Introduction

No known natural sources of PCBs exist. The United States banned production of these chemicals in 1977, when their ability to accumulate in the environment and to cause harmful effects became apparent [ATSDR 2000]. Today, the major source of exposure to ambient PCBs is environmental cycling of PCBs previously released into the environment.

Released Into the Environment

Between 1929 and 1977, more than 1.25 billion pounds of PCBs were produced in the United States [ATSDR 2000]. PCBs can be released into the general environment by or from

• Disposal of PCB-containing consumer products in municipal landfills
• Illegal or improper dumping of waste that contained PCBs, such as transformer fluids
• Leaks (fugitive emissions) from electrical transformers and capacitors containing PCBs
• Poorly maintained toxic waste sites

Once released into the environment, PCBs

• bioaccumulate and biomagnify as they move up the food chain,
• degrade relatively slowly, and
• are cycled and transported within the ecosystem [ATSDR 2000; Safe 2007].

PCBs have been identified in at least 500 of the 1,598 hazardous waste sites on the EPA's National Priorities List, and low levels of PCBs can be found throughout the world [ATSDR 2000].

Environmental Contamination

Once released into the environment, PCBs adsorb strongly to soil and sediment. As a result, these compounds tend to persist in the environment, with half-lives for most congeners ranging from months to years. PCBs leach from soil slowly, particularly the more highly chlorinated congeners, and translocate to plants via soil insignificantly.

Cycling of PCBs through the environment involves volatilization from land and water surfaces into the atmosphere, with subsequent removal from the atmosphere by wet or dry deposition, then revolatilization. In the general population, inhalation of these airborne PCBs is one route of exposure, in addition to the food source of exposure to PCBs.

Progress Check