Which of the following is a known source of PCB contamination in the environment?

Polychlorinated biphenyls (PCBs) are industrial chemicals that were widely used in various applications before their environmental and health impacts were fully understood. One of the primary sources of PCB contamination in the environment is electrical equipment. This includes transformers, capacitors, and other devices that utilized PCBs for their insulating properties. The widespread use of PCBs in electrical equipment before their ban has led to significant environmental contamination, as these substances can leach into soil and waterways and persist in the environment for long periods.

While other options, such as household cleaning products, pesticides, and food packaging materials, may contain various chemicals or materials that could be harmful, they are not recognized as sources of PCB contamination. Cleaners and pesticides typically do not involve PCBs, and although some historical food packaging may have been contaminated with PCBs, they are not a direct source like electrical equipment. Thus, the association of PCBs with electrical equipment is clear and well-documented, making it the correct answer regarding sources of PCB contamination.