Cesium-137 has a relatively long half-life (30 years), but it is also present in the ocean as a result of nuclear weapons testing in 1950s and 1960s.
Since mid-2011, I have worked with Japanese colleagues and scientists around the world to understand the scope and impact of events that continue to unfold today.
In June 2011, I organized the first comprehensive, international expedition to study the spread of radionuclides from Fukushima into the Pacific, and I or members of my lab have participated in several other cruises and analyzed nearly one thousand samples of water, as well as dozens of samples of sediment and biota.
This is in part because increases in cancer are hard to attribute to any single cause and it is difficult to detect small increases in cancer over time when 30 percent of us will get cancer of some form in our lifetimes.
We should always be concerned, but we should also realize that different levels, time, and manner of exposure can have widely varying health risks.
Because it was released in equal amounts with cesium-137, we can use its presence to determine how much contamination was released from the reactor site.
» More about iodine-131 and cesium-137 How will the radioactive material released in Japan affect humans?
» More about the human health risks of radiation Are the continued sources of radiation from the nuclear power plants of concern?
The site of the Fukushima Dai-ichi nuclear power plant is an ongoing source of radionuclides (pdf) in to the ocean—something I've seen evidence of in my data and published since 2011.
In the months after Fukushima, I also formed the Center for Marine and Environmental Radioactivity, in part to help share the most accurate, up-to-date information about radiation from human and natural sources and, when it became clear that there was no coherent and consistent source of government funding to monitor radiation in U. waters and to support public education, I formed a citizen-science/crowd-funding initiative called Our Radioactive Ocean at WHOI.
These are a few of the most common questions that people have been asking me.
At the height of the accident, levels in the ocean near the docks at the reactors were 50 million times higher than before the accident and, at those levels, were a direct threat to marine life.