Both the Massachusetts Department of Environmental Protection (MADEP) and the Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG) developed fraction-based approaches for assessing human health risks posed by total petroleum hydrocarbon (TPH) mixtures in the environment. Both organizations defined TPH fractions based on their expected environmental fate and by analytical chemical methods. They derived toxicity values for selected compounds within each fraction and used these as surrogates to assess hazard or risk of exposure to the whole fractions. Membership in a TPH fraction is generally defined by the number of carbon atoms in a compound and by a compound's equivalent carbon (EC) number index, which can predict its environmental fate. Here, we systematically and objectively re-evaluate the assignment of TPH to specific fractions using comparative molecular field analysis and hierarchical clustering. The approach is transparent and reproducible, reducing inherent reliance on judgment when toxicity information is limited. Our evaluation of membership in these fractions is highly consistent (？80% on average across various fractions) with the empirical approach of MADEP and TPHCWG. Furthermore, the results support the general methodology of mixture risk assessment to assess both cancer and noncancer risk values after the application of fractionation. 1. Introduction Contamination of the environment by petroleum products including crude oil, lubricating oils, and a wide variety of fuels is widespread. Typically, these petroleum products are complex mixtures containing hundreds to thousands of different hydrocarbon compounds, including aliphatic compounds (e.g., straight-chain, branched-chain, and cyclic alkanes and alkenes) as well as aromatic compounds (e.g., benzene and alkyl benzenes, polycyclic aromatic hydrocarbons). Once released into the environment, the composition of a petroleum hydrocarbon mixture can change due to weathering (http://facstaff.gpc.edu/~pgore/geology/geo101/weather.htm). During chemical weathering, components of petroleum mixtures can degrade and partition, such that the more soluble or volatile compounds can be readily transported to other environmental media and locations, while the relatively nonmobile and recalcitrant components (i.e., the weathered products) remain near the point of release. Thus, the actual petroleum hydrocarbon mixtures to which a population might be exposed will vary with the petroleum product released, environmental conditions, elapsed time following release, and exposure medium. Assessment of
References
[1]
U.S. Environmental Protection Agency, Integrated Risk Information System (IRIS), Office of Research and Development, Washington, DC, USA, 2010.
[2]
MADEP (Massachusettes Department of Environmental Protection), Characterizing Risks Posed by Petroleum Contaminated Sites: Implementation of the MADEP VPH/EPH Approach, Cleanup, Boston, Mass, USA, 2002.
[3]
MADEP (Massachusettes Department of Environmental Protection), Updated Petroleum Hydrocarbon Fraction Toxicity Values for the VPH/EPH/APH Methodology, Office of Research and Standards, Boston, Mass, USA, 2003.
[4]
TPHCWG (Total Petroleum Hydrocarbon Criteria Working Group), Selection of Representative TPH Fractions Based on Fate and Transport Considerations, vol. 3, Amherst Scientific Publishers, Amherst, Mass, USA, 1997.
[5]
TPHCWG (Total Petroleum Hydrocarbon Criteria Working Group), Development of Fraction Specific Reference Doses (RfDs) and Reference Concentrations (RfCs) for Total Petroleum Hydrocarbons (TPH), vol. 4, Amherst Scientific Publishers, Amherst, Mass, USA, 1997.
[6]
TPHCWG (Total Petroleum Hydrocarbon Criteria Working Group), Petroleum Hydrocarbon Analysis of Soil andWater in the Environment, vol. 1, Amherst Scientific Publishers, Amherst, Mass, USA, 1998.
[7]
TPHCWG (Total Petroleum Hydrocarbon Criteria Working Group), Composition of Petroleum Mixtures, vol. 2, Amherst Scientific Publishers, Amherst, Mass, USA, 1998.
[8]
TPHCWG (Total Petroleum Hydrocarbon Criteria Working Group), Human Health Risk-Based Evaluation of Petroleum Release Sites: Implementing the Working Group Approach, vol. 5, Amherst Scientific Publishers, Amherst, Mass, USA, 1999.
[9]
U.S. Environmental Protection Agency, Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures, EPA/630/R-00/002, U.S. Environmental Protection Agency, Washington, DC, USA, 2000.
[10]
U.S. Environmental Protection Agency, Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons, EPA/600/R-93/089, U.S. Environmental Protection Agency, Cincinnati, OH, USA, 1993.
[11]
L. K. Teuschler, “Deciding which chemical mixtures risk assessment methods work best for what mixtures,” Toxicology and Applied Pharmacology, vol. 223, no. 2, pp. 139–147, 2007.
[12]
M. Béliveau and K. Krishnan, “A spreadsheet program for modeling quantitative structure-pharmacokinetic relationships for inhaled volatile organics in humans,” SAR and QSAR in Environmental Research, vol. 16, no. 1-2, pp. 63–77, 2005.
[13]
M. Béliveau, R. Tardif, and K. Krishnan, “Quantitative structure-property relationships for physiologically based pharmacokinetic modeling of volatile organic chemicals in rats,” Toxicology and Applied Pharmacology, vol. 189, no. 3, pp. 221–232, 2003.
[14]
J. B. Knaak, C. C. Dary, F. Power, C. B. Thompson, and J. N. Blancato, “Physicochemical and biological data for the development of predictive organophosphorus pesticide QSARs and PBPK/PD models for human risk assessment,” Critical Reviews in Toxicology, vol. 34, no. 2, pp. 143–207, 2004.
[15]
R. Venkatapathy, C. Y. Wang, R. M. Bruce, and C. Moudgal, “Development of quantitative structure-activity relationship (QSAR) models to predict the carcinogenic potency of chemicals. I. Alternative toxicity measures as an estimator of carcinogenic potency,” Toxicology and Applied Pharmacology, vol. 234, no. 2, pp. 209–221, 2009.
[16]
T. A. Halgren, “MMFF VI. MMFF94s option for energy minimization studies,” Journal of Computational Chemistry, vol. 20, no. 7, pp. 720–729, 1999.
[17]
R. D. Cramer, D. E. Patterson, and J. D. Bunce, “Comparative molecular field analysis (CoMFA). 1. Effect of shape on binding of steroids to carrier proteins,” Journal of the American Chemical Society, vol. 110, no. 18, pp. 5959–5967, 1988.
[18]
H. Izumi, E. Kimura, T. Ota, and S. Shimazu, “A two-generation reproductive toxicity study of n-butylbenzene in rats,” Journal of Toxicological Sciences, vol. 30, pp. 21–38, 2005.
