Selenium at levels high enough to poison millions of high-risk Americans has been found in food from supermarkets across the country, according to a newspaper's seven-month investigation.

Toxic concentrations of selenium also taint the home-grown food and drinking water of hundreds, perhaps thousands, of farm and ranch families in several Western states, The Sacramento Bee reported Sunday.Selenium is a naturally occurring gray, non-metallic chemical element of the sulphur group. Its levels in commercial foods are high enough to expose even healthy adults to levels above federal guidelines, the Bee said.

The potential effects for healthy adults may be nothing worse than slight declines in overall health or resistance to disease and infection.

But for those living in the rural West and high-risk groups across the nation - the very young, old and the chronically ill - the effects can be much more serious, including severe digestive problems, kidney or liver damage, paralysis, even death, the newspaper said.

The Bee said its first set of tests established a clear danger to rural families in Oregon, Montana, South Dakota, Nebraska, Wyoming, Colorado and Nevada. The second set turned up elevated selenium in supermarket foods in seven American cities: Sacramento; Chicago; Washington, D.C.; Atlanta; Great Falls, Mont.; Rapid City, S.D.; and Montrose, Colo.

The findings were based on laboratory analyses of more than 200 water, meat, fish, egg, cereal grain and dairy product samples and on interviews with dozens of selenium victims, their doctors, public health experts and toxicologists.

Selenium has killed or deformed thousands of fish, waterfowl and other wildlife at Kesterson National Wildlife Refuge in California's central agricultural valley. Similar effects have been confirmed by federal studies in other parts of California and in Nevada, Utah and Wyoming.

Although the U.S. Interior Department is studying the selenium threat to wildlife, no agency is studying its toxic effect on people, the Bee said.

Selenium enters the human food chain from thousands of square miles of selenium-tainted soil in the West; by being added to livestock and poultry feed; and through the marketing by nutrition companies of selenium as a dietary supplement.

"People could get no more than a good bellyache from a single high exposure, or get very, very sick from prolonged intake," said Dr. Arthur Kilness, a researcher on selenium and a retired South Dakota surgeon.

According to the newspaper:

-A healthy adult would surpass the federal Food and Drug Administration's safe selenium level - 200 micrograms - by eating two six-ounce servings of the sampled foods a day. Those servings averaged 105 micrograms.

-A weekly menu prepared from the foods yielded seven straight days of intake averaging 410 micrograms. The National Academy of Science, the National Institutes of Health and others have stated that healthy adults suffer adverse effects above 500 micrograms.

-Five of 11 samples of baby food exceeded the safe level of 40 micrograms for infants. One four-ounce serving of oatmeal cereal had 83 micrograms. So far, no government or health agency has determined the toxic level for infants.