Arsenic geochemistry of the sediments of the shallow aquifer and its correlation with the groundwater, Rangpur, Bangladesh

The geochemical analysis of the shallow aquifer sediments of the area of investigation reveals that they are acidic in nature. The mean electrical conductivity of the deposits is 1.16 dS/m that indicates very low or negligible effects of salinity of the sediments of the Rangpur division. The median values of the concentrations of total organic carbon, total nitrogen and sulphur are 0.20%, 0.02% and 58.68 mg/kg, respectively. The trend of the average heavy metal concentrations of the investigated area can be shown as Fe > As > Cu > Zn. The average concentrations of arsenic of the sediments of the study area are 3.52 mg/kg. Sulphur is significantly, positively correlated with copper and zinc (p < 0.05) and insignificantly and positively correlated with arsenic content of the sediments that indicates that the copper and zinc occur as sulphide minerals. The mean concentrations of arsenic in the groundwater are 1.1793 μg/L. The concentration of all the water samples is below the permissible limit of World Health Organization (10 μg/L). The arsenic content of groundwater shows the positive correlations with the arsenic, iron and copper concentrations of the sediments. This implies that the arsenic of groundwater derived from the geogenic source, like the dissolution of arsenic bearing minerals of the aquifer sediments—pyrite and arsenopyrite. The acidic nature, texture and minor quantities of total organic carbon are the factors that also influence the low arsenic enrichment in the investigated sediments and its release to the groundwater. The contemporary arsenic specification research works showed that As(III) the most common species in natural water and foodstuffs and the arsenic is inorganic from source in Bangladesh.

Anthropogenic Organic Pollutants in Groundwater Increase Releases of Fe and Mn from Aquifer Sediments: Impacts of Pollution Degree, Mineral Content, and pH

In many aquifers around the world, there exists the issue of abnormal concentrations of Fe and Mn in groundwater. Although it has been recognized that the main source of this issue is the release of Fe and Mn from aquifer sediments into groundwater under natural environmental conditions, there lacks enough reliable scientific evidence to illustrate whether the pollutants imported from anthropogenic activities, such as organics, can increase this natural release. On the basis of time series analysis and comparative analysis, the existence of an increasing effect was verified through laboratorial leaching test, and the impacts of aquatic chemical environment conditions, such as pH, on the effect were also identified. The results showed that the increase of organics in groundwater made the release of Fe and Mn more thorough, which was favorable for the increase of groundwater concentrations of Fe and Mn. The higher the contents of Fe- and Mn-bearing minerals in aquifer sediments, the higher the concentrations of Fe and Mn in groundwater after the release reaches kinetic equilibrium. Lower pH can make the leaching more thorough, but the neutral environment also increases the amount of Mn. It can be deduced that the pollutants such as organics imported by anthropogenic activities can indeed increase the releases of Fe and Mn from aquifer sediments into groundwater, thus worsening the issue of groundwater Fe and Mn pollution. The findings provide a deeper insight into the geochemical effects of Fe and Mn in the natural environment, especially in the groundwater system.

Assessment of heavy metals contamination of the water resources in the vicinity of Barapukuria Coal Mine, Phulbari, Dinajpur, NW Bangladesh

The present research work shows that the concentrations of heavy metals can be expressed as Fe>Mn>Zn>Ni>Cr>Pb>Co>As in the groundwater of Phulbari area, Dinajpur, Bangladesh on the basis of their abundance. The Plio-Pleistocene Dupi Tila aquifer sediment is principally composed of quartz, feldspar and lithic grains and is characterized by low ZTR index. Seventeen groundwater samples have higher iron concentrations than the permissible limit of WHO, 2004. The chemical weathering of pyrite release iron in the natural water of the study area. The manganese content of two groundwater samples is higher than the acceptable limit. The high abundance of potassium in 11.11% water samples is indicative of the influence of agricultural activity in the investigated area. The factor analysis reveals the dominance of four factors that comprise 77.276% of the groundwater sample. The contamination index (Cd) for the heavy metals were performed and 88.89% of the groundwater samples have low contamination index. The calcium of the groundwater is resulted from the dissolution of carbonate rocks. The low arsenic concentrations indicate the fast flowing nature of the groundwater and/or low arsenic content of the aquifer sediments. The low cobalt content of the groundwater reflects the low cobalt concentration of the aquifer sediments. The heavy metal chemistry of the groundwater of the study area reveals that the quality of the water is influenced by the geogenic sources as well as the anthropogenic activities like coal mining and agricultural activities.