Toxic Legacy California Gold Rush
October 29, 2013

The Toxic Legacy Of California’s Gold Rush

[ Watch the Video: The Enduring Contaminant Legacy Of The California Gold Rush ]

Michael Harper for - Your Universe Online

The Gold Rush of the 1800s may seem a distant historical phenomenon at this point, but its effects are still being felt in California. According to a new study, the mercury used to extract gold from the foothills is now slowly trickling towards California’s Central Valley where fisheries, rice fields and wineries abound.

The miners helped create the area known today as the Yuba Fan where terraces and sluices were used to drain waste water into the Yuba River. Though the mercurial remains of gold mining have been relatively dormant all these years, the researchers say the loss of the local forests has increased the release of these pollutants by 400 percent.

A team of researchers from Scotland’s University of St. Andrews, the University of Exeter in England, Sonoma State University in California and the University of South Carolina used historical data and NASA satellite imagery to conduct their study which is now published in the Proceedings of the National Academy of Sciences.

"This new study addresses a gap in the general theory of the evolution of toxic sediment emplaced by industrial mining, which enables anticipation, prediction and management of contamination to food webs,” explains Michael Singer, associate researcher at UC Santa Barbara's Earth Research Institute.

According to Singer, mining for gold wasn’t a romantic venture at all; miners used a method called hydraulic mining which involved blasting the sides of foothills with high powered water hoses called monitors. These monitors were used to blast gold-bearing mud through sluices where it could later be removed. To make the gold easier to retrieve, miners mixed the water with mercury which caused the gold to sink to the bottom of the sluices. This practice dramatically affected the landscape of the area and even caused mudslides.

"People know there was gold mining in the Sierra Nevada and they know that there was mercury mining in the Coast Ranges, but they're not really sure of the modern-day impact, especially when the contaminant sources are not directly by the bay," said Singer. "People want to know what is causing contamination of the food webs of the Central Valley."

Mercury from this practice has already been found in San Francisco’s food supply, but according to Singer’s research, the mercury levels in the Yuba Fan are hundreds of times greater.

The team surveyed 105 sites along the Yuba River and two other rivers nearby and found what they considered relatively fresh mercury deposits. According to their research, this means the dangerous element is still stuck in the ground and capable of fouling food grown in the area. Mercury has already been shown to have washed from the foothills into the Yuba Fan after major floods in 1986, 1997 and 2006, but Singer and team now say there’s enough mercury in the area to continue contaminating food sources for the next 10,000 years.

"There is a lot of sediment left in the system that is highly contaminated and readily available to be remobilized and sent downstream just because it's sitting in unconsolidated sediments along the margins of a river that can become very big during a storm," Singer explained. "That susceptibility, coupled with projections for climate change in the region indicating more massive storms in the future, means that there is a dangerous synergy."