An in silico approach for evaluating a fraction-based, risk assessment method for total petroleum hydrocarbon mixtures.

Nina Ching Y Wang,Glenn E Rice,Joan Colman,Linda K Teuschler,Raymond S H Yang

doi:10.1155/2012/410143

Abstract

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.

Highlights

Contamination of the environment by petroleum products including crude oil, lubricating oils, and a wide variety of fuels is widespread
The aliphatic dendrogram suggests that some total petroleum hydrocarbon (TPH) assigned by Massachusetts Department of Environmental Protection (MADEP) to aliph2 may be more similar to compounds in aliph1 based on their 2D and 3D physicochemical properties
This hierarchical clustering is heuristic in the sense that it depends on physiochemical properties (CoMFA) only

Summary

Introduction

Contamination of the environment by petroleum products including crude oil, lubricating oils, and a wide variety of fuels is widespread. These petroleum products are complex mixtures containing hundreds to thousands of different hydrocarbon compounds, including aliphatic compounds (e.g., straight-chain, branchedchain, 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). 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. 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.

Methods

Results

Conclusion