exchange resin and the 82Br (tliz = 26 hr) spectrum is a major component of the total gamma spectrum of the sample (Figure 1). However, with the high resolution of the Ge (Li) detector, concentrations of bromide ion in the levels found in the many samples examined could be easily tolerated without causing any measurable error in Hg determination. No interference
was found for any other metal ion in the fish tissue studied, Furthermore, with the volume of l M H C l used in the rinse and sodium elution, no detectable mercury (as a loss) was found in these solutions after passing through the column, and only trace amounts of 24Nafremained on the column. This technique has advantages over other methods of traceHg analysis. Especially with the addition of “carrier” mercury after irradiation, the percent losses of sample mercury during chemical separation are lowered significantly compared to other methods. Elimination of chemical steps in the Bowen and Gibbons (1963) method shortens the analysis time per sample. In addition, several samples can be run simultaneously by one technician so that the total time for preparation and counting of each unknown can be lowered to about 10 to 15 min per sample. Acknowledgment
This work was supported by the Michigan Memorial Phoenix Project, which also donated laboratory space and reactor time, NSF grant GA-25563, and the Federal Water Quality Administration grant no. ~ ~ O ~ O - E LAlso, H . we thank Richard Grieg, U.S. Bureau of Commercial Fisheries, who supplied fish samples and the comparative data.
\
m
400
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800
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1200 1400
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ENERGY (KeW
Figure 1. The gamma spectrum of the ion-exchange resin containing Hg sample
Literature Cited Bowen, H. J. M., Gibbons, D., “Radio-Activation Analysis,” Oxford at Clarendon Press, 1963, pp 264 and 5. Ehman, W. D., Huizinga, - . J. R., Geochim. Cosmochim. Acta 17, 125 (1959). Griea. R.. Bureau of Commercial Fisheries. DeDartment of the Interior, Ann Arbor, Mich., personal comm;nication, 1970. LaFleur, P. D., National Bureau of Standards, Washington, D.C., personal communication, 1970. Received for review September 30, 1970. Accepted December 26, 1970. Dioision on Analytical Chemistry, 160th Meeting of the ACS, Chicago, Ill., September 1970.
Tritium Loss from Water Exposed to the Atmosphere J ; Henry Horton, John C. Corey, and Richard M. Wallace Savannah River Laboratory, E. I. du Pont de Nemours and Co., Aiken, S.C. 29801
Equations describing the loss of HTO from water into air and the gain of HTO in water when the overlying water vapor contains tritium but the solution does not are developed and verified by laboratory experiments. Results show that under environmental conditions, where the relative humidity is greater than S%, HTO is lost preferentially over HzO to the atmosphere because atmospheric moisture is virtually free of HTO. Results from a three-year study of the changes in tritium content of a large nonseeping outdoor basin are used to extend the laboratory studies to field situations. Data from this field study were used to calculate tritium loss from open basins. These calculations show, for example, that 90% of the tritium contained in an aqueous stream flowing at 15,000 liters per day will be lost to the atmosphere from a shallow basin with a surface area of 6000 m. 2 338 Environmental Science & Technology
S
mall quantities of tritium as HTO are found in much of the process water that is used in certain nuclear facilities. This tritium, usually a by-product of the fission of uranium, gets into the aqueous streams as a result of chemical processing (Albenesius and Ondrejcin, 1960). The tritium may also get into other streams as a result of the loss of moderator from heavy water moderated reactors. The heavy water contains tritium from the neutron activation of deuterium (MaticVukmirovic et al., 1964). Although there is no feasible way for nuclear facilities to remove and concentrate this small quantity of tritium from the process water, the water is usually released into streams or open basins excavated in the ground. From streams, tritium may be lost to the atmosphere or may flow to the ocean. From open basins, tritium may be lost to the atmosphere or may seep to the groundwater.
Tritium-level changes observed in Savannah River Plant (SRP) waste seepage basins that were exposed to the atmosphere led to a consideration of the theoretical principles involved in the transfer of tritium across an air-water interface. These principles were then demonstrated in laboratory tests and used to explain the concentration changes observed in one of these large basins. These principles are reported so that they may be useful to the management of waste streams that contain tritium. Theory
The evaporation of water into moist air is a dynamic process in which water molecules continuously evaporate from, and condense on, the surface. The overall rate of evaporation is the difference between the rate at which molecules leave the surface and the rate at which molecules (not necessarily the same ones) condense onto the surface. When tritiated water evaporates into moist air, the rates of the evaporation and condensation processes will be different for H 2 0 and HTO; both species will leave the surface, but in general, much more H 2 0 will return because the atmosphere contains very little HTO. The rate of water evaporation into the atmosphere is usually limited by the diffusion of water vapor through a quiescent layer of air near the surface (Dorsey, 1940). In this model, a stagnant layer of air, which does not mix with the rest of the atmosphere, exists at the surface. The air immediately adjacent to the surface is saturated with water vapor, while that at the other side of the quiescent layer has the same water content as the bulk of the atmosphere. Water vapor is transported by eddy diffusion, molecular diffusion, or both, across this concentration gradient from the surface into the bulk atmosphere. In any case, the steady-state solution of the diffusion equation with these boundary conditions yields the equation
where i refers to either component. Subscripts T and W' in the following equations refer to quantities related to HTO and H 2 0 , respectively. Constant K is assumed to be the same for both species because the thickness of the quiescent layer is the same and the diffusion coefficients are nearly the same. In typical environmental conditions, the amount of HTO present will be very small compared with that of H 2 0 . The mole fraction of HzO will then be one for all practical purposes, and Equation 2 will become identical to Equation l for Hz0. The mole fraction of HTO, similarly, can be replaced by the mole ratio of HTO to H20, nT/np, and Equation 2 can be expressed as (3)
where driTjdt is the rate of change of moles of tritium in the liquid phase under a unit area of surface, and nT and nw are the number of moles of HTO and HzO in the liquid under the same area. Because nT
