Polychlorinated biphenyls are a group of 209 different chemicals which share a common structure but vary in the number of attached chlorine atoms. An estimated 1.3 million pounds of different types of PCBs were dumped into the Hudson River by General Electric from 1946 until 1977, when they were banned. The international treaty on Persistent Organic Pollutants, drafted by 122 nations in Johannesburg in December 2000, targeted PCBs as one of the 'dirty dozen' chemicals to be phased out worldwide. PCBs are a probable human carcinogen. The International Agency for Research on Cancer and the Environmental Protection Agency classify PCBs as a probable human carcinogen. The National Toxicology Program has concluded that PCBs are reasonably likely to cause cancer in humans. The National Institute for Occupational Safety and Health has determined that PCBs are a potential occupational carcinogen. Studies of PCBs in humans have found increased rates of melanomas, liver cancer, gall bladder cancer, biliary tract cancer, gastrointestinal tract cancer, and brain cancer, and may be linked to breast cancer. PCBs are known to cause a variety of types of cancer in rats, mice, and other study animals. PCBs disrupt hormone function. PCBs with only a few chlorine atoms can mimic the body's natural hormones, especially estrogen. Women who consumed PCB-contaminated fish from Lake Ontario were found to have shortened menstrual cycles. PCBs are also thought to play a role in reduced sperm counts, altered sex organs, premature puberty, and changed sex ratios of children. More highly-chlorinated PCBs (with more chlorine atoms) act like dioxins in altering the metabolism of sex steroids in the body, changing the normal levels of estrogens and testosterone. PCBs tend to change in the body and in the environment from more highly-chlorinated to lower-chlorinated forms, increasing their estrogenic effects. PCBs accumulate in the body and in the ecosystem. Once PCBs enter a person's (or animal's) body, they tend to be absorbed into fat tissue and remain there. Unlike water-soluble chemicals, they are not excreted, so the body accumulates PCBs over years. This means that PCBs also accumulate via the food chain: a small fish may absorb PCBs in water or by eating plankton, and these PCBs are stored in its body fat. When a larger fish eats the small fish, it also eats and absorbs all the PCBs that have built up in the small fish. In this way, larger fish and animals can build up a highly concentrated store of PCBs. Some types of PCBs may degrade into nontoxic form while they are stored in the body, but this process can take many years. In the same way, PCBs accumulate in women and pass on to their infants through breast milk. This accumulation means that nursing infants may ingest PCB levels much higher than the levels in fish and other foods consumed by their mothers. PCBs have been found all over the world, including significant amounts in the Arctic and Antarctic, far from any sources. In fact, several studies have found very high levels of PCBs in the blood and breast milk of Inuit women. It is thought that PCBs spread through the air, after evaporating from contaminated water and sediments, as well as through the water. About Yihao Established in 2010, Yihao Circuit Technology Ltd. specializes in PCB board production and high-speed SMT mounting and soldering. Yihao has cooperated with nearly 1000 customers from more than 20 countries. We do business all over the world. In addition, we have established an overseas market department and customer service centers in the EU. If you are looking for a reliable merchandise of PCBs, please contact us now!
