SAN FRANCISCO Health warnings against eating mercury-laced fish caught in the lakes and rivers of Northern California are now commonplace, and a new government study indicates there’s no prospect of cleaning up the waterways anytime soon.
The culprits, it turns out, are the 49ers. Not the football team but the gold miners who flocked to the Sierra Nevada Mountains and the rivers of the region some 120 to 150 years ago.
Mercury pollution, the study found, was a major side effect of hydraulic gold mining that flourished for about 30 years after prospectors discovered in the mid-1850s that panning for gold was far less efficient than blasting away mountainsides with water cannons.
“We can’t clean all this up anytime soon because we don’t even know anywhere near all the sources,” said Frank Hunley, a member of the Water Pollution Committee of the Association of Bay Area Governments. “And just cleaning up the mines we do know about would cost tens of billions of dollars.”
Exposure to high levels of mercury can damage the brain and kidneys and harm developing fetuses. The slick quicksilver metal became entrenched in the Northern California food chain when miners poured it atop wet slurries of gravel and dirt, where it would alloy with gold and fall to the bottom of sluice boxes because the alloy was heavier than surrounding material.
When the runoff from mining operations reached rivers and lakes, mercury settled largely in muddy bottoms, where much of it was eventually consumed by small organisms that fish eat. The result: hazardous fish advisories have been routine for more than 20 years around the San Francisco Bay and along the rivers that drain into it.
Until recently, most mercury poisoning was blamed on modern industry. But a new U.S. Geological Survey report pins the blame on the miners of long ago. They carted more than 26 million tons of mercury into the Sierra Nevada, and about a third of that has so far washed into the scenic bay or been carried there by fish.
An unknown amount remains trapped in muddy bottoms behind hydroelectric dams and might break loose and become a greater danger if those dams are ever breached, as advocated by some environmentalists who favor the move to increase salmon spawning, the USGS warns.
Just one gram of mercury, if dispersed evenly, is considered enough to poison a 12-acre lake under today’s health standards.
“It’s a 150-year-old legacy we’re just now finding out about,” said Mike Hunerlach, a USGS hydrologist who co-authored the new report. “It’s probably going to continue at least another 15 years.”
Others say the problem could last much longer. The California Water Quality Control Board estimates that since mercury is a heavy metal that settles at the bottom of the Bay and is slow to wash out to sea, the contamination of fish may go on another 100 years or more.
The federal study found that millions of pounds of mercury most likely still remain both in old mine shafts and in gravel pits created by water cannons that blasted away loose hillsides.
Thousands of amateur gold seekers sift through the old mines and pits each year. One such recreational prospector last year took 4 pounds of gold alloyed with 40 pounds of mercury from an abandoned mine near the town of Grass Valley in the Sierra Nevada foothills east of Sacramento. The Environmental Protection Agency spent $1.2 million taking tons of mercury-laced dirt and water from that mine to assure no other amateur gold seekers would poison themselves.
The USGS reports that some abandoned mines contain so much mercury that beads of it can be scooped from their dirt floors.
But most amateur miners are not deterred by possible mercury poisoning. And health warnings like the Nevada County advisory urging anglers not to eat more than one fish a week caught in local waters are similarly disregarded, as river banks remain crowded.
“I’m not the least bit worried,” said Juan Gonsalves, a recreational gold miner who drives from Los Angeles to the Mother Lode region of Northern California three times a year to seek gold dust or nuggets in old mines. “I’ve been going into those mines for 10 years, and I’m fine. They can’t scare me off. I know there’s plenty of gold left in those mines, and I’m going to find my share.”