02/25/14

Duke University Research Implicates Biosolids - Without Even Testing Them

Duke University researchers are hoping to help improve the screening of chemicals for their potential impacts on soils and the environment.  They have developed a quick and inexpensive bioassay system that uses inhibition of denitrification activity in soil to detect impacts from chemicals such as the anti-microbial triclosan (TCS, commonly used in soaps).  They reported their research in a January paper in Environmental Science & Technology.

The research has received media attention: reported by Phys Org News, story in e! Science News and in North Carolina's Public Radio report WUNC 91.5.

As Greg Kester of the CASA biosolids program has pointed out, the particular research bioassay was not applied to biosolids.  Rather, the researchers used “a model denitrifier” (bacterial cultures) that were spiked with fresh samples of the chemicals being tested.  No biosolids or soils were used.  This kind of test has been shown in past research to not be representative of actual impacts from trace contaminants in biosolids.

In fact, Dr. Thomas Young of the University of California at Davis has tested the impacts of biosolids containing typical levels of anti-microbials.  As Kester reminds us, Dr. Young’s research found “that the increased N added with biosolids stimulates nitrogen cycling sufficiently to offset any detrimental impacts on the N cycling caused by TCS at realistic application concentrations.”   Biosolids contain traces of TCS and other antimicrobials, but, because the chemicals become transformed and bound as they go through the wastewater and solids treatment processes, they are not as available as fresh chemicals added to soil, and their impacts are negligible.  Meanwhile, the stimulating effects of the nutrients and organic matter in biosolids demonstrably boost soil microbial activity.  Dr. Young’s research was part of a workshop that NEBRA helped produce in May 2011 as reported in this summary.

The Duke research did not, in fact, do anything in “Determining the Ecological Impacts of Organic Contaminants in Biosolids…” as the paper’s title claims.  It did determine modeled ecological impacts of a few organic contaminants that are often found in biosolids, but the contaminants tested were not “in biosolids” when they were tested.  However, the research is useful in focusing additional attention on something that biosolids managers have an interest in: ensuring that chemicals used in society are tested thoroughly for all impacts, including through biosolids land application systems.  It benefits us all if biosolids can be safely and sustainably recycled to soils, because biosolids are naturally a reflection of what we use in daily life.