Identifying Creosote at Contaminated Sites: An Environmental Forensics Overview
Stephen D. Emsbo-Mattingly, Allen D. Uhler, Ph.D., Scott A. Stout, Ph.D. and Kevin J. McCarthy are senior consultants with Battelle Memorial Institute’s Environmental Forensics Investigation Group, Duxbury, Mass.
uhler@battelle.org
Creosote can constitute a significant source of polycyclic aromatic hydrocarbons (PAH) and phenols at many contaminated sites. The identification of creosote and the differentiation of creosote from other sources of PAH is often important because the cost for remediating many industrial areas is shared by the potentially responsible parties (PRPs) thought to have contaminated the site. Consequently, environmental forensic investigations commonly focus on the signature of the materials handled by each PRP in order to refute or implicate one or more PRP based on the chemical composition of the contamination. Unfortunately, PAH-producing PRPs, like former wood treating facilities, manufactured gas plants, coking operations and tar refiners often emerged symbiotically around centers of industry and transportation. The close spatial relationship among these PRPs complicates the forensic investigation by potentially creating multiple sources of chemically similar material. This article describes the manufacture of creosote with an emphasis on the similarities and differences from other PAH-enriched material, principally tar and tar-products, commonly encountered in industrial areas.
Background. The pharmaceutical industry originally used the term creosote in reference to the phenolic material derived from beechwood tar used as an antiseptic and for the treatment of chronic bronchitis. The term was
adopted by the wood treating industry when, in England around 1838, chemists first developed methods for isolating the tar acid fraction from coal tar for the protection of wood products (Rhodes, 1954). The demand for creosote
by the wood treating industry grew with the burgeoning railroad, electricity, telephone and maritime industries. The total material treated by wood preservatives between 1909 and 1919 grew from approximately 70
million ft3 to 145 million ft3 (Bateman, 1922). During this same period, creosote produced domestically from coal tar essentially replaced imported creosote.
Historical Practices. In the mid to late 1800's, tar was painted on wood and metal because it adhered well, retarded oxidation, resisted creeping and blistering and withstood the elements of nature better than most of the
alternatives (Grimwood, 1896). During the same time period, the wood treating industry began importing creosote for its superior performance in terms of toxicity and penetration. As a middle distillate of coal tar, creosote possessed an increased the molar fraction of tar acids and decreased the relative abundance of immobile heavy molecular weight materials (pitch). Between 1900 and 1940, the techniques for preparing the wood (debarking and drying) and applying the creosote (open vats and pressurized chambers) were developed and improved. Between 1910 and 1915, the demand increased dramatically for light oil (approximate boiling point range of 100°C to 220°C) that was used to manufacture secondary chemical products and automotive fuel (Downing, 1934). The prior removal of light oil from coal and petroleum tar decreased the concentrations of phenol and naphthalene in the middle oil from which creosote was refined. Scarce resources during World Wars I and II prompted chemical engineers to
experiment with the formulation of creosote in order to cost-effectively enhance the product's performance.
Creosote Performance Features. The performance features of creosote included: permanence, penetration, toxicity and hydrophobicity. Permanence is the ability of the creosote to stay in the wood. Evaporation, leeching
and chemical decomposition compromise permanence. Consequently, permanence is promoted by retaining an adequate amount of the heavy distillate fraction of tar. Penetration is the ability of the preservative to penetrate into
the wood. Initially, penetration was improved by increasing the relative abundance of the less viscous, light-weight fraction of coal tar or by the addition of selected water gas tars or petroleum distillates. However, penetration was greatly facilitated by improved treatment techniques. For example, chambers were built in which the wood was steam heated to burst the wood cells, desiccated under vacuum to remove residual moisture and saturated with creosote under pressure - sometimes in the presence of a penetration accelerant like zinc chloride (Fulweiler, 1921; Mattraw, 1986). Toxicity is the ability of the creosote to inhibit the growth of bacteria, fungi, insects and marine borers. Initially, toxicity was associated with the coal tar fraction containing tar acids. However, water gas tar, which
contains principally PAH and little to no tar acids, was used successfully between 1910 and 1915 for the preservation of railroad ties throughout the Middle Atlantic States (Fulweiler, 1921). This finding suggests that high PAH concentration may impart adequate toxicity to preserve wood for some applications. Finally, hydrophobicity is the ability of the preservative to repel water. This feature is improved by elevating the abundance of the heavier fraction of tar. In summary, the formulation of creosote requires the balancing of competing performance features. Permanence and hydrophobicity favor heavier creosote while penetration and toxicity favor lighter creosote.
Blended Creosote. Since the early 1900's, products marketed as creosote varied widely. The chemical composition of creosote changed from a straight run distillate (approximate boiling point range of 200°C to 400°C) to a
reformulated product (approximate boiling point range of 220°C to 355°C) containing non-marketable tar byproducts (pressed anthracene cake oil and phenanthrene), enhancement blends (heavy coal tar fractions improved
permanence; selected petroleum and tar fractions improved penetration) and/or bulking agents (selected water gas or oil tars). In other words, the composition of creosote depended largely on the industrial practices at the site and varied at any given time across the U.S. Today, when environmental forensic investigators attempt to differentiate creosote from other processed or unprocessed tar products, the effort is often confounded by the
weathering of PAH and the commingling of native material. Consequently, the forensic investigator must often rely on numerous forensic techniques for the differentiation of creosote in the presence of other pyrogenic material.
Identifying Creosote. The deconvolution of creosote signatures relies on a multidisciplinary approach and includes a combination of careful historical research, precise and accurate chemical analysis and geochemical
interpretation. As a theoretical example, creosote released from a site in 1955 might be associated with the removal of light oil constituents, naphthalene, and heavy molecular weight material relative to the unprocessed tar from which it originated. In addition, the industrial record might indicate that pentachlorophenol was used at the site and may have commingled with the creosote in the dewatering impoundments. Let us also imagine that an adjacent coal tar processing plant distilled only coal tar until 1922 when it began blending refined water gas tar with its creosote; thereby, potentially altering the relative abundance of tar acids, PAH source identification ratios and carbon isotope signatures. Once the subsurface migration pathways are assessed, the environmental forensic investigation
might focus on the chemical indicators of these historical practices to collectively fingerprint one or both PAH source(s).
A systematic and step-wise environmental forensic investigation (Uhler, et al., 1998) can increase the probability of successfully sourcing creosote. Initially, a comprehensive historical investigation of the industrial practices potentially affecting the impacted area should be performed. Thereafter, data gaps should be identified and project objectives described. In general, the less that is known about the site, the greater the need for numerous samples and chemical analyses. Secondly, a multidisciplinary team, including a forensic chemist, should compile a comprehensive list of potential chemistry methods and sample locations. This list should include a description of the utility of each method and sampling location. Thirdly, the multidisciplinary team should select the most appropriate analytical chemistry methods and sample locations for the environmental forensic investigation. The data generated by most environmental production laboratories using standard EPA methods is nearly useless for the environmental forensic investigator, because these data fail to comprehensively measure the chemical composition of refined and unrefined tar at the level of precision and accuracy necessary to perceive subtle differences among sources (Uhler, et al., 1998). For example, the EPA analytical methods for PAH establish no control criteria over mass discrimination on a gas chromatograph from the beginning to the end of an analytical sequence or among multiple analytical sequences. In addition, few, if any, EPA methods exist for the standardized assessment of distillation curves, bulk composition and petrographic analysis (see below). Sample locations should be selected that adequately represent the potential source(s), release(s) and background areas. Sample replicates should be collected to evaluate the analytical and matrix variability. Fourthly, a laboratory with a
specialization in tar chemistry should be contracted to perform the analyses. This experience is critical for reliably separating the tar fractions and measuring extremely high and low concentrations of analytes present in a single sample. Finally, all samples need not be analyzed by all methods. It is recommended that all samples be screened by the following methods: high-resolution hydrocarbon
fingerprint, alkylated PAH characterization and biomarker analysis. If the material cannot be differentiated at this point, a subset of samples representative of the source, release and background areas should be subjected to ancillary analyses.
If needed, the ancillary analyses selected to support the creosote investigation depend greatly on the potential sources of PAH and historical practices at each source location. A physical characterization might be performed on non-aqueous phase liquids collected from one or more sites and include measurements of specific gravity, viscosity, moisture content, ash content, total organic carbon, benzene soluble fractions, molecular weight and organic petrographic analyses (microscopic analysis of particulate structure). Ancillary analyses may also include the chemical characterization of soil, groundwater, tar and other relevant media. Depending on the objectives and other circumstances, the chemical characterization can include volatile organic compounds, metals, cyanide, tar acids, tar bases, elemental composition (carbon, hydrogen, sulfur, nitrogen and oxygen), sulfur forms (pyritic, organic and sulfate), aromatic sulfur compounds (thiophenes, benzothiophenes and dibenzothiophenes), simulated distillation curves (aliphatic and aromatic fractions), bulk and compound specific carbon isotopes (d13C and d14C activity for PAH and, possibly, n-alkanes). The utility of these ancillary analyses will be discussed in later installments of this column.
Summary. This article provides an overview of creosote from the vantage point of the environmental forensic investigator. It describes the variability of creosote manufacturing over time in the United States and the
extent to which this variability can confound and assist the differentiation of creosote from other tar-related materials. These industrial signatures are not likely evident in data produced for environmental regulatory
purposes. Rather, the identification of PAH sources requires a systematic and multidisciplinary plan, execution and interpretation.
References
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Uhler, A., S. Stout, K. McCarthy (1998). Increase Success of Assessments at Petroleum Sites in 5 Steps. Soil and Groundwater Cleanup. December/January 1998.
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