Mercury and the San Francisco Bay

Caution sign found along the San Francisco Bay showing fish to eat and not to eat.
Caution sign found along the San Francisco Bay showing fish to eat and not to eat.

The San Francisco Bay has an extensive history of mercury contamination dating back to the Gold Rush era.  During the Gold Rush, miners extracted gold ores from the earth using mercury. These deserted gold mines were never properly cleaned up, causing current contamination in the major tributaries (American, Yuba, Bear, and Feather River) of the Sacramento Delta, which flows into the San Francisco Bay.

What is Mercury? 

Mercury (Hg) is an element that is considered a heavy metal. Mercury is the only metal that forms into a liquid at room temperature. It has a silver appearance, but can evaporate into a colorless and odorless vapor.  Although mercury occurs naturally it is toxic to humans and animals.

Today, sources of mercury are located in our household items including but not limited to thermometers and some batteries. Mercury also occurs from the burning of fossil fuel and refining natural gas.

How does Mercury affect wildlife and the San Francisco Bay?

Earth naturally contains small amounts of mercury, but when it is extracted and water resources are susceptible it becomes hazardous. Once mercury enters waterways, it transforms into toxic methylmercury. As it works its way up the food chain, methylmercury becomes increasingly concentrated in a process known as bioaccumulation. Bigger fish have more methylmercury, because they feed on more fish containing the harmful substance. This is why humans and wildlife whose diets consist of mostly fish are more likely to have adverse effects from mercury. Some of the ways mercury affects humans and wildlife are:

  • Birth defects that disrupt development of the brain and nervous system.
  • Impaired cognitive thinking and motor skills in humans.
  • Reduced reproductive success in wildlife (mainly fish and birds). Like humans, wildlife also experiences muscle weakness and loss of coordination. These symptoms reduce their chances of finding prey, a mate, and escape routes.

There are several ways you can reduce exposure to mercury and prevent accidental contamination of wildlife habitat.

  1. Avoid buying products with mercury and properly dispose of any mercury thermometers, batteries, fluorescent bulbs, and electronics by taking it to your local household hazardous waste facility.
  2. Educate yourself about the health of the San Francisco Bay to avoid contaminated water, and catch the right fish for your gender and age group.
  3. Educate yourself about the safest fish to eat. Use the Monterey Bay Aquarium Seafood Watch guide. You can even download the app!
  4. Think green! Take public transportation, walk, or bike to reduce production of natural gas and fossil fuels, and support mercury reduction campaigns.