Which property is associated with Polychlorinated Biphenyls (PCBs)?

Polychlorinated Biphenyls (PCBs) are synthetic organic chemicals that were widely used in industrial applications, primarily due to their properties as electrical insulators and their stability. The correct association is that they are known to cause carcinogenic effects. Extensive research has demonstrated that exposure to PCBs can lead to serious health issues, including cancer. They are classified as probable human carcinogens by various health organizations due to their ability to bioaccumulate in the environment and in human tissues, leading to long-term health risks.

In contrast, the other options do not accurately reflect the characteristics or uses of PCBs. They are not natural biological compounds; rather, they are anthropogenic chemicals. Additionally, there is no evidence to support that PCBs are beneficial for plant growth, as they can actually have toxic effects on various forms of life. Lastly, PCBs are not used exclusively for agricultural purposes; their applications largely relate to electrical equipment and industrial processes, making "exclusively for agricultural purposes" an inaccurate statement regarding their use.