We conducted gamma spectrometric analyses on more than 200 arctic marine mammal tissue samples. These samples were primarily provided by subsistence hunters from northern Alaska, with a smaller number of samples from the Resolute region in Canada. The majority of samples (>90% ) had detectable levels of the anthropogenic radionuclide 137Cs, with a mean level observed in all samples of 0.67 Bq kg-1 dry weight ±0.81 (SD). Converted to wet weight, the mean was 0.21 Bq kg-1 ±0.19 SD. The median activity observed was 0.45 Bq kg-1 dry weight (0.18 Bq kg-1 wet weight) with a range from detection limits to 6.7 Bq kg-1dry weight (1.1 Bq kg-l wet weight). These findings confirm expectations that current anthropogenic gamma emitter burdens in marine mammals used in the North American Arctic as subsistence food resources are well below activities that would normally merit public health concern (~1000 Bq kg-1 wet weight). Some differences among species and tissues were observed. Beluga tissues had slightly higher mean burdens of 137Cs overall, and epidermis and muscle tissues in bowhead and beluga whales typically had higher burdens than other tissues analyzed. Low levels of the neutron activation product l08mAg (half-life 418 yr.), probably bioaccumulated from bomb fallout sources, were observed in 16 of 17 beluga livers analyzed, but were not found in any other tissues of beluga or in any other species sampled. A subset of 39 samples of various tissues was analyzed for the alpha and beta emitters 239,240Pu and 90Sr. Plutonium levels were near the threshold of detectability (~0.1 Bq kg-1 dry weight) in 6 of the 39 samples; all other samples had no detectable plutonium. A detectable level of 90Sr (10.3 ±1.0 Bq kg-1 dry weight) was observed in only one of the 39 samples analyzed, a bowhead epidermis sample. Although the accumulation of 108mAg has not been previously reported in any marine mammal livers, all of our analytical measurements indicate that only very low levels of anthropogenic radioactivity are associated with marine mammals harvested and consumed in the North American Arctic.
Species include: ringed seal (Phoca hispida); beluga whale (Delphinapterus leucas) and bowhead whale (Balaena mysticetus Tissues sampled included: liver kidney, muscle, blubber and epidermis (the last for whales only)
Some tissues also banked with Alaska Marine Mammal Tissue Archival Program (AMMTAP)
In devising an analytical strategy, we initially undertook detection of gamma emitters, which can be counted directly with minimal sample preparation. Following these analyses, we analyzed a subset of samples by alpha spectroscopy. These same samples were also chemically separated for gross beta counting to provide representative data on several other radionuclides of potential interest, specifically plutonium and 90Sr. Although 90Sr, as a chemical analogue of calcium, can be expected to be concentrated in bone, our analyses of 90Sr did not include bone tissue, as we examined only tissues normally consumed by subsistence users. Following harvest in 1996 or 1997, marine mammal samples (typically 500-1000 g) were collected by the Department of Wildlife Management, North Slope Borough. Samples were then separated by tissue and species, homogenized with a commercial food processor, and placed into a 500 mL or 1000 mL high-density polyethylene Marinelli beaker (Gamma Associates) designed for direct gamma spectroscopy. The beakers were labeled, sealed, frozen, and shipped to the Environmental Sciences Division, Oak Ridge National Laboratory (ORNL), Oak Ridge, Tennessee. Preparation of Resolute (Canada) samples differed in that 200-500 9 samples of tissue were dried in the field before shipment to Oak Ridge, so that only dry mass activities are available. Before counting, samples were in some cases repackaged to maximize the space within the container filled, thus assuring appropriate geometries and counting efficiency. Following wet weight determinations, samples were radioassayed using low-background, high-resolution, lithium drifted germanium or high purity germanium detectors equipped with a Canberra Genie personal computer system programmed to record the gamma spectra for one to 4096 channels. These detectors were shielded with layered lead and copper to minimize background radiation and x-ray interference. Calibration of our detectors within the Environmental Sciences Division of ORNL , was performed using certified mixed gamma standards with traceability to the National Institute of Standards and Technology (NIST). Background corrections were performed and control samples were analyzed daily to verify detector performance. The counting time was typically 48, hours or longer for each sample. After counting, samples were oven dried at 60°C for 24 to 72 hours to dryness, and the dry weights were recorded. Alpha and beta spectroscopy for 90Sr and 239,240Pu was undertaken by the Analytical Services Organization, ORNL, and the Environmental Survey and Site Assessment Program (ESSAP) of the Oak Ridge Institute for Science and Education (ORISE). Dried samples were removed from the Marinelli beakers and digested, with about two-thirds of the sample subjected to high-temperature ashing in a muffle furnace at 500 to 650°C. The ashed samples were then split in half, and 239,240Pu determinations were made by alpha counting after treatment by acid digestion, separation by ion exchange, and electrodeposition onto stainless steel disks (Laudeman et al., 1995). For the separate 90Sr determinations, digestion was achieved by high-temperature fusion with anhydrous potassium fluoride and pyrosulfate over a burner. Carrier solutions were added, and the sample was then dissolved in HCl and the 90Sr separated from 90Y. The strontium sulfate was purified and then deposited onto the planchet. The samples were beta counted and then recounted, allowing for ingrowth of the radiostrontium daughter product, yttrium. Following determination of all counts and yields, activities were calculated as follows: were beta counted and then recounted, allowing for ingrowth of the radiostrontium daughter product, yttrium. Following determination of all counts and yields, activities were calculated as follows: Activity = (G-B)¸[(t)(Q)(Y)(E)] where G was the gross count, B was the background count, t was the count time, Q was the sample quantity, y was the chemical yield, and E was the 90Y counting efficiency, with adjustments made for the ingrowth of yttrium calculated by [1 -e-(ln2164.1)T], where T is the yttrium ingrowth time. Minimum detectable activities for 90Sr varied among samples depending upon counting time and sample size, but were typically -0.1 to 0.6 Bq kg-l. Additional details on controls and quality assurance undertaken in the course of these measurements are available in Laudeman et al. (1995).
See above (methods) and Laudeman et al. 1995. Laboratory procedures manual for the Environmental Survey and Site Assessment Program. ORISE Report 95/A-65, Revision 9, Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831-0117, USA.
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA; Arctic Nuclear Waste Assessment Program
Concentrations and interactions of selected elements in tissues of four marine mammal species harvested by Inuit hunters in arctic Alaska, with an intensive histologic assessment, emphasizing the beluga whale