This Technical Practice Update (TPU), one in a series covering issues surrounding microconstituents, provides information on the sources of these compounds and potential human and environmental exposure. As defined here, microconstituents are natural and manmade substances, including elements and inorganic and organic chemicals. These are detected within water and the environment and a prudent course of action is needed to fully determine the potential effects on human health and the environment. These compounds include, but are not limited to, endocrine-disrupting compounds (EDCs) and are found in environmental media such as air, surface water, and groundwater. These chemical compounds are ubiquitous in modern life and exposure results from their widespread use and the longevity of many chemicals. This paper describes the large number of naturally occurring and manmade compounds including household chemicals, personal care products and pharmaceuticals, flame retardants, additives to plastics and packaging materials, veterinary medicines, industrial chemicals, and pesticides. It identifies challenges and future directions for scientific study to better understand the effects of these compounds and ways to decrease these sources from entering the environment. Published by WEF. 2007. Electronic download. 24 pages.