NEW IDRIA, Calif. - Abandoned mercury mines throughout central California's rugged coastal mountains are polluting the state's major waterways, rendering fish unsafe to eat and risking the health of at least 100,000 impoverished people.
But an Associated Press investigation found that the federal government has tried to clean up fewer than a dozen of the hundreds of mines - and most cleanups have failed to stem the contamination.
Although the mining ceased decades ago, records and interviews show the vast majority of sites have not even been studied to assess the pollution, let alone been touched.
While millions live in the affected delta region, the pollution disproportionately hurts the poor and immigrants who rely on local fish as part of their diet, according to a study conducted by University of California at Davis ecologist Fraser Shilling. His research found that 100,000 people, which he calls a conservative estimate, regularly eat tainted fish at levels deemed unsafe by the U.S. Environmental Protection Agency.
"Tens of thousands of subsistence anglers and their [families] are consuming greater than 10 times the U.S. EPA recommended dose of mercury, which puts them at immediate risk of neurological and other harm," Mr. Shilling said.
The legacy of more than a century of mercury mining in California - which produced more of the silvery metal than anywhere else in the nation - harms people and the environment in myriad ways.
Near a derelict mine in this California ghost town, the water bubbling in a stream runs Day-Glo orange and is devoid of life, carrying mercury toward a wildlife refuge and a popular fishing spot.
Other mercury mines are the biggest sources of the pollution in San Francisco Bay and the Sacramento-San Joaquin River Delta, the largest estuary on the Pacific Coast.
Records and interviews show that federal regulators have conducted about 10 cleanups at major mercury mines with mixed results, while dozens of sites still foul the air, soil and water. The AP's review also found that the government is often loath to assume cleanup costs and risk litigation from a failed project.
Mercury from mine waste travels up the food chain through bacteria, which converts it to methylmercury - a potent toxin that can permanently damage the brain and nervous system, especially in fetuses and children.
The federal government calls methylmercury one of the nation's most serious hazardous-waste problems, and the Centers for Disease Control and Prevention says it is a possible carcinogen.
Mercury is considered most harmful to people when consumed in fish. People who regularly consume tainted fish are at risk of headaches, tingling, tremors and damage to the brain and nervous system, according to the CDC.
The toxin is less of a threat in drinking water, which is filtered and monitored more closely.
Mining in California ceased decades ago, leaving behind at least 550 mercury mines, though no one knows for sure how many. One U.S. Geological Survey scientist says the total may be as high as 2,000.
In the 19th and 20th centuries, California produced up to 90 percent of the mercury in the U.S., and more than 220 million pounds of quicksilver were shipped around the world for gold mining, military munitions and thermometers. Much of the liquid mercury was sent to Sierra Nevada gold mines, where miners spilled tons of it into streams and soil to extract the precious ore.
For the Elem Band of Pomo Indians, whose colony is next to Clear Lake, the most mercury-polluted lake in the world, the mercury has made it unsafe to eat local fish.
Their colony was built in 1970 by the federal government over waste from the mine. Officials knew it was contaminated, but were not aware at the time how dangerous mercury was to people. The mine is now a Superfund site.
State blood tests on 44 volunteer adult tribe members in the 1990s found elevated levels of mercury. The average level was three times higher than found in people who do not eat tainted fish, but regulators said only one man was at immediate risk of brain damage or other harm.
Yet the EPA determined that the tribe's mercury levels were a serious enough threat for the agency to spend millions of dollars removing contaminated dirt from the colony's homes and roads.
Many have moved from the colony, leaving about 60 of what was once a community of more than 200 people.
"We are here to protect the environment, and sometimes we do it better than other times," said Daniel Meer, EPA's assistant Superfund director for the region. "We can't start cleaning up everything all at once."
"It took a hundred years to occur," said Mr. Meer. "And it may take a hundred years or more to solve."