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The purpose of this diary is to bring to the attention of those interested the most recent results of Kelp Watch 2014 a program dedicated to monitoring for the presence of Fukushima sourced radionuclides off our Pacific Coast.  This diary is the latest contribution to a series that aims to provide information about the impacts of the Fukushima Dai-ichi disaster on the North Pacific Ocean ecosystem and on North American public health. New results from the first sampling period (February to March 2014) of Kelp Watch 2014 were just released and can be found here. As with previously reported results no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites spread across the eastern Pacific. However, significant quantities of the short lived radioisotope 131-Iodine (half life ~8 days) were detected in samples collected in southern California.  Rather than being transported across the Pacific these isotopes were likely released locally in waste water that carries significant 131-I because of its application in nuclear medicine to treat thyroid maladies.

Full results for the first February to March 2014 sampling period can be found here along with details about the goals and approach of Kelp Watch 2014.

Because of its relatively short half life of ~2 years radioactive 134-Cs serves as a useful tracer of Fukushima impact as it was released in significant quantities, with many other isotopes, into the environment after the disaster in March 2011.  All other legacy sources of the human produced isotope have occurred far enough in the past that any 134-Cs present in the environment faithfully reflects release from Fukushima.  All samples of kelp collected from the Pacific by Kelp Watch 2014 thus far have not had detectable levels of 134-Cs suggesting that isotopes from Fukushima are not significantly affecting radioisotope activities in these organisms to date.

The authors summarize findings about 134-Cs and its longer lived cousin 137-Cs (half life ~30 yr) as follows:

Cesium-137 was detected in all West Coast samples at very low levels. This isotope is still detectable in the marine environment due to above-ground nuclear weapons testing that took place mostly in the 1950s and 1960s. The very low limits set on the shorter-lived Cesium-134 mean that the Cs-137 cannot be directly tied to the Fukushima releases and is more likely due to these "legacy" sources.
In southern California kelp samples significant 131-I, which can represent a significant radiological health risk given its propensity to concentrate in the thyroid gland and induce cancer, activities were detected (up to 152 Bq/kg at Long Beach CA).  Rather than being attributable to release from Fukushima given that ocean transport is quite slow relative to 131-I decay Kelp Watch 2014 attributes the presence of 131-I to local sources.  These local sources likely reflect waste water input to the coastal ocean that contains 131-I from nuclear medical applications in hospitals and clinics in the area.  In the words of the program scientists:

 

If this I-131 were the result of a release of nuclear waste, there would be a variety of other fission-produced isotopes that would be present as well. The fact that none of these other products are present indicates that the Iodine-131 is a pure source — in which medical use is the only such use of pure I-131 compounds. We attribute the presence of I-131 in kelp to its release to the environment from its use as a medical radiopharmaceutical.
Ongoing monitoring of seawater and marine organism activity concentrations of radioisotopes from Fukushima will help to determine the likely impacts on the ecosystem and public health along North America's Pacific coast resulting from the disaster.  I will report new results as they are made available.

Originally posted to MarineChemist on Tue Jun 10, 2014 at 03:19 PM PDT.

Also republished by SciTech and Japan Nuclear Incident Liveblogs.

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