Final answer:
Older transformers may contain PCBs (polychlorinated biphenyls), which are cancer-causing agents known as carcinogens. PCBs were used in coolant liquids and can biomagnify, leading to increased health risks, particularly the risk of cancer.
Step-by-step explanation:
The cancer-causing agent that older transformers may contain is PCBs (polychlorinated biphenyls). PCBs were once widely used in coolant liquids for electrical equipment such as transformers, until their use was banned in 1979 due to their health hazards. These substances are known as carcinogens, which means they can cause cancer. PCBs, along with heavy metals such as mercury, lead, and cadmium, are known to biomagnify, which means they become more concentrated in the bodies of organisms higher up the food chain. Exposure to high levels of PCBs has been linked to several types of cancer, making it a serious concern for human health.