Any environmental contaminant that is resistant to environmental degradation through photolytic, biological or chemical processes. Such substances can have significant impact on health and the environment, as they persist in the environment, bioaccumulate in animal tissue and so biomagnify in food chains.
A xenobiotic (Greek, xenos "foreign"; bios "life") is a compound that is foreign to a living organism. Principal xenobiotics include: drugs, carcinogens and various compounds that have been introduced into the environment by artificial means.