Potable water suppliers and regulatory agencies are expressing concerns with new classes of environmental contaminants generated from human activities, generally referred to as “microconstituents.” These concerns have grown due to the increased ability to detect microconstituents at relatively low concentrations and quantify their adverse health impacts. Microconstituents include more than 100,000 compounds, such as:
- Pharmaceuticals (pain relievers, antibiotics, medications)
- Personal care products (soap, shampoo)
- Flame retardants (polyurethane foam on furniture, electronics, textiles)
- Perfluoro-chemicals (non-stick coatings)
Of particular concern is that a number of these are endocrine disrupting compounds, which can be carcinogenic, mutagenic, or cause previously unseen health effects.
MICROCONSTITUENT OCCURRENCE
Contaminants are often present in the sub-nanogram per liter concentration, which requires challenging and costly analytical techniques for identification. Often occurring in domestic wastewater effluent, microconstituents can accumulate in raw water supplies. These contaminants can pass in detectable quantities through conventional potable water treatment plants to consumers. In addition, an increased movement towards indirect potable reuse could create larger concentrations of microconstituents in raw water supplies. Through ongoing research, the United States Geological Survey has determined that most surface water bodies have some evidence of microconstituents.
REGULATIONS
Currently microconstituents are not regulated by national drinking water standards. However, media coverage about the contaminants has spurred an increase in environmental and public interest. The U.S. Environmental Protection Agency (EPA) has published a draft water quality criterion for one microconstituent—nonylphenol—and facilitated a voluntary phase-out for additional compounds.
It is expected that initial microconstituent regulations will be implemented on a state-by-state basis. California has recently established a public health goal for n-nitrosodimethylamine (NDMA), a microconstituent and known carcinogen. This goal will likely serve as an eventual NDMA regulation in California. Other states are also examining the effects of these compounds on human health.
TREATMENT
Currently the EPA is conducting treatability studies for microconstituents from a process efficiency and cost standpoint. Also, technologies—including granular activated carbon, reverse osmosis, and oxidant-enhanced ultraviolet light—are available to reduce and remove microconstituents in potable water. However, certain compounds are relatively difficult to remove or destroy due to technological or cost limitations, so multi-faceted treatment programs, including public drug take-back/disposal programs and industrial pretreatment, are alternative solutions. Above all, an integrated control and treatment approach will be required for the management and removal of microconstituents.
Donald M. Thompson, Ph.D., P.E., is a senior vice president and has 30 years of advanced water treatment process and design experience, with a focus on membrane technologies.