( 2 3 ) Heft. R. E.. presented at the Third International Conference o n Nuclear Xlethods in Environinental and Energy Research, ('o Iumhia, M o . . Oct 10.13, 1977. (24) Honner. N. A , , Hazan. F.,Camp, D. C.. ('hcrn. I n s t r u m . , 6, l M 6 (1975). (25) Ondov. .J. M., Zoller. LV. H., Olniez. K.. Aras. N. K . , Gordon, C. E.. Kanticelli, I,. A,. Ahle, K. H.. Filhy. R. H., Shah, K. R., Ragaini. R. C., Aria/. Chr>ni.,47, 1102-9 (1975). ( 2 6 ) Ondov, .J. hl.. Kagaiiii. R. C.. Heft. R. E., Fisher. G.I,,, Silherrnan, I).. l'rentire, H. A , , Proceedings of the 8th Materials Research Synipcibium, Methods and Standards f o r Environmental Mensuremetit, (;aithershurg, Md.. Sept 2 0 - 2 4 , in press; 1,awrence 1,iverinore I,ahoratory, Preprint U('HId-78194, 1976. ( 2 7 ) McVain, J . D.. Gooch,.J. P.. Smith, tv. H . , J . A i r P o / / u t .('uritrfd . h , 5 i J ( . , 25, 117 '11 (19Y,?l). ( 2 8 ) Ensor, I). S..('ahill. 'I. A , , Sparks, I,. E.. presented at the 68th Annual Meeting of the, Air Pollution Control Association, Boston. J u n e 2-15, Paper No. MRI 75 Pa-1317s 1975. (29) Ensor, D. S., .Jackson, B. S.. Calvert, S., Lake, C., CVallon, 1). V., Nilaii, R. E., Campbell, K. S., Cahill, T. A,. Flocchini. K. G , "Evaluation o t a Particulate Scruhher o n a ( ' o a - F i r e d Lltility Boiler", prepared for I' S . Envirt~nnientalProtection Agetic>-.Office 01' Research and I)evc~lopnient,FVa~hingtoii.11.C.. F:P.4-600/27,5-074, 197r). (30) 0ndi)v. .J. &I., Iiagaini, R. V.,Riermann. A. H., ('hoquette. C. E., Gordon. (;, E., Zoller, iV. H . , presented at the 17:Ird iKational Meeting ol the American Cheinical Society. Kea. Orleans, March 25, 1977.Abstract ENYT-124; Lawrence 1,iverinore 1,ahoratory.
Preprint UCRL-78825, 1977. (,'il) Hiermann, A. H., Ondov, J . M.,"Respiratory Retention Function Applied to Particle Size Distrihution", Lawrence Livermore Lahoratory, Report UCRL-52185, 1976. ( 3 2 ) Ondov. *J. M., Ragaini, K. C., Hiermann. A. H . , submitted for puhlication in Atmos. E n v i r o n . , 1978; Lawrence Livermore Laboratory, Preprint UCKL.80254. 1978. ( 3 3 ) Hiermatin. A. H.. in Metals and Ceramics Division, Quarterly Reports. Lawrence Livermore Laboratory. 1977. (:34) Natusch, D. F. S.. LVallare, ,J, R.. Evans. C. A,. S(.irricc, 183, 202 4 ( 1 9 7 4 ) . (:is) I,inton, K.W., Loh, A,, Natusch, D.F.S., Evans. C. A,. ,Jr., LVilliams. P., Science, 191,852-4 (1976). (36) Schroeder, H. A,, Environment, 13, 18-24, 29-32 (19711. ( 3 7 ) Fed. Regist , No. 1910.94 (20-098-74-9),121-127 (July 19741.
c'ii,t,d for rct*icic March I S , 1978. A c t r p t c d Jariuar\ 12, 1979. I'rtz/irnirinr> ciccourits o/ the, work dcscribed in t h i s p a p c r wrrc p r c ,\c~ritc'd a t t h o 172nd L V a i ~ o n aM/ c So( irt? , Di~isicinof Eni,ironmenta/ Aug 29 Scpt 9, 1976, orid a t t h e 7 1 s t A r ~ n u a Mertirig / of t h Air ~ l ' i ) / / u t i or? ('on trol Association i n 1 \V(irA p r f o r r n e d ur1dr.r t h c au.\pic h? tht. Lnii r(Jricf3l,ii,e,rniorP Jfl,5-h"V(;-48. Rcfererice t o a c o m p a n y or product n a m e doc.\ riot i m p / > cipproia/ or re,cf)r?iniCridafionof t h e product h? thc I 'niwrsit?, 1)f ('a/i/orriia or t h r I '.S'. Departrnt'rit of Ericrg? ti, rhc rrc/usiori of 11fhc3rbt h a t arc' * u i t a b / c .
NOTES
Tritium Oxidation in Surface Soils. A Survey of Soils Near Five Nuclear Fuel Reprocessing Plants James C. McFarlane", Robert
D. Rogers, and Donald V. Bradley, Jr.
Environmental Monitoring and Support Laboratorv, U.S. Environmental Protection Agency, P . 0 Box 15027, Las Vegas, Nev. 891 14 -
-
~
._ ~-~
T h e oxidation of elemental tritium into tritisted water b> soil microorganisms represents a previoucly unsuspected pathway for tritium contamination of food. Soils from around potential point source emissions of tritium were tested and all were found to have the capacity of rapidly oxidizing tritium.
Our previous work ( I , 2) showed that soil microorganisms are responsible for a rapid oxidation of elemental tritium to tritiated water. This laboratory work pointed to a possible hazard and a pathway of food contamination previously uiisuspected. Our work also showed that plants rapidly incorporated tritium ( 3 )when exposed in a growth chamber and t h a t the route of contamination depended on the oxidation of H'I' in the soil. In past accidental releases of elemental tri tiurn, very little attention has been given to evaluating soil and plant contamination. However, the present data indicate that soil and plants would be the primary accumulation sites and, therefore, the most sensitive media for sampling. Elemental tritium is produced in nuclear power reactors a n d is released during reprocessing of the fuel elements. Currently there are nuclear fuel reprocessing facilities operating near Aiken, S.C., Arco, Idaho, Hanford, Wash., and a small experimental unit near Oak Ridge, Tenn., and a new facility is constructed, but inoperative, at Barnwell, S.C. We undertook the project reported here to determine if the soil microorganisms capable of tritium oxidation existed near
these facilities and, if so, to find out if their activity was sufficient to be considered important in the event of a tritium release.
Methods r > .
I ritium oxidation was determined in the following manner. Representative soils were collected from the vicinity of each of these facilities and analyzed for their tritium oxidation potential. T h e physical and chemical properties of these soils are found in Table I. T h e soils (200 g, dry weight basis) were incubated for 7 days at 30 "C in 1S-cm petri dishes; daily additions of water were made to maintain them at 50% of their water-holding capacity. T h e incubation period ensured that the microbial populations in each culture were active and a t a stable level of activity. Field conditions were not maintained during the incubation period in order to create optimal conditions for tritium oxidation. After the incubation period, moist soil equivalent to 20 g on a dry weight basis was removed. T h e 20-g samples were placed in 1 -I,round-bottomed flasks and enough water was added to bring each sample to 1.10% of its water-holding capacity. T h e flasks were closed with rubber stoppers and the resultant soil slurry was spread over the inner surface by shaking. After the flasks had been flushed with air, 1.5 pCi of elemental tritium was injected through the rubber stopper with a gas-tight syringe (5-cin:' iiijection of HT in N2).These bottles were then stored a t 30 "Cfor various periods of time before analysis.
This article not subject to U.S. Copyright. Published 1979 American Chemical Society
Volume 13, Number 5, May 1979
607
Table 1. Physical and Chemical Properties of Soils
%
%
%
cation exchange capacity, mequiv/100 g
22.1 32.1 23.7 26.2 90.9 91.7 90.9 89.0 80.8 84.5 35.1 45.8 47.8 47.6
14.4 18.3 19.0 11.1 1.6 1.8 2.6 2.0 3.0 2.2 3.7 2.4 17.5 14.6
3.9 4.1 6.2 3.4 0.4 0.6 0.7 0.6 0.5 0.4 0.6 0.5 0.6 1 .o
4.1 1 .o 15.3 2.9 0.3 0.3 2.1 0.3 5.4 7.2 8.9 9.6 12.2 12.4
sand, soil type
Clairbornea silt loam Armucheea silt loam Collegedale a silt loam Fullerton Chertya silt loam Blanton loamy sand Fuquay sand NorfolkCloamy sand Blanton sand Burbank loamy sand Quincy loamy sand Ritzvilled silt loam Warden very fine sandy loam Bernicetoh e sandy loam Pancheri'silt loam
ow matter,
clay,
HT
PH
oxidation rate, Vmax = % h-'
5.7 4.7 5.2 4.7 5.1 4.9 5.0 4.6 7.3 7.4 6.9 7.1 a.1 8.2
34 f 3 59 f 8 39 f 3 65 f a 49 f 9 44 f 9 12f2 15f2 35 f 3 30 f 3 31 f 7 48 f 8 48 f 7 66 f 6
a Anderson County, Tenn., near.0ak Ridge National Laboratory, U.S. Department of Energy (DOE) reservation. Aiken County, S.C., near Savannah River DOE reservation. Barnweil County, S.C., near Allied Gulf nuclear fuel reprocessing plant, under construction. Franklin County, Wash., near the Hanford DOE reservation. E Butte County, Idaho. 'Jefferson County, Idaho, near the National Engineering Laboratory, DOE reservation.
T h e reaction was stopped by opening the flask to allow the remaining elemental tritium to escape and by adding 50 mL of benzene. T h e water was distilled in a benzene and water azeotrope ( 4 ) and t h e amount of tritium recovered as water was determined by liquid scintillation. T h e reaction rate was determined by analyzing replicate samples a t various times. This produced a series of measurements which yielded curves that are described by a regression function known as t h e exponential growth model:
Y = P1[1- exp(-P2t)]
+E
(1)
where Y = the amount of tritium converted to H T O a t any time, PI = the asymptotic tritium concentration (nanocuries), P2 = the reaction rate parameter (hours-'), t = time in hours, a n d E = the error function, assumed to be Gaussian. Each data set was fit to this regression model using a nonlinear least-squares program. T h e derivative of Formula 1with respect to time gives the velocity of the reaction:
At time zero t h e velocity is maximal and equals PlP2. If the concentration of converted oxidized tritium is expressed in terms of percent or as a fraction, PI equals 1.0 and P2 therefore equals the maximum velocity of the reaction. T h e dimensions in these tests were in units of the fraction of tritium converted per hour; multiplying by 100 yielded t h e percent of H T converted t o H T O per hour. Results a n d Discussion From the test results we generated a family of curves which represent different rates of tritium oxidation. T h e maximum velocities occurred a t T = 0. I n these experiments, atmospheric hydrogen, a t an accurately known concentration of 0.50 ppm (vo1:vol) ( 5 ) ,was the dominant source of elemental hydrogen. Maximum velocities were calculated and are presented in
608
Environmental Science & Technology
Table I to compare rates for various soils. Because these soils had been incubated a t 50% of their water-holding capacity to bring the microorganism populations to a high level of activity, comparisons are of potential activities which do not necessarily represent field activities. T h e reaction rates observed ranged from 12% per hour to 66% per hour and were generally independent of the soil type or soil chemical properties. These rates are sufficiently rapid t o account for significant oxidation of H T if it were present in t h e environment. I t is probable that significant quantities of tritium would be found in t h e soil following a release or leakage of HT. T h e amount would obviously depend not only on microbial activity but also on air mixing near the soil surface, duration of exposure, and HT concentration. Our findings suggest t h a t appropriate sampling schemes should be developed t o quantify the importance of microbial oxidation of HT as a factor in plant and water contamination. Acknowledgment We thank Darrell L. Gallup, Idaho State Soil Scientist, Rector H. Moneymaker, Anderson, Tenn. Soil Survey Party Chief, Donald C. Hallbick, South Carolina State Soil Scientist, and Richard C. Harriman, Soil Scientist in Pasco, Wash., all of the U S . Soil Conservation Service, for collection and classification of soil samples and Dr. Robert Kinnison, US. Environmental Protection Agency, for statistical assistance. Literature Cited (1) Rogers, R. D., Bradley, D. V., Jr.. McFarlane, J. C., unpublished report. ('2) McFarlane. J. C.. Rogers. R. D.. Bradlev. D. V., Jr., Enuiron Str (4) Moghissi, A. A,, Bretthauer. E. %'.. Crompton, E. H.. Anal. C'hern , 45, 1665-6 (1973).
(5) Ehhalt. D. H.. Heidt. L. E.. Lueh. R. H.. Rouer, N., "Vertical Prot'iles of CH4,H P , CO, NPO,and C 0 2 in the Stratosphere", Third Conference on CIAP. U.S. Department of Transportation, 1974.
Receiued f o r reuieic; A u g u s t 21, 1978. Accepted Nouernber 13, 1978.
