by Jay T. Cullen / TimesColonist.com / November 21, 2013 /
Since the Fukushima Daiichi disaster on March 11, 2011, there are many reports of the potential impact of radioactivity from Fukushima causing harm to sea life and people on the West Coast of North America.
But radioactivity from Japan poses no danger and little risk to us on the West Coast.
A commonly used unit to measure radioactivity is the Becquerel (Bq for short), which represents an amount of radioactive material where one atom decays per second. When we talk about the radioactivity measured in seawater, the measurements are reported per litre of seawater (Bq/L). Almost all the radioactivity in seawater is the result of naturally occurring radionuclides that have been transported or deposited in the oceans by natural processes. For example, over time radioactive elements in rocks and minerals are delivered to the ocean through the erosion of the continental crust.
The average radioactivity of seawater is about 14 Bq/L, of which nine-10ths comes from the naturally occurring elements potassium and rubidium. The remainder is fallout from atmospheric nuclear-weapons testing in the 20th century. So the natural level of radioactivity on average in the oceans is about 13 Bq/L, against which radioactivity resulting from human activities and disasters should always be discussed.
The radioactive element Cesium 137 (Cs-137) was released in large quantities from Fukushima into the Pacific. Pre-Fukushima levels of Cs-137 in the North Pacific, present from Cold War-era nuclear testing, represented 0.007 per cent of the natural radioactivity in a litre of seawater.