Chemical Speciation of Heavy Metals in Ground and Surface Waters

H. S. Hundal, Kuldip Singh, and Dhanwinder Singh. Soils, Punjab Agricultural University, Ludhiana, India

Metal speciation in natural waters is of increasing interest and importance because Of toxicity, bioavailability, environmental mobility. Biogeochemical behavior, and potential risk in general are strongly dependent on the chemical species of metals. The present study aims to determine the distribution of chemical species of dissolved heavy metals in shallow (45 feet deep) and deep aquifers (200 feet deep) and surface waters from Buddha Nala stream and Sutlej River's from village Walipur of Punjab, north-west India. Before sampling the water was drawn for half an hour to emptied the hand pump and tube well pipes to collect the fresh water from the shallow and deep aquifers, respectively. For surface water, samples were collected from the centre of Buddha Nala and Sutlej water streams. Polyethylene bottles of 50 ml volumes were used for collection of water samples. Field measurements of redox potential (Eh) were also made at the time of water sampling. The samples were put in a cooled ice box during transportation and stored refrigerated until analysis (at 50 C). The pH of water samples was determined using Elico model L 110 glass electrode in combination with calomel as reference electrode on pH meter. The electrical conductivity of water samples was measured by Elico model CM-84 conductivity bridge. The carbonates and bicarbonates concentrations were measured by titration with a known volume of water against standard sulphuric acid using phenolphthalein and methyl red as indicators, respectively. The chloride concentration in water samples were measured by titrating a known volume against standard N/40 silver nitrate solution using potassium chromate as indicator. All samples were filtered and acidified prior to analysis. The acidified water samples were analyzed for Cd, Ni, Pb, Zn, Cu, Fe, Mn and S on Inductively Coupled Argon Plasma of Thermo Electron corporation iCAP 6000. The geochemical speciation model Visual MINTEQA2 Version 3.11 was used to calculate the equilibrium concentrations of dissolved and solid species for different heavy metals found in surface and ground water samples. Heavy metals concentrations (except zinc) were considerably high in waste water of Buddha Nala stream due to disposal of Industrial effluents comparative to shallow, deep aquifers and surface water of Sutlej River. In all water compositions, except waste water of Buddha nala Zn, Cd, Ni, and Mn were predominantly present (93-97%) as divalent cation forms. About 95 % of the total dissolved iron in shallow and deep aquifers was in ferrous (Fe2+) form due the occurrence of reduced status in underground waters. In Sutlej River, 90 % of the total dissolved iron was computed to be in ferric (Fe3+) form due to oxidized (+226 mV) water status. The free activity of Pb2+ ion were 52, 33, 39, and 34% of the total dissolved lead in waters of hand pump, tube well and surface waters of Buddha nala and Sutlej River, respectively. Significant contribution of Me(OH)+ (29%) and Me(CO)3 aq (27%) complexes were computed for all the metals in Buddha nala water stream and ultimately these complexes eventually contributes to the higher concentration of these elements in this aqueous system. Appreciable fraction of Me(OH)+ were also found for Cu and Pb in shallow and deep aquifers and Sutlej River waters. The Me(CO3) aq species were also found for Cu and Pb in waters of shallow and deep aquifers abstracted by hand pump and tube well, respectively.

Among the copper minerals, copper hydroxide [Cu(OH)2], amorphous and crystalline tenorite [CuO] were identified as the solid phase in aquifer materials of shallow and deep waters and in the bed sediments of Buddha Nala and Sutlej River waters. Malachite [Cu2(OH)2CO3] mineral was found in materials of shallow, deep water aquifers and in bed sediments of Sutlej Rivers. Their could be the possibility of the existence of copper carbonate [CuCO3] and Langite [(Cu)4(OH)7HSO4], Atacamite [Cu2(OH)3Cl], Antlerite [Cu3SO4 (OH)4] and Brochantite [CuSO43Cu(OH)2] in wastewater of Buddha Nala. The occurrence of these different copper minerals in aquifer materials for ground water and bed sediments could eventually be the primary factors for controlling the concentration of copper in water sampled from different sites. Among zinc minerals, Smithsonite [ZnCO3] was found to be present in shallow aquifer materials and in the bed sediments of Buddha Nala waste water. Zinc hydroxide [Zn(OH)2 ] was recorded in aquifer material of shallow water, bed sediments of Buddha Nala and Sutlej river waters. Nickel carbonate [NiCO3] and Nickel hydroxide [Ni(OH)2] mineral were identified in bed sediments of Buddha Nala waste water only. Similarly the Rhodochrosite [MnCO3] mineral for manganese and Hydrocerrusite [(Pb)3(OH)2(CO3)2] mineral for lead solid phases were identified in bed sediments materials of Buddha Nala waste water site. The most common minerals of lead Cerrusite [PbCO3] and lead hydroxide [Pb(OH)2] were found in aquifers material of shallow, deep waters as well as in the sediments of Buddha Nala waste and Sutlej Rivers waters. In case of iron, Siderite [FeCO3] mineral was identified in the shallow aquifer materials and in the sediments under waste water of Buddha Nala. The reduced form of mineral for iron as ferrous hydroxide [Fe(OH)2 ( c)] was found in the bed sediments of Buddha Nala waste water. The identification of this mineral illustrates that bed sediments under waste water of Buddha Nala were highly reduced conditions. The redox potential recorded for waste water at the time of sampling also showed low value of redox status (-253 mV).