A halogenated compound is a combination of one or more chemical elements that includes a halogen; halogens are a group of elements that include fluorine, astatine, chlorine, bromine and iodine. Halogens comprise the seventh column of the periodic table of the elements.
Both synthetic and organic compounds that include a halogen are considered to be halogenated compounds; this includes compounds like carbon tetrachloride, vinyl chloride and methylene chloride. Some of these halogenated compounds, especially those that are considered halogenated volatile organic compounds, are very dangerous and can be highly a harmfully toxic, carcinogenic or mutagenic to humans and other animals. For example, there are several pesticides, including the notoriously dangerous chemical pesticide, DDT, that are halogenated compounds.
Although DDT has been used to control disease, including malaria and typhus, it has also been harmful to natural ecosystems. This halogenated compound, which includes the halogen chlorine, was sprayed liberally across the United States in the mid-1900s. In her famous environmentalist treatise "Silent Spring," Rachel Carson wrote about this harmful chemical's dangerous environmental impact, which included the ease with which it is absorbed into soils and the impact it had on animals such as birds. DDT causes eggshells to thin, jeopardizing bird embryos. This was a major contributing factor in the endangerment of the bald eagle.