Occurrence Of Arsenic In Groundwater Research Articles

The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

Avala Mountain is accommodated 15 km southward from the city of Belgrade and extends over the area of about 10 km2. Avala Mountain is a cultural and historical heritage of Belgrade qualified by the Law on Environmental protection. The area is abundant with water springs that have been exploited by tourist facilities and local population. By analyzing groundwater sampled from several springs and wells located in a vicinity of the Avala magmatic entity here we study the occurrence, concentration and origin of arsenic pollutant. The investigated springs are accommodated within the faulted complex of Mesozoic carbonate and clastic sediments, serpentinite, further intruded by the Tertiary magmatic rocks. By using the concentrations of the major and minor components(e.g. Cr, Ni, Fe, Mn) in groundwater, the relationship between groundwater and local lithostratigraphic units is outlined. Chemical analysis of the investigated waters shows that arsenic concentration in groundwater of the investigated area is in range from 3.0 to 102.0 ?g/l. Arsenic concentrations over the maximum allowed value in drinking water (10 ?g/l) are detected in more than 55% cases. The occurrence of arsenic in groundwater can be attributed to local igneous rocks, i.e. to the process of oxidation of sulphide minerals with As (major or minor presence) ? primarily arsenopyrite or pyrite. Groundwater with higher concentration of arsenic (above10 ?g/l) is exploited as drinking water used by tourists and by local population. Along term use of the water with high concentration of arsenic impose a major health risk.

A study on the arsenic concentration in groundwater of a coastal aquifer in south-east India: an integrated approach

The occurrence of arsenic in drinking water and its detrimental effects have drawn much attention in recent years. Several studies have been conducted in the deltaic plains of River Ganga, NE part of the India, and in other countries, but no systematic study was conducted in South India on occurrence of arsenic in groundwater. The main aim of this study is to determine the level of arsenic in groundwater and to understand the relation with other geochemical parameters of groundwater in the south-eastern coastal aquifer at Kalpakkam region, India. This region is represented by three different lithologies, viz. charnockites, flood plain alluvium and marine alluvium. Twenty-nine representative samples of groundwater were collected and analysed for major ions, metals and isotopes such as 2H and 18O. In addition, geophysical method was also attempted to understand the subsurface condition. The spatial variation in arsenic (As) indicates that higher concentration was observed around the landfill sites and irrigated regions, which was supported by geochemical, statistical and isotopic inferences. The variation in the As with depth, lithology and sources has been clearly brought out. Though the values of As does not exceed the drinking water permissible limit (10 mg/l), it has reached a near permissible level of 8.7 ppb. Hence, it is essential to understand the geochemical behaviour of As for a proper future management of the water resource in the study area.

Factors affecting temporal variability of arsenic in groundwater used for drinking water supply in the United States

The occurrence of arsenic in groundwater is a recognized environmental hazard with worldwide importance and much effort has been focused on surveying and predicting where arsenic occurs. Temporal variability is one aspect of this environmental hazard that has until recently received less attention than other aspects. For this study, we analyzed 1245 wells with two samples per well. We suggest that temporal variability, often reported as affecting very few wells, is perhaps a larger issue than it appears and has been overshadowed by datasets with large numbers of non-detect data. Although there was only a slight difference in arsenic concentration variability among samples from public and private wells (p=0.0452), the range of variability was larger for public than for private wells. Further, we relate the variability we see to geochemical factors—primarily variability in redox—but also variability in major-ion chemistry. We also show that in New England there is a weak but statistically significant indication that seasonality may have an effect on concentrations, whereby concentrations in the first two quarters of the year (January–June) are significantly lower than in the second two quarters (July–December) (p<0.0001). In the Central Valley of California, the relation of arsenic concentration to season was not statistically significant (p=0.4169). In New England, these changes appear to follow groundwater levels. It is possible that this difference in arsenic concentrations is related to groundwater level changes, pumping stresses, evapotranspiration effects, or perhaps mixing of more oxidizing, lower pH recharge water in wetter months. Focusing on the understanding the geochemical conditions in aquifers where arsenic concentrations are concerns and causes of geochemical changes in the groundwater environment may lead to a better understanding of where and by how much arsenic will vary over time.

Geochemical occurrence of arsenic in groundwater of Bangladesh: sources and mobilization processes

Total arsenic, dissolved organic carbon (DOC), iron, major cations and anions were measured in tube-well waters used for drinking by people to investigate the geochemical condition of subsurface aquifer, source of arsenic and mechanism of arsenic release to groundwater of Bangladesh. Solid phases of total arsenic, iron, manganese and aluminum oxide and organic carbon (TOC) content in sediments were determined to find out their interrelationships. Arsenic concentrations in groundwaters vary from 0.03 to 0.75 mg/l with the mean value of 0.41 mg/l that exceed the maximum permissible limit of WHO (0.01 mg/l) and Bangladesh (0.05 mg/l) for drinking water. Arsenic concentrations demonstrate negative covariation with the concentrations of sulfate and nitrate but correlate weakly with iron concentrations and positively with those of ammonium ions. Dissolved iron exhibits a negative covariance with the concentrations of sulfate. Very low concentrations of nitrate and sulfate and high concentrations of dissolved iron and ammonium ions demonstrate the reducing condition of subsurface aquifer. These relationships suggest that oxidation of arsenic-rich pyrite is not responsible for the increased concentrations of arsenic but reflect the dependence of As concentration on the reductive processes. Arsenic is strongly correlated with DOC concentrations. Borehole data demonstrate the arsenic enrichment in organic matter-rich fine-grained clayey silt and silty sand than in sandy sediments. Arsenic contents are well correlated with those of iron, manganese and aluminum oxides in fine particle fraction of sediments, whereas arsenic is significantly correlated with TOC in large particle fraction. Sequential chemical leaching exhibits that arsenic is mainly present in three phases: (1) oxide phase of Fe and Mn, (2) organic matter and (3) sulfide and silicate phases. Since the distribution of arsenic in the subsurface sediments is not solely controlled by a single solid phase, the dissolution–desorption from different phases contributes to the total arsenic concentrations in groundwater. Microbial oxidation of organic matter (including localized peat layer) and reductive dissolution of Fe and Mn oxyhydroxide are the important processes to mobilize arsenic. The combined effects of NaHCO 3 and high pH values also play a significant role to mobilize arsenic from surface of iron oxides, other minerals and subsurface sediments. The very strong relationship between arsenic and bicarbonate concentrations in groundwater of Bangladesh and high pH values (8.03–8.7) of the Ganges sediments support the hypothesis. This paper reports first about arsenic leaching by the combined effects of NaHCO 3 and high pH values in Bangladesh.

Arsenic in ground-water under oxidizing conditions, south-west United States

Concentrations of dissolved arsenic in ground-water in alluvial basins of Arizona commonly exceed 50 μg L(-1) and reach values as large as 1,300 μg L(-1). Arsenic speciation analyses show that arsenic occurs in the fully oxidized state of plus 5 (As+5), most likely in the form of HAsO4(∼2), under existing oxidizing and pH conditions. Arsenic in source areas presumably is oxidized to soluble As before transport into the basin or, if after transport, before burial. Probable sources of arsenic are the sulphide and arsenide deposits in the mineralized areas of the mountains surrounding the basins. Arsenic content of alluvial material ranged from 2 to 88 ppm. Occurrence and removal of arsenic in ground-water are related to the pH and the redox condition of the ground-water, the oxidation state of arsenic, and sorption or exchange. Within basins, dissolved arsenic correlates (P<0.01) with dissolved molybdenum, selenium, vanadium, and fluoride and with pH, suggesting sorption of negative ions. The sorption hypothesis is further supported by enrichment of teachable arsenic in the basin-fill sediments by about tenfold relative to the crustal abundance and by as much as a thousandfold relative to concentrations found in ground-water. Silicate hydrolysis reactions, as defined within the alluvial basins, under closed conditions cause increases in pH basinward and would promote desorption. Within the region, large concentrations of arsenic are commonly associated with the central parts of basins whose chemistries evolve under closed conditions. Arsenic does not correlate with dissolved iron (r = 0.09) but may be partly controlled by iron in the solid phase. High solid-phase arsenic contents were found in red clay beds. Large concentrations of arsenic also were found in water associated with red clay beds. Basins that contain the larger concentrations are bounded primarily by basalt and andesite, suggesting that the iron content as well as the arsenic content of the basin fill may play a role in the occurrence of arsenic in ground-water. Under oxidizing conditions in Arizona, arsenic in ground-water appears to be controlled in part by sorption or desorption of HAsO4(∼2) on active ferric oxyhydroxide surfaces.

New war gases for old?

The occurrence of arsenic in groundwater is a recognized environmental hazard with worldwide importance and much effort has been focused on surveying and predicting where arsenic occurs. Temporal variability is one aspect of this environmental hazard that has until recently received less attention than other aspects. For this study, we analyzed 1245 wells with two samples per well. We suggest that temporal variability, often reported as affecting very few wells, is perhaps a larger issue than it appears and has been overshadowed by datasets with large numbers of non-detect data. Although there was only a slight difference in arsenic concentration variability among samples from public and private wells (p = 0.0452), the range of variability was larger for public than for private wells. Further, we relate the variability we see to geochemical factors—primarily variability in redox—but also variability in major-ion chemistry. We also show that in New England there is a weak but statistically significant indication that seasonality may have an effect on concentrations, whereby concentrations in the first two quarters of the year (January–June) are significantly lower than in the second two quarters (July–December) (p < 0.0001). In the Central Valley of California, the relation of arsenic concentration to season was not statistically significant (p = 0.4169). In New England, these changes appear to follow groundwater levels. It is possible that this difference in arsenic concentrations is related to groundwater level changes, pumping stresses, evapotranspiration effects, or perhaps mixing of more oxidizing, lower pH recharge water in wetter months. Focusing on the understanding the geochemical conditions in aquifers where arsenic concentrations are concerns and causes of geochemical changes in the groundwater environment may lead to a better understanding of where and by how much arsenic will vary over time.