The purpose of this post is to report the most recent results of Kelp Watch 2015 , a program dedicated to monitoring for the presence of Fukushima contamination off our Pacific Coast. This post is the latest in a series dedicated to the public dissemination of 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. New results from the third sampling period (January through March 2015) of Kelp Watch 2015 were released on April 6, 2015 and can be found here. As with previously reported results here, here and here no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites spread along our Pacific coast. The absence of 134Cs in kelp suggests that ocean transport of Fukushima contamination had yet to reach North American coastal water. As the contaminated water reaches the shoreline in the coming months Kelp Watch 2015 will help to track the arrival of the plume in time and space. Continue reading Kelp Watch 2015: Most Recent Results Looking for Fukushima Contamination
The most recent results of Kelp Watch 2014 , a program dedicated to monitoring for the presence of Fukushima sourced radionuclides off our Pacific Coast, are reported in this post. This post is the latest contribution to a series dedicated to the dissemination of 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 second sampling period (June to August 2014) of Kelp Watch 2014 were just released and can be found here. As with previously reported results here and here no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites spread across the eastern Pacific coast. However, significant quantities of the short lived radioisotope 131-Iodine (half life ~8 days) continued to be found in Los Angeles County and San Diego 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. The absence of 134-Cs in kelp suggest that ocean transport of Fukushima contamination has yet to reach North American coastal water.
Kelp Watch 2014 is a joint initiative between Dr. Steven Manley (Department of Biological Sciences, California State University- Long Beach) and Dr. Kai Vetter (UC Berkeley and Lawrence Berkeley National Laboratory). The program involves the analysis of kelp samples collected by citizen-scientists along the Pacific coast for Fukushima derived radioisotopes. Because of their sedentary existences and propensity to concentrate isotopes in their tissues kelp are useful sentinel organisms with which to monitor the timing and extent of the Fukushima impacted plume of seawater as it progressively affects more of the North American west coast.
Samples were collected June to August of this year at various sampling locations along the coast with some kelp obtained from Chile and Tasmania (where little Fukushima impact is expected) to serve as reference locations.
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. Similar to previous work by this program all samples of kelp collected from the Pacific by Kelp Watch 2014 in June to August of this year had no detectable (detection limit ~ 0.04 Bq/kg dry weight of kelp) 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.
Significant Iodine-131 (131-I, half life ~8 days), which can represent a significant radiological health risk given its propensity to concentrate in the thyroid gland and induce cancer, activities continue to be detected (up to 251 Bq/kg at Long Beach CA) in southern California kelp samples. This 131-I is not likely 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 which are likely waste water inputs to the coastal ocean that contains 131-I from nuclear medical applications in hospitals and clinics in the area.
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. As always, I will report new results as they are made available and we look forward to more work from this quality monitoring program.
The purpose of this post is to summarize results from various studies that monitored the timing of arrival and activity of radioactive iodine falling from the atmosphere in western North America following the Fukushima disaster in 2011. Determining the activity of 131-I (half life ~8 day) in rain and seaweed, which serves as a biological monitor, is important because of the isotopes short half life and its propensity to concentrate in the human body, specifically the thyroid gland. This combination of rapid energy release and biological tissue targeting can represent a potential radiological health risk. Measurements of 131-I in rain collected in the San Francisco Bay area and southern British Columbia, Canada indicate that the atmospheric transport brought contaminated air from Fukushima to North America by March 18 roughly 1 week after the earthquake and tsunami. Depending on location, activities of 131-I in rain peaked between March 20-24 and were observed to decrease to background levels in the first week of April. Peak activities in seaweed occurred later on March 28 and were observed to return to background levels in mid-May. Maximum 131-I activities in rain resulting from Fukushima were a factor of 10 lower for rainwater and a factor of 40-80 lower for seaweed compared to similar measurements made following the Chernobyl disaster in 1986. Observed 131-I activities suggest that the upper limit of radiation dose to the public resulting from Fukushima was similarly an order of magnitude lower than that from Chernobyl suggesting that the short and long-term impact on human health in western North America is expected to be minor.
How Scientists Talk About Radioactivity
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).
131-Iodine Releases From Fukushima
As a result of the great eastern Japan earthquake and tsunami on March 11, 2011 three of six reactors melted down resulting in releases of radionuclides from the Fukushima Dai-ichi nuclear power plant to the environment. In terms of absolute activity released and potential for causing harm to organisms, 131-I (half life ~8 day) was one of the most significant. Given its volatility and the damage to reactor fuel rods large releases of ~2000 PBq (petaBequerel = 10^15 Bq) to the atmosphere and ocean occurred in the weeks following the disaster. Prevailing atmospheric circulation brought this plume of contaminated air to North America within one half life of 131-I where rain and fallout of aerosol particles delivered 131-I and other isotopes to land and coastal waters.
Monitoring of 131-I in the environment is important because as an essential nutrient when concentrated in the human body in the thyroid gland the decay of the isotope can cause damage resulting in negative health impacts like cancer. After the triple meltdowns stations in North America began monitoring the activities of released radionuclides in air, rainwater and seaweed to determine the risk to public health.
Rainwater activities of 131-I
Rainwater in the San Francisco Bay area was monitored and the results published in the open-access, peer reviewed journal PLOSOne in 2011 by Norman and co-workers. Measurements were made for the period March 16-26, 2011 on rainwater collected in Oakland, Berkeley hills and Albany, CA. Results of these measurements are summarized in the figure below:
Similar activities and timing of arrival of the atmospheric plume of 131-I were observed in southern British Columbia, Canada. Chester and colleagues published this work in the peer-reviewed Journal of Environmental Radioactivity in 2013. Maximum activity of 131-I of 5.8 Bq/L was detected in the Vancouver, BC area nine days after the Fukushima disaster on March 20, 2011. The activity of 131-I returned to background by early April 2011. Results are summarized in the figure below.
131-I levels in seaweed are known to correlate strongly with levels in rain and seaweeds are useful monitors for human made radionuclides in the environment as the concentrate isotopes from their surroundings and are geographically widespread. Seaweeds were collected along the Canadian west coast by Chester and colleagues and analyzed for 131-I following the Fukushima disaster. Results of these analyses are summarized in the figure below:
Maximum 131-I was detected in BC seaweed on March 22 near Vancouver and on March 28 off the west coast of Vancouver Island some 250 km to the west of the city. Peak activities were 130 and 67 Bq/kg respectively. By mid-May activities had returned to background activities in the seaweed.
Summary: Health Implications and Comparison to Chernobyl
The maximum levels of 131-I in rainwater can be compared to limits allowed in drinking water in both the USA and Canada. Maximum activities in rain were in the range ~6-16 Bq/L. For example the maximum allowable concentration (MAC) or activity allowed in Canadian drinking water is 6 Bq/L. The MAC for 131-I is calculated using a reference dose level of 0.1 mSv (where mSv = 0.001 Sv) for 1 year’s consumption of drinking water, assuming a consumption of 2 L/day at the MAC. This compares to an effective dose received by someone living in Vancouver of about 1.3 mSv. Given the short half-life of 131-I of ~8 days the actual dose attributable to Fukushima fallout in precipitation is likely to be much lower than the 0.1 mSv upper limit on which the drinking water MAC is based.
Indeed, comparing measurements in the studies above to measurements made on the west coast of North America in the aftermath of the Chernobyl disaster in 1986 suggests that doses experienced by the public post Fukushima fallout were an order of magnitude lower. Measurements in the same species of seaweed in 1986 (behind paywall) are compared to the measurements of Chester and others here:
The calculated dose estimates to Canadians following the Chernobyl disaster were on the order of ~1 micoSievert (0.000001 Sv) (What is a Sievert, Sv?) while the peak 131-I activities present in rainwater after Fukushima suggest an upper dose of 0.1 microSv which is an order of magnitude lower dose.
These data have led health professionals in the US and Canada to expect that short-term and longer-term impact of Fukushima on public and environmental health to be very small compared to other radiological impacts from natural and legacy sources of radiation.