Kelp Watch

UPDATE 1/15/2017: More Seaborne Radiation from Fukushima Detected on the West Coast

UPDATE 12/03/2015: Higher Levels of Fukushima Cesium Detected Offshore 

UPDATE 11/11/2014: Fukushima Radioactivity Detected 100 Miles from Eureka

Kelp Watch 2014 is a scientific campaign, based on collaboration between Dr. Steven L. Manley (Department of Biological Sciences, California State University- Long Beach) and Dr. Kai Vetter (UC Berkeley and Lawrence Berkeley National Laboratory), and designed to determine the extent of possible radionuclide contamination (primarily Cesium-137 & -134) of our kelp forest ecosystem from seawater arriving from Fukushima in 2014. Initiated by Dr. Manley in early November 2013, the project relies on sampling canopy blades of the Giant Kelp (Macrocystis) and Bull Kelp (Nereocystis) several times during 2014. The project started as California centric but has continued to grow beyond the California coastline and includes locations in Baja-Mexico, Oregon, Washington, British Columbia and Alaska. A site off the Chilean coast will serve as a “reference” sample. Although kelps (brown seaweeds of the Order Laminariales) do not occur in tropical waters, related brown seaweed, Sargassum, will also be collected from waters off Hawaii and Guam. To date a total of 48 separate populations will be sampled, 31 in California waters, led by 52 marine scientists and numerous assistants. The participants are primarily from academia but also include educators from private organizations. Initially, all participants agreed to participate “pro bono.” Recently, however, USC-Sea Grantand California State University Council on Ocean Affairs, Science & Technology (COAST) have agreed to contribute funds to the project, which will help defray the costs associated with collecting and processing the kelp.”

“Several institutions, Moss Landing Marine Laboratory (CSU), Coastal and Marine Institute (SDSU) and CSU- Long Beach, have volunteered to serve as regional processing centers. Processed kelp samples will be sent to Lawrence Berkeley National Lab (UC-Berkeley) for detailed radionuclide analysis involving 4 scientists. As data becomes available it will be posted here for public access.”

2014 Results

Sample Humboldt 2/28/2014 (HSU-1)


Collection Date 02/28/2014
Species Nereocystis
Coordinates +41.055719, -124.144775
Collector Frank Shaughnessy, Aleika Vicente, and Greg O’Connell
Affiliation Humboldt State University
Status Analysis complete


Isotope Result (Bq/kg dry weight)
K-40 3968 ± 9
U-238 series (early) 20.1 ± 3.5
U-238 series (late) 2.15 ± 0.07
Th-232 series (early) 1.05 ± 0.18
Th-232 series (late) 0.18 ± 0.02
Be-7 1.96 ± 0.79
I-131 not detected (< 1.8)
Cs-137 0.23 ± 0.04
Cs-134 not detected (< 0.04)

The table shows the radioactive isotopes measured in the kelp samples, corrected to time of collection during the first sampling period (February to March 2014). Some samples were taken beyond this period due to logistical issues. All data is based on a single sample size (n=1) of 6.5 kg fresh weight of blade tissue.

The kelp samples were dried and milled into a powder and then sent to LBNL to be measured with a high-purity germanium detector. As expected, all kelp samples contained significant amounts of naturally occurring radioactivity, primarily due to potassium-40 (K-40) since dried kelp has a high potassium content. Also found were smaller amounts of other naturally occurring radioactive isotopes, including Beryllium-7 which is acosmogenic nuclide present in air and rain, and portions of the Uranium-238 and Thorium-232 radioactive decay chains.

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. For more information on radiocesium, please visit the FAQ: Why Cesium?.

For a sense of scale, the K-40 activities ranged from 2500 to 4500 Becquerels per kilogram dry weight (Bq/kg dwt), where one Becquerel is one nuclear decay per second, while the Cs-137 was detected in all samples at levels ranging from 0.08 to 0.44 Bq/kg, or about 10,000 times lower than K-40. The upper limits set for Cs-134 are approximately 0.04 Bq/kg, or 100,000 times lower than some of the K-40 levels.

Two kelp samples obtained from the Chilean coast had very low to undetectable levels of Cs-137. This is consistent with the lower levels of Cs-137 known to be in the southern oceans. Because kelps are not found in the tropics, related brown seaweeds, Sargassum sps. were sampled from Hawaii and Guam. The samples from Hawaii and Guam were consistent with the North American samples, showing no signs of Fukushima radioactivity.

Iodine-131 was seen in kelp from southern California, primarily Los Angeles and Orange Counties. This most likely comes from water treatment plants processing medical waste: please see Iodine-131 From Local Inputs.

Table Notes:

  • All uncertainties quoted are “one-sigma,” meaning that they represent a 68% confidence range for the quantity measured. Detection limits are also “one-sigma” in that they give the 68% confidence upper limit.
  • Radioactive isotopes are measured in units of Becquerels per kilogram dry weight (Bq/kg dwt). One Becquerel is one nuclear decay per second.
  • Data are decay-corrected to the date the sample was collected.


Update Log:

  • 5/7/2014 10:15 – initial data posted
  • 6/10/2014 13:00 – remainder of sample data posted

 See More Information at