Polychlorinated biphenyls, or PCBs, are a group of synthetic organic chemicals made up of two linked benzene rings with chlorine atoms attached. They were widely used in electrical equipment, heat exchangers, and other industrial applications due to their chemical stability and insulating properties. However, their production was banned in many countries in the late 1970s due to environmental and health concerns. PCBs are persistent in the environment and can accumulate in the food chain, leading to potential health risks for humans and wildlife. Exposure to PCBs has been linked to various health issues, including cancer, immune system problems, and developmental effects in children. Cleanup and regulation efforts continue to address their impact on ecosystems.