IONIC CONSTITUENTS AND HEAVY METAL CONTAMINATION OF NATURAL WATER IN COAL MINING AREA OF NORTH-WEST REGION OF BANGLADESH

Abstract

Judgment of water quality in modern agriculture is essential for irrigating various crops as well as drinking and industrial uses. A research work was conducted during February-April, 2006; to assess the ionic concentration of groundwater and surface water of Phulbari Upazila at Dinajpur district. Exactly, 108 water samples were collected from different locations and analyzed for pH, EC, TDS, cations (Ca, Mg, Na, K, P, B, Zn, Mn, Fe, As) and anions (HCO3, Cl, SO4, NO3), SAR, SSP, RSC, Hy and COD. Among studied parameters for irrigation purposes, the pH values (pH = 6.24 to 7.98) indicated that the waters were slightly acidic to slightly alkaline. EC and SAR was categorized as C1S1, C2S1 and C3S1 which revealed that waters carried ‘low’ to ‘high’ salinity but ‘low’ alkalinity hazards. ‘Fresh’ and ‘brackish’ waters were rated by TDS values. SSP values were found as ‘excellent’ to doubtful’. ‘Suitable’ and ‘soft’ to ‘very hard’ classes were observed as per RSC and Hr values, respectively. B toxicity was not detected and can be regarded as ‘excellent’ but the Cl toxicity was found only in 2 samples. In respect to heavy metals, higher concentration of arsenic (As > 0.10 mg L”') was found in 10 samples most of them were in shallow to middle depth but rest of the samples were in safe limit. Assessment of drinking water quality, a remarkable amount of Na, K, Ca, Mg, P, HCO3, CO3, Cl, NO3 and SO, were present. Moreover, the concentration of Mn, Cu and Zn were within the safe limit with some exceptions. Arsenic (As) contamination was found in 29 samples which exceeded the permissible limit (> 0.05 mg L”' or 5 ppb). No water samples were found ‘suitable’ for all kinds of industrial uses considering their chemical properties but some waters could ‘safely’ be used for the specific industries. Iron chips and taro » methods were tested to remove arsenic (As) from contaminated water. Taro method showed better result than iron chips method even the outflow rate was 7.2 L hr’. Therefore, it is suggested that taro method may be used to purify polluted water in the study area before specific uses.