A new research report from the Center for Environmental Security at Arizona State University suggests that sewage sludge may provide a useful tool for assessing human exposure and bioaccumulation of potentially hazardous substances. Contrary to comments that GallonDaily has heard for years from municipal officials, the research shows that sewage treatment plants do not provide a pathway for removal of many potentially toxic substances. In fact many toxic substances are absorbed on to the sewage sludge which may then be spread on farm fields from which location the chemicals find their way into the environment, often in considerable quantity.

The most abundant chemicals of emerging concern found in analysis of a sample of US sewage sludge were brominated flame retardants, surfactants (nonylphenol and its ethoxylates); antimicrobials triclosan and triclocarban; and antibiotics azithromycin, ciprofloxacin, and ofloxacin. The researchers were surprised by the presence of some of these, for example BFRs should only be used on products which are not likely to be flushed down the drain, and by the persistence of others. This last finding suggests that products which are biodegradable in water under laboratory conditions may not behave in the same way when discharged into sewers or flowed in aqueous solution through sewage treatment plants.

The authors suggest that

• the present work explored the new approach of using biosolids as an analytical matrix to identify potentially harmful, mass-produced chemicals of human health concern.
• chemicals sequestered in biosolids may serve as an early warning system for determining potential bioaccumulative chemicals and chemical body burdens in population.
• screening of sewage sludge can serve to identify transformation products of man-made and natural compounds which likely are persistent and bioaccumulative but for which production and environmental loading data are unavailable.
• the eight compounds falling into the “most abundant” category have to be considered priority contaminant candidates from a public health perspective, deserving scrutiny with respect to their potential for exposure, bioaccumulation and potential adverse health effects in biota, including humans.
• an interesting correlation was found between chemicals that bioaccumulate in humans and those that persist during wastewater treatment and accumulate in sludge.
• further work is needed to validate and carefully define the limits of the chemical prioritization approach presented in the paper.

The paper has been published in the Nature Publishing Group open access peer-reviewed journal Scientific Reports and can be found at http://www.nature.com/srep/2014/140116/srep03731/full/srep03731.html