Sources of PCBs and Mercury Contamination

PCBs and mercury have different histories in California, but they both pose a public health risk to people eating fish from the San Francisco Bay today.  Also known as “legacy pollutants,” these substances were once commonly used in industrial and electrical applications, building materials, and household items.


Old power supply transformer containing PCBs (Photo by Sturmovik, Wikipedia)

PCBs are a group of man-made chemical compounds that were once used in many industrial, construction and electrical applications.  They were widely used by many industries because of their low electrical conductivity, high boiling point, chemical stability and flame-retardant properties.  The largest use of PCBs was in electrical equipment, including transformers and capacitors, but they were also widely used in a variety of other applications, including hydraulic fluids, dust control, flame retardants, lubricants, paints, sealants, wood preservatives, inks, dyes and plasticizers.  PCBs have also been found in a variety of non-liquid materials, including construction materials such as insulation, roofing and siding materials.

PCBs were made in the U.S. for 50 years until the manufacturing of PCBs was banned in 1979.  Their import, export and distribution in commerce were also banned, and PCBs uses were restricted to totally enclosed applications.  The U.S. EPA has authorized other minor uses, but the unavailability of PCBs and health concerns ended their use in new applications.  Demolition of older buildings are potential sites of ongoing concern.


Compact Fluorescent Lightbulbs have mercury filaments
Cinnabar, a natural source of mercury (Photo by James St. John, Wikipedia)

Mercury exists naturally in the Earth’s rocky crust as a stable element, but two things have led to harmful amounts of mercury in the Bay:

  •  Legacy and ongoing human activity has concentrated and released unnaturally large amounts of it into the environment (historic mercury, gold & silver mining in the 1800s and artisanal mining today, fossil fuel combustion, concrete production, consumer goods).
  •  Newly available mercury – from human activity – deposits from air, washes or seeps into local waterways, and is then turned into its toxic form (methylmercury) by bacteria that live in wet soils and aquatic environments. Methylmercury is a neurotoxin.
How toxic mercury enters and accumulates up the aquatic food chain (adapted by E. Lennon, original image by B. Higman, Ground Truth Trekking)

When in-use, mercury is safely contained in batteries, fluorescent lightbulb filaments and other consumer goods.  However, people must be sure not to dispose of these products in the trash. 

If contaminated waste is disposed of in the trash, it will go to a landfill, where the mercury either gets into groundwater, or is incinerated, goes into the air and then eventually gets into water.  Instead, bring these products to local household hazardous waste programs for disposal.