TORSHAVN, Faroe Islands — Bjoerg Petersen knits her brow and chews her lip as she tries to navigate a mind-frazzling maze. She pushes her blond bangs from her forehead, rubbing it with such vigor that she seems determined to reach deep into her brain and yank the answer out.
When she succeeds, her face lights up with a wide, gap-toothed grin. When she fails, she frowns, turning to the next page of the test.
At the age of 7, Bjoerg is a typical first-grader in all but one way: Her brain has been probed by scientists since she was 2 weeks old.
Bjoerg and about 1,700 other Faroese schoolchildren are the subjects of one of the longest and most intensive environmental experiments ever conducted on humans.
Ongoing for nearly 20 years, the tests strongly suggest that a mother's consumption of mercury-tainted seafood -- whale in the case of the Faroe Islanders -- damages her fetus' brain as it grows in the womb, impairing her child's intelligence in subtle ways.
Once a year, Bjoerg has electrodes fastened to her head, measuring in milliseconds how rapidly her brain receives signals. She has been asked, countless times, to recall lists of numbers and shopping items.
She has searched the crevices of her mind in vocabulary tests, tapped computer keys to measure her reaction time, arranged and rearranged blocks in patterns, and copied drawings more times than her parents can remember. She has been surrendering samples of her hair and blood since she was born. And she will probably continue to be examined by neuropsychologists until she reaches adolescence.
The children of these remote North Atlantic islands, just below the Arctic Circle, have become sentinels for the rest of the world, warning of the dangers of mercury.
The 7-year-olds most highly exposed in the womb lag behind their schoolmates in some skills -- particularly short-term memory, vocabulary and attention spans -- by as much as a school year, comparable to a decline of five or six IQ points. A physical change also has been detected: a slight slowing of the brain's responses to signals.
The latest evidence, the results of tests on these children at 14 years published Friday, suggests that at least some of the neurological effects are long-lasting, perhaps permanent.
The findings, although partly contradicted by another large study, have had worldwide repercussions, prompting the U.S. government since 2001 to warn women of childbearing age to limit the amounts and types of fish they eat.
Children born in the Faroe Islands, part of Denmark, are highly exposed because the Faroese eat the blubber and meat of pilot whales, which contain mercury concentrations 100 times greater than fish. Pilot whales accumulate mercury by eating fish contaminated with the metal, which builds up in the ocean from emissions from power plants and other industrial operations.
The typical American carries one-tenth the mercury found in the mothers of children tested in the Faroes. But in many regions, including California's coast, people who frequently eat ocean fish absorb as much mercury as the islanders, sometimes more.
One San Francisco physician reported last year that excessive levels of mercury were common in upper-income women and children among her patients, particularly those who regularly ate swordfish.
"The available data indicate that mercury is present all over the globe, especially in fish, in concentrations that adversely affect human beings," the United Nations Environment Program stated in its 2003 Global Mercury Assessment.
'Mad Hatter' Syndrome
Proof that mercury damages the brain dates back at least 200 years, to 19th century "mad" hatters poisoned by the chemical used to cure felt. But it wasn't until the 1950s that the dangers to fetuses became known.
At Japan's Minamata Bay, where a chemical factory dumped tons of mercury, thousands of children were born with mental retardation and other severe problems. Similar poisoning occurred in Iraq in the 1970s, the result of contaminated grain. Toxicologists say mercury ranks among the most dangerous and widely dispersed contaminants. It is one of a few found to harm humans at doses commonly encountered in the environment.
Mercury is a natural element in the Earth's crust, but its levels in the environment have increased threefold since preindustrial times and, in some areas, are still rising.
Every year, coal-burning power plants and waste incinerators worldwide spew about 1,500 tons into the air, more than half in Asia, according to the U.N. report.
In the United States, power plants emit about 3% of the global total. The Bush administration in December backed reducing the annual U.S. output from 48 tons to 15 by 2018, but environmentalists are calling the proposed regulations inadequate.