[MUSIC] Hello, everyone. In this video, we will look into 2 common types of VOCs. They are namely, formaldehyde and tetrachloroethylene. Formaldehyde is a confirmed carcinogen for humans. Formaldehyde is a colorless, flammable gas with a pungent smell. The chemical formula of formaldehyde is CH2O, belonging to aldehydes - the CHO group. In an indoor environment, formaldehydes are emitted from building materials and furnishings, like insulation materials, plywood, and textiles. Increasing temperature and humidity levels can increase formaldehyde emissions. Moreover, formaldehydes are released during fuel combustion processes. When you use gas stoves or kerosene heaters, formaldehydes are produced. Cigarette smoking also releases formaldehydes. Furthermore, formaldehydes are applied in cosmetics, personal care products, and even food, as preservatives. Formaldehydes are also used in cleaning products, such as dishwashing liquids and carpet cleaners. Plastics and resins also involve formaldehydes. Some pressed wood products contain formaldehyde resins. In addition, dyes and lacquers also release formaldehydes to the environment. While inhaling low levels of formaldehyde, most formaldehydes are degraded and leave your body. However, inhaling high levels of formaldehyde, some formaldehydes enter your bloodstream. High formaldehyde concentration leads to some health effects, such as irritation of respiratory tract and eyes. If the formaldehydes are absorbed through the skin, it may result in skin irritation. In the studies of animals, exposure to formaldehydes for a long period of time can cause nose cancer. Tetrachloroethylene is a kind of colorless and nonflammable liquid with a sharp, sweet smell. The chemical formula of tetrachloroethylene is C2Cl4. It is commonly used as a cleaning agent for dry cleaning. Once tetrachloroethylene is released to the air, it takes a long time to degrade. It takes several months for half of them to degrade. Tetrachloroethylene is also photo-oxidized in the air, with the presence of sunlight forming toxic fumes of phosgene. Dry cleaning machines are almost the largest indoor source of tetrachloroethylenes. Moreover, the clothes after dry cleaning also release tetrachloroethylenes. Tetrachloroethylene can also be detected in the water supply and ambient air. Under a low concentration condition, most tetrachloroethylenes in your body are removed through breathing. While some may stay for a few days before leaving your body, some health effects are caused by exposure to high concentration of tetrachloroethylene. For example, irritation of the skin, upper respiratory tract, and eyes. Tetrachloroethylene also cause neurological effects, such as dizziness, fatigue, headaches, sweating, and incoordination. Tetrachloroethylene can also damage your kidney and liver. Given a number of negative health effects, the state of California, USA, banned the use of tetrachloroethylene for dry cleaning completely by 2023. To conclude, in this video we introduced both formaldehyde and tetrachloroethylene and their sources. Finally, we discussed the health effects they cause.