuconazole, and myclobutanil were found in at least one of the 40 samples collected, while chlorothalonil was not found. Azoxystrobin was detected most frequently, in 35 percent of the samples. In 2006, five additional fungicides registered for use in control of ASR were included in the analytical method. One or more of the fungicides (azoxystrobin, pyraclostrobin, trifloxystrobin, metconazole, propiconazole, tebuconazole, tetraconazole, myclobutanil) were detected in 12 of the 16 streams sampled from areas in the South and Midwest during May-September, 2006. Azoxystrobin was detected most frequently (40 percent of the samples) and the highest concentration was 1.1 μg/L in a small predominantly cotton and soybean watershed. The highest concentrations of azoxystrobin were measured prior to the spread of ASR in 2006, and the detections in streams might be related to use on other crops. Concentrations of the fungicides measured were about 100 times lower than aquatic toxicity levels. These results show that ASR fungicides were found in streams before extensive spread of ASR in the United States.
H42A-07
Relations Among the Use, Occurrence, and Flux of Azoxystrobin, Propiconazole, and Other Fungicides in US Streams, 2005-06
Fungicides account for 10 percent of global pesticide use (0.25 million metric tons per year), and 6 percent of US use (33 thousand metric tons per year). Some fungicides such as chlorothalonil have been in use for decades (first US registration in 1966), while others such as azoxystrobin were introduced in the last decade (first US sales in 1996). Fungicide fate and transport is not well understood, but recent investigations have detected fungicides in precipitation, groundwater, streams, and streambed sediment. The occurrence of Asian soybean rust in the Southern US is of concern because of the increase in fungicide use that would result if it spreads to the Central US during the growing season. In the Central US many growers have never used fungicides to protect soybeans. The purpose of this study is to collect baseline data on fungicide occurrence in streams prior to the spread of Asian rust to soybeans in the Central US and the anticipated increase in fungicide use to control the rust. These data are then used to investigate relations among the occurrence and flux of fungicides in US streams, and the use of those products within the associated drainage basins. Water samples from streams in the Southern and Central US were collected in 2005 (26 sites, 40 samples) and 2006 (16 sites, 41 samples), and analyzed for up to 11 fungicides. This is the first study to monitor for several of these fungicides in environmental samples from locations in this region of the US. Chlorothalonil was used in all study basins but only detected in one sample from 2006. Azoxystrobin was detected in one or more samples from 12 of 26 sites in 2005 and 10 of 16 sites in 2006. Estimated daily fluxes of azoxystrobin ranged from zero to 440 grams/day but were not significantly correlated (p value = 0.3) with estimated azoxystrobin use in the upstream watershed. Estimated daily fluxes of propiconizole ranged from zero to 360 grams/day and were correlated (p value = <0.0001) with estimated propiconizole use. Results indicate that fungicides can readily enter aquatic systems where they may have toxic effects, and that their occurrence and flux in streams may be correlated with regional patterns of fungicide use.