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The topic area of this study extends to three distinct environs (i) water (ii) farm soil (iii) vegetables. All three environs were separately sampled in time and space. Natural water's dissolved load consists of predominantly about 90% or more of four metals present as cations; Na+, K+, Ca+2 and Mg+2 along with their anions as CO3-2, HCO3-, SO4-2, NO3-, Cl-, PO4-3. A known stoichiometry of their mass-charge balance is maintained. The more 'naturally' fresh the water the more balanced is this mass-charge (the moles of cations along with their charges are equated to the moles of anions and their charges). Rest of the dissolved load consists of trace presence of heavy metals and organic matter.
Last two decades have witnessed a significant change in the elevated levels of trace metals in natural waters mainly due to anthropogenic activities as mining, fossil fuel combustion or industrial processes in addition to natural abundance of these metals in the soil of the catchments. Organic matter seems to interact with trace metals. However, these interactions do not follow known pathways and stoichiometry.
3.2 Industrial Waste Water Samples
Karachi has two industrial estates; Sind Industrial Trading Estate (SITE) Shershah and Korangi Industrial Estate (KIE). SITE of Karachi is one of the largest and oldest industrial estates of Pakistan. It was established in 1953 and is located at Latitude 24°ï€®ï€µï€´ï‚¢ and Longitude 67°ï€®ï€±° in the district south, Karachi. Various types of industries are located in this area. Approximately 60% of these industries are textile mills while others deal in pharmaceutical, chemicals, detergents, iron, vegetable oils, beverages and food products.
Malir Valley, Long: 67°ï€®ï€´ï€±ï‚¢ East, Lat: 25°ï€®ï€´ï€´ï‚¢ï€ North situated in the east of Karachi city, remained very important during last century because of its water supply to Karachi city from Dumloti wells, now have dried up and serve as pumping location for city water supply from Keenjhar Lake to its eastern. The Malir valley bed now supports vegetable crops and orchards. The effluents from the factories of KIE drain in Malir River through a channel. Industrial Waste Water (IWW) samples were taken from the channel carrying factory effluents before these get mixed with domestic waste water carried by the Malir River closest to the farmland. Adjoining these industrial effluents streamlets and Malir River has emerged a vast plane of vegetable cultivation by these two sources of water. IWW samples were free of domestic waste water mix up and were collected along effluent stream in pre detergent cleaned and water rinsed Teflon bottles. During sampling, bottles were rinsed three times with sampled water and filled at a depth of one meter below the surface at six sampling sites 10 m apart and capped. Conductivity, dissolved oxygen, total dissolved solids and pH were measured on site. Samples were labeled and transported to the laboratory and stored overnight in the refrigerator at about 4oC prior to analysis.
3.3 Treated Water Samples
Raw water, piped and pumped, from two lakes, Haleji and Keenjahar, recharged by River Indus, is filtered, treated with alum and chlorinated before being supplied to the city's domestic users for primarily drinking, washing and watering odd indoor plants. This source of water was used to irrigate small strips of vegetable crops next to the laboratory of this study. Water samples were taken periodically from the tap water to irrigate the vegetables. The mode and apparatus of sampling was same as for Industrial Waste Water.
3.4 Root Vegetables and Soil Samples
The root vegetables beet (Beta vulgaris L.), carrot (Daucus carota L.), potato (Solanum tuberosum L.), radish (Raphanus sativus L.), turnip (Brassica rapa glabra L.), sweet potato (Ipomoea batatas) and associated soils were sampled. Each vegetable was sampled at 6 places across a hectare of randomly selected farms at each sampling site, varying in size 1-2 ha.
The soil samples were scooped from the same spot as the vegetable sample. Each sample was portioned into six aliquots for replicate runs and statistical evaluation.
3.5 Site Measurements
Field method was used to observe the color because platinum-cobalt standard method is not convenient to be used on the field. The color of the water was compared with that of glass disks held at the end of metallic tubes containing glass comparator tubes of the sample and distilled water. The color of the sample was matched with the color of the reference tube of clear water.
Mercury glass thermometer was used to measure the ambient air temperature at the time of sampling at the site, avoiding direct solar heat radiations, about 1 m above the ground level. The temperature of the water sample was measured by dipping thermometer directly in the water sample.
The pH of water samples was measured with a pre-calibrated pH meter (TS-1, Suntex, Taiwan) with combined glass and internal reference electrodes. The pH meter was calibrated by immersing its electrode in a standard buffer solution of pH 7 then in other buffer solutions with pH 4 and 9.
3.5.4 Electrical Conductivity (EC)
Electrical conductivity of water samples was measured with pre calibrated [KCl (0.01M) indicated EC OF 1372 µS/cm at 25°C] conductivity meter (120 Orion, Houston, TX).
3.5.5 Total Dissolved Solids (TDS)
A measured volume of the sample was filtered through weighed Whatman no. 42 filter paper. Insoluble substances on the filter paper were washed with 20 to 30 mL of de-ionized water. The filter paper was dried along with the insoluble substances affixed to it in an oven at 100 to 110°C. The filter paper was weighed after drying and cooling, and the amount of suspended solids calculated in mg·L-1 from the weight difference.
3.5.6 Dissolved Oxygen (DO)
Dissolved oxygen (DO) was measured with direct immersion of a DO probe into the sample solution.
3.6 Laboratory Measurements
The alkalinity of the water samples was determined by titrating them with standard HCl solution using methyl orange as an indicator. The color changed from yellow to pinkish as end point.
(1) Hydrochloric acid (HCl) solution (0.1N)
Hydrochloric acid 37% (2.1mL) was diluted and volume made up to 250mL with deionized water.
(2) Sodium carbonate solution (0.1N)
Na2CO3 pre dried (1.325g) was dissolved and volume was made up to 250mL with deionized water.
(3) Methyl orange indicator solution
Methyl orange (0.125g) was dissolved in deionized water and volume was made up to 250mL.
Standardization of Titrant (HCl)
The titrant HCl (0.1N) solution was standardized by titrating it against standard Na2CO3 solution using methyl orange as indicator. After standardization the HCl solution was diluted to 0.02N.
In 10mL water sample 2-3 drops of methyl orange were added and was titrated against standard 0.02N HCl solution up to the color change from yellow to pinkish end point.
Alkalinity in mg/L as CaCO3 = A- N - 50000 / mL of samples (S)
A = Volume of titrant (HCl) solution consumed for sample
N = Normality of titrant (HCl) solution
S = Volume of test sample in mL
50000 = Constant to convert alkalinity in equivalent weight mg/L as CaCO3
The acidity of the water samples was determined by using cation exchange chromatography. 10mL of water sample was passed through charged cation exchange resin and collected the effluent (i.e.H+ ions). 10mL of effluent was titrated with standard NaOH solution using phenolphthalein as an indicator. The color changed from colorless to pink as end point.
(1) Sodium hydroxide (NaOH) solution (0.2N)
NaOH (2g) was dissolved and volume was made up to 250mL with deionized water.
(2) Oxalic acid solution (0.1N)
H2C2O4 .2H2O (0.63g) was dissolved and volume was made up to 100mL with deionized water.
(3) Phenolphthalein indicator solution
Phenolphthalein (1.25g) was dissolved in 125mL of ethanol and volume was made up to 250mL with deionized water.
Standardization of Titrant (NaOH)
The titrant NaOH (0.2N) solution was standardized by titrating it against standard H2C2O4 .2H2O solution using phenolphthalein as an indicator. After standardization the NaOH solution was diluted to 0.02N.
In 10mL effluent 2-3 drops of phenolphthalein were added and was titrated against standard 0.02N NaOH solution up to the color change from colorless to pinkish end point.
Acidity in mg/L as CaCO3 = A- N - 50000 / mL of samples (S)
A = Volume of titrant (NaOH) solution consumed for effluent
N = Normality of titrant (NaOH) solution
S = Volume of effluent in mL
50000 = Constant to convert alkalinity in equivalent weight mg/L as CaCO3
Water hardness was measured by complexometric titration at pH 10 adjusted with (NH4Cl-NH4OH) buffer solution. Titration was carried out with disodium salt of ethylenediamine tetra acetic acid (Na2EDTA.2H2O) using Eriochrome black-T as the indicator. Color change from wine-red to blue was the end point (Salami and Egwin, 1997) .
(1) Buffer solution (NH4NO3-NH4OH)
Ammonium chloride (33.8g) was dissolved in 286mL concentrated ammonium hydroxide and the volume was made up to 500mL with deionized water.
(2) Erichrome black-T (EBT) indicator
Erichrome black-T (0.25g) was mixed well with (50g) NaCl. The mixture was valid up to one year.
(3) Na2-EDTA solution (0.01M)
Disodium salt of ethylenediamine tetra acetate (1.862g) was dissolved in deionized water and volume was adjusted to 500mL.
(4) Standard Calcium carbonate (CaCO3) solution (0.01M)
Calcium carbonate (0.5g) was dissolved in deionized water and volume was made up to 500mL.
Standardization of EDTA (0.01M) solution
EDTA solution (0.01M) was standardized by titrating it with standard CaCO3 solution (0.01M) using Erichrome black-T (EBT) indicator. The blank was also run following same procedure.
In the sample (10mL), buffer solution of pH 10 was added (1mL) and about 5mg (EBT) indicator and titrated with EDTA (0.01M) solution. The color change from reddish to blue was noted as end point. Same procedure was repeated for blank using deionized water in the place of sample. A minimum of three replicate measurements were recorded for each sample.
Hardness in mg/L as CaCO3 = (A- B) - M - 50000 / mL of samples (S)
A = Volume of titrant (mL) consumed for sample
B = Volume of titrant (mL) consumed for blank
M = Molarity of EDTA solution
S = Volume of sample in mL
50000 = Constant value
3.6.4 Sulphate (SO4-2)
The sulfate concentration in the water samples was determined by turbidimetric method. The sulfate ions are precipitated in acidic medium (HCl) with reaction of BaCl2 to produce BaSO4 as a white turbid suspension measured spectrophotometerically through calibration curve.
(1) Barium chloride crystals (BaCl2)
0.05g of BaCl2 was added in each water sample.
(2) Conditioning reagent
NaCl (15g) was dissolved in 60mL of deionzed water, 6mL HCl, 10mL glycerol and 20mL of 95% isopropyl alcohol or ethanol were added in NaCl solution.
(3) Stock solution of sulfate
Sulfate solution (1000 ppm) was prepared by dissolving 0.148g sodium sulfate in 100mL distilled water. Required solutions were prepared by appropriate dilution.
Water sample (25mL) was transferred into Erlenmeyer flask and added 1.25mL of conditioning reagent with constant stirring by magnetic stirrer. Barium chloride crystals (0.05g) were added and stopwatch was started. The absorbance was recorded on spectrophotometer after each 30 seconds up to 4 minutes at 420nm. Maximum absorbance was selected from eight readings recorded at various time intervals. Finally calibration curve at time interval 2 minute was selected. A blank was run following same procedure with 25 mL of deionized water. The sulfate concentration in water samples was calculated from calibration curve.
3.6.5 Chloride (Cl-)
Chloride concentration in water samples was determined spetrophotometrically at λ515 nm (Rand et al., 1976), with the color indicator N, N-diethyl-p-phenylene-diamine (DPD). Calibration curve of standard solutions (ppm) was used to determine chlorine concentration in water samples. To each of these solutions three DPD tablets were added and stirred to dissolve. The chlorine present in the water samples was reacted with the DPD indicator forming a red color compound which was allowed to develop for a 10 minutes and then measured the absorbance at 515 nm. The concentration was measured through calibration curve.
3.6.6 Biological Oxygen Demand (BOD)
The samples were analyzed immediately after collection otherwise these were stored at freezing temperature by adding 5mL HNO3 in 500mL sample solution. A 100 mL sample was placed in each of 5 BOD bottles; one palette of lithium hydroxide was placed inside the cap of each bottle before tightly recapping and all bottles were shifted to a biological oxygen demand (BOD) monometer (DR 2010,Hach, Loveland, CO), started at zero mercury level, and stored at 20°C for 5 days. After completion of the five-day incubation period close and take it out from the incubator and measure the BOD level with the help of mercury scale which is attached with each bottle (Aslam, 2009) .
3.6.7 Chemical Oxygen Demand (COD)
COD determination is the measure of biodegradable organic matter in water. Usually this test is employed to monitor and control oxygen consumption by both organic and inorganic pollutants. HACH U.S.A EPA approved method for COD was used for preparing calibration curve and analyzed samples with the help of COD reactor. For chemical oxygen demand (COD), 2 mL sample was added to a reagent (conc. 0-15 g·L-1) vial; digested in a COD reactor (DR 2010 Spectrophotometer, Hach) at 150°C for 2 h; aerated for a few minutes at room temperature and measured at λ250 nm on a spectrophotometer against a reagent blank vial containing deionized water.
3.6.8 Metal Assay
188.8.131.52 Determination of Heavy Metals in Water Samples by AAS
Water samples were cleared of organic matter by wet ashing method (Radojevic and Bashkin, 1999) . Five hundred-mL samples of wastewater were evaporated to 20 mL on a hot plate and 5 mL HNO3 added; heating continued with HNO3 being added until the solution cleared. The analyte solution was filtered, insolubles were removed and the volume made up to 100 mL with deionsed water. Samples were analyzed with an Atomic Absorption Spectrophotometer (PE 2380, Norwalk, VT, USA) equipped with a thermal atomizer, air-acetylene flame, autosampling and autodilution. External calibration was used for quantitative analysis.
184.108.40.206 Determination of Heavy Metals in Root Vegetables Samples by AAS
Vegetable samples were washed with distilled and de-ionized water to remove soil particles from the surface dehydrated at 80oC for 48 h and pulverized. Tissues were dissolved in 5 mL of HNO3 and wet ashed as for water samples. Samples were cooled and filtered through Whatman no. 42 filter paper into a 100 mL Erlenmeyer flask and made up to mark with de-ionized water.
220.127.116.11 Determination of Heavy Metals in Soil Samples
For heavy metal extraction, 1g dried sample of soil was digested in 5 mL HNO3 at 80°C until a transparent solution was obtained. This transparent solution was then filtered through Whatman number 42filter paper and diluted 100mL with deionized water. The concentration of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the filtrate was determined by using Atomic Absorption Spectrophotometer (PE 2380, Norwalk, VT, USA) fitted with a specific lamp of particular metal using appropriate drift blanks. External calibration was used for quantitative analysis.
Instrumental condition selected for the detection of Heavy Metals by Atomic Absorption Spectrophotometer (AAS)
Acetylene flow (L/min)
Lamp current (mA)
Measurement time (seconds)
The five standard solutions (with concentrations 1.0, 2.0, 3.0, 4.0, and 6.0) ppm respectively) of respective metal were run to calibrate the instrument. The standard solution (2.0 or 3.0 ppm) was run after each 6 samples, to check signal drift. When the relative error increased above 5%, the instrument was recalibrated by running the standards.
18.104.22.168 Determination of Heavy Metals in Commercial Root Vegetables Samples by
The vegetable samples were collected from local market. The vegetables were cleaned to remove visible soil and then washed thoroughly with tap and deionzed water and dried in sunlight for 10 days. Elements present in the sample were determined by a scanning electron microscope, JEOL Model JSM 6380 (LA), Standardless with ZAF correction method. For SEM images air dried 5µm sample tissues of Beet, Carrot, and Radish; 10µm of Turnip and 20µm Potato and Sweet Potato were scanned by raster method.