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instead of 30 m), primarily because of low concentrations of dissolved Fe and As (von Bromssen et al., 2005; Jakariya et al., 2007). The paper discusses the relation between the colour of the sediments and groundwater redox conditions. This study revealed that the sediment colour is a reliable indicator of high and low As concentrations that can be used by local drillers to target low-As groundwater. The presence of As contamination of shallow fluvio-deltaic aquifers in the Bengal Basin has also resulted in increasing exploitation of groundwater from deeper aquifers that generally contain low concentrations of dissolved As (Stollenwerk, 2003). However, infiltration of high-As groundwater induced by increased pumping of these aquifers clearly indicate the possible risks for an increase in As concentrations. The following paper (Stollenwerk et al., 2007-this volume) presents a study on the investigation of the adsorption capacity for As of sediment from a low-As aquifer near Dhaka, Bangladesh. At this site a shallow, chemically reduced aquifer with 900 μg/LAs overlies a more oxidized aquifer with b5 μg/L As. Since no thick layer of clay was present at the site to inhibit vertical transport of groundwater, there was an apparent risk for an increase in the concentration of dissolved As in the deeper aquifers. Laboratory experiments and geochemical modeling were used to show that oxidized sediments have a substantial but limited capacity for removal of As from groundwater.
The problem of geogenic As is not only restricted to the Bengal Basin and its surrounding region. DissolvedAs in groundwaters from coastal aquifers used extensively for human consumption has led to widespread concern in eastern Australia. In the next paper O'Shea et al. (2007-this volume), discuss about the source of naturally occurring As in a coastal sand aquifer of eastern Australia. The study suggests that As is regionally derived from erosion of As-rich stibnite(Sb2S3) mineralisation present in the hinterland. Fluvial processes have transported the eroded material over time to deposit an aquifer lithology elevated in As. The findings of this study indicate that any aquifer containing sediments derived from mineralised provenances may be at risk of natural As contamination. Groundwater resource surveys should thus incorporate a review of the aquifer source provenance when assessing the likely risk of natural As occurrence in an aquifer.
In the next paper (Jakariya et al., 2007-this volume) analytical results of field test kits and laboratory measurements by AAS as a “gold standard” for As in water for 12,532 TWs in Matlab Upazila in Bangladesh were compared. The study indicated that the field kit correctly determined the status of 87% of the As levels compared to the Bangladesh Drinking Water Standard (BDWS)
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of 50 μg/L, and 91% of the WHO guideline value of 10 μg/L. However, due to analytical and human errors during the determination of As by the field test kits, there were considerable discrepancies in the correct screening of As concentrations between 10–24.9 μg/L and 50–99.9 μg/L. Proper training of the field personnel, verification of the field test kit results with laboratory analyses, and further development of the field test kits, will improve the accuracy of As measurements at low concentrations.
The concluding short contribution in this section (Vuki et al., 2007-this volume) deals with a study on the speciation of As in spring waters located along Tumon Bay in the small island of Guam in Western Pacific Ocean. Earlier investigation conducted by the Guam Environmental Protection Agency (GEPA, 2002) on total concentrations of As in groundwater springs and seepages at Guam indicated concerns over As contamination resulting predominantly from anthropogenic sources. Although more detailed studies are required for a detailed evaluation of the extent of As contamination in Guam. The results of this study show that total As concentrations in the spring water samples ranged from b0.3–1.2 μg/L with inorganic arsenate As(V) the dominant species. The low concentrations of dissolved As are also consistent with the values recorded for the groundwater wells in the northern part of Guam (GWA, 2003). These concentrations are much lower than the previously reported values, probably due to a much more rigorous methodological approach; this suggests the need for and requires further investigations on the status of As contamination in groundwater on the island.
3.2. Arsenic in agricultural soils and miningenvironment
The first article in this section (Saha and Ali, 2007- this volume) deals with the dynamics of arsenic in agricultural soils irrigated with As-contaminated groundwater in Bangladesh. Arsenic concentrations in the soil layers of 12 rice fields located in four Asaffected areas and two unaffected areas in Bangladesh were monitored systematically. This study clearly shows enrichment of As in the top soil of rice fields irrigated with As-contaminated groundwater (79–436 μg/L), compared to areas where irrigation water contained very lowAs (b1 μg/L).The study also revealed significant spatial and temporal variations of As concentrations in the contaminated rice field. Arsenic concentration of rice field soils increased significantly by the end of the irrigation season. About 71% of the As that was applied to the rice field with irrigation water accumulated in the top 0 to 75 mm soil layer. Most of this As was leached from the soil during the following wet season. It is very important that the observed spatial and temporal
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variability of As in rice field soils is taken into consideration in the future studies on As contamination of rice production.
There are several hot spots in Poland where soils have very high concentrations of As, caused both by natural geochemical enrichment and long-lasting ore mining and processing operations (Karczewska et al., 2004, 2005). Detailed investigations are therefore necessary to estimate the total concentrations of As in soils in such hot-spot-areas, its chemical fractionation, and potential solubility to evaluate the risks for mobilization of As. In the second article in this section (Krysiak and Karczewska, 2007-this volume) an attempt has been made to assess the levels and environmental risk associated with possible increases in As mobility under changing pH and redox conditions in soils and waste material in two areas of former As mining and processing activities Zloty Stok (Zlote Mts.) and lezniak (Kaczawskie Mts.) in SW Poland. Arsenic concentrations were measured in twenty six soil samples collected from 12 sites, and represented a broad spectrum of soil properties and parent material origin, including natural soils, mine spoils, slags and tailings. Most soils in the area had extremely high concentrations of As (range 100?3,500 mg/kg), both of natural and anthropogenic origin. Sequential extraction techniques suggested that the main species of As in all soils were those bound to iron (Fe) oxides, whereas the contributions of mobile and specifically sorbed As forms were relatively low. In tailings and tailing-affected alluvial soils, As occurred mainly in residual forms, however these soils also had considerable amounts of mobile As. In all other soils, mobile As forms were very low.
The last paper in this section (Eapaea et al., 2007-this volume) discusses the dynamics of As in the mining sites of Pine Creek Geosyncline of Northern Territory of Australia. This study examined the mobility and retention of As in soil and sediments from five mine sites in the region, based on measuring the operationally- defined forms of As in soils and other sediments using a modified sequential extraction procedure. The study revealed that As was present both in soluble and loosely bound forms, such as Al–As, Fe–As, Ca–As associations, Fe(OH)3 occluded As, organic bound As and residual As in sediment phases. Two general management principles were suggested for trapping the mine waste contaminants to minimize dispersion of As and heavy metals into the environment. These included prevention of direct discharge to creeks or water ways and discharges into constructed wetland with aquatic macrophytes to trap sediment that provides organic matter for arsenic and heavy metal retention.
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3.3. Biogeochemistry of arsenic
This section contains three articles describing the aspects of biogeochemical interactions of As and toxicology. The first article deals with Arsenicicoccus bolidensis, a novel As-reducing actinomycete in contaminated sediments near the Adak mine (Routh et al., 2007). At Adak, a small mining town in the V?sterbotten district of Northern Sweden, high-As concentrations are encountered in surface and groundwater, sediments, and soil. In spite of the oxic conditions, As-rich surface and ground water samples indicate a predominance of As(III) species (up to 83%). Several microorganisms potentially involved in As cycling were isolated from the sediment enrichment cultures (Routh et al., 2007-this volume). Results from laboratory investigations show that A. bolidensis (a novel gram-positive, facultatively anaerobic, coccus-shaped actinomycete) actively reduced As(V) to As(III) in aqueous media. The second article (Chen et al., 2007-this volume) reveals that arbuscular mycorrhizal fungi (AMF) may play an important role in protecting plants against As contamination. However, little is known about the direct and indirect involvement of AMF in detoxification mechanisms. A compartmented pot cultivation system (?cross-pots?) investigated the roles of AMF Glomus mosseae in plant phosphorus (P) and As acquisition bym Medicago sativa, and P–As interactions. The results indicate that fungal colonization dramatically increased plant dry weight by a factor of around 6, and also substantially increased both plant P and As contents (i.e. total uptake). Irrespective of P and As addition levels, AMF plants had shoot and root P concentrations 2 fold higher, but As concentrations significantly lower, than corresponding uninoculated controls. The decreased shoot As concentrations were largely due to “dilution effects” that resulted from stimulated growth of AMF plants and reduced As partitioning to shoots. The study provides further evidence for the protective effects of AMF on host plants against As contamination, and have uncovered key aspects of underlying mechanisms.
The third article in this section (Krishnamohan et al., 2007-this volume) deals with the systematic study of the urinary As methylation and porphyrin profile of C57Bl/6J mice chronically exposed to sodium arsenate. The results indicate that As interferes with the function of enzymes responsible for haem biosynthesis leading to alteration in the porphyrin profile. The levels of total As were significantly related to dose. No significant differences in the urinary As methylation pattern between control and test groups were observed. Coproporphyrin I (Copro I) showed a significant dose response relationship after 12, 14 and 20 months of exposure.
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