Q3 2018 Report

INL Site

Agricultural Product, Wildlife, and Soil Sampling

Another potential pathway for contaminants to reach humans is through the food chain. The ESER Program samples multiple agricultural products and game animals from around the INL Site and Southeast Idaho. Specifically, milk, alfalfa, grain, potatoes, lettuce, large game animals, and waterfowl are sampled. Milk is sampled throughout the year and large game animals are sampled whenever large game animals are killed onsite from vehicle collisions. Alfalfa is collected during the second quarter, lettuce and grain are sampled during the third quarter, while potatoes are collected during the third or fourth quarter. Waterfowl are collected in either the third or fourth quarter. See Table A-1, Appendix A, for more details on agricultural product and wildlife sampling. This section discusses results from milk and wildlife samples available during the third quarter of 2018.

Milk Sampling

Milk samples were collected weekly at Idaho Falls and Terreton. Monthly samples were collected at five other locations around the INL Site (Figure 12) during the third quarter of 2018. In addition to the local locations, commercially-available organic milk (from Colorado) was purchased as a control sample each month. All samples were analyzed for gamma emitting radionuclides, with particular emphasis on 131I.  Semi-annual samples were collected and analyzed for 90Sr and tritium during the second quarter.

Neither 131I nor 137Cs was detected in any weekly or monthly samples during the third quarter. No other human-made gamma-emitting radionuclides were found either. Data for 131I and 137Cs in milk samples are listed in Appendix C, Table C-6.

Figure 13

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Lettuce Sampling

Lettuce sampling was completed during the third quarter. A total of nine samples were collected, including a commercially-available sample from a grocery store and a duplicate sample at Idaho Falls (Figure 13). Seven lettuce samples were collected from portable planters at Atomic City, EFS, the Federal Aviation Administration (FAA) Tower, Howe, Idaho Falls (including a duplicate), and Monteview. Soil from the vicinity of the sampling locations was used in the planters. This soil was amended with potting soil as a gardener in the region would typically do when they grow their lettuce.  In addition to the portable samplers, a sample was obtained from a garden in Blackfoot.

No human-made gamma-emitting radionuclides were found in any of the samples. Strontium-90 was detected in one sample from EFS. Strontium-90 is present in the environment as a residual of fallout from aboveground nuclear weapons testing, which occurred between 1945 and 1980. This is the likely source for the measured result. Data for 137Cs and 90Sr in all lettuce samples taken during the third quarter are listed in Appendix C, Table C-7.

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Potato Sampling

Locally-grown potatoes from seven southeast Idaho locations (Figure 14) and one duplicate from Fort Hall were analyzed for gamma-emitting radionuclides like 137Cs and for 90Sr. A control sample from a local grocery store (grown in Washington state) was also analyzed. No human-made gamma-emitters were found in any sample. Strontium-90 was not reported in any sample.  Data for potato samples are listed in Appendix C, Table C-8.

Grain Sampling

Grain sampling (wheat and barley) was completed during the third quarter of 2018.  A total of 10 grain samples (including one duplicate from Rupert) were collected from local grain growers (Figure 15).  In addition, a commercially-available sample was obtained from outside the local area. All samples were analyzed for gamma-emitting radionuclides and 90Sr. 

No human-made gamma-emitting radionuclides were detected in any grain sample.  None of the 11 grain samples collected in 2018 contained a detectable concentration of 90Sr. Data for 137Cs and 90Sr in all grain samples taken during the third quarter are listed in Appendix C, Table C-9.

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Large Game Animal Sampling

Muscle and thyroid tissue were collected from an elk killed by a car. Liver tissue was also collected from two of the three game animals. No manmade gamma-emitting radionuclides were detected (Appendix C, Table C-10).

Soil Sampling

Soil samples were collected at twelve boundary and distant locations in the third quarter (Figure 16).  Undisturbed locations sampled historically and representing areas of maximum potential airborne deposition as well as population centers and unaffected regions were selected for this purpose. All surface (0-5 cm) samples, including one duplicate sample collected at Atomic City, were analyzed for gamma-emitting radionuclides, 241Am, 238Pu, 239/240Pu, and 90Sr. Results can be found in Appendix C, Table C-11.  In addition, all subsurface (5-10 cm) samples were analyzed for gamma-emitting radionuclides.

Cesium-137 was detected in all soil samples (Figure 17) at concentrations consistent with historical measurements and is most likely present from fallout from past atmospheric nuclear weapons testing, which were carried out mainly in the 1960s.  The majority of 137Cs is present in surface soils at an average ratio of 2.5:1 (surface soil concentration to subsurface soil concentration). Analysis of the geometric mean of areal concentrations of 137Cs in surface soil over time indicate that concentrations are decreasing at a rate consistent with the approximate 30-year half-life of this radionuclide (Figure 18).

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Strontium-90, another fallout radionuclide, was detected above 3s in one surface soil sample and above 2s in three other samples at levels within historical measurements (Figure 19). Current results are typically below detection levels and it is thus apparent that 90Sr is becoming more undetectable in surface soil. Mean annual (geometric) concentrations of 90Sr in surface over time appear to decrease at a rate which exceeds that projected for radioactive decay (Figure 20). Strontium-90 is more mobile than 137Cs in alkaline soils and the accelerated decrease may be due to other processes in the soil, such as movement into lower depths or uptake by plants.

No accumulation of either 137Cs or 90Sr on surface soil is indicated as a result of operations at the INL Site.

Transuranic radionuclides (including isotopes of plutonium) are present in our environment as a result of global fallout from above-ground nuclear weapon tests. Until 1979 the integrated deposition in the north temperate zone (40-50° latitude) was estimated for 128Pu (1.5 Bq/m2 [0.04 nCi/m2]); 239/240Pu (58 Bq/m2 [1.6 nCi/m2]); 241Pu (730 Bq/m2 [19.73 nCi/m2]) and 241Am (25 Bq/m2 [0.68 nCi/m2]) (Bunzl et al 1987). Measurements of 238Pu, 239/240Pu, and 241Am made by the DOE Radiological and Environmental Sciences Laboratory (RESL) during the same time period are shown in Table 1. The estimated fallout lies within the 95% confidence intervals reported for 239Pu (both years) and 239/240Pu (1978). The concentrations of 241Am measured in surface soils in 1978 and 1980 are about half of the fallout concentrations estimated for 1979.

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Table 1. Radionuclides in offsite surface soilsa (1978 and 1980)

Based on the estimated fallout presented in Table 1, 238Pu would not be expected to be detected very often in the environment. Not surprisingly, no particular trend in 238Pu has been observed over time by the ESER program because it is infrequently detected (about 10% of the time since 2008). In addition, the half-life of 238Pu is 87.7 years so about 25% of the original activity has decayed. Plutonium-238 was detected above 3s in only one ESER sample, collected at Mud Lake South (Table C-11), (9.49 ± 2.74 pCi/kg or 0.61 nCi/m2) and above 2s in two other samples (maximum of 10.9 ± 4.38 pCi/kg or 0.48 nCi/m2) 2018 (Figure 21).

Plutonium-239 and -240 have long half-lives (24,100 years and ‎6,561 years, respectively) and thus these fallout radionuclides persist in the environment (Figure 22). Six of the 13 samples analyzed in 2018 had detectable concentrations (greater than 3s) of 239,240Pu (Table C-11). Three more samples had 239,240Pu concentrations greater than 2s, which could be considered detected. The highest result (46.40 ± 7.50 pCi/kg or 1.54 nCi/m2) is slightly higher than would be expected from estimated fallout (1.16 nCi/m2), as shown in Table 1, but well within historical measurements (Figure 23).

No statistical trend is discernible, most likely because of several factors. These include:

  • the heterogeneous nature of soils (variation of particle size and soil chemistry) and consequently of radionuclide concentrations across the area sampled
  • nonuniform redistribution of contaminated soil via deposition and resuspension resulting from differences in wind, vegetation cover and topography
  • the use of multiple laboratories, which have different procedures and detection limits, over the past four decades
  • the small subsample analyzed. Radiochemical analyses of soil samples involve the consumption of a small subsample (typically only 5 g) which represents about 0.25% of the original sample weight. Although the sample is dried and sieved (< 35 mesh or 0.5 mm), the subsample is not homogeneous and not necessarily representative of the entire sample collected. [Note: Gamma analyses, on the other hand, can be performed on a much large sample size (~500 g)].

Americium-241 is not produced directly in nuclear explosions but is the decay product of the fallout alpha-emitter 241Pu (half-life 14.4 y). For this reason, the 241Am activity in the environment is expected to increase as 241Pu decays. Americium-241 was detected (>3σ) in only three of the 13 samples collected in 2018 (Table C-11). The highest result (34.10 ± 8.61 pCi/kg or 2.25 nCi/m2), collected from Mud Lake, is about 93% higher than expected from that projected from estimated fallout (Figure 24). Soil concentrations in samples collected by ESER appear to show an increasing trend with time, although no statistically significant trend was evident.

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Radiation in Our World

Radiation has always been a part of the natural environment in the form of cosmic radiation, cosmogenic radionuclides [carbon-14 (14C), Beryllium-7 (7Be), and tritium (3H)], and naturally occurring radionuclides, such as potassium-40 (40K), and the thorium, uranium, and actinium series radionuclides which have very long half lives. Additionally, human-made radionuclides were distributed throughout the world beginning in the early 1940s. Atmospheric testing of nuclear weapons from 1945 through 1980 and nuclear power plant accidents, such as the Chernobyl accident in the former Soviet Union during 1986, have resulted in fallout of detectable radionuclides around the world. This natural and manmade global fallout radioactivity is referred to as background radiation. MORE

Radiation Exposure and Dose

The primary concern regarding radioactivity is the amount of energy deposited by particles or gamma radiation to the surrounding environment. It is possible that the energy from radiation may damage living tissue. When radiation interacts with the atoms of a given substance, it can alter the number of electrons associated with those atoms (usually removing orbital electrons). This is called ionization. MORE