Streams poisoned by mercury: A legacy of gold mining

Mercury is an efficient magnet for gold. The early California miners routinely lined their sluices with the silvery globules to amalgamate the precious metal. Up to 10 percent of an estimated 65,000 tons of mercury extracted from the Coast Range between 1850 and 1920 was lost to streams in the Coast and Sierra mountains. Modern gold miners working suction dredges still find pockets of the Argonauts' quicksilver lodged deep in the "guts" of rivers.

Poisoned streams

Fish advisories due to mercury contamination
1 San Francisco Bay/Delta system
Species
Bass: Striped - larger than 27 inches
Bass: Striped - larger than 35 inches
Shark: Larger than 24 inches
All fish except anchovy, herring, salmon, smelt
Advisory
No consumption: Populations at risk (1)
No consumption: All consumers
No consumption: Populations at risk
Restricted consumption (2): All consumers
2 Santa Clara County (3), Alamitos Creek, Alamden Reservoir, Calero Reservoir, Guadalupe Creek, Guadalupe River, Guadalupe Reservoir
Species
All fish
Advisory
No consumption: All consumers
3 Napa County: Lake Berryessa
Species
All fish
Bass: Largemouth, smallmouth
Catfish: Channel, white
Trout: Rainbow
Advisory
No consumption: Populations at risk
Restricted consumption: All consumers
4 Solano County: Lake Herman
Species
Bass: Largemouth
Advisory
Restricted consumption: All consumers
5 Lake County: Clear Lake
Species
All fish
Bass: Largemouth
Blackfish: Sacramento
Catfish: Brown, bullhead, channel, white
Crappie: Black
Hitch
Advisory
No consumption: Populations at risk
Restricted consumption: All consumers
6 San Luis Obispo County: Lake Nacimiento
Species
Bass: Largemouth
Bass: Largemouth
Advisory
No consumption: Populations at risk Restricted consumption: All consumers
(1) Populations at risk: Children, pregnant women and women of child-bearing age.
(2) Restricted consumption: Quantity and frequency should be restricted by indicated population to no more than one meal per month.
(3) All Santa Clara County locations include associated percolation ponds.



Mercury in the ecosystem
Mercury in aquatic environments takes on a vicious life of its own. Bacteria converts the metal into the more toxic methyl-mercury, which can be taken up by insects, the fish that eat the invertebrates and humans who eat the fish. Mercury's concentration increases at each level up the food chain in a process known as biological magnification.
Mercury contamination Health effects of mercury

* Deteriorates the nervous system

* Impairs hearing, speech, vision and gait

* Causes involuntary muscle movements

* Corrodes skin and mucous membranes

* Causes chewing and swallowing to become difficult



Recovering mercury
The mercury that stuck to the gold was removed and recovered by heating the amalgam. The quicksilver changed from a solid to a gas in the furnace. Upon cooling, the mecury vapor coverted to liquid for reuse.
Mercury recovery 1. The amalgam of gold and mercury was placed in the furnace and heated.

2. Mercury turns to gas at a lower temperature than gold, so the vapor would be composed of mercury.

3. The mercury vapor was then cooled further down the pipe into liquid mercury.



Sources: Tom Suchanek, a research ecologist at the University of California, Davis; Information Center for the Environment, UC Davis; California Department of Conservation Division of Mines and Geology; Teale Data Center; CALFED Program

Bee graphic: Mitchell Brooks