Atmospheric Technetium-99 Moses Attrep, John A. Enochs, and Larry D. BrozI Department of Chemistry, East Texas State University, Commerce, Tex. 75428
Technetium-99 has been isolated from 13 rain samples collected in 1967. The sizes of these samples were 53.5 to 233 liters. The concentrations of "Tc vary from 0.14 X to 1.7 X lO-ZpCi/liter.
T
he natural terrestrial occurrence of technetium, as 99Tc,has been established in pitchblende as a spontaneous fission product of 23RU (Kenna and Kuroda, 1961). This isotope has also been detected in rain (Attrep, 1962), in which it was assumed that the atmospheric 99Tc is a fission product from nuclear detonations. A recent report by Golchert and Sedlet (1969) describes a radiochemical analysis of 99Tcin water samples in which surface samples had an average concentration of 4.65 pCi/liter. This report represents the examination of 9gTcin a larger number of rain samples in order to confirm the atmospheric presence of this isotope. Among all the radioactive isotopes produced from nuclear detonations, 99Tchas not been studied in detail. Since technetium as the pertechnetate ion behaves like iodide with respect to the thyroid system, it is worthwhile to establish the presence of 99Tcin the atmospheric inventory of radioactive isotopes. Large rain samples were collected over six months in 1967 and were examined for 99Tc. The basic approach to the problem is similar to that of fallout studies of shorter-lived radioisotopes produced from nuclear devices detonated in the atmosphere. Due to its relatively long half-life (fl,? = 2.15 X IO5 years), the activities of 99Tc were expected to be low. Experimental For the radiochemical separation of 99Tcfrom rain, samples ranging from 53.5 to 233 liters were taken. The samples were collected with a 3 m X 3-m rain collector located on top of the Science Building of East Texas State University in Commerce, Tex. Periodic cleanings of the collector and the polyethylene receptor were made with dilute nitric acid and distilled water. Freshly collected rain was immediately acidified with nitric acid and stored in glass vessels until evaporation could be conducted. Prior to evaporation, the rain samples were made basic with sodium hydroxide to eliminate volatilization of technetium as TcrO;. Rhenium, as ammonium perrhenate, was added as a carrier for technetium, and copper and molybdenum were also added. The evaporated concentrate was acidified and filtered. The residue was thoroughly washed. Hydrogen sulfide was passed through the hot solution 1 hr or longer. The sulfides were filtered, washed, and dissolved in ammonical hydrogen peroxide. The solution was evaporated to about 150 ml while keeping the solution basic at p H 8 or above. Alcoholic a-benzoinoxine was added and the precipitate was allowed to digest overnight at room temperature. The molybdenum a-benzoinoxine precipitate was filtered off and the p H of the solution was adjusted to precipitate the copper 1
Presently serving in the US.Navy.
344 Environmental Science & Technology
a-benzoinoxine. The copper precipitate was removed by filtration, and the filtrate again was reduced in volume. This filtrate was then passed through a cation-exchange column (Dowex 50W-X8, 100 to 200 mesh, H+ form) and the column was washed with distilled water. The effluent was made basic and the volume was reduced to 50 to 100 ml, which was finally made 5N with respect to sodium hydroxide. The pertechnetate and perrhenate ions were extracted into four 25-ml portions of methyl ethyl ketone. Chloroform, 125 ml, was added to the methyl ketone fraction and the pertechnetate and perrhenate ions were back-extracted with four 25-ml portions of distilled water. The aqueous fraction was made 2 N with sulfuric acid, copper (11) was added, and hydrogen sulfide was passed through the hot solution for at least 1 hr. After filtration, the sulfides were dissolved with ammonical hydrogen peroxide and the solution was carefully reduced to 5 ml, keeping the solution basic. The solution was neutralized with nitric acid and loaded on an anion-exchange column (Dowex 1 X 8, 200 to 400 mesh, NOs- form, 1-cm i.d. X 20 cm), and then washed with a small portion of distilled water. The perrhenate ~~
~~
Table I. 99Tc Concentrations in Rain Sample Collected a t Commerce, Tex. Vol of rain. Q Q activity, T~ liters pCi/liter Collection date 126 (0.77 i. 0.10) x 10-2 4/12 and 13/67 4/17 and 18/67 4/20 and 21/67 4/25/67 4/30/67
100
(0.22 i 0.22) x 10-2
4/30/67 5/3/67
100
(0.55 rt 0.23) X
5/3/67 5/14/67
100
(0.43 i 0.06) X
5/14/67
100
(0.23 i 0.03) x 10-2
100
(0.14 i 0.03) X
5120167 5/20 and 21/67 5/20-22/67
53.5
(1.7 i 0 . 3 ) X
5/29 and 30167
88.5
(0.89 i 0.19) X
6/22/67 6/30/67
100
( 1 . 4 i 0.2) X lo-?
6/30/67 7/1/67
100
(0.65 i 0.10) X lo+*
7/1/67 7/3/67 7113/67 7/15/67
165
(0.63 i 0.10) X
7/19/67 9/7/67 9/14/67 9,120 and 21/67
233
(0.63
151
(0.18 i 0.03) X
i 0.10)
x
and pertechnetate ions were eluted with 0.25M sodium perchlorate at a flow rate of 0.5 to 0.6 ml/min at room temperature. The rhenium fraction was analyzed spectrophotometrically according to Kenna (1961). Copper (11) was added to the technetium fraction, which was acidified with sulfuric acid, and hydrogen sulfide was passed through the solution while heating for 1 hr. The sulfides were cooled, filtered, mounted, and counted. The chemical yields averaged 25 %, based on the amount of rhenium recovered. A reagent blank was conducted with the above procedure. The blank indicated no activity. It was then assumed that there was no contribution of activity from the reagents used. Radioactive measurements were conducted on a Tracerlab Omniguard Low Level Beta Counter. The background of the counting system was about 0.3 cpm. Results and Discussion Identification of the 99Tc activity is based on indirect evidence. The observed activity in the rain samples followed the chemistry of technetium. Because the activities of these samples were low, and the half-life is so long, customary identification is impossible. Samples were counted for over two years with no decrease in activity; this is expected from the long-lived 99Tc. The half-thickness of the 0.29 MeV beta particle of 99Tc is 7 mg/cm2 of aluminum for the counter employed in this investigation. For the most active samples, this experiment was conducted with use of aluminum absorbers. The results gave half-thickness values of 7 mg/cm2 =t1, even for activities about 0.5 cpm. With this evidence, it was assumed the observed activities of these technetium fractions are attributed to 99Tc. The experimental results of the QQTc activities are given in Table I. The concentrations of 99Tcvary from 0.14 X
pCi/liter rain to 1.7 X pCi/liter rain. The average 9QTc pCi/liter or 2.3 X lo9 atoms/ concentration is 0.65 X liter. The 1961 and 1962 rain samples (Attrep, 1962) contained 99Tc concentrations of the order 0.2 X pCi/liter and 4.4 X pCi/liter, respectively. These values are in agreement with the results reported here. Although the activities of Q9Tcfound in this investigation are low and appear negligible, respresenting no major environmental contamination, the significance of these results lies in the ability of detection as well as the confirmation of this isotope in the atmospheric environment. Attention has been brought to environmental 99Tcin water samples by Golchert and Sedlet (1969). Some 150 1-liter naturally occurring surface water samples were analyzed in which approximately 80 of these results were below the detection limit of their analysis. Those remaining ranged from 0.5 pCi/liter to 49.4 pCi/liter with an average of 4.65 pCi/liter. These values are much greater than those reported here, and no comparison is made since the location of sample collection was not noted. Since the availability and use of this fission produced nuclide have increased in recent years, it is interesting to note that 99Tcis becoming widespread both in the atmosphere and in the natural water systems. Literature Cited Attrep, M., Jr., M. S. thesis, University of Arkansas, Fayetteville, Ark., 1962. Golchert, N. W., Sedlet, J., Anal. Chem. 41, 669-71 (1969). Kenna, B. T., Anal. Chem. 33,1130 and 1 (1961). Kenna, B. T., Kuroda, P. K., J. Inorg. Nucl. Chem. 23,142-4 (1961). Receivedfor review June 12,1970. Accepted December 26,1970. This investigation was supported by the Faculty Research Grants at East Texas State Uniuersity and the Robert A . Welch Foundation.
Ultrafiltration for the Control of Recycled Solids in a Biological System Frederick W. Hardt, John C. Young, Lenore S. Clesceri, and Donald R . Washington’ Bio-Environmental Engineering Division, Rensselaer Polytechnic Institute, Troy, N . Y . 12181
rn The use of low-pressure ultrafiltration is described as a means of liquid-solids separation for a high solids activated sludge system. (The concentrated microbial system ranged from 20 to 30 grams per liter volatile suspended solids.) The experimental apparatus consisted of a completely mixed biological reactor from which the activated sludge was recirculated across ultrafilter membranes. The quality of the final effluent was monitored by measurements of chemical oxygen demand, total organic carbon, and phosphorus and compared with measurements of these constituents in the soluble portion of the reactor mixed liquor. Gel-filtration chromatography, used to determine the molecular size
distribution of simple and macromolecules in the reactor mixed liquor and ultrafiltrate, showed a gradual accumulation of macromolecules of approximate molecular weights between 700 and 1200. The molecular size distribution in the ultrafiltrate ranged from approximate molecular weight 30 to 800. The effect of pressure ultrafiltration on the bio-mass, monitored by oxygen uptake studies, showed a net decrease in respiratory activity with time of ultrafiltration. The high solids microbial culture maintained 75 to 95 reduction of chemical oxygen demand. The overall chemical oxygen demand removal efficiency of the high solids ultrafiltration system, however, exceeded 98 %.
D
separation have been investigated. The method found to be most effective in separating microorganisms from the final effluent was membrane ultrafiltration. This unit operation is defined as “the hydraulic pressure activated separation of solutions into their individual components by passage through synthetic membranes” (Michaels, 1968). The process is not new and has been used by biologists for the separation and concentration of large molecular-weight species such as proteins and polypeptides. The feature which made the process
wing the past four years, concentrated activated sludge systems have been studied at Rensselaer Polytechnic Institute. The concentrated microbial systems under investigation ranged from 20 to 50 g/liter volatile suspended solids (vss). At these levels, microbial suspensions normally do not settle by gravity. Consequently, other means of Present address: Water Resources Center, Ohio State University, Columbus, Ohio 43210.
Volume 5, Number 4, April 1971 345
