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The toxicity of PCBs: Why are they banned internationally?
Polychlorinated biphenyls (PCBs) are an important class of organic chlorine compounds. These chemicals were once widely used in many fields such as the manufacture of carbonless copy paper, heating transfer fluids, and as dielectrics and coolants for electrical equipment. . PCBs were banned from production in the United States in 1978 as their potential harm to the environment and human health was discovered. In 2001, their production was banned globally by the Stockholm Convention. However, due to their persistence, PCBs remain widespread in the environment, posing a long-term threat to ecosystems and public health.
PCBs are believed to cause cancer in animals and may be carcinogens in humans, according to the U.S. Environmental Protection Agency (EPA).
Physical and chemical properties
PCBs is a light yellow viscous liquid that is hydrophobic and has extremely low solubility in water, but high solubility in most organic solvents and oils. Their high thermal conductivity and relatively stable chemical properties made them industrially popular. PCBs can be decomposed under high heat or catalytic conditions, but their refractory nature makes them persist in the environment.
Toxicity mechanisms and effects
Due to differences in structure and toxicity of PCBs, they can be divided into two major categories: coplanar and non-coplanar structures. Coplanar PCBs are similar to dioxins and can activate the aryl hydrocarbon receptor (AhR), thereby causing interference in intracellular signaling. Non-coplanar PCBs mainly have toxic effects on the nervous system and immune system.
Exposure to these toxic compounds has been shown to cause a range of health problems, including reproductive and developmental defects.
Transportation and transformation in the environment
PCBs can enter the environment through various routes, including waste disposal and use. Because they accumulate in water, they pose a particular risk to marine ecosystems. In addition, the intracellular bioaccumulation process also exacerbates ecotoxicity, especially in organisms at high trophic levels.
Effects on human health
The main route of human exposure to PCBs is through food, such as contaminated fish and dairy products. In addition, PCBs can also be exposed in work environments, such as e-waste recycling plants. Studies show that long-term exposure to PCBs can cause skin diseases, liver damage and developmental disorders.
It has been reported that long-term exposure to high concentrations of PCBs may cause birth defects, developmental delays and immune system problems.
Continuing pollution and future challenges
Although the production of PCBs has been banned, they still exist in older equipment and other products. With the development of science and technology and the improvement of environmental awareness, how to effectively remove existing PCB pollution and prevent the formation of new pollution will be a major challenge for environmental protection in the future. Some experts recommend safer alternatives to reduce reliance on PCBs and promote environmental recovery.
Ultimately, in the face of such persistent toxic substances, we should reflect on: While pursuing economic development, have we ignored the inseparability of environment and health?
