3.2Effective dose due to ingestion and inhalation of 222Rn in waterWhere is the effective dosefor inhalation, is the Rnconcentration in water (kBq/m3) , is the Rn in air toRn in water (10-4), F is the equilibrium factor between Rn and it’sprogenies(0.4),I is the average indoor occupancy time per individual (7000ha-1)and DCF is the dose conversion factor for Rn exposure (9nSv(Bqhm-3)). Where is the effective dose for ingestion, is the222Rn concentration in water(kBq/m3), is the weighed estimate of waterconception(730 l/a) and EDC is the effective dose coefficient for ingestion(3.5nSv/Bq) respectively1. 3.
3Procedure to determine the uranium concentration in water using LED FluorimeterThe uraniumanalyzer is a compact analytical instrument to measure uranium concentration intrace levels (ppb) in aqueous environmental samples 4 The concentration ofuranium in water samples were measured using Laser fluorometer. It works on theprinciple of detection of fluorescence of uranyl complex formed by the additionof an inorganic reagent called fluran 5,6. A standard stock solution of 1.179g U3O8 was diluted to specific concentrations for regularcalibration of the system. Sodium pyrophosphate (5 %) was used as thefluorescence-enhancement agent and for the formation of the uranyl complex,because uranyl phosphate complexes are stable. A 5 ml of water sample was placedin a dry and clean cell, 1 ml of 5 % sodium pyrophosphate (pH 7) was added andfluorescence counts were noted.
The instrument was calibrated with standarduranium solution of a known concentration. The concentration of uranium (ppb)in samples was calculated using the following equation:Where D1 isthe fluorescence counts due to sample only, D2the fluorescence counts due to sample and uranium standard, V1the volume of uranium standard added (ml), V2the volume of sample taken (ml) and C is the concentrationof uranium standard solution (ppb). 3.3 Ingestion dose due toUranium in drinking water:Ingestion dose was estimated using the intake of uranium throughdrinking water pathway for different age groups according to the water intakerates as presented in.
According to the ICRP-60, dose coefficients for infantsis 1.2×10-7, 6.8 ×10-8for children and 4.5 ×10-8 SvBq-1 for male and female adults 7.3.
4 Effective doseTotal effectiveradiation dose was calculated considering drinking of 730 ly-1. Thiscorresponds to 2 liter of water consumed daily by the people. Dose conversionfactor (DCF) is equal to 4.
5 × 10?8 SvBq-1 for 238U.The annual radiation ingestion dose due to uranium intake through the drinkingwater pathway was calculated using the following equation:Ingestion dose (Sv.y-1)= Uranium concentration (Bq .l-1) x Intake of water (l.y-1)x Dose conversion factor (Sv Bq-1).
I. RESULTSAND DISCUSSION238U and 222Rn were measured inwater samples collected from bore well in and around Kodagu distrct and theresults are given in table 1. Uranium concentration in the studied watersamples varies from 0.013 to 0.083 Bq l-1 with an average of 0.
046Bq l-1. Radon concentration varies from 6.38 to 30.69 Bq l-1with an average of 13.49 Bq l-1. The total dose due to U and 222Rnconcentration in water varies from 33.93 to 158.
46 ?Svy-1 with anaverage of 69.97 ?Svy-1. The average annual effective dose due to Uand 222Rn concentrations in bore well water samples are below theMCL limit recommended by EPA, WHO and AERB. The annual effective dose is wellbelow the recommended limit of 100 ?Svy-1 8-10. Maximum U concentration in ground water isobserved at Chettalli. Higher concentration of uranium in this region may bedue to presence of granite rocks present in this region. The concentration ofuranium in water varies from one place to the other depending on lithology,geomorphology and other geological conditions.
Uranium easily dissolves inwater and occurs both in dissolved and particulate forms. It can enter foodchain from soil, water and fertilizers. Even though the most parts of the studyarea contains different types of gneisses and granite rocks the uraniumconcentration in water depends on the depth of the bore well and uraniumcontent in the host aquifer rock. The variation between radon concentration anduranium concentration in water is shown in figure 2. A poor correlation hasbeen observed between radon concentration and uranium concentration in water.