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CEMP Air Monitoring in Response to the
Fukushima Nuclear Power Plant Accident

Update: June 6, 2011
The latest air particulate air sample data is posted (table 2) for the remaining routine CEMP stations for the time period 3/13-3/30/2011.

Update: April 18, 2011
The air sampling results table has been reorganized into two separate tables to allow easier identification of trends.

On March 11, 2011, a large earthquake and resulting tsunami damaged the Fukushima Nuclear Power Plant in Japan. The damage caused the failure of cooling and safety systems resulting in the atmospheric release of radiological materials from the reactor site. In response, the CEMP installed additional air samplers at existing sampling stations in our network to determine if radiological materials could be detected from the incident.

On March 21, air samplers equipped with glass fiber filters backed by charcoal cartridges were co-located with existing CEMP routine air samplers at the Las Vegas and Henderson stations. These samplers have the capabilities of collecting air particulates as well as iodine not attached to dust particles. Samples were collected every two to three days through April 4 and sent to UNLV-RSL for gamma spectroscopy analysis. In addition, particulate air-sample filters were collected from the routine CEMP samplers located in Las Vegas, Henderson, and Boulder City. These samples are normally collected every two weeks but were pulled early to coincide with the first set of samples from the charcoal-filter equipped units. The routine air filters from the remaining CEMP stations will also be sent for gamma-spectroscopy analysis as they are received under the routine collection schedule.

The radioactive isotopes iodine-131, cesium-134 and 137, xenon-133, and tellurium-132 were initially detected in air samples collected at the CEMP air-monitoring stations in Las Vegas and Henderson, NV, during the week of March 20, 2011. The detection of these isotopes is consistent with the release and subsequent atmospheric transport of volatile radioactive isotopes from the nuclear power plant accident that occurred in Fukushima, Japan, on March 11, 2011.

From a public health standpoint, it is the measurements of the isotopes of iodine 131 and cesium-137 that are of most interest. The reason for this interest is because if high concentrations of iodine-131 are inhaled or ingested, the radioactive iodine can concentrate in the thyroid and thereby increase the risk for cancer in that organ. Additionally, cesium is chemically similar to potassium and so will behave like potassium in the body, therefore inhalation or ingestion of high concentrations of radioactive cesium can build up in multiple locations throughout the body, which can lead to an increase in risk for various cancers.

The highest concentrations of iodine-131 and cesium-137 detected by the CEMP air-monitoring stations in Las Vegas and Henderson, NV, likely peaked in the sampling period between March 23 and March 25, and have been decreasing significantly since then. Furthermore, radioactive iodine-131 dissipates (by radioactive decay) quickly, falling by half every eight days, so if no more is produced, it is essentially gone in 80 days. Even though radioactive cesium-137 has a half life (30 years) that is much longer than that of iodine-131 (only 8 days), experts who studied exposure to radioactive emissions from the Chernobyl Nuclear Power Plant accident could not link an increase in cancers to short-term exposures to such low concentrations of radioactivity from iodine-131 and cesium-137 as are being measured from Japan at the CEMP air-monitoring stations to date. Also, these small activity concentrations of iodine-131 and cesium-137 have been detected by the CEMP air-monitoring stations over a short-time period, therefore exposures also will be of short duration. Consequently, the small activity concentrations of iodine-131 and cesium-137 detected by the CEMP air-monitoring stations from the Fukushima NPP accident in Japan, in combination with the short duration of exposure expected means that there is no public health hazard at this time. Substantiating this point is the fact that even an intake over a 16-day period of the highest concentrations measured at the CEMP air-monitoring stations (between March 23 and March 25) would yield essentially the same additional dose as that from exposure to cosmic rays during a round trip airplane flight between New York and Los Angeles (3 milli-rem or 30 micro-Sv).

Preliminary Air Sampling Results

Table 1. Samples employing a charcoal filter

CEMP Station Sampling Period Cs-137
Activity (pCi/L)
Activity (pCi/L)
Activity (pCi/L)
Activity (pCi/L)
Activity (pCi/L)
Henderson, NV 3/21 - 3/23/2011 N.D. 4.3E-4 1.8E-5 N.D. N.D.
Henderson, NV 3/23 - 3/25/2011 9.3E-5 1.1E-3 N.D. 6.0E-5 7.8E-5
Henderson, NV 3/25 - 3/28/2011 6.1E-6 2.4E-4 N.D. N.D. N.D.
Henderson, NV 3/28 - 3/30/2011 N.D. 1.8E-4 N.D. N.D. N.D.
Henderson, NV 3/30 - 4/1/2011 N.D. 2.6E-5 N.D. N.D. N.D.
Henderson, NV 4/1 - 4/4/2011 N.D. 3.13E-5 N.D. N.D. N.D.
Las Vegas, NV 3/21 - 3/23/2011 N.D. 5.0E-4 2.4E-5 N.D. N.D.
Las Vegas, NV 3/23 - 3/25/2011 8.6E-5 1.0E-3 N.D. 6.0E-5 7.3E-5
Las Vegas, NV 3/25 - 3/28/2011 6.7E-6 2.7E-4 N.D. N.D. 4.7E-6
Las Vegas, NV 3/28 - 3/30/2011 N.D. 1.6E-4 N.D. N.D. N.D.
Las Vegas, NV 3/30 - 4/1/2011 N.D. 4.8E-5 N.D. N.D. N.D.
Las Vegas, NV 4/1 - 4/4/2011 N.D. 3.43E-5 N.D. N.D. N.D.

Table 2. Samples employing a particulate filter only

The data shown in Table 2 represent two main subgroups of analyses. The samples collected from the first eight sampling locations (Boulder City through St. George) were analyzed within days after collection. Isotopes of Cs-137, Cs-134, I-131 and Te-132 were detected in this sample group as a result to the immediate response by CEMP to determine whether measureable radioactivity emitted from the damaged nuclear power plants near Fukushima Japan could be detected in Nevada. The remaining samples for the CEMP network were collected and analyzed under the routine collection procedures and schedule in place for the CEMP. As can be observed in Table 2, the samples from this group of locations (Overton through Tecopa) show only the detection of Cs-137 and Cs-134. I-131 and Te-132 are notably absent. These two isotopes have a very short half-life, I-131 (8 days) and Te-132 (3.2 days), relative to the Cs isotopes. Because there is a one month lag time between collection and analysis for routine CEMP samples, and only trace amounts of activity from Japan were being collected, I-131 and Te-132 in these samples had decayed to non-detectable levels.

CEMP Station Sampling Period Cs-137
Activity (pCi/L)
Activity (pCi/L)
Activity (pCi/L)
Activity (pCi/L)
Activity (pCi/L)
Boulder City, NV1 3/17 - 3/23/2011 4.7E-5 2.2E-4 N.D. 1.9E-5 3.6E-5
Henderson, NV1 3/17 - 3/23/2011 4.5E-5 2.3E-4 N.D. 1.9E-5 3.6E-5
Las Vegas, NV1 3/17 - 3/23/2011 4.4E-5 2.2E-4 N.D. 2.2E-5 3.5E-5
Duckwater, NV2 3/16 - 3/27/2011 2.8E-5 7.6E-5 N.D. N.D. 2.2E-5
Pahrump, NV2 3/16 - 3/27/2011 3.9E-5 9.3E-5 N.D. 1.9E-5 3.9E-5
Amargosa, NV2 3/16 - 3/28/2011 3.3E-5 4.2E-5 N.D. 1.2E-5 2.6E-5
Garden Valley, NV2 3/16 - 3/29/2011 3.4E-5 6.5E-5 N.D. 7.3E-6 2.7E-5
St. George, UT2 3/16 - 3/29/2011 2.8E-5 8.9E-5 N.D. 6.9E-6 2.3E-5
Overton, NV3 3/14 - 3/27/2011 2.7E-5 N.D. N.D. N.D. 2.6E-5
Mesquite, NV3 3/14 - 3/28/2011 2.1E-5 N.D. N.D. N.D. 2.7E-5
Cedar City, UT3 3/14 - 3/28/2011 1.6E-5 N.D. N.D. N.D. 2.4E-5
Milford, UT3 3/14 - 3/28/2011 2.0E-5 N.D. N.D. N.D. 2.2E-5
Delta, UT3 3/14-3/28/2011 1.9E-5 N.D. N.D. N.D. 2.2E-5
Pioche, NV3 3/14 - 3/28/2011 2.4E-5 N.D. N.D. N.D. 2.6E-5
Caliente, NV3 3/14 - 3/28/2011 1.9E-5 N.D. N.D. N.D. 3.0E-5
Alamo, NV3 3/14 - 3/28/2011 2.3E-5 N.D. N.D. N.D. 2.1E-5
Twin Springs, NV3 3/15 - 3/29/2011 2.5E-5 N.D. N.D. N.D. 1.8E-5
Nyala, NV3 3/15 - 3/30/2011 2.0E-5 N.D. N.D. N.D. 1.8E-5
Stone Cabin, NV3 3/16 - 3/30/2011 3.0E-5 N.D. N.D. N.D. 2.5E-5
Ely, NV3 3/18 - 3/28/2011 2.3E-5 N.D. N.D. N.D. 1.6E-5
Rachel, NV3 3/14 - 3/27/2011 3.1E-5 N.D. N.D. N.D. 3.5E-5
Tonopah, NV3 3/14 - 3/28/2011 3.3E-5 N.D. N.D. N.D. 3.5E-5
Goldfield, NV3 3/14 - 3/28/2011 2.6E-5 N.D. N.D. N.D. 2.4E-5
Sarcobatus, NV3 3/13 - 3/27/2011 2.4E-5 N.D. N.D. N.D. 2.9E-5
Beatty, NV3 3/14 - 3/27/2011 1.9E-5 N.D. N.D. N.D. 2.0E-5
Indian Springs, NV3 3/14 - 3/28/2011 3.7E-5 N.D. N.D. N.D. 3.0E-5
Tecopa, CA3 3/13 - 3/28/2011 3.5E-5 N.D. N.D. N.D. 3.1E-5

N.D. = not detected
1 The collection of these air-particulate (paper) filters from air samplers at these locations was performed earlier than scheduled to coincide with the timing of the first set of samples obtained from paper-filter and charcoal-filter equipped air sampling units.
2 Additional air-particulate samples chosen for immediate analysis to initially represent the CEMP network.
3 Air particulate samples from the remaining CEMP stations for the time period 3/13 to 3/29 collected and analyzed under the routine collection schedule

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