The purpose of this post is to give a brief overview of how the activity of radionuclides correspond to the concentration of radionuclides measured in environmental samples. There appears to be some confusion in the public and within the scientific community as to how units are used and the degree of their interchangeability. This post is somewhat technical but falls into the category of “In Case You’re Interested” (ICYI), an acronym I am shamelessly borrowing from a fine book (Everything and More: A Compact History of Infinity) by one of my favorite writers David F. Wallace.
Radio interview related to broadcast by CBC Daybreak North on Dec. 10, 2014 by George Baker. The live radio broadcast highlights efforts of volunteer, citizen scientists Laurel Stueck (student) and Cheryl Paavola (Instructor and Science Lab Tech) at Northwest Community College – Prince Rupert collecting the first seawater sample there in November 2014.
This post reports on a recently published peer reviewed study by Steinhauser and colleagues in the journal Science of the Total Environment (behind pay wall) comparing the Chernobyl and Fukushima nuclear accidents. The post is part of an ongoing effort to communicate the results of scientific studies into the impact of the Fukushima disaster on the environment. A majority of the radioactivity released from both Chernobyl and Fukushima can be attributed to volatile radionuclides (noble gases, iodine, cesium, tellurium). In contrast, the amounts of more refractory elements (including actinides like plutonium), released by Chernobyl was ~four orders of magnitude (10,000 fold) higher than releases from Fukushima. The most cited source term for Chernobyl is 5300 PBq (excluding noble gases) while a review of published studies of Fukushima carried out by the authors above allow an estimate for the total atmospheric source term of 520 (a range of 340–800) PBq. Monitoring of air, soil and water for radionuclides after the respective accidents indicate that the environmental impact of Chernobyl is likely to be much greater than the Fukushima accident. The post is relatively information dense as I have provided data tables for those who are interested in the estimates and the peer-reviewed studies from which they come. Apologies up front to those who find such information tedious. Continue reading Comparing the Environmental Impacts of the Chernobyl and Fukushima Disasters
The purpose of this post is to report on new results coming out the crowd-funded Our Radioactive Ocean program headed up by Dr. Ken Buesseler of Woods Hole Oceanographic Institution. This post is part of an ongoing series dedicated to scientific inquiry into the impact of the triple meltdowns at Fukushima on the health of the North Pacific Ocean and residents of the west coast of North America. Measurements of the cesium radioisotopes 134-Cs (half life ~ 2 years) and 137-Cs (half life ~30 years) were made on samples collected on a transect between Monterey Bay CA and Dutch Harbor AK this summer. Because of its relatively short half life 14-Cs serves as an unequivocal tracer of Fukushima contamination in the environment. Fukushima derived 134-Cs was detected at offshore stations with a maximum activity of ~ 2 Bq/m^3 and total 137-Cs activities of ~7 Bq/m^3 of seawater. Measurements have yet to detect 134-Cs in nearshore waters sampled up and down the North American west coast. These activities of Cs are orders of magnitude below levels thought to pose a measurable risk to human health or marine life, according to international health agencies.
For a primer on radioactivity in the ocean and the units used to discuss radioactive elements in the environment please visit this post.
At a great majority of sites sampled along the coast and offshore the activity of 134-Cs is below detection limit (~legacy contamination resulting from atmospheric weapons testing in the 20th century. Similar to previous work by Dr. John Smith of the Department of Fisheries and Oceans Canada the presence of the contaminated plume of seawater owing to releases from Fukushima can be detected in offshore stations (150 – 1500 km) with levels of 134-Cs approaching 2 Bq/m^3 and total 137-Cs (bomb + Fukushima) of about ~7 Bq/m^3. These levels of 137-Cs are similar to levels in the North Pacific Ocean that were present in 1990 owing to the combined effects of Chernobyl and weapons testing fallout as shown in the figure below.
The activities of radiocesium being detected offshore are well below levels thought to represent significant radiological health risks to marine organisms or residents of the west coast of North America. To this point no 134-Cs from the contaminated plume approaching the coast has been detected in nearshore waters. Ongoing monitoring by programs like Our Radioactive Ocean and its partner program InFORM which are making measurements of contamination in seawater and marine organisms will be key to understanding impacts of the Fukushima on our environment.
This post reports on the most recent study of plutonium releases from Fukushima to the Pacific Ocean. The post contributes to an ongoing effort to report peer-reviewed studies on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the health of the Pacific ecosystem and residents of the west coast of North America. Plutonium is an alpha-emitting isotope that carries significant radiological health risks if internalized with risk of exposure increasing with the activity of Pu isotopes in the environment. Previous work indicates that 239,240-Pu releases from Fukushima were about 100,000 and 5,000,000 times lower than releases from the Chernobyl disaster in 1986 and 20th century weapons testing respectively. Initial measurements of Pu isotopes in seawater and marine sediments off the coast from Fukushima indicated no detectable change occurred in Pu inventories in the western Pacific after the disaster. More recent and more expansive work supports earlier studies drawing the conclusion that up to two years after the accident the release of Pu isotopes by the Fukushima accident to the Pacific Ocean has been negligible.
A paper by Bu and colleagues was recently published in the peer-reviewed journal Environmental Science and Technology which investigated the activity of Pu isotopes marine sediments collected within 30 km of the Fukushima reactor sites. 239,240,241-Pu and radiocesium isotopes (134-Cs and 137-Cs) were measured. Given that Pu is a particle reactive element that would tend to be concentrated in sediments such measurements should help to determine the extent and degree of Fukushima derived Pu in the marine environment. Sample collection sites are indicated in the map below.
While initial releases from the plant and ongoing releases due to groundwater infiltration and terrestrial runoff have been negligible thus far according the authors they rightly point out that significant inventories of Pu are insecurely stored at the Fukushima site. So far estimates suggest that about 2.3×10^9 Bq of 239,240-Pu or 580 milligrams of the isotopes have been broadcast to the environment from Fukushima. Bu et al. (2014) estimate that contained within the roughly 270,000 tons of radioactive liquid waste stored in large tanks at Fukushima there exists approximately a further 1×10^8 Bq of 239,240-Pu. Given that future earthquakes or other events could mobilize this Pu, continued monitoring of Pu isotopes in the marine environment is necessary and prudent.