According to Predicting global killer whale population collapse from PCB pollution, the new study published on Science, due to the persistent toxic chemical pollution in the ocean, at least half of the orcas now on earth are destined to die. Although polychlorinated biphenyl, this venomous chemical has been banned around the world since 1900s, it is still leaking into the oceans and their widespread use in industry leads to global distribution. It is also persistent in natural environment that enables them stably accumulating in the marine food chain. Since killer whale is the top predator on the chain, the species is the most affected animal on Earth and to killer whales’ natural feature, they are among the largest marine predators and they are especially sensitive to PCB pollution. In the dead body of orcas, scientists found that the PCB concentration is 100 times the level of safety. For those living ones, PCB has a great effect on their reproductive and immune system. Orca’s fat-rich milk will transmit high doses of toxin to newborns. As monitoring this highly mobile species is a great challenge, people haven’t paid enough attention to it. The Stockholm Convention on Persistent Organic Pollutants, which entered into force in 2004, aims to address this problem, but its actual effect is far behind schedule. Also, with the development of global economy, the problems Orcas facing are more, including the loss of key  prey species such as tunas and sharks caused by overfishing and meanwhile  they are enduring increased underwater noise pollution. Based on research data, the orca population number in Japan, Brazil, the Northeast Pacific, the Strait of Gibraltar and the United Kingdom are totally collapsing, but the scientists mark, if we could take action to clean up oceans globally, although the process may last for years, the orcas may be fortunate to reappear in the open air.