fReprinted from Nature, Val. 262, No. S571, pp. 745—748, August 26, 1976) 407902 A Plutonium levels in Kwajalein Lagoon V. E. Noshkin, R. J. Eagle & K. M. Wong Biomedical and Environmental Research Division, Lawrence Livermore Laboratory, University of California, Livermore, California 94550 Reported plutonium levels in fish from both Kwajalein and Enewetak lagoons, suggest that Kwajalein Lagoon contains significantly more plutonium in its environment than would be expected from worldwide fallout levels alone, although quantities of plutonium greater than fallout concentrations In an assessment of the possible plutonium dose to man from food and other environmental pathways, Wilson et a.° compiled, in the form of lognormal median concentrations,all the plutonium survey data collected at Enewetak Atoll] during 1972 and 1973 (ref. 1). The concentration values forail the fish muscle samples taken are reproduced here in Table 1, together with similar lognormal mean concentrations compiled from Kwajalein Atoll who supplement their diet with foods from Atoll and muscle, bone, and gut concentrations, also from the same survey data!, for fish collected off three islands of Kwajalein Atoll (W. R. Robison, private communication). Wilson et al.® found no significant differences in mean plutonium concentrations among four fish groups, which included, amongothers, planktonic and detritus feeders, grazing herbi- have not been detected in the lagoon water. If there is no reason to reject the published fish data, then individuals on the local marine environment may have plutonium body burdens similar to the low levels predicted for individuals on similar diets at Enewetak Atoll. KWAJALEIN ATOLL (9°N 167°40’E) is located in the western (Ralik) chain of the Marshall Islands. In the same island chain and some 300 miles to the north-west is Enewetak Atoll (11°20’N 162°20’E), one of the United States nuclear testing sites during the 1940s and 1950s. It has been reported! that no immediate debris from the nuclear tests at Enewetak and Bikini (another Pacific test site) was deposited at Kwajalein. Measurements during 1972 and 1973 between 5 and 15°N, over a wide range of longitudes, indicated concentrations of between 0.22 and 0.44 pCi m~* for ?3°-24°Py in Pacific surface water?'*. The mean #39,240Py) concentration in the surface waters of Kwajalein and other Pacific atoll lagoons located in this latitude band, therefore, would be expected to be similar to the surface oceanic level (0.34 +0.11 pCim—%). This is not true of Enewetak Lagoon. In late 1972, the average measured concentration of 74*74°Py in the lagoon surface water? was 39 pCi m~*, approximately 100 times the level predicted from worldwide fallout. Clearly, some components of the atoll contaminated by fallout debris during the tests are contributing substantial amounts of ?°4°Pu to the lagoon water masses. The difference in ?°9:74°Pu concentrations between the two lagoonsis a direct reflection of the activity levels in the environments of the two atolls. [t also follows that if plutonium uptake in living organisms is expressed in terms of a concentration factor (the concentration of plutonium in the tissue of the marine organism divided by its concentration on an equivalent weight basis in the surrounding water), invertebrates, fish, or other marine organisms can be useful as indicator species of the level of environmental contamination. Schell and Watters* have given ?**:?4°Pu concentrations in various organs of selected marine organisms collected at Enewetak and Kwajalein atolls. They concluded, however, that the plutonium and americium concentrations in the convict surgeon fish from Enewetak Atoli, for example, are notsignificantly higher than those measured at the control station, Kwajalein Atoll. The mantle and muscle tissues of a clam (Tridacna sp.) collected in the south-eastern region of Enewetak Atoll were, moreover, found to contain only one-sixth as much plutonium as those of a Tridacna sp. collected at Kwajalein Atoll’. On the other hand, the viscera and kidney of the same Enewetak Atoll clam had higher concentrations Pepto of the Kwajalein Atoll specimen. J) OTE foe 4 the same survey! data for fish bone and gut from Enewetak _ vores, bottom-feeding carnivores, and pelagic carnivores. Accordingly, they based their predictions of exposures to plutonium from ingestion of marine foods on the mean concentration of plutonium in the muscles of all the fish taken from the lagoon of Enewetak Atoll. Significantly, however, the 230.240Py in the lagoon water ranged from | to 96 pCi m~? at the fish samplingsites?. Radionuclide concentration independentof environment? The data of Schell and Watters*, together with those of Table 1, show that average levels of ?99-24°Pu in fish bone, muscle, and gut from Enewetak Atoll are similar to, or even lower than, those of the fish indigenous to the contro] station, Kwajalein Lagoon. There are several possible important conclusions that can be derived from these data. Thefirst is that fish collected for consumption by man will contain, on average, essentially the same concentrations of plutonium radionuclides regardless of the source or level of plutonium in the local environment. Obviously, such a conclusion would greatly affect future plans for releasing low-level transuranics to the marine environment. Furthermore, it would force us to concede that the concept of a plutonium concentration factor for fish is meaningless. Also, it conflicts with a large body of plutonium concentration data for Atlantic fish species that derive their plutonium body burdens from worldwide fallout levels in the Atlantic Ocean. For example, for a number of Atlantic species, including bottom feeders, water-column feeders, and large predators®-®, a lognormal median ofall available bone concentration data is only 1 x 1074 pCi g~! (wet or dry), 900 times less than that for the bones of the Kwajalein fish (Table 1). A similar large discrepancy remains when the concentrations in the muscle of the Atlantic and Kwajalein fish are all normalised to an equivalent weight basis (wet or dry). Plutonium levels in the Atlantic waters (where someof thefish were caught) range only between 0.2 and 1,1 pCi m~, according to Bowenef al.®, Calculating a concentration factor from the data for Atlantic fish and water and using a value of 0.4 pCi m~? as the assumed mean plutonium level from fallout in the Kwajalein Lagoon, provides values of between 0.2 and 1.0 10-4 pCi g~! for the bone of fish for this lagoon. These values are orders of magnitude lower than the lognormal median