Trace amounts of radiation from the Japanese nuclear disaster have been detected in several states as far apart as California and Massachusetts, but state and federal health officials say there is no cause for alarm.

Radioactive material that escaped into the environment from the Fukushima Daiichi nuclear power plant has drifted around the world. The radioactive isotopes detected are primarily iodine, though there are several other elements as well.

Iodine and cesium are more worrisome from a health perspective because they gather in specific organs in the body and are easily digested. But the concentrations that have come from the power plants in Japan are orders of magnitude smaller than those measured in the region around the plant.

In California, the measurements taken on March 16 through 18 at several locations found concentrations of less than one picocurie per cubic meter of air. A picocurie is a measure of radiation decay events. A single cure is 3.7 billion decays every second. A picocurie is one trillionth of a curie, or about 0.37 decays every second.

Various isotopes of cesium were found at concentrations of thousandths of a picocurie. Other elements that were found include Tellurium, Ruthenium and Zirconium.

The human body has about one microcurie of potassium-40 naturally, which is about a million times as much radiation as in the samples detected.

The U.S. Environmental Protection Agency is coordinating with state authorities to monitor milk supplies. Rainwater, the EPA says, is safe to drink.