Very small amount of radiation from iodine-131 was detected in a milk sample that was tested from US northwest, say US authorities.
"These findings are a minuscule amount compared to what people experience every day. For example, a person would be exposed to low levels of radiation on a round trip cross country flight, watching television, and even from construction materials," said Patricia Hansen, an senior scientist at the Food and Drug Administration (FDA).
She was referring to results from a cow's milk sample taken March 25 from Spokane, Washington; it found 0.8 pCi/L of iodine-131, "which is more than 5,000 times lower than the Derived Intervention Level set by the US Food and Drug Administration," an FDA statement said.
The agency said that it had boosted monitoring "of milk, precipitation, drinking water, and other potential exposure routes ... in response to the ongoing situation in Japan."
A 9.0 magnitude March 11 earthquake and tsunami knocked out the cooling systems of the Fukushima plant's six reactors -- triggering explosions and fires, releasing radiation and sparking global fears of a widening disaster.
Radiation from the plant northeast of Tokyo has wafted into the air, contaminating farm produce and drinking water, and seeped into the Pacific Ocean.
In a stop-gap measure to contain the crisis at the plant, crews have poured thousands of tons of water onto reactors where fuel rods are thought to have partially melted, and topped up pools for spent fuel rods.
But the run-off of the operation has accumulated in the basements of turbine rooms connected to three reactors and filled up tunnels, making it too risky for workers to go near to repair cooling systems needed to stabilize the plant.