Radioactive isotopes are constantly spewed from the destroy Fukushima Daiichi nuclear plant and are easily picked up by the jet stream and transported across the North Pacific in storm systems.  When these weather fronts hit the mainland, the rains wash the radioactive particles out of the air and spreads them over everything that receives precipitation.   The US West Coast and especially British Columbia, specifically the Vancouver area, get hit the hardest.  As the jet stream migrates up and down the coast during the rainy season, the highest levels of radioactivity will accumulate, logically, in the areas of higher rainfall.   The more the rain, the higher the radiation concentration in the soil.  The radiation, of course, is not all washed out at once and continues to be transported and dumped on the US and Canada from West to East with measurable amounts of contamination ultimately having been recorded in multiple locations of Europe.  Note - Some winter storm systems come upward from the tropics and the Hawaii area (known as the 'pineapple express' storms) are much less contaminated.

Everything from trees to shrubs and all agricultural crops uptake the Fukushima radiation from the now contaminated soil and eventually spread through the entire food chain.  Nothing is spared.  The hay and grasses growing in contaminated soil are consumed by beef and dairy cattle and that is how radiative isotopes wind up in the animals and their milk products. That's why Cesium 137 was found in the milk of Vermont dairy cattle in the months after the 3-11 disaster...and that is why you'll hear nothing from the EPA about radiation in our crops, meat and dairy products.   Only covered greenhouses were and are spared being hit with radioactive rains.