Study on Ground water, Riverwater and Tannery Effluent Quality in Southwestern Dhaka, Bangladesh: Insights from Multivariate Statistical Analysis

摘要

Twenty three groundwater samples, three riverwater samples and a tannery effluent were collected from Hazaribagh area in Bangladesh; in order to evaluate their geochemical composition and quality. The physicochemical parameters pH, EC, DO, hardness, HCO_3~-, Cl~-, SO_4~(2+), NO_3~-, P, Na~+, K~+, Ca~(2+), Mg~(2+), Fe, Mn, Cu, Zn, Pb, Cd and Cr were measured in these samples. Groundwater was dominantly of Ca-Mg-HCO_3 type with Ca~(2+) and HCO_3~- being the dominant cation and anion, respectively. Na~+ -normalized Ca~(2+) versus HCO_33~- and Na~+ -normalized Ca~(2+) versus Mg~(2+) plots showed that the groundwater samples were influenced by carbonate dissolution. Average concentration of Fe, Pb and Cd exceeded World Health Organization (WHO) limits in relation to groundwater and riverwater. DO saturation in river water was 200 times lower than the standard limit, making it unable to sustain aquatic life. Principal Component Analysis (PCA) extracted five PCs using the correlation matrix to reflect the processes influencing the chemical composition of groundwater having about 75.61% of total sample variance. PC1 may have been derived from lithogenic sources; geochemical weathering of minerals contributes the enrichment of groundwater with these major cations. On the contrary, PC 2, PC 3, PC 4 and PC 5 can be considered as a mixed source from both lithogenic and anthropogenic inputs. PCA for river water extracted two PCs using the correlation matrix, explaining 100% of total sample variance. The source of PC 1 loading variables would be geogenic while PC 2 could be released from anthropogenic sources, specifically derived from industrial effluents and municipal wastes. Comparison between the industrial area and surrounding areas clearly show that increase of ions in shallow aquifers may be due to the industrial activities. In the long run this will have diverse impacts on groundwater of these areas, as well as may contaminate the overall groundwater system, especially in times when Bangladesh would face water shortage.