Geochemical Color Maps of the Dhaka Water, Bangladesh—New Map Presentations for Toxic Metals and Isotopes

摘要

This research investigated the water qualities and distribution of heavy metals concentration in rain, river, ground and supply waters, providing a baseline in Dhaka Urban, Bangladesh, against which future changes can be assessed. The water sample was collected in the Dhaka central zone, from a site located in the center of the Bengal Delta plain between 23䓨'N - 23䓶'N latitude and 90䓔'E - 90䓟'E longitude which is affected by environmental pollution for high traffic, industrialization and because of its rapid urbanization. The water samples were analyzed for heavy metals by Inductively Coupled Plasma Mass-Spectrometry (ICP-MS), major ions by Ion-Chromatography (IC), water tracer (δ18O and δD) by Mass-Spectrometry (MS), following the standard techniques. Elevated EC and chloride (Cl-) are the markers of wastewater, providing an indication of impacts in the Buriganga River water. The relative concentrations of major ions were presented in the form of Piper and Stiff Diagram. The color maps were constructed to present ions distribution over the areas. The stream reaches directly in Buriganga River from leather industries which may reflect the naturally low dissolved oxygen (DO) 0.3 - 3.5 (mg/L), where aquatic life can’t survive. Uranium contents U238 (0.1 - 2.7 μg/L) are not exceeding the WHO guideline level of 30 μg·L-1. Significant portion of Cs133 (0.05 - 0.32 μg/L), Se (0.03 - 0.12 μg/L), B (50 - 2986 μg/L) and Cr (0.55 - 18.59 μg/L), could be increased in Buriganga River areas by the effect of local sources like leather industry. Zn (10 - 1466 μg/L) in the Dhaka Rain and Pb (4 - 6 μg/L) in Dhaka Water occur mainly in industrial and the high traffic areas, respectively. The isotopic (δ18O/δD) distributions have been evaluated for understanding of contaminant sources in groundwater and wastewater recharge from Buriganga River to adjacent depleted groundwater system. The results indicate that the magnitude of pollution problem depends on the size of the area affected, rapid groundwater depletion, polluted river water recharge and the type of the pollutant involved and finally that makes the complex in Dhaka Geochemical pattern.