Contaminants of Emerging Concern in the Water Cycle.

In the past decade, the scientific community and general public have become increasingly aware of the potential for the presence of unregulated, and generally unmonitored contaminants, found at low concentrations (sub-mg/L) in surface, ground and drinking water.   The most common pathway for the introduction of these chemicals is from an upstream direct discharge of wastewater effluent.  In the US, there are more than two dozen communities that draw their drinking water from streams that consist of more than 50 % wastewater during low flow conditions.  The US Geological Survey (USGS) and US Environmental Protection Agency (USEPA) have been working on a series of collaborative research projects to determine the complex mixtures of chemicals that are commonly present in wastewater effluent, the persistence of these chemicals in surface and ground waters, the removal of these chemicals during drinking water treatment, the formation of by-products during chlorination and the presence of these chemicals in finished drinking water.  Taken as a whole, these studies demonstrate that to understand the comprehensive environmental impact of contaminants of emerging concern, their persistence, removal efficiencies during waste and drinking water treatment, as well as the potential for by-product formation, must be known.