Toxic chemicals released into the environment and their effect have been the subject of study in a new research at the Arizona State University.
Rolf Halden and colleagues have suggested that a number of high production volume (HPV) chemicals-that is, those used in the U.S. at rates exceeding 1 million pounds per year, are likely to become sequestered in post-treatment sludge and from there, enter the environment when these so-called biosolids are deposited on land.
"With each of these compounds, we are engaged in an experiment conducted on a nationwide scale. Odds are, some of these chemicals will turn out to be bad players and will pose problems for ecosystems, public health or both," said Halden.
Halden's group applied a new empirical model for estimating the fraction of mass loading of chemicals in raw sewage expected to endure in digested sludge.
Chemicals that become sequestered in digested sewage sludge are a potential cause for concern in part because the treated sludge is often subsequently applied to land, including land designated for agricultural use.
Halden's group screened some 207 HPV chemicals, using a model that predicted that two thirds of these compounds are likely to accumulate in digested sludge to greater than fifty percent of their initial mass loading in raw sewage. Eleven of these chemicals were flagged as compounds of special concern and deemed potential hazards to human and environmental health.
In order to better gauge which chemicals may go on to present human health and environmental risks following sequestration in sludge, the group conducted a computer or in silico analysis.
The method provides a streamlined and economically attractive means of isolating those chemicals deserving more in-depth field analysis. The group applied a new empirical model able to predict the fraction of total mass of a hydrophobic chemical likely to persist in biosolids after wastewater treatment.
Another advantage of the new model, applied by Halden Randhir Deo from the University of Guam, is simplicity. The model only requires two input values in order to estimate a chemical's environmental persistence. The chemicals to be screened were taken from the High Production Volume Information System database maintained by the EPA to monitor the environmental fate of chemicals produced in amounts exceeding 1 million pounds per year.
The empirical model was developed and tweaked to produce the best agreement between the mathematical framework based on a given chemical's physical properties and actual measurements derived from large sewage treatment plants.
The physical characteristic found to play the largest role in a chemical's persistence in sludge was its sorption potential-the tendency of molecules of the chemical to adhere to the surface of other molecules. In the case of the HPV chemicals under consideration, high sorption values among hydrophobic chemicals caused them to stick to other particles and be sequestered from the degradative processes used to treat wastewater.
The bulk of the chemicals included in the HPV study were used for industrial purposes and included antidegradants, antioxidants, metal chelators, intermediates, by-products, catalysts, flame retardants, phenylating agents, plasticizers, heat storage and transfer agents, lubricants, solvents, anticorrosive agents, and others.
The study also identified five mass-produced chemicals used as flavors and fragrances that were predicted to persist in sludge in fifty percent or greater amounts of their initial mass loading in raw sewage.
The findings were reported in the Journal of Environmental Monitoring.