In silico screening for unmonitored, potentially problematic high production volume (HPV) chemicals prone to sequestration in biosolids† Randhir P. Deo and Rolf U. Halden * Received 25th January 2010, Accepted 27th July 2010 DOI: 10.1039/c001559h Thousands of high production volume (HPV) chemicals are used in the US at rates exceeding 450 000 kg (1 million pounds) per year, yet little is known about their fates during wastewater treatment and upon release into the environment. We utilized a recently introduced empirical model to predict the fraction of the mass loading (in raw sewage) that is expected to persist in digested sludge following conventional municipal treatment of chemical-laden sewage. The model requires only two readily available input parameters, a compound’s log K OW value and a dimensionless curve fitting parameter (p fit ). Following refinement of the fitting parameter and cross-validation of the model using the Jackknife method, we predicted the mass fractions of 207 hydrophobic HPV chemicals (log K OW of $4.0) that are expected to accumulate in digested municipal sludge during conventional wastewater treatment. Using this screening approach in conjunction with information from toxicity databases, we identified 11 HPV chemicals that are of potential concern due to (i) their propensity to accumulate and persist in sludge (>50% of mass loading), (ii) unfavorable ecotoxicity threshold values, and (iii) structural characteristics suggestive of environmental persistence following release of these HPV chemicals on land during biosolids recycling. The in silico screening approach taken in this study highlights existing environmental monitoring needs and may guide risk management strategies for biosolids disposal. Introduction Several thousands of organic chemicals are produced or used in the US in quantities exceeding 450 000 kg or one million pounds per year. These so-called high production volume (HPV) chem- icals are used in residential, institutional, and commercial/ industrial settings and are discharged in whole or in part into municipal sewage. Their fate in wastewater treatment plants (WWTPs) is mostly unknown. 1,2 Of particular concern are the hydrophobic organic chemicals (HOCs) with high sorption potential, i.e., those having a loga- rithmic n-octanol–water partitioning coefficient (log K OW ) of >4.0. 3 Hydrophobic chemicals are known to preferentially sorb to particulate matter and become part of the primary and secondary sludge produced during conventional wastewater treatment. Sequestration of chemicals in sewage sludge limits their availability to aerobic biodegradation in the activated sludge treatment step and during anaerobic digestion. 4–6 Hydrophobic compounds in raw sewage entering WWTPs have the potential to become enriched in digested sewage sludge (biosolids) to concentrations of several orders of magnitude higher than those found in raw sewage. 7 For HPV chemicals, this enrichment process can result in the occurrence of pollutants in digested sludge at parts per million (ppm) concentrations. 8 Disposal of digested municipal sludge on land as soil conditioner or fertilizer 2 can provide a mechanism by which problematic wastewater constituents are reentering the environment, thereby providing a potential human and ecological health hazard. Similar to the REACH regulations in Europe, 9 the US Envi- ronmental Protection Agency (EPA) is responsible for protecting the human health and the environment through earlier identifi- cation of potentially toxic chemical substances. However, despite ongoing monitoring programs for biosolids, currently there are The Biodesign Institute at Arizona State University, Center for Environmental Biotechnology, 1001 S. McAllister Avenue, P.O. Box 875701, Tempe, AZ, 85287, USA. E-mail: halden@asu.edu; Fax: +1 480 727 0889; Tel: +1 480 727 0893 † Electronic supplementary information (ESI) available: Figures S1–S2; Tables S1–S2. See DOI: 10.1039/c001559h Environmental impact Over 4000 chemicals are used in the US at rates exceeding 450 000 kg per year. The majority of these have never been tested for ecotoxicity and human health risks in greater detail. Testing and monitoring all mass-produced chemicals are cost-prohibitive and impractical. In the present work, an empirical model was applied to predict which chemicals contained in raw sewage may persist during wastewater treatment and become sequestered in digested sewage sludge destined for application on land. The presented model identified a small subset of compounds that exhibit unwanted qualities such as pronounced persistence to biodegradation and significant toxicity to environmental receptor organisms. Chemicals identified in this modeling exercise deserve further attention by environmental scientists concerning risks posed to humans and the environment. 1840 | J. Environ. Monit., 2010, 12, 1840–1845 This journal is ª The Royal Society of Chemistry 2010 PAPER www.rsc.org/jem | Journal of Environmental Monitoring Downloaded by google on 19 March 2011 Published on 19 August 2010 on http://pubs.rsc.org | doi:10.1039/C001559H View Online