Polychlorinated biphenyls (PCBs), also known as isopropylated tris(4-chlorophenyl) methane, are a class of man-made synthetic organic compounds, which are fluorinated compounds produced by replacing the hydrogen atoms on the biphenyl benzene ring with chlorine. The widespread application of polychlorinated biphenyls in industrial production has led to international air pollution issues.

PCBs are man-made organic compounds used in industrial production as heat carriers, transformer oil, and lubricants, among others. The waste discharged from factories using PCBs is a key source of PCB environmental pollution. For example, only 20% to 30% of PCBs produced in the UK and Japan each year are consumed in use, with the remaining 70% to 80% discharged into the natural environment.

After PCBs pollute the air, water, and soil, they accumulate in plants according to the food chain. For example, wheat and wheat grass in a certain province in the UK contain PCBs at a concentration of 0.3ppm, and the PCB content in milk reaches 28ppm.

In addition to strictly prohibiting the production and application of PCBs in our country, scientific research has been conducted on the reasonable solutions for disposing of waste and finding non-hazardous substitutes for PCBs. Many countries have set allowable intake levels for PCBs. Evaluation indicates that daily intake of PCBs ranging from 5 to 20mg (based on a weight of 1 kilogram) is considered safe.