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### The Significance of Dibenzofuran in Creosote and Creosote - Treated Railroad Ties This explanatory document has been prepared in response to USEPA’s request for additional information regarding (a) the presence of dibenzofuran in creosote and creosote - treated wood, and (b) whether the presence of dibenzofuran can indicate the concurrent presence of the polychlorinated version s of these compounds, viz., polychlorinated dibenzo p - dioxins and dibenzofurans ( PCDD/F

– often collecti vely termed dioxins). As discussed in the sections below, dibenzofuran (a) is an un - substituted heterocyclic organic compound with two benzene rings and one fused furan ring, (b) is distinctly different from the polychlorinate d versions of the compound ( r eportable dioxins/furans in Table 1 below )

– the latter are formed as a result of various degrees of substitution of t he hydrogen atoms in dibenzofuran with chlorine, and (c) has a unique CAS number that is different from the CAS numbers for the reportable dioxins/furans . The refore, the presence of dibenzofuran does not automatically translate into the presence of reportable dioxins/furans. Background In the preamble of the February 7 , 2013 Commercial and Industrial Solid Waste Incineration Units: Reconsideration and Final Amendments; Non - Hazardous Secondary materials That Are Solid Waste; Final rule (see page 9173) EPA lists “dioxins” in addition to “dibenzofurans” as contaminants known to be present in creosote - treated railroad ties. EPA’s listings appear to be based on an IP (International Paper) railroad tie sample from 1989/1990 contained nearly 900 ppm dibenzofuran and that creosote can contain up to 4.5 % of dibenzofuran. However, n o data exists on the class of dioxins that would include 2,3,7,8 - t etrachlorodibenzo - p - dioxin or any other dioxins. In discussions with EPA staff, it became clear that an assessment of why “dioxins” would not form or be present in creosote wood would hel p justify why testing for dioxin rather than just dibenzofurans would not be necessary . Dibenzofuran is a distinctly different compound from PCDD/F The reportable form of dioxins/furans, in reality , represents the 17 specific isomers of dioxins and fur ans, 7 polychlorinated dibenzo - p - dioxins or PCDDs and 1 0 polychlorinated dibenzofurans or PCDFs, each of which has a specific CAS No. as shown in Table 1 below. Dibenzofuran , (CAS No. 132 - 64 - 9) , on the other hand, is a heterocyclic organic compound with the chemical structure shown below . It is an aromatic compound that has two benzene rings fused to one furan ring in the middle. All of the numbered carbon atoms have a hydrogen atom bonded to each of them (not shown in the image). Dibenzofuran is an aromatic ether having the chemical formula C 12 H 8 O.ncas i March 7 , 2013

2 Table 1 . Reportable “Dioxin and dioxin - like Compounds” CAS NO. COMPOUND ABBREVIATED NAME 1746 - 01 - 6 2,3,7,8 - tetrachlorodibenzo - p - dioxin 2,3,7,8 - TCDD 40321 - 76 - 4 1,2,3,7,8 - pentachlorodibenzo - p - dioxin 1,2,3,7,8 - PeCDD 39227 - 28 - 6 1,2,3,4,7,8 - hexachlorodibenzo - p - dioxin 1,2,3,4,7,8 - HxCDD 57653 - 85 - 7 1,2,3,6,7,8 - hexachlorodibenzo - p - dioxin 1,2,3,6,7,8 - HxCDD 19408 - 74 - 3 1,2,3,7,8,9 - hexachlorodibenzo - p - dioxin 1,2,3,7,8,9 - HxCDD 35822 - 46 - 9 1,2,3,4,6,7,8 - heptachlorodibenzo - p - dioxin 1,2,3,4,6,7,8 - HpCDD 3268 - 87 - 9 1,2,3,4,6,7,8,9 - octachlorodibenzo - p - dioxin 1,2,3,4,6,7,8,9 - OCDD 51207 - 31 - 9 2,3,7,8 - tetrachlorodibenzofuran 2,3,7,8 - TCDF 57117 - 41 - 6 1,2,3,7,8 - pentachlorodibenzofuran 1,2,3,7,8 - PeCDF 57117 - 31 - 4 2,3,4,7,8 - pentachlorodibenzofuran 2,3,4,7,8 - PeCDF 70648 - 26 - 9 1,2,3,4,7,8 - hexachlorodibenzofuran 1,2,3,4,7,8 - HxCDF 57117 - 44 - 9 1,2,3,6,7,8 - hexachlorodibenzofuran 1,2,3,6,7,8 - HxCDF 72918 - 21 - 9 1,2,3,7,8,9 - hexachlorodibenzofuran 1,2,3,7,8,9 - HxCDF 60851 - 34 - 5 2,3,4,6,7,8 - hexachlorodibenzofuran 2,3,4,6,7,8 - HxCDF 67562 - 39 - 4 1,2,3,4,6,7,8 - heptachlorodibenzofuran 1,2,3,4,6,7,8 - HpCDF 55673 - 89 - 7 1,2,3,4,7,8,9 - heptachlorodibenzofuran 1,2,3,4,7,8,9 - HpCDF 39001 - 02 - 0 1,2,3,4,6,7,8,9 - octachlorodibenzofuran 1,2,3,4,6,7,8,9 - OCDF Dibenzo furan

When the hydrogen atoms in positions 1, 2, 3, 4, 6, 7, 8 and 9 in the dibenzofuran molecule (see figure) are substituted with chlorine, this results in one of the 10 polychlorinated dibenzofurans listed in Table 1. Thus, the molecule dibenzofuran is not the same as polychlorinated dibenzofurans or PCDFs , and has its own CAS No. (132 - 64 - 9) . In fact, wiki pedia ( http://en.wikipedia.org/ wiki/Dibenzofuran ) makes specific mention of the following inaccurate characterization : “ Dibenzofurans can also inaccurately refer to polychlorinated dibenzofurans (PCDFs), a family of organic compounds with one or several of the hydrogens in the dibenzofuran structure replaced by chlorines. For example, 2,3,7,8 - tetrachloro dibenzofuran (TCDF) has chlorine atoms substituted for each of t he hydrogens on the number 2, 3, 7, and 8 carbons (see structure below). Polychlorinated dibenzofurans are much more toxic chemicals than the parent compounds with properties and chemical structures similar to polychlorinated dibenzodioxins . These groups t ogether are often inaccurately called dioxins .”ncas i March 7 , 2013

3 2,3,7,8 - Tetrachlorod ibenzo furan

The general structure for PCDFs is as follows

Thus, while “ creosote ” used in preparing railroad ties may indeed have high levels of dibenzofurans ( up to 4.5% or 45 ,000 ppm) , and the dibenzofuran concentration in one RR sample treated with creosote was measured at ~ 900 ppm, this compound is just an organic and should not be confused with dioxins or furans, which are clearly multiple chlorine - substituted forms of dib enzofurans and dibenzodioxins (the latter has the same structure as PCDFs except the two benzene rings are fused to one dioxin ring in the middle as shown below). The general structure for PCDDs is as follows

Are dioxins formed either during creos o te application or creos o te manufacture ? As discussed earlier, dibenzofuran is neither a chlorinated dioxin nor a chlorinated furan, and the term s “dioxins” or “PCDD/Fs” are specifically reserved for 17 specific chlorinated dioxins and furans each with its own CAS numbers . EPA also requested information on whether “dioxins” can be form ed either during the manufacture of creosote (mainly from coal tar) itself or during the application of creosote to railroad ties (for preservation). The second aspect, viz., the potential for dioxin formation during the application process of creosote to railroad ties, can be readily dismissed as r eaction mechanisms other than some form of combustion or the bleaching of pulp with chlorine have never been reported . Trace levels of dioxins, especially the octa chlorinated types (OCDD and OCDF), are ubiquitous in nature. Trace amounts (mainly OCDFs) havencas i March 7 , 2013

4 been detected in ground and river water, and even in virgin wood and bark. The phenomenon of poor combustion of biomass during forest fires and other non - industrial biomass burning, which results in OCDD/Fs being continually formed and re - deposited on the forest floor, is generally assumed to be origin of these OCDD/Fs in nature. There is also no evi dence in published literature on PCDD/F formation during the manufacture of creosote. Creosote applied to railroad ties is manufactured predominantly by distilling coal tar, a byproduct from the coking plants of steel mills ( http://apps.kemi.se/flodessok/floden/kemamne_ eng/kreosot_eng.htm ). It is made from the “medium” distillates of coal tar that have boiling points in excess of 200  C. Occasionally, there is discussion on “dioxins” in the context of remediation of wood preservation sites. However, this is invariably in the context of pentachlorophenol (PCP) that is also used by wood preservers besides creosote. Dioxins are believed t o be a common impur ity in commercial - grade PCP ( http://www.epa.gov/region4/superfund/sites/npl/florida/amercreopenfl.html .