By Jay T. Cullen
The purpose of this post is to report the most recent and last results from Kelp Watch 2015, a program dedicated to monitoring for Fukushima derived contamination along the Pacific Coast of North America. This post is the latest in a series dedicated to public outreach and dissemination of scientifically derived information about the impacts of the Fukushima Dai-ichi disaster on the health of the North Pacific Ocean ecosystem and health of North American residents. Results from the fifth sampling period (March 2 through June 3 2016) were released on July 15, 2016 and can be found here. As with previously reported results here, here, here, here, and here no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites along our Pacific coast or elsewhere in the Pacific (see sampling sites). The absence of 134Cs in kelp suggests that ocean transport of Fukushima contamination had yet to reach persistently high enough levels in North American coastal water to bioaccumulate in kelp. The levels of Fukushima derived contamination in kelp in 2016 will not pose a significant risk to the health of the kelp or other species, including humans, which rely on them as a foodstuff.
Samples were collected March to June of 2016 from Juneau AK in the north down to Humboldt County CA in the south along the Pacific Coast .
Full results for the fifth sampling period can be found here along with details about the goals and approach of Kelp Watch 2015. Owing to its relatively short half life of ~2 years radioactive 134Cs serves as a useful tracer of Fukushima impact because it was released in significant quantities into the environment after the disaster in March 2011. All other sources (atmospheric nuclear weapons testing in the 20th century and Chernobyl in 1986) of the man made isotope have occurred far enough in the past that any 134Cs detected in the environment serves an unmistakable fingerprint of Fukushima impact. Similar to previous work by this program all samples of kelp collected from the Pacific by Kelp Watch 2015 during the winter and spring of 2016 had no detectable (detection limit ~ 0.05 Bq kg-1 dry weight of kelp) levels of 134Cs indicating that isotopes from Fukushima are not significantly affecting radioisotope activities in these organisms to date. This is despite the fact that Fukushima contaminated seawater has been detected periodically at the coast and most notably in Ucluelet BC where the first shoreline seawater sample with Fukushima contamination was collected on Feb. 19, 2015. The fact that the kelp is still free of 134Cs is likely related to the lack of persistent contact with Fukushima contamination owing to the dynamic nature of coastal currents, coastal upwelling of less contaminated water from depth, significant inputs of contamination free freshwater runoff or a combination of these factors given sampling location.
Similar to citizen science collected coastal seawater samples along the British Columbia coast there may be slightly higher levels of 137Cs in kelp collected at more northerly latitudes compared to southern sampling locations. This may reflect the arrival of the contaminated seawater from Fukushima at the coast and the bifurcation of the North Pacific Current as it approaches North America. The levels of 137Cs in the kelp are too low to pose health risks to kelp or its consumers.
Continued monitoring of seawater and marine biota by projects like KelpWatch 2015 and InFORM will help to determine levels of Fukushima derived contamination along the North American coast and the corresponding risks to ocean and public health.