The California Coastal Commission has released a report saying that waterborne radiation levels off its coast from the 2011 Fukushima nuclear accident are "far below that of naturally-occurring radioactive elements in the ocean".
"Over the last three years, the radioactive ocean plume has been carried eastward by ocean currents, becoming increasingly diluted as it spreads over an ever-larger area and mixes to greater depths," the report states. "The leading edge of the plume appears to have reached North America off of Vancouver Island, and could possibly reach California within the next year."
The report notes that Fukushima-derived radionuclides, chiefly cesium 137, are "expected to be only slightly above the pre-accident background".
Cesium 137 has a half-life of 30 years.
"Radioactive cesium derived from Fukushima has been detected at low levels in the tissues of highly-migratory fish species such as Pacific Bluefin tuna, which appear to have accumulated the cesium in their juvenile rearing grounds in the western Pacific," the report adds.
It also points out that levels of Fukushima-derived radionuclides in air, drinking water, food, seawater, and marine life in California "are extremely low relative to the pre-existing background from naturally-occurring radionuclides".
This "supports the idea that it will pose little additional risk to humans or marine life".
"However," the report cautions, "it should be noted that the long-term effects of low-level radiation in the environment remain incompletely understood, and that this understanding would benefit from increased governmental support for the monitoring of radioactivity in seawater and marine biota and the study of health outcomes linked to radiation exposure."