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3. IDENTITY AND ANALYSIS OF TOTAL PETROLEUM HYDROCARBONS TOTAL PETROLEUM HYDROCARONS

17
3. IDENTITY AND ANALYSIS OF TOTAL PETROLEUM HYDROCARBONS
3.1 INTRODUCTION
Petroleum hydrocarbons (PHCs) are common site contaminants, but they are not generally regulated
as hazardous wastes. Methods for sampling and analysis of environmental media for the family of
PHCs are generally thought of as TPH methods. For purposes of this profile, the term TPH refers
not only to analytical results, but also to environmental and health properties of PHCs. In part due to
the complexity of TPH components themselves, little is known about their potential for health or
environmental impacts. As gross measures of petroleum contamination, TPH results simply show
that petroleum hydrocarbons are present in the sampled media. Measured TPH values suggest the
relative potential for human exposure and, therefore, the relative potential for human health effects.
The assessment of health effects due to TPH exposure requires much more detailed information than
what is provided by a single TPH value. This chapter, Chapter 5, and the accompanying Appendix E
provide more detailed physical and chemical properties and analytical information on TPH and its
components.
The federal government has left much of the specific regulation and oversight of crude oil production/
refining to the states. Leaking underground storage tanks (LUST) are the most frequent causes of
federal and state governmental involvement in petroleum hydrocarbon problems. Soil contamination
has been a growing concern, because it can be a source of groundwater (drinking water) contamination;
contaminated soils can reduce the usability of land for development; and weathered petroleum
residuals may stay bound to soils for years. Positive TPH test results may require action on the part
of land owners, local or state governments, and engineering firms called on to remove or reduce the
TPH problem.
ATSDR has the responsibility for health assessment at National Priorities List (NPL) hazardous
waste sites, many of which have petroleum hydrocarbon contamination. Specific contaminants that
are components of TPH, such as BTEX (benzene, toluene, ethylbenzene, and xylene), n-hexane, jet
fuels, fuel oils, and mineral-based crankcase oil, have been studied by ATSDR and a number of
toxicological profiles have been developed on individual constituents and petroleum products. The TOTAL PETROLEUM HYDROCARONS

18
3. IDENTITY AND ANALYSIS OF TOTAL PETROLEUM HYDROCARBONS
ATSDR profiles relevant to petroleum products are listed in Table 3- 1. However, TPH itself has not
been as extensively studied by ATSDR and no previous profile was developed. Although several
toxicological profiles have been developed for petroleum products and for specific chemicals found in
petroleum, TPH test results have been too nonspecific to be of real value in the assessment of its
potential health effects.
Several approaches are discussed in this document for interpreting TPH and related analytical results.
The TPH approach taken by EPA and others, through the mid-1990s, followed general risk
assessment approaches for chemical mixtures. In all approaches there is a need to reduce a
comprehensive list of potential petroleum hydrocarbons to a manageable size. Depending on how
conservative the approach is, methods that have been used select: (1) the most toxic among the TPH
compounds (indicator approach); (2) one or more representative compounds (surrogate approach, but
independent of relative mix of compounds); or (3) representative compounds for fractions of similar
petroleum hydrocarbons. ATSDR has taken, in part, the third approach in keeping with the Total
Petroleum Hydrocarbons Criteria Working Group (TPHCWG), but has developed its own set of TPH
fraction representatives, many of which overlap those of the TPHCWG. In addition, this profile
provides information on petroleum products, where such information exists. TPH risk (screening)
values for fractions presented in this profile are based on the ATSDR MRLs previously developed for
individual constituents and petroleum products. These MRLs are summarized in Appendix A. This
fraction approach is the most demanding in information gathering and because of that would appear
to be the most rigorous approach to date. Sections 6.1.2 and 6.1.3 contain a more comprehensive
discussion of the approaches. The identity, chemical-physical, and analytical information discussed
and listed in this chapter, in Appendices D and E, and in Chapter 5 are integral to defining TPH.
3.2
CHEMICAL AND PHYSICAL INFORMATION
Petroleum products are complex mixtures of hundreds of hydrocarbon compounds, ranging from light,
volatile, short-chained organic compounds to heavy, long-chained, branched compounds. The exact
composition of petroleum products varies depending upon (1) the source of the crude oil (crude oil is
derived from underground reservoirs which vary greatly in their chemical composition) and (2) the
refining practices used to produce the product.
TOTAL PETROLEUM HYDROCARONS

20
3. IDENTITY AND ANALYSIS OF TOTAL PETROLEUM HYDROCARBONS
During the refining process, crude oil is separated into fractions having similar boiling points. These
fractions are then modified by cracking, condensation, polymerization, and alkylation processes, and
are formulated into commercial products such as naphtha, gasoline, jet fuel, and fuel oils. The
composition of any one of these products can vary based on the refinery involved, time of year,
variation in additives or modifiers, and other factors. The chemical composition of the product can be
further affected by weathering and/or biological modification upon release to the environment. The
following subsections present overviews of petroleum products. Also, a master list of individual
aliphatic and aromatic compounds found in TPH is provided in Appendix D. Further information on
whole petroleum products, their identity, major components, and physical/chemical properties is
found in Appendix E.
Automotive Gasoline. Automotive gasoline is a mixture of low-boiling hydrocarbon compounds
suitable for use in spark-ignited internal combustion engines and having an octane rating of at least
60. Additives that have been used in gasoline include alkyl tertiary butyl ethers (e.g. MTBE), ethanol
(ethyl alcohol), methanol (methyl alcohol), tetramethyl-lead, tetraethyl-lead, ethylene dichloride, and
ethylene dibromide.
Other categories of compounds that may be added to gasoline include anti-knock agents, antioxidants,
metal deactivators, lead scavengers, anti-rust agents, anti-icing agents, upper-cylinder
lubricants, detergents, and dyes (ATSDR 1995a).
Automotive gasoline typically contains about 150 hydrocarbon compounds, though nearly 1,000 have
been identified (ATSDR 1995a). The relative concentrations of the compounds vary considerably
depending on the source of crude oil, refinery process, and product specifications. Typical hydrocarbon
chain lengths range from C
4
through C
l2
with a general hydrocarbon distribution consisting of
4-8% alkanes, 2-5% alkenes, 25-40% isoalkanes, 3-7% cycloalkanes, l-4% cycloalkenes, and
20-50% aromatics (IARC 1989a). However, these proportions vary greatly. Unleaded gasolines
may have higher proportions of aromatic hydrocarbons than leaded gasolines.
Table E-1.b (Appendix E) presents ranges and weight percentage means for a representative subset of
the hydrocarbon compounds identified in gasoline. In cases where data are not available, the range
and mean are left blank. TOTAL PETROLEUM HYDROCARONS

21
3. IDENTITY AND ANALYSIS OF TOTAL PETROLEUM HYDROCARBONS
Stoddard Solvent. Stoddard solvent is a petroleum distillate widely used as a dry cleaning solvent
and as a general cleaner and degreaser. It may also be used as a paint thinner, as a solvent in some types
of photocopier toners, in some types of printing inks, and in some adhesives. Stoddard solvent is
considered to be a form of mineral spirits, white spirits, and naphtha; however, not all forms of mineral
spirits, white spirits, and naphtha are considered to be Stoddard solvent (ATSDR 1995b).
Stoddard solvent consists of 30-50% linear and branched alkanes, 30-40% cycloalkanes, and lo-20%
aromatic hydrocarbons. Its typical hydrocarbon chain ranges from C
7
through C
12
in length.
Although a complete list of the individual compounds comprising Stoddard solvent is not available (Air
Force 1989) some of the major components are presented in Table E-2.b (Appendix E). Alcohols,
glycols, and ketones are not included in the composition, as few, if any, of these types of compounds
would be expected to be present in Stoddard solvent (ATSDR 1995b). Possible contaminants may
include lead (<1 ppm) and sulfur (3.5 ppm).
Jet Fuel. Jet fuels are light petroleum disti