This spring, scientists tested kelp along the West Coast to see if the abundant sea plant had absorbed any radiation from Japan's Fukushima nuclear power facility.
The results were negative, meaning radioactive isotopes associated with Fukushima hadn't reached North America yet.
This week, researchers are collecting a second round of kelp to see if things have changed over the past few months.
It's all part of a project started by CalState Long Beach marine biologist Steven Manley called Kelp Watch 2014.
The green, rubbery plant is able to soak up radioactive isotopes like a sponge, making it an ideal "canary in the coal mine" when it comes to radiation surveys, Manley said.
"If it comes into the kelp bed, we will be able to pick it up," he said.
Once this second round of samples has been collected, the specimens will be dried out and analyzed at a lab in Berkeley.
Manley says his team is looking for the isotopes of cesium-134 and cesium-137 -- both of which are associated with radioactive material.
"In fact we pick up cesium-137, not from Fukushima but from the 50s and 60s from atomic weapons testing. So that material is in the water and we still see it in kelp today," he said.
Those levels of cesium are very low and harmless to humans, Manley said. When water from Fukushima reaches West Coast kelp beds, the amount of Cesium in the plant should jump dramatically.
There are more than 40 sampling sites contributing to Kelp Watch, ranging from as far north as Alaska to Baja California in the south.
Manley expects the results from this latest collection effort to be ready in about a month. And he says there’s a chance they’ll show no signs of additional radiation.
Scientists had expected radiation-tainted water from Fukushima to reach the West Coast this year based on models of ocean currents. But factors like weather and ocean salinity could delay the arrival.
A similar project by the Woods Hole Oceanographic Institution in Massachusetts called Our Radioactive Ocean has also been testing West Coast water samples. That effort so far hasn't found any evidence of Fukushima radiation.
Researchers say the radioactive plume from Japan has dispersed over the last three years and when it does reach North American shores, it will most likely be so diluted that it won't pose a threat to humans.