Materials and Methods

Bangalore is the principal administrative, cultural, commercial, industrial and knowledge capital of the state of Karnataka. Greater Bangalore spatial extent was expanded to 741 km² includes the city, neighboring municipal councils, and outgrowths, in December 2006. The field sampling was done in the vicinity of Varthur Lake.

Varthur Lake: Varthur Lake is situated in the eastern periphery of Bangalore City and a part of the internationally famous Whitefield Township. Varthur is a Hobli and part of Bruhat Bangalore Mahanagara Palike (BBMP). The lake ecosystem is an integral part of Bangalore, although unplanned urbanization and industrialization have led to the contamination of these water bodies. Varthur Lake, with a spatial extent of 216 ha, is the second largest lake in Bangalore city. Recently, siltation and encroachment, the spatial extent of the lake has been reduced to 165.75 ha and also one of the most polluted lakes in Bangalore due to (i) the sustained inflow of untreated and partially treated domestic sewage, (ii) discharge of untreated industrial effluents (through stormwater drains and through trucks (who discharge untreated effluents), (iii) dumping of solid waste in the lake, drains and in the buffer zone. The wetland water accounts to irrigate 625 ha of agricultural fields in the command area for growing crops like rice, ragi millet, coconut, flowers, and various fruits and vegetables. Earlier reports have indicated the possible uptake of trace elements by plants grown in the command area of the lake (Ramachandra et al., 2011; Jumbe and Nandini, 2009). Field samples of vegetables grown using the lake water in the command area of Varthur Lake (Varthur) were collected to assess the level of heavy metal uptake (figures 1 - 3).

Heavy metal analysis: The collected vegetable samples were analyzed using ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy) technique to assess the level of heavy metal in acid digested samples.

Digestion procedure: For the water sample, the digestion was carried out with an acid combination of nitric and sulfuric acids at a ratio of 10:1. The plant samples were digested using nitric, sulfuric, and perchloric acids combinations of 5:1:1. Nitric and sulfuric acid combination 5:1 was used for the digestion of soil samples. A temperature range of 60-70˚C was maintained during digestion of samples and additional volumes of acids were added till the sample becomes transparent. The digested samples were transferred into a 50 ml standard and made up to the mark using distilled water. The samples were then transferred into small plastic (tarsons) bottles, capped and labelled (APHA, 1999).

Preparation of standards: A stock solution of 1000 ppm was prepared for the analysis of heavy metals such as Cd, Cu, Pb, Cr, and Ni. The chemicals used for standard preparation are; Cadmium sulphate (Cd), Potassium dichromate (Cr), Copper sulfate (Cu), Lead nitrate (Pb), and Nickel sulfate (Ni). Standards were prepared in a range of 1, 10, and 20 ppm from the stock solution in 2% HNO₃. The prepared standards were then fed into ICP-OES to obtain a calibration curve.

ICP-OES: Emission spectroscopy using ICP was developed in the mid-1960’s as a rapid, sensitive, and convenient method for the determination of metals in water and wastewater samples. Dissolved metals are determined in filtered and acidified samples. Total metals are determined after appropriate digestion. Care must be taken to ensure that potential interferences are dealt with, especially when dissolved solids exceed 1500 mg/L.

Principle: ICP source consists of a flowing stream of argon gas ionized by an applied radiofrequency field typically oscillating at 27.1 MHz. This field is inductively coupled to the ionized gas by a water-cooled coil surrounding a quartz ‘‘torch’’ that supports and confines the plasma. A sample aerosol is generated in an appropriate nebulizer and spray chamber and is carried into the plasma through an injector tube located within the torch. The sample aerosol is injected directly into the ICP, subjecting the constituent atoms to temperatures of about 6000 to 8000°K. Significant reduction in chemical interferences is achieved with the almost complete dissociation of molecules. The light emitted from the ICP is focused onto the entrance slit of either a monochromator or a polychromator that affects dispersion. A precisely aligned exit slit used to isolate a portion of the emission spectrum for intensity measurement using a photomultiplier tube. The monochromator uses a single exit slit/photomultiplier and may use a computer-controlled scanning mechanism to examine emission wavelengths sequentially. The polychromator uses multiple fixed exit slits and corresponding photomultiplier tubes; it simultaneously monitors all configured wavelengths using a computer-controlled readout system (APHA, 1999).

Procedure: Initially, the instrument was calibrated using blank. After calibration with blanks, standards of three different concentrations were fed alternating with blank to obtain a calibration curve. The samples were fed into the instrument in a similar way to standards. At the end of the analysis, blank was again fed into the instrument. The results were obtained via a computerized readout system.

Calculations: Dilution correction factor = Final weight or vol. / Initial weight or vol.

Interference correction factor, K = Apparent conc. of element / Actual conc. of an interfering element.

Figure 1: Varthur lake and sampling sites

Figure 2: Sampling sites 1 and 2 (N: 12.95247, E: 077.73963 and N:12.95277, E: 077.73876)

Figure 3: Sampling site 3 (N: 12. 94473, E: 077.74554)