Indian J. Pliys. 73A (2), 2 2 5 -2 3 6 (1999)
U P A
an international journal
and ^^®Po in the soils o f M ysore, Karnataka, India
N Nagaiah, S Malini. L Paramesh and P Venkataramaiah*
Department of Studies in Physics. University ol Mysore, Mtinasagangoin, Mysore-570 006, India
Received 18 February 1998. accepted 8 September 1998
A bstract : 'Hie soil samples collected trom the selected locations were analysed for ~^^Ra and ^^^*Po activity Tlie results reveal lliat the activity ot ranges from 2 0 ± 0 4 Bq kg ^ to 12 9 ± 1 3 Bq kg" ^ whereas that of ranges from 7 6 ± 1.2 Bq kg" * to U ^ 4 2 4 Bq kg * Tile activity ratios of “ ^*^Po to ~“^Ra vary by an order of magnitude from place to place The systeniatjcs (vf these ratio.s on tlie distances of the sampling sites from catchment /one water divide towards neighbouring river basins, have been observed
Keywords Radioactivity, "^^’Po to - ‘■^Ra ratio, topography26n PACS Nos. : 29 40 Me. 29 90 +r
1. In tro d u c tio n
Radium has always attracted particular attention from the viewpoint ol its hcaltii ha/aid to tlie public. This stems from the fact that -~^Ra has a high degree o f radioioxicity, is bone
seeking, has a long half life of 1600 y and as an alpha emitter, has a high potential for causing biological damage fl].
Radium is present in all rcK*ks and soils in viiriable amounts. It can also arise from m an’s exploitation of the radioactive minerals of U, Th e tc as part of the nuclear fuel cycle.
Phosphatic minerals like apatite (Cas(P04)3F. Cl, OH), copper, gold, lignite, coal and such other ores contain uranium and its long lived daughter products, namely --^’Ra, ""^'Th,
^^^’Po e tc . The mining and processing of these minerals for metal recovery can also bring about an enhancem ent in the radium levels in the environment well above the normal background levels.
'Kuvempu UmversUy, Shimoga-577 451. India
® 1999 I ACS
R adium is chem ically sim ilar to calcium and it is absorbed from the soil by plants and passed up the food chain to hum ans. B ecause radium in fo o d originates from soil and radium content o f soil is variable, there is considerable variability in the radium content o f foods. A s a hom ologue o f calcium , a m e u b o lic a lly essen tial elem ent, radium clo sely follows the calcium m etabolism process in m an, with eventual deposition in bones o f about 80% o f the total body radium . TTiis results in the buildup o f radon (“ ^Rn) and its daughters, thereby causing significant radiation exposure. It is estim ated that [2] the annual effective dose equivalent to bone from deposited radium is about 70 pS v, using a quality factor o f 10 for the dose from alpha em issions.
T he ‘ '®Po (Ti/2 = 138 days) content o f soil m ay be by origin, eith er a product o f the decay o f radionuclides o f the chain that were present in the soil o r else the result o f precipitation o f ^^^Rn decay products from the atm osphere. O ver a long period o f tim e, soil accum ulates both 2*®Pb (Ti/j = 22 years) and ^‘°Po from rock, to w hich it ow es its origin, and from atm ospheric precipitation. It is estim ated that [2] the average daily intake o f from dietary sources is about 0.11 Bq under norm al circum stances.
T he concentration and m ovem ent o f ^*°Po in the environm ent depends to a large extent on the parent radionuclides ^'°Pb, present in various environm ental m atrices. Since -'^'Po em its 5.3 M eV alpha particles it produces a considerably greater biological effect than
‘ ^'’Pb w hich is a beta em itter. It is estim ated [3] that the equivalent dose resulting from a single disintegration o f ^’opo is thousand tim es greater than the decay o f ^lopb. Therefore, M organ et al f4] have included ^‘°Po in the group o f m ost highly toxic radioisotopes.
T h e ra d iatio n do se receiv ed by h um anbeing at any p lace, d ep en d s upon the concentration o f the radionuclides present there. In order to relate the observed dose at any place with the radioelem ents present in the environm ental m atrix, one needs the know ledge o f the concentration o f the various radioactive elem ents present in the environm ent.
M ysore (12‘’1 8 ' N latitude and 76° 4 2 ' E longitude) is located in the southern p art o f K arnataka, India and it is know n for its beautiful envirom m ent. A large n u m b o ' o f different types o f industries h ave already com e u p around M ysore. T h is is d efin itely going to enhance the air pollution. T he establishm ent o f Rare M aterials Project (R M P), a D A E unit near M ysore was under opposition from the local public on the apprehension th at there w ould be radioactive em anations from the plant resulting in environm ental hazards.
From the above m entioned factors, it can be understood that th e study o f natural background radiation as w ell as the concentration o f radionuclides in the environm ental m atrices such as soil, w ater, air, vegetables and crops is very im portant. T h erefo re, a detailed study has been undertaken to get the base line data about the activity o f radioactive elem ents in the environm ental m atrix for the future assessm ent o f the im pact due to various industries including RM P. In the present investigation, the activity o f ^ ^ R a an d ^’°P o has been m easu red in so il sam ples collected from different places around M ysore. F rom the
and^^^Po in the soils of Mysore, Karnataka, India
227 m easured activiU es o f and 2'°P o, an attem p t has b een m ade to understand the dependence o f ^“ ’Po to ratio on soil porosity and granular size and the topography o f the study area. T his type o f study has not been m ade so far in this part o f the country and hence happens to be the first o f its kind in this area.2. Materials and methods
Soil sam ples collected from the selected locations (Figure 1) were m ixed thoroughly and extraneous m aterials like plant leaves, roots, m at portions, pebWes etc were rem oved. The
Fi|air« 1. Soil .sampling sues with to raUo
sam ples were then oven dried at 1 10°C over night, cooled, crushed and sieved through 100 m esh. The oven dried sam ple was used for the estim ation o f ^-*Ra and^'^Po activity.
2.1. Mea.surement of^^^Ra activity:
About 10 g o f soil sam ple was refluxed with 25 m l of concentrated nitric acid to r one hour and w as then treated with perchloric acid and nitric acid m ixture to rem ove organic m atter present in it. It was then evaporated to dryness. The dried residue was then treated with 20 ml o f 1 : 1 nitric acid and w as again refluxed for about an hour. These steps were repeated for 5 to 6 tim es and then the white residue obtained was filtered through W hatm an N o. 42 filter paper, collecting the filtrate in a 100 ml standard flask and it was m ade up to the m ark
w ith distilled w ater [S]. The activity o f ^ ^ R a (Bq kg*‘) in the sam ple w as then m easured b y m a n o m e try m ethod [6] using the following relation,
A ctivity » [ ( 5 ±5Z>) (6 9 .6 7 x 1 0 -3 ) (16.67) 1 0 0 0 (a sh % )]/(£ ^ A B .C W . 100), w here 5 is the background subtracted counts per m inute,
SD is the standard deviation,
Ec is the collection efficiency o f the scintillation cell, A s 1 - exp(-X0) is the radon buildup factor,
w here A is the decay constant o f radon (1.258 x 10“^ p er m inute), 6 is th e buildup time in the bubbler,
B = I - exp(-A 7) is the buildup factor in the scintillation cell during counting period o fT = 1000 s,
C = exp(-A r) is the radon decay factor in the delay tim e t betw een collection o f radon and the m id time o f counting and
W is the w eight o f the soil sam ple taken for analysis (in g).
T he background o f the scintillation cell was extrem ely low o f the order o f 0.5 cpm . T he efficiency o f the scintillation cell was m easured using the ^^'^Ra standard and it w as found to be 74%.
2.2. Measurement of^'^Po activity:
T he solution after the analysis o f w as evaporated to dryness and the resid u e w as then converted into chloride m edium by treating it with tw o 5 m l portions o f concentrated hydrochloric acid. T he solution was then e v ^ o r a te d to dryness. T he d ried residue w as d issolved in 20 m l o f concentrated hydrochloric acid and the solution w as then d iluted to 4 0 0 m l w ith d istilled w ater, so that the final concentration o f the solution b ecam e 0.5 N. T h en the so lu tio n w as used for th e a n aly sis o f ^*®Po by e lectro ch em ical d isp lacem en t m eth o d [5]. T he activ ity o f ^lopo (B q kg"0 w as ca lc u la ted using the follow ing relation.
Activity = {S±SD ) (1000) (100 - A f)/(£ ) (Ep) (W) (100) w here S is the background subtracted counts per sec,
SD is the standard deviation,
A/ is the m oisture content o f the soil sam ple (% ), E is the efficiency o f alpha counting system (fraction), Ep is the plating efficiency (fraction) and
is th e w eight o f the soil sam ple ta k ra for analysis (in g).
T h e efficien cy o f the plating w as determ ined using a standard 3>°Po sam ple.
T he stan d ard sam ple w as brought to solution form by em ploying chem ical proced u re as
and^^^Po in the soils of Mysore, Karnataka, India
229 explained above. T he co n ten t presen t in the solution (0.5 N H Cl m edium ) w as then plated o n to a silver d isc an d the recovered activ ity w as m easured using alp h a counting sy sto n . T he overall plating efficiency was found to be 90% .3. Results and discussion
The activities o f ^^^Ra and ^‘^Po m easured in the soil sam ples u e given in Table I . It can be seen from the table that the activity o f ^^®Ra ranges from 2 .0 ± 0.4 to 12.9 ± 1.3 Bq k g r',
Tabic 1. Activity of and in the soils of Mysore.
SI.
No.
Locatjon 2“ R a (B q k g -') ^ 0 p o (B q k g -')
1 Adjacent to BE Ml..* 5 .7 1 0 .8 15.611.6
2 Aralaguppe 3 .3 1 0 .7 12.311.8
3 Basupura 3 .2 1 0 .6 10.01 i.s"
4 Belagula 12.911.3 10.011.0
5 Belavadi 6 .2 1 0 .9 32.5 1 2 8
6 Binhundi 2 .0 1 0 .4 15.511.9
7 Bogadi 3 .5 1 0 .6 14.01 1.8
8 Bommanahalb 3 2 1 0 .5 19.21 1.8
9 Chikkadanahalh 2 .5 1 0 5 17.1 1 1.7
10 Crhikkanahalli 6 3 1 0 .8 9 .7 1 1.6
U Gaudagere 7 .8 1 0 .9 37.312.4
12 Gopalapura 4 .8 1 0 8 8 8 1 1 7
13 Hulikere 3 .3 1 0 .6 9 .0 1 1 .5
14 Kallalialb 2 4 1 0 6 8 0 1 1 4
15 Lakkanakoppal 3 .2 1 0 .6 1 1 3 1 1 6
16 Maidanahallj 4 .5 1 0 .8 11.612.0
17 Megalapura 5 .7 1 0 .8 26.1 1 1 .8
18 Manikyapura 2 .8 1 0 .6 15.711.9
19 Naganahalli 12.91 1.3 35.412.3
20 Ramanahalli 4 .6 1 0 .7 7 .9 1 1 .6
21 Salhundi 2 .0 1 0 .5 15.71 1 9
22 Yalachahalb 5 .7 1 0 .9 7 .6 1 1 2
23 Yelawala 6 5 1 0 .8 2 7 .411.8
*BEML = Bharat Earth Movers Limited.
with a m ean value o f 4 .4 ± 0.7 Bq kg*', w hereas that o f ^'®Po is found to range from 7 .6 ± 1.2 to 37.3 ± 2.4 Bq kg ' w ith a m ean value o f 14.5 ± 1.7 Bq kg*’ . T he o bserved activity o f
^^*Ra is h ig h e r than the values reported fo r C oastal K arnataka [7] (0.3 - 2 .84 B q kg*'), w hereas it is low w hen com pared to the values reported for K aiga [8] (3.2 - 21.6 Bq kg*'), K alpakkam [9] (9.0 - 2 5.0 Bq kg*'), Ireland [10] (48.1 - 107.3 B q kg ') a n d U S A [11]
(8.5 - 155.4 B q kg*'). The activity o f 22«Ra observed in the soils o f M ysore is w ithin the average range o f 2.6 - 26.3 Bq kg*' as reported for the Indian soils [12].
T be activity o f m easured in the soils o f M ysore is slightly high com pared to the values reported for C oastal K arnataka [7] (6.2 - 18.9 Bq kg~*) and M angalore [7]
(1.2 - 13.7 Bq k g '') , whereas it is low com pared to the values reported fo r K aiga (13j (35.7 - 142.9 Bq kg"'), K alpakkam [9] (44.4 Bq k g "') and USA [14] (8.1 - 128.3 Bq kg'*).
H owever, the activity o f ^'®Po m easured in the soils o f M ysore is within the w orld average range o f 8.1 - 219.0 Bq kg~* [3].
It can also be seen from the table that the activity o f is low w hen com pared to that o f ^*°Po. TTie trend in the variation o f the activity o f ^"*Ra an d ^’**Po observed in the present investigation is sim ilar to w hat has been observed elsew here [7 -1 0 ,1 3 ,1 4 ],
From the m easured activities o f ^^*Ra and ^*®Po, the ratio o f ^’**Po to ^^®Ra has been calculated and is shown in Table 2. It can be seen from the table that the ^'®Po to ^^*®Ra ratio
Tabk2. RaUo of to and effective granular sizes of soils.
SI.
No.
Location 210po/22«Ra Effective granular size (p)
1 Adjacent to BEML* 2.7 155
2 Aralaguppe 3.7 136
3 Bastipura 3.1 151
4 Belagula 0.8 158
5 Belavadi 5.2 171
6 Birihundj 7.8 153
7 Bogadi 4.0 161
8 Bommanahalb 6.0 165
9 Chikkadanahalb 6.8 153
10 Chikkanahalli 1.5 177
11 Gaudagere 4.8 153
12 Gopalapura 1.8 172
13 Hubkere 2.7 146
14 Kallahalli 3.3 138
15 Lakkanakoppal 3.5 136
16 Maidanahalli 2.6 163
17 Megalapura 4 6 170
18 Manikyapura 5.6 171
19 Naganahalli 2.7 144
20 Ramanahalb 1.7 138
21 Salhundi 7.9 144
22 Yalachahalb 1.3 163
23 Yelawala 4.2 166
BEML = Bharat Eaith Movers Limited.
varies w idely from 0.8 - 7.9. Since ^*°Po occurs in the decay chain o f ^^^Ra, one w ould ex pect th at in an isolated and undisturbed dom ain the ratio to b e n ear unity. H ow ever, such a d o m ain is ra rely realised. In tb e actual experience, tbe ratio is influenced to different d eg rees b y several param eters such as i) soil porosity, ii) particle size distribution o f tbe
and in the soils of Mysore, Karnataka, India
231 soil, iii) surface and subsurface water movem ents and iv) differential transport o f radioactive elements inside tbe soil dq>endin8 upon tbe topography of tbe area, soil type etc. Hence, an attempt has been made to link the observed vdi«ss of this ratio to the above parameters.The observed values of ^'°Po to “ ®Ra ratio for various locations are also sbovm in Figure 1. A close observation o f the g eo g r^ h ical disuibutian of these ratios reveal very interesting features. Tbe system atics o f these ratios are studied with respect to rhikkjtdjtnahalH, which lies along the catchment zone water di|ride o f the region. It is found that the higher values o f these ratios occur all along tbe s(4th-east o f Cbikkadanahalli, whereas the ratios appear to cluster towards north-east of Cbiljkadanaballi. The [nesence o f KRS (Krishna Raja Sagar) dam towards the northern side o f Cbikkadanahalli might influence the subsoil water movements which would d e f i n i t e affect the concentration o f various elements including radioelements. Hence to understand the dependence of ^“’Po to --*Ra ratio on the above factors, they have been studied with respect to the sampling kKations.
'Phe grain size analysis has shown tbe dominance o f sand ficactions in tbe Cauvery river side and hence the porosity is expected to be relatively mote, and a decrease towards the Kabini river .side. This factor however has a little influence on tbe ^'°Po to ratio when compared to the geology o f the area.
Figure 2. Variation of ^^*^Po to ^^^Ra ratio with respect to distaaoe from catchment zone water divide.
The disuibution of the ratios of ^‘®Po to “ *Ra is studied with respect to the distances of tbe sampling sites frean a common point o f the catchmmit zone water divide towards both Kabini and Cauvery river sides (Figure 2). It can be seen firom tbe figure that tbe ratio 73A(2)-14
increases faster with the length o f oyeriand flow path towards the Kabini river side, w hereas the increase in the ratio is slow towards the Cauvery riv o ' side. H ie faster increase tow ards Kabini river side m ay be attributed to the steep topographic and subsequently the hydraulic gradients with large length o f m ovem ent (elevation varies from 8(X) m to 700 m ), w hereas the slow in a e a s e towards Cauvery river side m ay be attributed to the low topographic and hydraulic gradients (Figures 3 and 4).
Further, the topogra]duc gradient is not uniform in this regicm, since the elevation varies from 780 m - 800 m - 760 m as w e go from the w ater divide tow ards K RS. This indicates that the subsoil w ater m ovem ent and also the surface w ater m ovem ent due to the topographic gradient m ight definitely affect the concentration o f various elem ents including radioelem ents.
F urther, the dependence o f the ^‘®Po to 2**Ra ratio on the geology o f the area is studied. It is know n that [15} the pegm atitic intrusions into the Precam brian gneisses and
and^^^Po in the soils of Mysore, Karnataka, India
233 schists are found near KRS (Figure 5), wtaicb are rich in trace elem ents including the rare earth and radioactive elem ents. T he relatively higher 22«Ra activity observed in the CauveryFigure 4. Pattern of ground water flow in the study area.
Figure 5. Geological features of the area of study.
river side m ay b e attributed to the presence o f pegm atites in these areas. O n the othetfaand, there is n o ex isten ce o f pegm atites tow ards the K abini riv er side, resulting in the low er activity o f ^“ R a a n d hence the higher ^‘°Po to ratio in these areas.
In order to understand tbe dependence o f ^‘°Po to ratio on tbe granular size, die effective granular sizes in all the soil sam ples have been detm m ined follow ing th e sieve analysis m ethod [16]. T he results are show n in T able 2. The correlation betw een to ratio and the effective granular sizes fo r all the sam ples (irrespective o f sides) has been studied and is found to be very low (negative). However, the correlation c o e ffic ia it is found to be 0.93 (negative) w hen tbe places w hich exist only in the straight band tow ards Kabini river side are considered (Figures 6(a) and 6(b)). In general, when all they were p u t together (Figure 6(a)), th^'plot'has show n m ore scatteredness. W h ra the flow regim es w ere
--- j j _ — --- ---
y . .0 00536 X 4 6865 a*
I • -0 032
£ srti 4 -
O*
ofv
• 4
OOi O
« ° o -
ir $ii$(micr9n)
F igurf 6(a)» Plot of ^^^Po to ratio versus effective granular size (irrespective of sides).
gcv
Y - - O 067 X + 20 5458 r • - 0 93
Ott
-T-
lao
G ro n u lo r tls a (mieran) —»•
Figure 6(b)* Plot of ^^®Po to^^^Ra ratio verruj effective granular size (Kabini river side).
considered along witb tbe distance o f transport, a type o f correlation has been obtained as in F igure 6(b). In H g u re 6(a), th e stations w hich are falling outside tbe flow regim es have been discarded [11, IS, 7, S, 23 and 14] and a new plot has been draw n (Figure 6(c)). It is
clearly seen from this figure that the relationships betw een the activity ratio and the granularity o f the soil sam ples are significant and evident.
and 2iOpo /„ the soils of Mysore. Karnataka, India
235QfQnukii «jzt(micron)
f^i^ure 6(c). Plot of -^^Po to ratio versus effective granular size (Cauvery river side).
It can be seen from the above discussion that the granular size plays a dominant role in the Kabini river side, whereas its influence on the ^‘opo to ratio is very less in the Cauvery river side, Tlus clearly shows that the presence o f KRS dam towards the nothem side o f ( ’hikkadanahally strongly influences the variation o f ^lopo to ratio in the Cauvery river side.
4. C onclusions
It can be concluded that the activity ranges o f 22fiRa and 2'«Po observed in the present investigation are sim ilar to the levels oteerved at other places. It can also be concluded that the topographic and hydraulic gradients would strongly influence the system atics o f - '“Po to R a ratio. Further, the soil characteristics, in particular, the granular size would also partially account for the observed ratio.
Acknowledgments
The authors gratefully thank Dr. M R aghavayya, Rare M aterials Project, BA RC Unit, Ratnahally, M ysore for providing facilities for the estimation o f 22«Ra activity and also for tile useful discussions, l l i c authors are highly indebted to Dr. D V G opinath, Form er D irector, H ealth and Safety D ivision. BA RC. Bom bay for very useful suggestions.
They wish to express their gratitude to Prof. A B alasubram anian and Dr. K Byrappa, D epartm ent o f G eology. U niversity o f M ysore for their useful di.scussions. T his work was carried out under a research project sponsored by the Atom ic Energy Regulatory Board and B oard o f R esearch in N uclear Sciences, D epartm ent o f Atom ic Energy, Governm ent o f India.
References
IAEA Tech. Rep. Ser. (Vienna, Austna) 310 Vol. 1 (1990)
United Nations Scientific Committee on the Effects of Atomic Radiation 37th Session, SuppL No. 45 (A/37/45) (United NaUons, New York) (1972)
Y D Parfenov Atomic Energy Rev. 1215 (1974)
K Z Morgan, W S Snyder and M R Ford Health Phys. 10 151 (1964) M A R Iyengar PhD Thesis (University of Bombay, India) (1983)
M Raghavayya, M AR Iyengar and P M Markose Bulletin of Radiation Protection 3 11 (1980)
K Siddappa, N Lingappa, A P Radhakrishna, H M Somashekarappa and Y Narayana Project Report on Baseline Radiation Background Studies in the Environment of Coastal Karnataka including Kaiga (1991) H M Somashekarappa PhD Thesis (Mangalore University, India) (1993)
M A R Iyengar, M P Rajan, S Ganapathy and P R Kamath Sources of Natural Radiation Exposure ir, a Low Monazite Environment (Technical Irformation Centre, US Department of Atomic Energy, Houston) p 1090 (1980)
A P Vinogradov The Geochemistry of Rare and Dispersed Chemical Elements in Sods 2nd edn. (New York : Consultants Bureau) (1959)
[11] T E Myrick, B A Berven and F F Haywood Health Phys. 48 631 (1983) [12] U C Mishra and S Sadasivan J. Sa. Indus. Res. 30 62 (1971)
[13] N Karunakara M Phil Dissertation (Mangalore University, India) (1993) [14] US Atomic Energy Commission Report A T (11-1) p 1733 (1980)
[15] J Swaminath and M Ramaknshnan Memoirs. GeoL Surv. India, Calcutta 112 23 (1981) [16] B C Punmia Soil Mechanics and Foundations (New Delhi: Standard Book House) (1935)
m [2J [3]
14]
[5]
[6] [7]
[8]
m
[10]
