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Toxic mercury remnants of gold rush will seep into San Francisco area waterways for millennia


In the mid-1800s, gold mining released more than a cubic kilometer of mercury-laden sediments into Northern California’s Sierra Nevada foothills. The sediments fanned out and inundated rivers that flow into the San Francisco Bay. The mercury contamination resulted from the hydraulic mining processes of the era that used mercury to separate gold from gravel. An estimated 13000 tons of mercury was used during the 19th century gold rush in the Sierra Nevada and Klamath-Trinity Mountains. Researchers estimate that 90 percent of the mercury is still trapped within the sediments.

Sampling site uphill San Francisco Bay

"They didn't just pan for gold," says Michael Singer. "That's a romantic notion of gold mining. It was actually an industrial process whereby they sprayed giant high-pressure hoses, invented in 1852, at upland hillsides to wash the sediment downstream." (Credit: "Hydraulic mining at Rockerville, Dak.", Library of Congress via Wikimedia Commons)

Transport of contaminated sediments into the San Francisco Bay Delta has contaminated the food web and poses a huge risk to the lowland ecosystems and to the human population as well because a lot of people eat fish from this system. Within the aquatic environment, mercury may be transformed to methylmercury, a mercury species that accumulates in fish, amphibians and waterfowl. Numerous waterways in Northern California downstream of mining activities therefore post warnings about fish consumption.

The new study
Up to now, the processes by which Hg is delivered to lowlands and the patterns of its floodplain deposition were only poorly understood. To understand how flooding and erosion may trigger future releases of the poison, the research group led by Michael Bliss Singer measured mercury levels in sediments at 105 locations upstream of the bay. Levels of mercury in the sediment were up to hundreds of times higher than background levels.

“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,” says Michael Singer, associate researcher at University of California, Santa Barbara’s Earth Research Institute.

The team analyzed topographic maps, streamflow data and satellite images, and used computer modeling to show that mercury stored in immense Sierran human-made sediment deposits is carried by the Yuba River and other nearby streams to the Central Valley lowlands. The heavy metal tends to be loosened during major floods that occur about once a decade, most recently in 1986 and 1997.

Drawing on historical flood data to predict sediment flow, the team reports that the mining sediments will continue to release mercury into waterways over at least the next 10,000 years unless something is done to prevent mercury-laden sediment from eroding and ending up in the state's agricultural heartland. As climate change intensifies the area’s rainstorms, the researchers predict, the flood-driven discharges should become even more frequent.

"The problem is very serious indeed," said lead author Michael Singer of the University of St. Andrews in Scotland.

The analysis was undertaken at the University of St. Andrews in Scotland. The findings have been published in the journal Proceedings of the National Academy of Sciences.

While the source of contamination in California is mostly historic, mercury pollution related to gold mining is ongoing in other regions of the world. In 50 countries small‐scale miners recover gold by amalgamation process, using excessive quantities of mercury. Fifteen million artisanal gold miners apply this process and 100 million people might depend upon these activities.  Artisanal gold mining worldwide is responsible for one third of all mercury released into the environment – approximately 1000 tons/year.
Michael Sperling

The original study

Michael Bliss Singer, Rolf Aalto, L. Allan James, Nina E. Kilham, John L. Higson, and Subhajit Ghoshal, Enduring legacy of toxic fan via episodic redistribution of California gold mining debris, Proc. Nat. Acad. Sci., Published online October 28, 2013. doi: 10.1073/pnas.1302295110

Related studies

Patrick M. Donovan, Joel D. Blum, Donald Yee, Gretchen E. Gehrke, Michael B. Singer, An isotopic record of mercury in San Francisco Bay sediment, Chem. Geol., 349–350 (2013) 87–98. doi: 10.1016/j.chemgeo.2013.04.017

Gretchen E. Gehrke, Joel D. Blum, Mark Marvin-DiPasquale, Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes, Geochim. Cosmochim. Acta, 75 (2011) 691–705. doi:10.1016/j.gca.2010.11.012

Ben K. Greenfield, Andrew Jahn, Mercury in San Francisco Bay forage fish, Environmental Pollution 158 (2010) 2716- 2724. doi:10.1016/j.envpol.2010.04.010

Scott Lecce, Robert Pavlowsky, Gwenda Schlomer, Mercury contamination of active channel sediment and floodplain deposits from historic gold mining at Gold Hill, North Carolina, USA, Environ. Geol., 55 (2008) 113–121. doi: 10.1007/s00254-007-0970-9

Daniel A. Cristol, Rebecka L. Brasso, Anne M. Condon, Rachel E. Fovargue, Scott L. Friedman, Kelly K. Hallinger, Adrian P. Monroe, Ariel E. White, The Movement of Aquatic Mercury Through Terrestrial Food Webs, Science, 320 (2008) 335. doi: 10.1126/science.1154082

Charles N. Alpers, Michael P. Hunerlach, Jason T. May, and Roger L. Hothem, Mercury Contamination from Historical Gold Mining in California, U.S. Geological Survey, Fact Sheet 2005-3014 Version 1.1, Revised October 2005. http://pubs.usgs.gov/fs/2005/3014/fs2005_3014_v1.1.pdf

Aaron J. Slowey, James J. Rytuba, Gordon E. Brown, Speciation of Mercury and Mode of Transport from Placer Gold Mine Tailings, Environ. Sci. Technol., 39/6 (2005) 1547–1554. doi: 10.1021/es049113z

Ronald Eisler, Mercury Hazards from Gold Mining to Humans, Plants, and Animals, Rev. Environ. Contam. Toxicol., 181 (2004) 139-198. doi: 10.1007/0-387-21733-9_4

Michael P. Hunerlach, Charles N. Alpers, Mark Marvin-DiPasquale, Howard E. Taylor, and John F. De Wild, Geochemistry of Mercury and other Trace Elements in Fluvial Tailings Upstream of Daguerre Point Dam, Yuba, River, California, August 2001, Scientific Investigations Report 2004-5165. http://pubs.usgs.gov/sir/2004/5165/

Jason T. May, Roger L. Hothem, Charles N. Alpers and Matthew A. Law (2000), Mercury Bioaccumulation in Fish in a Region Affected by Historic Gold Mining: The South Yuba River, Deer Creek, and Bear River Watersheds, California, 1999, U.S. Geological Survey, Open-File Report: 00-367 (2000) http://ca.water.usgs.gov/archive/reports/ofr00367/ofr00367.pdf

Michelle I. Hornberger, Samuel N. Luoma, Alexander van Geen, Christopher Fuller, Roberto Anima, Historical trends of metals in the sediments of San Francisco Bay, California, Mar. Chem., 64 (1999) 39–55. doi: 10.1016/S0304-4203(98)80083-2

Jerry Miller, Robert Barr, David Grow, Paul Lechler, Dorothea Richardson, Karen Waltman, John Warwick, Effects of the 1997 Flood on the Transport and Storage of Sediment and Mercury within the Carson River Valley, WestCentral Nevada, J. Geol., 107/3 (1999) 313-327. doi: 10.1086/314353

Studies from other regions of the world

Samuel A. Beal, Brian P. Jackson, Meredith A. Kelly, Justin S. Stroup, Joshua D. Landis, Effects of Historical and Modern Mining on Mercury Deposition in Southeastern Peru, Environ. Sci. Technol., Article published online October 14, 2013. DOI: 10.1021/es402317x

Jennifer Baeuml, Stephan Bose-O’Reilly, Raffaella Matteucci Gothe, Beate Lettmeier, Gabriele Roider, Gustav Drasch, Uwe Siebert, Human Biomonitoring Data from Mercury Exposed Miners in Six Artisanal Small-Scale Gold Mining Areas in Asia and Africa, Minerals, 1 (2011) 122-143. doi: 10.3390/min1010122

Vincent K. Nartey, Raphael K. Klake, Ebenezer K. Hayford, Louis K. Doamekpor, Richard K. Appoh, Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas of the Birim North District of Ghana, J. Environ. Prot., 2 (2011) 1227-1239. doi: 10.4236/jep.2011.29141

Catherine Tomicic, David Vernez, Tounaba Belem, Michčle Berode, Human mercury exposure associated with small-scale gold mining in Burkina Faso, Int. Arch. Occup. Environ. Health, 84 (2011) 539–546. doi: 10.1007/s00420-011-0615-x

Víctor González-Carrasco, Patricio C. Velasquez-Lopez, Jesús Olivero-Verbel, Nerlis Pájaro-Castro, Air Mercury Contamination in the Gold Mining Town of Portovelo, Ecuador, Bull. Environ. Contam. Toxicol., 87 (2011)250–253. doi: 10.1007/s00128-011-0345-5

Paul Cordy, Marcello M. Veiga, Ibrahim Salih, Sari Al-Saadi, Stephanie Console, Oseas Garcia, Luis Alberto Mesa, Patricio C. Velásquez-López, Monika Roeser, Mercury contamination from artisanal gold mining in Antioquia, Colombia: the world’s highest per capita mercury pollution, Sci. Total Environ.,  410–411 (2011) 154–160. doi: 10.1016/j.scitotenv.2011.09.006

J.A. Acosta, S. Martine-Martinez, A. Faz, R. Millán, M.A. Munoz, T. Terán, R. Vera, Characterization of the potential Mercury contamination in the Aapolobamba Gold Mining area, Bolivia, Span. J. Soil Sci.,  1/1 (2011) 86-99. DOI: 10.3232/SJSS.2011.V1.n1.06

E. E. Kwaansa-Ansah, N. Basu, J.O. Nriagu, Environmental and Occupational Exposures to Mercury Among Indigenous People in Dunkwa-On-Offin, a Small Scale Gold Mining Area in the South-West of Ghana, Bull. Environ. Contam. Toxicol., 85 (2010) 476–480. doi: 10.1007/s00128-010-0141-7

J.J. Berzas Nevado, R.C. Rodríguez Martín-Doimeadios, F.J. Guzmán Bernardo, M. Jiménez Moreno, A.M. Herculano, J.L.M. do Nascimento, M.E. Crespo-López, Mercury in the Tapajós River basin, Brazilian Amazon: A review, Environ. Int., 36 (2010) 593–608. doi: 10.1016/j.envint.2010.03.011

Sarah Strode, Lyatt Jaegle, Noelle E. Selin, Impact of mercury emissions from historic gold and silver mining: Global modeling, Atmospheric Environment 43 (2009) 2012–2017. doi: 10.1016/j.atmosenv.2009.01.006

Kevin H. Telmer, Marcello Veiga,  World Emissions of Mercury from Artisanal and Small Scale Gold Mining, in: N. Pirrone and R. Mason (eds.), Mercury Fate and Transport in the Global Atmosphere, Springer, New York, 2009, pp.  131-172. doi: 10.1007/978-0-387-93958-2_6

Jose Marrugo-Negrete, Luis Norberto Benitez, Jesús Olivero-Verbel, Distribution of Mercury in Several Environmental Compartments in an Aquatic Ecosystem Impacted by Gold Mining in Northern Colombia, Arch. Environ. Contam. Toxicol., 55 (2008) 305–316. doi: 10.1007/s00244-007-9129-7

Stephan Bose-O’Reilly, Beate Lettmeier, Raffaella Matteucci Gothe, Christian Beinhoff, Uwe Siebert, Gustav Drasch, Mercury as a serious health hazard for children in gold mining areas, Environmental Research 107 (2008) 89–97. doi: 10.1016/j.envres.2008.01.009

Gavin Hilson, Rickford Vieira, Challenges with minimising mercury pollution in the small-scale gold mining sector: Experiences from the Guianas, Int. J. Environ. Health Res., 17/6 (2007) 429-441. doi: 10.1080/09603120701633396

Cláudia Carvalhinho Windmöller, Regis Costa Santos, Maycon Athayde, Helena Eugęnia Leonhardt Palmieri, Distribution and speciation of mercury in sediments from gold mining sites in iron quadrangle (Minas Gerais), Quim. Nova, 30/5 (2007) 1088-1094. doi: 10.1590/S0100-40422007000500007

J.R. Ikinguraa, H. Akagib, J. Mujumbaa, C. Messoa, Environmental assessment of mercury dispersion, transformation and bioavailability in the Lake Victoria Goldfields, Tanzania, J. Environ. Manag., 81 (2006) 167–173. doi: 10.1016/j.jenvman.2005.09.026

Nelia Cortes-Maramba, Jose Paciano Reyes, Ana Trinidad Francisco-Rivera, Hirokatsu Akagi, Rose Sunio, Lynn Crisanta Panganiban, Health and environmental assessment of mercury exposure in a gold mining community in Western Mindanao, Philippines, J. Environ. Manag., (2006) 126–134. doi: 10.1016/j.jenvman.2006.01.019

Antonio Garcia-Sanchez, Felicia Contreras, Meliton Adams, Fernando Santos, Airborne total gaseous mercury and exposure in a Venezuelan mining area, Int. J. Environ. Health Res., 16/5 (2006) 361-373. doi: 10.1080/09603120600869315

Sean A. Shaw, Tom A. Al, Kerry T.B. MacQuarrie, Mercury mobility in unsaturated gold mine tailings, Murray Brook mine, New Brunswick, Canada, Appl. Geochem., 21 (2006) 1986–1998. doi: 10.1016/j.apgeochem.2006.08.009

Xinbin Feng, Qianqin Dai, Guangle Qiu, Guanghui Li, Lei He, Dingyong Wang, Gold mining related mercury contamination in Tongguan, Shaanxi Province, PR China, Applied Geochemistry 21 (2006) 1955–1968. doi: 10.1016/j.apgeochem.2006.08.014

Zuleica C. Castilhos, Saulo Rodrigues-Filho, Ana Paula C. Rodrigues, Roberto C. Villas-Bôas, Shefa Siegel, Marcello M. Veiga, Christian Beinhoff, Mercury contamination in fish from gold mining areas in Indonesia and human health risk assessment, Sci. Total Environ., 368 (2006) 320–325.  doi: 10.1016/j.scitotenv.2006.01.039

A.K. Donkor, V.K. Nartey, J.C. Bonzongo, D.K. Adotey, Artisanal Mining of Gold with Mercury in Ghana, West Afr. J. Appl. Ecol., 9 (2006) 1-8. http://www.ajol.info/index.php/wajae/article/download/45666/29146

D. Limbong, J. Kumampung, D. Ayhuan, T. Arai, N. Miyazaki, Mercury Pollution Related to Artisanal Gold Mining in North Sulawesi Island, Indonesia, Bull. Environ. Contam. Toxicol., 75 (2005) 989–996. doi: 10.1007/s00128-005-0847-0

H. Taylor, J.D. Appleton, R. Lister, B. Smith, D. Chitamweb, Mkumbo, J.F. Machiwa, A.L. Tesha, C. Beinhoff, Environmental assessment of mercury contamination from the Rwamagasa artisanal gold mining centre, Geita District, Tanzania, Sci. Total Environ., 343/1–3 (2005) 111–133. doi: 10.1016/j.scitotenv.2004.09.042

Oscar Betancourt, Alberto Narváez, Marc Roulet, Small-scale Gold Mining in the Puyango River Basin, Southern Ecuador: A Study of Environmental Impacts and Human Exposures, EcoHealth, 2 (2005) 323–332. doi: 10.1007/s10393-005-8462-4

Pablo Higueras, Roberto Oyarzun, Javier Lillo, Jorge Oyarzún, Hugo Maturana, Atmospheric mercury data for the Coquimbo region, Chile: influence of mineral deposits and metal recovery practices, Atmos. Environ., 39 (2005) 7587–7596. doi: 10.1016/j.atmosenv.2005.06.059

Lazaro J. Oliveira, Lars D. Hylander, Edinaldo de Castro e Silva, Mercury Behavior in a Tropical Environment: The Case of Small-Scale Gold Mining in Poconé, Brazil, Environ. Pract., 6 (2004) 121-134. doi: 10.1017/S1466046604000237

A. J. Gunson, Marcello M. Veiga, Mercury and Artisanal Mining in China, Environ. Pract., 6 (2004) 109-120. doi: 10.1017/S1466046604000225 

R.C Churchill, C.E Meathrel, P.J Suter, A retrospective assessment of gold mining in the Reedy Creek sub-catchment, northeast Victoria, Australia: residual mercury contamination 100 years later, Environ.  Pollution, 132/2 (2004) 355–363. doi: 10.1016/j.envpol.2004.03.001

S. Allen Counter, Leo H. Buchanan, Fernando Ortega, Göran Laurell, Elevated blood mercury and neuro-otological observations in children of the Ecuadorian gold mine, J. Toxicol. Environ. Health A, 65 (2002) 149 – 163. doi: 10.1080/152873902753396785

Jason S. Ogola, Winnie V. Mitullah, Monica A. Omulo, Impact of gold mining on the environment and human health: a case study in the Migori gold belt, Kenya, Environ. Geochem. Health, 24 (2002) 141–158. doi: 10.1023/A:1014207832471

Jan H. Mol, Joyce S. Ramlal, Carlos Lietar, Marc Verloo, Mercury Contamination in Freshwater, Estuarine, and Marine Fishes in Relation to Small-Scale Gold Mining in Suriname, South America, Environ. Res. A,  86 (2001)  183-197. doi: 10.1006/enrs.2001.4256

Peter van Straaten, Mercury contamination associated with small-scale gold mining in Tanzania and Zimbabwe, Sci. Total Environ., 259 (2000) 105-113. doi: 10.1016/S0048-9697(00)00553-2

J.D. Appleton, T.M. Williams, N. Breward, A. Apostol, J. Miguel, C. Miranda, Mercury contamination associated with artisanal gold mining on the island of Mindanao, the Philippines, Sci. Total Environ., 228 (1999) 95-109. doi: 10.1016/S0048-9697(99)00016-9

Related information (mercury pollution by gold mining)

BRI/IPEN: Global Mercury Hotspots, BRI/IPEN, January 2013
Blacksmith Institute: Mercury pollution
WorstPolluted.org: 2012 - Artisanal gold mining
WorstPolluted.org: 2011 - Artisanal gold mining
WorstPolluted.org: 2010 - Top six toxic threaths: Mercury
UNEP: UNEP: Reducing Mercury in Artisanal and Small-Scale Gold Mining (ASGM)

Related EVISA Resources

Link database: Mercury exposure through the diet
Link database: Environmental cycling of mercury
Link database: Environmental mercury pollution

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