Beyond TPH: health-based evaluation of petroleum hydrocarbon exposures.

The term "total petroleum hydrocarbons" (TPH) is a widely used, but loosely defined, parameter quantified by a number of different methodologies for expressing the aggregate amount of petroleum hydrocarbon compounds (PHCs) in a sample. Because of the shortcomings associated with comparing data from different methods, and the difficulty of assessing potential toxicities of complex mixtures of hydrocarbons, a new approach at more fully and explicitly defining the PHC composition of samples and predicting human noncancer health risks from those exposures has been developed. This new approach is the subject of this paper. This method can be used to perform site-specific risk assessments or to develop health-based cleanup standards for petroleum hydrocarbons. The technique divides the broad chemical classes of PHC (i.e., saturated versus unsaturated) into subgroups of compounds based on numbers of carbon atoms in the compounds within each subgroup. The mass of compounds in each subgroup is then translated into discrete estimates of health risk for specified exposure scenarios. The subgroups were identified from qualitative and quantitative changes in the nature of noncancer toxicities recorded in the literature. For saturated compounds, toxicity changes as carbon chain length increases (measured by numbers of carbon atoms). A "reference compound" was chosen for each range of compounds, usually because its toxicity was relatively well characterized. A published oral reference dose (RfD) was identified for these compounds, or in the absence of a published value, an oral dose-response value was developed from available toxicity information. For saturated PHCs (alkanes, cycloalkanes, and isoalkanes) the subgroups' reference compounds and assigned toxicity value used are C5 to C8 (n-hexane, 0.06 mg/kg/day); C9 to C18 (n-nonane, 0.6 mg/kg/day); and C19 to C32 (eicosane, 6.0 mg/kg/day). For unsaturated compounds (aromatics), one reference RfD was identified for all compounds: C9 through C32 (pyrene, 0.03 mg/kg/day). Dependent upon the analytical technique used for separation of compounds, the unsaturated alkenes may be grouped and subsequently quantified with either the saturate or unsaturate groups. The implications of possible association with either group and contributions to risk estimates are probably not significant. Alkenes make up a small fraction of most fuel products, and they bear structural similarity to the alkanes and are not particularly toxicologically active. If grouped analytically with the aromatics the alkene contribution to toxicity estimates would likely be minor and not be an underestimate of its true toxicity. The mass of PHC in each segment of a chromatogram is quantified and converted to a medium-specific concentration which is then entered into standard medium intake equations to arrive at a daily dose of PHC. This dose is then used with the toxicity value identified for the particular segment of the chromatogram to derive a hazard quotient. The quotients can then be summed across fractions to yield a total hazard index. The noncancer health risks from the aromatics benzene, toluene, and xylenes are evaluated separately using standard risk assessment techniques.

Reconciling science and policy in setting federal drinking water standards--four states' perspectives.

After almost 20 years of experience with implementing the Safe Drinking Water Act and eight with Amendments to the Act, the individual states within the United States have gained valuable experience while trying to reconcile the legal mandates provided by the statutes with the science underlying them. This paper presents four different topics illustrating the problems of reconciling these two issues in the regulation of toxic chemicals in drinking waters. It presents these from the perspectives of the states of Massachusetts, Rhode Island, Connecticut, and New Jersey and offers suggestions for improved program efficiency based on considerations of comparative human health risks. The approach and schedule for controlling toxic chemicals used through 1994 are first examined and a recommendation is made for more flexibility in the rate at which chemicals are regulated. Recent U.S. EPA proposals to more stringently control radon in drinking waters are presented in the context of all sources of radon exposures, illustrating the intersection of science, laws, and economic consequences of regulatory initiatives. Inhalation and dermal exposures as a result of using chemically contaminated drinking waters are then discussed with the suggestion of the possible underprotectiveness of some present standards. Finally, the difficulty faced by the states and federal government in the control of naturally occurring arsenic exposures through drinking water is also presented and an argument is made for more local flexibility in the application of health-based standards.