D. M. Nelson, G. P. Romberg, and W. Prepejchal

Transcription

1 r. - ^ fusmcaimt ^ABK OSTERMN LIBRARY RADIONUCLIDES IN LAKE MICHIGAN FISH Introduction D. M. Nelson, G. P. Romberg, and W. Prepejchal S P 2 6 «MAY ? northwesternm,ch,gancollegelibrary II 3 30: * ' "* One apseot of the siting of nuclear power plants on Lake Michigan which has received considerable attention is the question of reactor-produced radionuclides entering the aquatic ecosystem. Once released into the environment, many of these isotopes reconcentrate in the biota, producing potentially important routes to man. Since fish constitute the most important food sources derived from Lake Michigan, it is important to know the concentrations of radionuclides present in food fishes, as well as any changes in these concentrations near power reactors. In assessing the biological significance of reactor-produced isotopes, it is necessary to consider also the natural radioactivity and the substantial inventories of nuclides already present in Lake Michigan owing to the testing of nuclear weapons. In order to provide baseline information needed to evaluate any additional radioactive releases, fish samples were collected from Lake Michigan during 1970 and 1971 and analyzed for gamma-ray emitting radionuclides. Data collected during October 1970 at the Big Rock Nuclear Reactor near Charlevoix, Michigan (a 7 0-MW boiling water reactor completed in 196 2) indicated radionuclide concentrations in fish to be higher than expected for fish elsewhere in the lake. ^ A repeat sampling trip was made to Big Rock in June of 1971, as well as several visits to the Point Beach Nuclear Reactor near Two Rivers, Wisconsin (a 480-MW pressurized water reactor completed in 1970). Methods. Fish were obtained from the discharge channels at Point Beach and Big Rock Point nuclear reactors by spearing (employing Scuba divers) as well as by seining. Argonne for radioactivity analysis. Samples were labeled, frozen, and returned to In addition, samples of anadromous i

2 fishes (coho, Chinook and steelhead salmon) were collected by the Fisheries Division of the Michigan Department of Natural Resources at their weir stations on the Little Manistee and Platte rivers. These samples were also shipped frozen to Argcnne for analysis. Large fish were prepared for analysis by separating the edible and inedible portions, while small fish were counted whole, either individually or composited in order to provide enough sample for analysis. Radioactivity analysis consisted of gammaray counting bulk samples on low background 4"x4" Nal(Tl) crystals, followed by a least squares analysis of the resultant pulse height spectra. Sample geometries were either 2000-ml Marinelli beakers or 500-ml plastic freezer containers. Occasionally samples were too small and only partially filled the counting containers, A correction factor was then applied to correct for the nonstandard geometry. Detection limits vary depending upon counting time and sample size, but in general, concentrations of Cs, 65 Zn, or 54 Mn greater than 10 pci/kg, and 95 Zr or 6^Co greater than 5 pci/kg were detectable. weight basis. All data are reported on a wet Results and Discussion The three sites available for our fish sampling during 1971 present an interesting combination of properties. The Point Beach site had no history of radioactive release prior to 1971, and our measurements did not show increased radioactivity in organisms near the discharge point due to the section's small releases. While no measurements were made at the Manistee and Platte river sites, it is probably safe to assume that these areas are free from non-fallout artificial radioactivity. The Big Rock site, however, has been exposed to routine releases for almost ten years; during 1970, for example, a total of ~ 4.7 Ci ex- (2) eluding tritium was released, of which ~ 1,25 Ci was Cs. Although this is small compared to the total Lake Michigan inventory of Cs due to (3) fallout 6000 Ci), it is sufficient to cause local increases in the

3 143 sediments and organisms near the discharge point. Because of a change in waste handling procedures, the frequency of scheduled radioactive releases was decreased before our 1971 sampling trip, and there had not been a radioactive release for 48 days prior to our visit. Because of the low radioactive release rate from the Point Beach Reactor, it has been assumed that Cs values in fish collected there are representative of general lake conditions and may be used as backgrounds for the fish collected at Big Rock. This assumption 40 is supported by the fact that no nuclides other than Cs and K were detected in the Point Beach fish, while many of the Big Rock fish contained measurable amounts of Zn, Co, and Cs. Also, those fish collected from the Manistee and Platte rivers had Cs concentrations comparable to Point Beach fish. Tables 1 and 2 tabulate the pertinent data concerning individual 40 samples collected in As expected, Cs and natural K were detected in varying amounts in all fish samples collected at the three sampling locations. Figure 1 summarizes the data for these two isotopes (as the Cs/K ratio) for most samples collected during From the data in Tables 1 and 2 it may be shown in general the Cs/K ratio is 20 to 30% higher in the edible portion than in the inedible. For consistency, the Cs/K ratio in those fish counted whole (alewife, chubs, smelt, suckers, small steelhead, perch, and bluegill) should possibly be increased 10 to 15%, since only the edible portion of the other fish was used in Figure One method of estimating the contribution of Big Rock effluent to the Cs content of fish caught at the Big Rock site is to compare concentration levels found there directly with those found at Point Beach. Samples of alewife, carp, bass, and sucker were collected at both reactors and can be used to make this comparison. In alewife there is no apparent difference in radioactivity content at the two sites, possibly reflecting the migratory nature 1 37 of these fish. Carp from Big Rock are slightly higher in Cs than those from Point Beach; however, the individual fish are extremely variable. The two carp from Big Rock having the highest Cs concentrational also have

4 144 TABLE 1. Radionuclide Concentrations in Lake Michigan Fish during 1971 No. of Total wt Part CS, K, CSA, Species Location Date fish less eggs, counted pci/kg gag pcl/g g Sucker PB (a) 1 July filets,. 185 (10) 3.83(4) (b) 48 ICJ carcass 103 (10) 2.85 (5) 36 PB 25 Aug whole 84 (2) 2.78 (1) 30 PB 17 Sept whole 149 (10) 3.96 (5) 38 Carp PB 19 May whole 112 (1) 2.31 (1) 48 PB 19 May whole 186 (1) 3.48 (1) 53 PB 23 June filets 124 (5) 4.59 (2) 27 carcass 42 (8) 2.26 (3) 19 PB 23 June filets 363 (2) 4.01 (2) 90 carcass (4) 2.05 (3) 67 eggs 115 (9) 2.51 (6) 46 PB 23 June filets 192 (3) 3.78 (2) 51 carcass 132 (5) 3.27 (3) 40 PB 1 July whole 147 (9) 2.93(4) 50 PB 1 July filets 424 (3) 4.26 (3) 100 carcass 156 (5) 2.18 (3) 71 PB 1 July filets 269 (4) 4.78 (2) 56 carcass 77 (3) 2 01 (1) 38 PB 1 July filets 229 (4) 4.35 (3) 53 carcass 76 (8) 2.31 (3) 33 eggs 63 (25) 2.07 (7) 30 PB 1 July filets 118 (7) 4.32 (2) 27 carcass 39 (16) 1.87 (3) 21 eggs 45 (29) 2.10(6) 21 PB 1 July filets 234 (3) 3.99 (2) 59 carcass 64 (9) 2.10(3) 31 PB 1 July filets 102 (13) 4.15 (3) 24 carcass 53 (18) 2.18 (4) 24 PB 22 July filets 57 (13) 4.11 (2) 14 carcass 23 (24) 1.85 (3) 12 PB 24 Aug filets 155 (4) 4.06 (2) 38 carcass 68 (2) 1.64(1) 41 PB 24 Aug filets 90 (7) 4.27 (3) 21 carcass 42 (3) 2.51 (1) 17 PB 24 Aug filets 73 (13) 3.95 (3) 18 carcass 45 (10) 2.21 (3) 20 PB 25 Oct filets 268 (2) 4.09 (2) 65 carcass 95 (4) 2.19 (2) 43 PB 25 Oct filets 358 (3) 3.82 (3) 94 carcass 178 (3) 2.69 (3) 66 PB 25 Oct filets 540 (1) 4.22 (1) 128 carcass 164 (1) 2.24(1) 73 Bass PB 1 July 856 filets 295 (5) 3.27 (5> 90 carcass 133 (8) 1.96 (7) 68 PB 25 Aug.? 382 filets 95 (15) 3.35 (7) 28 carcass 59 (22) 2.11 (9) 28 PB 17 Sept.? 466 filets 182 (9) 3.63 (6) 50 carcass 120 (12) 1.78 (10) 67 PB 17 Sept filets 154 (5) 5.28 (3) 29 carcass 93 (5) 2.88 (3) 32 Alewife PB 19 May? cm 205 (11) (9) 63 whole? cm 196 (8) (6) 55 whole PB 2 July? cm 117 (10) (7) 55 whole? cm 139 (5) (4) 57 whole? cm 199 (3) (2) 67 whole PB 2 July? 1563 mixed whole 131 (3) (3) 57 PB 2 July? 1382 mixed whole 185 (2) (1) 58 PB 2 July? 830 mixed whole 281 (3) (3) 87

5 TABLE 1. (contd.) No. of 1 37 Total wt Part Cs, K, Cs/K, Species Location Date fish less eggs, counted pci/kg g/kg pci/g g Chubs PB 1 July 1803 whole 184 2) ) 60 PB 1 July? 1770 whole 188 2) ) 63 Smelt PB 19 May? 902 whole 199 4) ) 72 PB 19 May? 251 whole 274 3) ) 74 Steelhead PB 17 Sept filets 276 1) ) 76 PB 28 Sept filets 540 1) ) 127 carcass 256 2) ) 118 PB 28 Sept filets 167 7) ) 42 carcass 105 8) ) 36 PB 26 Oct dried filets 412 1) ) 112 dried 157 1) ) 95 carcass PR 30 Nov filets 410 1) ) 96 carcass 207 2) ) 77 PR 30 Nov filets 317 1) ) 62 carcass 126 3) ) 40 LMR 1 Dec filets 575 1) ) 130 carcass 241 1) ) 99 LMR 1 Dec filets 509 1) ) 105 carcass 225 1) ) 96 LMR 1 Dec filets 300 1) ) 69 carcass 154 2) ) 56 Coho PB 23 June 1 ~2000 carcass 365 3) ) 150 PB 23 June 1 ~ 3000 whole 322 1) ) 133 TR 27 Oct filets 452 1) ) 99 carcass 134 1) ) 69 LMR 1 Dec filets 486 1) ) 117 carcass 207 1) ) 92 LMR 1 Dec filets 561 1) ) 120 carcass 293 1) ) 98 LMR 1 Dec filets 406 1) ) 87 carcass 150 1) ) 82 LMR 1 Dec filets 482 1) ) 113 carcass 233 1) ) 95 eggs 170 6) ) 70 Chinook LMR 1 Dec filets 531 1) ) 125 carcass 244 1) ) 93 LMR 1 Dec filets 550 2) ) 129 carcass 239 2) ) 85 LMR 1 Dec filets 592 1) ) 157 carcass 299 1) ) 125 eggs 293 2) ) 106 Brown Trout PB 23 June whole 378 1) ) 130 PB 1 Aug filets 633 2) ) 164 carcass 298 4) ) 134 PB 28 Sept whole 541 1) ) 159 eggs 211 4) ) 112 PB 28 Sept filets 510 2) ) 125 carcass 259 3) ) 120 eggs 134 8) ) 63 PB 28 Sept filets 513 2) ) 131 carcass 243 3) ) 106 PB 28 Sept filets 613 1) ) 134 carcass 278 1) ) 121 PB 28 Sept filets 643 2) ) 162 carcass 316 3) ) 134 eggs 205 5) ) 88 PB 28 Sept filets 730 2) ) 170 carcass 332 3) ) eggs 194 6) ) 77

6 TABLE 1. (contd.j No. of Total wt Part Cs, K, CSA, Species Location Date fish less eggs, counted pciag g/kg pci/g g Lake Trout PB 2 July 1 ~2100 whole 329 (2) 2.08 (3) 158 Perch PB 17 Sept whole 505 (2) 2.48 (3) 204 ' a 'pb = Point Beach; LMR = Little Manistee River; PR = Platte River. Numbers in parentheses are one standard deviation counting errors as (c) Carcass is part of fish left after the meat and eggs are removed. the highest Zn concentrations, indicating that they had spent more time near the plant than those with lower Cs concentrations. In contrast to the data on alewife and carp, Cs concentrations in bass and suckers show a clear difference between the two reactor sites with the Big Rock samples being at best twice 6 5 as high. two highest carp, are also relatively high in These fish, like the Zn, implying that they had spent enough time near the plant to acquire a measurable body burden of this isotope. From these comparison data it appears that fish with limited ranges caught at Big Rock acquire Cs concentrations approximately double those acquired by similar fish living elsewhere in the lake, while fish with wider ranges may not be significantly different. This increase at Big Rock may be due either to effluent from the station or to a greater availability of fallout Cs. A second method exists for estimating the fraction of a fish's body burden derived from Big Rock effluent. Cs This station at present releases 134Cs (r. / = 2.05 yr) at about one-half the rate of Cs release ( 134 Cs/ 134 Cs = ~0. 5). Assuming no isotopic discrimination, the Cs/ Cs ratio in an organism should then be a measure of the relative contribution 134 of reactor-produced Cs, the Cs/ Cs ratio in fallout being essen- tially zero (< 0.01). A ratio near 0.5 implies nearly all of the Cs to be of recent station origin, while a lesser ratio means one of two things: either part of the Cs is of fallout origin, or the Cs is of station origin but

7 TABLE 2. Radionuclide Concentration of Fish Collected near the Big Rock Reactor Species Date No. of fish Total wt. less eggs, g Part counted CS, pciag K, gag CSA, pci/g 134 Cs, pciag 6 5 Zn, pciag 60 Co, pciag Sucker 15 June whole 2 37(4) (a) 3,44(3) (a) 69 <21 (b) 153(11) < whole 317(3) 3.00(2) 105 < 18 < 42 12(23) 16 June whole 256(3) 3.28(2) 78 22(26) 344(5) 124(5) whole 346(8) 3.73(13) 93 < (13) < June whole 229(3) 3.64(2) 63 < (6) 15(34) whole 320(3) 3.64(2) 88 < (8) 7(47) Carp 16 June (3) 4.27(3) 92 24(36) 145(15) < 19 fil6ts (c) carcass 170(3) 2.11(2) 81 24(13) 1653(1) 15(16) 17 June filets 159(8) 3.67(4) 43 < 40 < 78 < 27 carcass 139(6) 2.70(3) 51 < 19 < 36 < filets 181(11) 4.50(4) 40 < 52 < 96 < 24 carcass 94(8) 2.26(3) 42 < 21 94(19) 11(31)» filets 239(5) 4.04(3) 59 < 34 < 76 < 15 carcass 105(6) 2.01(3) 52 < 15 65(16) 14(18) " filets 523(2) 3.47(2) 151 < 19 < 34 6(47) carcass 189(2) 1.33(3) (14) 416(3) 50(5) eggs 152(7) 2.33(6) 65 < 30 < 97 < 22 Bass 15 June whole 405(7) 3.02(8) (34) 417(14) < June whole 608(4) 2 74(7) (27) 890(6) < June filets 624(2) 3.57(2) 175 < 24 53(30) < 15 carcass 500(2) 3.36(2) (32) 314(5) < June filets 608(1) 3.43(2) (19) 54(15) < 10 carcass 311(2) 1.99(3) (40) 282(5) < 15 Alewife 16 June 71 ~ whole 215(3) 3.57(2) 60 < 18 < 33 8(35) 16 June 71 ~ whole 199(3) 3.12(2) 64 < 9 < 30 < 8 17 June 71 ~ whole 215(3) 3 41(2) 63 < 10 < 39 < 9 Steelhead 15 June whole 541(2) 4.11(2) (7) 1410(2) 215(3) 16 June whole 267(15) < (9) 200(18) 17 June 71 1 ' 292 whole 303(9) 4.40(6) 68 < (6) 55(38) 17 June whole 186(11) 3.07(6) 61 < (5) 194(10) Bluegill 15 June whole 830(5) 4.01(8) 207 < 135 < 288 < June whole 667(5) 3.44(7) 192 < 94 < 174 < 57 Numbers in parentheses are one standard deviation counting errors as %. 'k'lf counting error is greater than 50%, the value is listed as < 3 <r. Carcass is that part of the fish which is left after the meat and eggs are removed.

8 T I I I I 1 I 1 BLUEGILL > 1 0 POINT BEACH PERCH BIG ROCK 0 * LITTLE MANISTEE LAKE TROUT OR PLATTE RIVER 0 1 BROWN TROUT COO 0 CHINOOK ** * C0H0 * 0 ** * 0 0 STEELHEAD 0 * * 0 * * 0 o» (large) STEELHEAD (small) SMELT 00 CHUBS 00 ALEWIFE 8 /o 0 BASS cp 0 0 M CARP (M &0 O O SUCKER FIG. 1. Cs/K ratio in Lake Michigan fish. Trout, salmon, bass, and carp were measured as fillets, the others as whole fish. old enough to have allowed some of the 1 "Cs to decay away. With this second method in mind it is instructive to reexamine the data in Tables 1 and 2. In suckers, for example, a comparison between the Big Rock samples (average Cs concentration ~285 pci/kg) and the Point 1 37 Beach samples (125 pci/kg) implies ~160 pci/kg excess Rock suckers. Cs in the Big Continuing this reasoning, if all of this excess were derived from recent Big Rock Station effluent, these fish should contain ~80 pci/kg 134Cs. The actual measured 134 Cs content is ~10 pci/kg ( 134 Cs/ Cs ~ 0.035), implying that either most of the excess was derive from fallout or the excess came from very old Big Rock effluent. Other 134 organisms (crayfish and periphyton) collected near the discharge point had Cs/ Cs ratios of 0.2 to 0.3. Evidently much of the Cs available for uptake by these organ- 134 isms was of recent plant origin. The very low Cs/ Cs ratio in suckers

9 149 then would suggest that the excess Cs at Big Rock may be due to increased abundance or availability of fallout Cs rather than uptake of Cs released from the station. A similar analysis may be applied to any of the other fish. 134 Only in a small number of bass and trout samples is the Cs/ Cs ratio high enough to support a recent station contribution of greater than 20% to the total Cs concentration. The question of nuclide source is more straightforward for the other isotopes detected in this study. Unlike Cs, the isotopes Zn, Co, 134 and testing. Cs do not have appreciable inventories in the lake due to weapon The fish samples collected away from the Big Rock reactor were consistently below our detectability limits for each of these isotopes. Any concentrations of these isotopes in fish collected near the station are thus attributable to station discharges. From Table 2 it may be seen that aside from and ^^K, ^Zn is the most frequently detected isotope at Big Rock and occurs in the highest concentrations. inedible fractions, the From the data on those fish which were measured as edible and 6 5 as the concentration on a whole fish basis. Zn concentration in flesh is less than 20% as high In the two carp samples containing ^Co concentrations of this isotope in flesh are also less than 20% as high as whole body concentrations. Cesium-134 may be assumed to distribute similarly to concentrations) Cs (flesh concentrations ~50% higher than whole body Using the present data, a reasonable upper estimate can be made of the radiological importance of eating fish caught at Big Rock. No large game fish were available from the plant discharge during the sampling period, but the samples which were obtained should be representative of the resident population near the plant and should reflect the upper limit of radionuclide concentrations to be expected in other fish. Using the conservative assumption that 100 g per day of fish flesh are consumed and that this fish has radioactivity content equal to the sample showing the highest concentrations of reactor produced isotopes (small rainbow trout collected June 15, 1971), the gamma-ray emitting nuclides present in these fish would contribute 0.3% of the maximum allowed daily intake recommended by the N.C.R.P. (see Table 3).

10 TABLE 3. Contribution of Big Rock Fish Toward the Maximum Permissible Ingestion of Radionuclides Estimated flesh con- centration, pci/kg Isotope Concentration in "hottest" sample of small rainbow trout, pci/kg Allowable daily intake (general population), pci (4) Intake from 100 g flesh, pci Fraction of allowed daily intake 134 Cs , Cs , Zn , Co , Z.0029 References 1. Nelson, D. M., G. P. Romberg, and W. Prepejchal. Radionuclide Concentrations near the Big Rock Point Nuclear Power Station. Proc. 14th Conf. on Great Lakes Research, Toronto, April, 1971, in press. 2. Sinderman, R, Consumers Power Co. Personal communication. 3. Ayres, J. C., Lake Michigan Environmental Survey. Great Lakes Research Division, University of Michigan, Ann Arbor, Mich., November 1970, Special Report # Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides in Air and in Water for Occupational Exposure. U.S. Dept. of Commerce, Nat. Bur. Stds., Handbook 69, August 1963.