pact and of t h e acceptability of field disposal of t h e product waste.
residual toxicity was probably due t o emulsified aromatic hydrocarbons from the “inert ingredients” of t h e formulation and/or t o chlorinated products from t h e reaction of hypochlorite with these ingredients. Hypochlorite oxidation does degrade diazinon a t a rate acceptable for use as a field method for disposal of wastes containing this pesticide. It is a simple and inexpensive a p proach t h a t uses common reagents a n d would appear t o be ideal for field use. However, this study has shown t h a t hypochlorite does not detoxify all formulations of diazinon and t h a t t h e diazinon-hypochlorite reaction does yield products (Le., trichloroacetate and chloroform) t h a t may cause environmental problems if disposed of in t h e field. These results demonstrate the need for careful study of any chemical disposal system before its use is recommended. Such studies should follow a n approach similar t o t h a t used in this effort (Figure 1) and must include bioassay comparisons t o assure t h a t the degraded material has been acceptably d e toxified. As seen in this study, disappearance of t h e parent compound and identification of nontoxic products are not sufficient justifications for using a specific disposal method. An otherwise acceptable procedure may be unsafe for use because of toxic impurities, unidentified toxic products (from t h e pesticide and/or formulation), and/or toxic “inert” ingredients t h a t are not detoxified by t h e chemical system. Screening bioassay of t h e material before and after chemical degradation should help t o determine if t h e system has been detoxified. T h e combination of bioassay and chemical d a t a allows a more accurate assessment of t h e environmental im-
Literature Cited (1) Miller, T. H., USAMEERU Report No. 73-01, AD 757603, Aug 1972. ( 2 ) Faust, S. D., Gomaa, H. M., Enuiron. Lett., 3, 171 (1972). (3) Meier, E. P., Warner, M. C., Dennis, W. H., Randall, W. F., Miller, 7’. A., IJSAMRRDL Technical Report 7611, AD A036051, Nov 1976. (4) Meier, E.P., Dennis, W.H., Jr., Cooper, Li’. J., Warner, M. C., Rosencrance, A,, Randall, W.F., Bull. Enciron. Contam. Toxicol., to be published. (51 Litchfield. .J. T.. Wilcoxon. F.. J . Pharmacol. Exa. T h e r . . 96. 99-133 (1949). (6) Snyder, R. E., Tonkin. M. E., McKissick, A. M., Final Report. Contract No. DADA 17-73-C-3112,U.S. Army Medical Bioengineering Research and Development Laboratory, Fort Detrick, Frederick. Md.. Seot 1975. ( 7 ) Epstein, .I., Baue;, V. E., Saxe, M., Demek, M. M . , J . A m . C h e m . Soc., 78, 4068 (1956). (8)Gomma. H. M.. Suffet. I. H.. Faust. S. D.. Residue Reu.. 171 (1972). (9) Hsieh, D. P. H., Archer, T. E., Munnecke, D. M., McGowan, F. E.. Enciron. Sci. Technol., 6 , 8 2 6 (1972). (10) Rosenhlatt, D. H., “Disinfection--Water and *astewater”, .Johnson, .J. D., Ed., Ann Arbor Science Puhlishers. Ann Arbor, Mich., 1975, pp 249-276. (11) Margot, A., (issin, H., Helts. Chim. A c t a , 40, 1562 (1967). (12) dohannes, H., Kernmerling, W.,Wasser B o d e n , 24, 235 (1972). (13) (;rimme, L. H., Pharm. I’nserer Zeit, 2, 61 (1973). Keceiced /’or rei,ieu, September 18, 1978. Accepted J a n u a r j , 8, 1979.
Elemental Emissions from a Coal-Fired Power Plant. Comparison of a Venturi Wet Scrubber System with a Cold-Side Electrostatic Precipitator John M. Ondov+, Richard C. Ragaini, and Arthur H. Biermann Lawrence Livermore Laboratory, University of California, Livermore, Calif. 94550
Emissions of elements in total suspended particles and in discrete particle-size intervals are compared for two coal-fired electrical generating units equipped with venturi scrubbers a n d one unit with a cold-side electrostatic precipitator (ESP). Coal and particulate emission samples were analyzed by instrumental neutron activation analysis, atomic absorption spectroscopy, and X-ray fluorescence. Emissions of Cr, Mn, Zn, Co, Ni, and Cu from t h e scrubbers were enhanced, probably because of corroded internal metal surfaces. Concentrations of many toxic elements, including Br, As, Se, S b , U, V, a n d Cr, in aerosols emitted from t h e scrubber were up to 170 times greater than in aerosols from the ESP. T h e scrubber emitted a greater proportion of aerosol mass in particles of respirable sizes. We conclude t h a t the wet scrubbers reduced the potential inhalation hazard from particulate emissions less effectively t h a n a n ESP of comparable efficiency. Coal use for electric power generation in the United States is expected t o increase from 3.6 t o 5.1 X 10” kg by 1980 (1, 2). Even now, release of potentially toxic substances t o the a t mosphere is of concern (3-6), and the possibility of adverse effects of these substances has stimulated considerable interest in t h e control of particulate emissions. Electrostatic precipitation and wet scrubbing processes are t h e two major strategies employed t o control particulate 598
Environmental Science & Technology
emissions a t coal-fired electrical utility stations. Commercial wet scrubbers are very efficient in removing supermicron particles a n d reduce plume visibility greatly (7, 8). Besides controlling particulate emissions, t h e units simultareously reduce SO2 emissions (7, 9). T h u s particulate scrubbers can be used both with and as flue-gas desulfurization systems. However, current commercial wet particulate scrubbers rely principally on impaction and interception mechanisms and theoretically should not remove efficiently t h e smaller, submicron particles (7, 8, 10, 11 ). In addition, resuspension of droplets from mist eliminators can augment t h e emission of fine particles from scrubbers (12).Of the types of scrubbers used on coal utility boilers, high-energy, venturi scrubbers are among the most efficient in removing submicron particles (7, 10)
In view of the greater respirability of fine particles (13) and t h e well-established concentration of many elements in fine particles from coal combustion ( 5 , 14-20), the emission of substances from wet scrubbers and electrostatic precipitators must be scrutinized. In this work we compare elemental emissions and particle-size distributions from two power units equipped with high-energy, variable-throat, venturi wet scrubbers and a unit equipped n i t h a cold-side ESP. Each of t h e units was in use a t a Western coal-fired power plant a t which t h e same coal was burned in all units. Because fly-ash elutriation and particle-size characteristics of the boilers were
0013-936X/79/0913-0598$01.00/0 @ 1979 American Chemical Society
~
~
.
Table I. Design and Operating Parameters of the CoalFired Utility Boilers Equipped with a Venturi Wet Scrubber or Electrostatic Precipitator System scrubber._ units .. a.- ._ . no. 1 no. 2
parameter
boilers tY Pe efficiency, YO excess air, % max steam capacity,
front-fired
ESP unit
front-fired front- and rear-fired
87 15 160
87 12.5 203
88.7 16 654
254
322
1026
54 20.2
54 20.2
117 23
650
650
800
99.2e (99.7 f 0.1)s
99.2"
97'
kg/s
control devices flue gas flow rate at inlet, m3/s temp, O C suspended particle concn at inlet, mg/m3 SO2 concn at inlet, ppm efficiency of particulate removal, YO
a Liquid-to-gas ratio, 1.4 L/m3 (actual); make-up water for the system, 6.4 to 7.6 m3/min. liquid delay time in the venturi-cycle loop, about 2 min; liquid temperature leaving the scrubber, 54 OC;pH of liquid in the thickener maintained at 7.5 by the addition of lime, suspended solids in recirculated flow maintained at 6 % At maximum generating capacity. Nominal value at 21 O C . Measured at outlet sampling location. e Nominal value. 'Estimated from elemental penetrations and plantdesign data. Measured during February sampling period at a differential venturi pressure of 36.8 mmHg and 9 5 % of maximum electrical generating capacity.
similar, t h e relative effectiveness of t h e two types of control devices can be evaluated for trace element removal by comparing their emissions.
Experimental
Power Units. Three separate units, designated as 1,2, and 3, with respective maximum steam capacities of 160,203, and 654 kg/s were tested. Blended, pulverized, surface-mined, subbituminous coal from t h e same source was burned in each of t h e units. All three boilers operated d r y bottom without fly-ash reinjection. Flue gasses from both of t h e scrubberequipped units (1 and 2) were fed through a n air heater before entering t h e scrubber. Gasses from t h e scrubber passed through a mist eliminator, a wet, induced-draft fan, a n d a n other mist eliminator. T h e scrubbing solution was continuously recycled from t h e cyclone separator t o t h e venturi. Blowdown from the cyclone was sent to a thickener where lime (CaCO.3) was added. T h e scrubber systems were designed t o remove 99.2% of t h e incident particulate material a n d also removed 30 t o 35% of t h e SOz. Gasses leaving t h e boiler of t h e ESP-equipped unit flowed through two cold-side precipitators, which were arranged in a chevron design, before exiting through a 91-m stack. T h e total specific collecting area of t h e E S P was 4760 cm2/rn:'. When all sections were operating properly, n e t removal efficiency of t h e E S P was typically 97%. Other specifications for t h e boilers a n d control devices are listed in Table I. Sampling. Samples were taken with a modified, EPA-type sampling train as described previously ( 2 0 ) .T h e same filter materials (47-mm, 0.4-pm pore, Nuclepore membranes) a n d University of Washington Mark 111 and Mark V source test cascade impactors ( 2 1 ) were used in each of t h e units. T h e impactors, respectively, provided 8 and 12 discrete fly-ash size fractions for chemical analysis ranging from 1 0 . 1 t o 230 Ctm.
_
_
_
Table II. Typical Coal Consumption and Efficiencies of Energy Conversion
power unit
load lactor, %
coal consumption, gls X lo4
energy conversion efficiency, BtulkWh
scrubber-equipped units 1 (Feb 76) 2 (June 75)
100 100
2.74 3.58
1.00 x 104 1.02 x 104
94 82
9.71 8.57
9.47 9.38
ESP-equipped units (July 75)
(July 75)
x x
103 103
Samples were collected at t h e outlets of t h e scrubber mist eliminators a n d in-stack a t t h e 61-m level of t h e E S P equipped unit during two periods in J u n e and July 1975. Scrubber maintenance was performed several months before sampling in June. Additional samples were collected from t h e first scrubber a n d t h e ESP unit along with inlet a n d outlet testing during a third period in February 1976 shortly after scrubber maintenance. Records of plant-operating d a t a collected hourly include gross generating load, coal consumption, a n d proximate analyses. Energy-conversion efficiencies (determined monthly), status of ESP sections, and scrubber venturi pressure (hourly) were obtained from plant personnel. Velocity, temperature, a n d pressure of t h e stack gas were monitored continuously during each sampling. Samples of coal, E S P fly ash, bottom ash, a n d scrubber slurry were also taken during t h e stack fly-ash collections. Plant Operation. During t h e sampling period in J u n e , operation of t h e scrubber-equipped units remained relatively stable. During t h e sampling period in July, 4 of t h e 32 precipitator sections were inoperative b u t compliance with emission standards (215 ng/J) and precipitator efficiency (97% for total suspended particles) were maintained by operating at reduced loads. In February, failure in t h e precipitator resulted in a 10- t o 20-fold increase in emissions. These data are not reported. Analyses. Stack-, E S P - , and bottom-ash, scrubber-slurry, scrubber-lime, a n d coal samples were analyzed for u p t o 43 elements by instrumental neutron activation analysis (INAA) a s previously described (22, 23). Filter, fly-ash, and coal samples were analyzed for P b , Cd, and Be by atomic absorption spectroscopy (AAS). Nickel, Pb, and Cd were determined in coal and fly-ash samples by energy-dispersive, X-ray fluorescence analysis (XRF) (24).Results from these techniques were verified by analyses of National Bureau of Standards' s t a n d a r d reference materials, coal (SRM 1632) and coal flya s h ( S R M 1633), a n d through interlaboratory comparisons of S R M samples ( 2 5 , 2 6 ) Size distributions of particles collected on several individual impactor stages, backup filters, and total filters, Le., 47-mm filter preceded only by a n inlet nozzle, were determined by scanning electron microscopy (SEM). T h e treatment and results of these d a t a were discussed previously (20) Data Normalization. Rates of atmospheric discharge of minor a n d trace element species in each sample were computed from t h e stack concentrations and gas velocities. Emission rates were further normalized t o t h e boiler heat input t o account for differences in coal consumption, electric power production, and efficiency of energy conversion of each unit. T h e heat input was computed from the gross generating load a n d energy-conversion efficiency of each unit. Coal consumption rates were computed from t h e gross generating load ( L ) ,the known thermal efficiency (a monthly average E ) , a n d t h e heat content of t h e coal (Q,) a s follows: Volume 13, Number 5, May 1979 599
a u n - r i g u 'aiel uoisriru~
600
Environmental Science & Technology
Table 111. Concentrations of Elements in Coal Burned during Sampling Periods (Fg/g) elements
June 75
July 75
AI As Ba
30 100 f 4990 (7) 2.03 f 0.43 (7) 466 f 108 (7) 1.51 f 0.17 (7) 0.97 f 0.20 (6) 6 300 f 1610 (7) 0.053 f 0.020 (7) 24.9 f 2.0 (7) 54.4 f 11.5 (2) 1.94 f 0.17 (7) 6.12 f 0.52 (7) 0.590 f 0.084 (6) 14.0 f 0.5 (2) 5 940 f 740 (7) 8.30 f 1.72 (2) 0.25 f 0.05 (6) 0.037 f 0.007 (4) 1 690 f 170 (6) 13.0 f 1.0 (7) 1 950 f 460 (4) 2.4 f 0.9 (1) 56 f 24 (6) 2 970 f 370 (7) 4.4 f 0.5 (2) 10.7 f 0.5 (2) 9.95 f 1.96 (7) 5 800 f 1000 (7) 0.656 f 0.086 (7) 2.84 f 0.20 (7) 1.41 f 0.11 (7) 88 f 13 (7) 0.509 f 0.038 (7) 5.95 f 0.41 (7) 1 120 f 222 (6) 2.13 f 0.11 (7) 22.9 f 3.0 (4) 0.99 f 0.40 (2) 15.8 f 1.4 (6) 55.6 f 8.7 (7)
30 300 f 3600 (15) 2.73 f 0.71 (11) 418 f 88 (14) 1.67 f 0.14 (9) 0.96 f 0.18 (2) 5 360 f 730 (15) 0.061 f 0.019 (10) 25.6 f 1.7 (15) 71 f 20 (4) 1.98 f 0.25 (14) 5.19 f 0.29 (15) 0.70 f 0.08 (15) 13.4 f 1.2 (6) 5 720 f 380 (15) 8.8 f 1.4 (11) 0.065 f 0.015 (5) 0.0415 f 0.0046 (13) 1 820 f 250 (14) 14.3 f 0.8 (15) 2 330 f 470 (11) 2.60 f 0.54 (15) 54.1 f 1.6 (15) 2 940 f 160 (15)
Be
Br
Ca Cd
Ce CI co Cr
cs cu Fe
Ga Hg In K La Mg Mo Mn Na Ni Pb Rb Sb
Sb
sc Se Sr Ta Th Ti U V W Zn Zr a
Averages and standard deviations: number of samples given in parentheses.
Btu X 1 X 0.126 g*h coal flow = L ( k W ) X E kW.h Btu s-lb
62,.
Rates of coal consumption and t h e efficiencies of energy conversion are listed in Table 11. Consumption rates of individual elements were obtained by multiplying their concentrations in coal (Table 111) by t h e coal consumption rate. Overall penetrations of individual elements were computed by dividing t h e emission rate by t h e consumption rate. P e n etrations are independent of t h e concentrations of elements in coal. Elemental concentrations in particles associated with t h e observed distributions were determined by INAA of impactor samples. Using SEM analysis, density measurements, a n d INAA, we corrected elemental mass o n impactor backup filters for excess mass resulting from particle bounce-off a n d reentrainment t o provide a more accurate estimate of t h e small particle component (see ref 20). Particle-size distributions of several elements from both t h e scrubber-equipped (unit 1) and ESP-equipped units are shown in Figures 1A through D. Normalized emission rates (ng/J) are plotted vs.
a Feb 76
-
29 500 f 2390 (7) 2.84 f 0.84 (6) 420 f 167 (7) 1.2 f 0.6 (7) -
5 620 f 860 (7)
0.17 f 0.02 (7) 27.0 f 2.0 (7) 48 f 17 (1) 2.08 f 0.22 (7) 7.02 f 1.28 (7) 0.72 f 0.16 (7) 12.7 f 0.6 (7) 6 470 f 570 (7) 8.48 f 1.25 (7) 0.10 f 0.02 (5) 0.039 f 0.006 (5) 1 730 f 260 (7) 13.4 f 0.8 (7) 2 240 f 753 (6) 2.67 f 0.26 (6) 60.2 f 20.0 (7) 2 930 f 248 (7) -
10.2 f 1.2 (16) 9.05 f 0.53 (15) 5 200 f 800 (2) 0.572 f 0.049 (15) 2.77 f 0.11 (15) 1.55 f 0.15 (15) 87.2 f 8.9 (15) 0.492 f 0.038 (15) 5.73 f 0.32 (15) 1220f200(14) 1.85 f 0.19 (15) 22.1 f 3.2 (9) 0.80 f 0.24 (5) 14.7 f 1.7 (15) 52.2 f 5.9 (15)
12.1 f 0.7 (7) 12.1 f 1.8 (7) 5 800 f 600 (12) 0.614 f 0.095 (7) 2.98 f 0.20 (7) 1.74 f 0.25 (7) 97.7 f 8 . 3 (7) 0.513 f 0.056 (7) 6.21 f 0.67 (7) 1 230 f 180 (6) 2.12 f 0.25 (7) 24.9 f 3.1 (4) 99%, but below 1pm drops off rapidly with decreasing particle size. T h e aerodynamic 50% cut-off diameter for t h e scrubber was about 0.75 pm, and its efficiency for TSP’s was 99.7 f 0.1%(see Table I). T h e negative efficiency for the collection of very small particles is attributed t o mist entrainment a n d flash volatilization of liquid droplets t h a t contain dissolved a n d suspended solids. Unfortunately, t h e mechanical failures noted above prevented measuring optimum ESP performance. T h e ESP efficiency curve, however, agreed qualitatively with t h a t typical of a cold-side ESP shown in Figure 3 (27). These curves are characterized by high collection efficiencies of both supermicron and submicron particles, with a shallow minimum for particles in t h e 0.1- t o 1.0-pm range. Thus, we would expect submicron particles to penetrate the scrubber more effectively than the ESP. As noted above, the relative effectiveness of the two types of control devices may be inferred from particulate emission rates from each, if t h e particle size distributions of
Table V. Mass Median Aerodynamic Diameters (MMAD) of Elements in Aerosols Emitted from Two Coal-Fired Electrical Generating Units (pm) ESP unit, July 1975
elements
scrubber unit, Feb 1976 M M A R a pm
Cr, Cs, Rb, Zr
elements
10.7-12.3 9.1-10.0
AI, Br, Ce, Co, Dy, Eu, Fe, Hf, K, La, Lu, Mg, Nd, Sc, Sm, Ta, Tb, Th, Ti Ca, Mn, Na, Se As, Ba, Ga, In, Mo, Sb, U, V , W, Zn total suspended particles small mode large mode
7.9-8.6 4.4-6.3
Co, Cr, Ni Fe, K, Mg, Na, Zn AI, Br, Ce, Dy, Hf, Lu, Sc, Sm, Th, La Ca, Ga. In, Mo
7.1-12 3.0-4.0 1.4-2.1
As, Ba, Sb, Se, U, V. W
0.49-0.59
f
I
1.69-0.81
0.13 (mgc = 1.42) 8.1 (ugc= 2.2)
0.33 (usc = 1.57)d 0.80 ( m g C = 1.20)d
a Range of median values of MMADs from distributions of up to S I X impactor samples. standard deviation Data from SEM analyses of filter sample collected in June 1975.
1
MMAD,a p m
---
, , , , , , I
I
I
I
Determined from SEM particle counting techniques (20). Geometric
99.98 -
I I I I I -
--
f---
ae I
t
I
i
9998 95-
5
2
90-
A A
+
+
t
A
+ A
AoA
-i 5
I
I-./
L1.o - 4 0 ~ 1.
A -4,
-
0
A"ooo
A
~
-
A
A
-
0
60
.-0
0
-25
-
I
I
99.8-+
8
I
I
-
I
I
--
-1
10
L 100
Aerodynamic diameter, pm Figure 2. The venturi wet scrubber system is inefficient in removing particles of submicron diameters 10-1
aerosols entering t h e two devices are known. Size distributions of particles entering both a icrubber system (unit 1) and t h e E S P were measured with cascade impactors during the February experiment. T h e distributions of S c (Figure 4), a n element which is independent of particle size, indicate t h a t normalized rates of mass flow (mass/unit heat input) and particle-size distributions are nearly the same for particles -.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. Environ., 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(1974). (: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 this p a p c r wrrc prc,\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 in 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 to a c o m p a n y or product n a m e doc.\ riot i m p / > cipproia/ or re,cf)r?iniCridafion of 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 t o have the capacity of rapidly oxidizing tritium. ~
Our previous work ( I , 2) showed t h a t soil microorganisms are responsible for a rapid oxidation of elemental tritium t o tritiated water. T h i s laboratory work pointed t o a possible hazard a n d 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 t h e route of contamination depended on t h e 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, t h e present data indicate that soil and plants would be the primary accumulation sites and, therefore, t h e most sensitive media for sampling. Elemental tritium is produced in nuclear power reactors a n d is released during reprocessing of t h e 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., a n d a new facility is constructed, but inoperative, at Barnwell, S.C. We undertook t h e project reported here t o determine if t h e soil microorganisms capable of tritium oxidation existed near
these facilities and, if so, t o find out if their activity was sufficient t o 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 t h e 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 a t 30 "C in 1S-cm petri dishes; daily additions of water were made to maintain them a t 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 t h e incubation period in order t o create optimal conditions for tritium oxidation. After t h e incubation period, moist soil equivalent t o 20 g o n a dry weight basis was removed. T h e 20-g samples were placed in 1 -I,round-bottomed flasks and enough water was a d d e d to bring each sample t o 1.10% of its water-holding capacity. T h e flasks were closed with rubber stoppers a n d the resultant soil slurry was spread over t h e inner surface by shaking. After the flasks had been flushed with air, 1.5 pCi of elemental tritium was injected through t h e 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
