Through the processes of atmospheric transport and deposition, many anthropogenic contaminants such as industrial organics, pesticides, and trace metals have become widely distributed around the globe. Due to the phenomenon of long-range atmospheric transport, even the most remote areas of the plant are not out of range of contaminants emitted from distant anthropogenic sources. Many of these airborne contaminants are toxic and persistent, can bioaccumulate, and may remain biologically harmful for long periods of time. Although airborne contaminants are considered primarily a human health problem, there is increasing concern that they may have deleterious ecological consequences. When sensitive terrestrial plants and other biota experience chronic exposure to low concentrations of airborne toxic chemicals, sublethal effects may occur, with subsequent impacts on ecosystem structure and function.