By Jonathan Kellogg and Jay T. Cullen
Results from surface water samples collected in August 2014 during three oceanic research cruises are now available. These seawater samples were analyzed to characterize the distribution of Fukushima derived radionuclides 137-Cesium (137Cs half life ~30 years), and 134-Cesium (134Cs half life ~2 years). Based on the distribution of 134Cs, the Fukushima plume was not consistently present yet on the BC coast. It is likely that peak concentrations of radiocesium will be present offshore in the next year.
Offshore sampling operations in 2014 and results
The data were obtained through sampling operations on three research expeditions in August 2014:
- Eureka, CA to Dutch Harbor, AK (funded by Our Radioactive Ocean)
- Sidney, BC to the Chukchi Sea (funded by Fisheries and Oceans Canada)
- Sidney, BC to Ocean Station Papa (50 N, 145 W), aka, Line P (funded by Fisheries and Oceans Canada)
The highest measured activities were found ~1500 kilometers offshore near Ocean Station Papa and off the California coast where 137Cs was >5 Bq m-3 and 134Cs levels were <2 Bq m-3. Pre-Fukushima 137Cs contamination was present throughout the sampled area at low levels, ~1-2 Bq m-3, reflecting atmospheric nuclear weapons tests conducted in the 1950-60’s and fallout from the Chernobyl nuclear accident in 1986 (all 134Cs activity from these past events had decayed away by 2011). Current levels of contamination pose negligible risk to the human or marine ecosystem health.
To explore the data in greater detail, see the map below
What are we measuring and why?
The triple meltdowns at the Fukushima Dai-ichi nuclear power plant (NPP) released many different radioisotopes to the environment, however only a very few of these are both measurable and unique to Fukushima. A reliable finger-print radioisotope for Fukushima is Cesium-134 (134Cs half life ~ 2 years). This is because 134Cs is only produced appreciably in nuclear reactors and it has a relatively short half-life, so that 134Cs from other human sources, like the Chernobyl NPP disaster in 1986, are no longer present in the environment. Other isotopes such as Cesium-137 (137Cs half life ~30 years) are not positive indicators of Fukushima since they were also a products of atmospheric testing in the 20th century and Chernobyl and are still present in the environment from these legacy sources.
These observations will help to determine how well models predicted the progression of ocean borne contamination across the Pacific Ocean. Understanding the spread of this contamination provides important information on the impact of the Fukushima Dai-ichi disaster on the health of the Pacific ecosystem and the North American public. The evolution of the contaminant plume in time and space also helps the scientific community to better understand ocean mixing which is a key parameter toward understanding the oceans role in mitigating atmospheric greenhouse gas increases and climate change.
How scientists talk about radioactivity in the environment
Scientists use a variety of units to measure radioactivity. A commonly used unit is the Becquerel (Bq for short) which represents an amount of radioactive material where one atom decays per second and has units of inverse time (per second). Another unit commonly used is disintegrations per minute (dpm) where the number of atoms undergoing radioactive decay in one minute are counted (so 1 Bq = 60 dpm). The measurements above represent that numbers of Bq detected in a cubic meter of seawater.
Note: Data reported on here have been previously presented in public presentations given by the project and its partner organizations (e.g. 19:07 in the public lecture given by Drs. Buesseler and Cullen at the Vancouver Aquarium this past September).