Spatial Variability Of Arsenic Research Articles

Spatial variability of arsenic in Indo-Gangetic basin of Varanasi and its cancer risk assessment

The Indo-Gangetic alluvium is prime region for intensive agricultural. In some areas of this region, groundwater is now becoming progressively polluted by contamination with poisonous substances like arsenic. Intensive irrigation with arsenic contaminated ground water in dry spell results in the formation of As(III) which is more toxic. Thus groundwater quality assessment of Gangetic basin has become essential for its safer use. Therefore we under took study on the spatial variability of arsenic by collecting georeferred groundwater samples on grid basis from various water sources like dug well, bore and hand pumps covering the river bank region of Ganga basin. Water quality was investigated through determination pH, EC, TDS, salinity, Na, K, Ca, Mg, SAR, SSP, CO3, HCO3, RSC, Cl, As, Fe, Zn, Mn and Cu, etc. Results pointed severe As contamination in ground water of three sites of the study area. ARC GIS software is now able to process maps along with tabular data and compare them well, to provide the spatial visualization of information and using this tool, the Geographical Information System (GIS) of arsenic was developed. It was noticed from spatial maps that concentration of arsenic was more near the meandering points of Ganga.

Characterization of regional cold-hydrothermal inflows enriched in arsenic and associated trace-elements in the southern part of the Duero Basin (Spain), by multivariate statistical analysis

Naturally occurring arsenic in groundwater exceeding the limit for potability has been reported along the southern edge of the Cenozoic Duero Basin (CDB) near its contact with the Spanish Central System (SCS). In this area, spatial variability of arsenic is high, peaking at 241μg/L. Forty-seven percent of samples collected contained arsenic above the maximum allowable concentration for drinking water (10μg/L).Correlations of As with other hydrochemical variables were investigated using multivariate statistical analysis (Hierarchical Cluster Analysis, HCA and Principal Component Analysis, PCA). It was found that As, V, Cr and pH are closely related and that there were also close correlations with temperature and Na+. The highest concentrations of arsenic and other associated Potentially Toxic Geogenic Trace Elements (PTGTE) are linked to alkaline NaHCO3 waters (pH≈9), moderate oxic conditions and temperatures of around 18°C–19°C. The most plausible hypothesis to explain the high arsenic concentrations is the contribution of deeper regional flows with a significant hydrothermal component (cold-hydrothermal waters), flowing through faults in the basement rock. Water mixing and water-rock interactions occur both in the fissured aquifer media (igneous and metasedimentary bedrock) and in the sedimentary environment of the CDB, where agricultural pollution phenomena are also active.A combination of multivariate statistical tools and hydrochemical analysis enabled the distribution pattern of dissolved As and other PTGTE in groundwaters in the study area to be interpreted, and their most likely origin to be established. This methodology could be applied to other sedimentary areas with similar characteristics and problems.

Spatial Distribution of As-Concentrations in the Contaminated Site by the Highly Toxic As-Chemicals

A total of 2668 surface soil samples (-0.5 m ~ 0 m) and 637 sub-layer soil samples (-1.0 m ~ -0.5 m) were collected from a contaminated site with an area of 26.19 hectares and analyzed the concentration of arsenic, so as to get the spatial distribution of arsenic concentrations in the soil contaminated by highly toxic As-chemicals. The results indicated that spatial correlation of arsenic content in surface soil was moderate. The optimal semivariogram model was the exponential model, and the best interpolation model was simple Kriging interpolation. The arsenic content of sub-layer was similar to that of surface soil in space structure, but weakly correlated. Analysis on the arsenic content in vertical sections showed that contamination was mainly concentrated in surface soil. The arsenic content in most of the collected samples reduced as the soil layer depth increased. Spatial variability of arsenic could be significantly affected by anthropogenic factors such as excavation & destruction of highly toxic As-chemicals and farming.

Spatial variability of arsenic in relation with some soil forming factors

Soil and water samples collected from Bijar area were analyzed in order to investigate arsenic contamination sources and their human risk potentiality assessment. Routine physical and chemical characteristics, iron oxides and arsenic contents were measured in 227 soil samples. Spatial variability of arsenic was calculated using inverse distance weighting (IDW) to assess the arsenic contamination potential. Furthermore, the relationships between soil parent material, physico-chemical characteristics and the spatial distribution of arsenic were analyzed. Topsoil arsenic concentration showed significant correlations with clay (r = 0.77), sand (r = -0.45), silt (r = -0.48), Fe oxides contents (r = 0.65) and cation exchange capacity (r = 0.65) statistically. The highest arsenic concentrations were observed in the map delineations with higher clay, Fe 2 O 3 and cation exchange capacities. Parent materials derived from Ferich igneous (or pyroclastic) rocks and mudstone (arsenic source parent materials) composed of significantly higher arsenic contents, compared to the rest parent material types. Spatial variability analyses demonstrated that considerable extent of the studied soils was potentially contaminated by arsenic. The distribution map of arsenic contaminated areas was rasterized by IDW which confirmed that arsenic contamination in the studied area originated from some specific point sources (arsenic bearing parent materials) and spread over the lower positions by water pollution and erosiondeposition processes. Key words: Parent materials, IDW, Physicochemical characteristics.

Spatial variability of arsenic in some iron-rich deposits generated by acid mine drainage

Potential contamination of rivers by trace elements can be controlled, among others, by the precipitation of oxyhydroxides. The streambed of the studied area, located in “La Châtaigneraie” district (Lot River Basin, France), is characterised by iron-rich ochreous deposits, acidic pH (2.7–4.8) and SO 4–Mg waters. Beyond the acid mine drainage, the presence of As both in the dissolved fraction and in the deposits is also a problem. Upstream, at the gallery outlet, As concentrations are high (As max = 2.6 μmol/l and up to 5 wt% locally, respectively, in the dissolved and in the solid fractions). Downstream, As concentrations decrease below 0.1 μmol/l in the dissolved fraction and to 1327 mg/kg in the solid fraction. This natural attenuation is related to the As retention within ochreous precipitates (amorphous to poorly crystalline Fe oxyhydroxides, schwertmannite and goethite), which have great affinities for this metalloid. Upstream, schwertmannite is dominant while downstream, goethite becomes the main mineral. The transformation of schwertmannite into goethite is observed in the upstream deposits as schwertmannite is unstable relative to goethite. Furthermore, thermodynamic calculations indicate that the downstream goethite is not able to precipitate in situ according to the water chemistry. Goethite mainly results from the transformation of schwertmannite and its solid transport downstream. Moreover, as highlighted by leaching experiments carried out on the ochreous precipitates, this transformation does not seem to affect the As-retention in solids as no release of As was observed in the solution. Arsenic may either be strongly trapped by co-precipitation in the present minerals or it may be quickly released and re-adsorbed on the precipitate surface.

Spatial variability of arsenic in 6000 tube wells in a 25 km2 area of Bangladesh

Arsenic concentrations measured by graphite furnace atomic absorption range from < 5 to 900 μg/L in groundwater pumped from 6000 wells within a 25 km2 area of Bangladesh. The proportion of wells that exceed the Bangladesh standard for drinking water of 50 μg/L arsenic increases with depth from 25% between 8 and 10 m to 75% between 15 and 30 m, then declines gradually to less than 10% at 90 m. Some villages within the study area do not have a single well that meets the standard, while others have wells that are nearly all acceptable. In contrast to the distribution of arsenic in the 8–30 m depth range which does not follow any obvious geological feature, the arsenic content of groundwater associated with relatively oxic Pleistocene sand deposits appears to be consistently low. The depth of drilling necessary to reach these low‐As aquifers ranges from 30 to 120 m depth within the study area.