ncasi March 7, 2013

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### The Significance of Dibenzofuran in Creo sote and Creosote-Treated Railroad Ties

This explanatory document has been prepared in r esponse to USEPA’s request for additional information regarding (a) the presence of dibenzofuran in creoso te and creosote-treated wood, and (b) whether the presence of dibenzofuran can indicate the concurrent presence of the polychlorinated versions of these compounds, viz., polychlorinated dibenzo p-dioxins and dibenzofurans (PCDD/F – often collectively 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 polychlorinated versions of the compound (reportable dioxins/furans in Table 1 below) – the latter are formed as a result of various degrees of substitution of the hydrogen atoms in dibenzofuran with chlorine, and (c) has a unique CAS number that is diffe rent from the CAS numbers for the reportable dioxins/furans. Therefore, the presence of dibenzofur an does not automatically translate into the presence of reportable dioxins/furans.

Background

In the preamble of the February 7, 2013 Commerc ial 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 ad dition 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 dibe nzofuran. However, no data exists on the class of dioxins that would include 2,3,7,8-tetrachlorodibenzo-p-di oxin 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 help 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, re presents the 17 specific isomers of dioxins and furans, 7 polychlorinated dibenzo- p-dioxins or PCDDs and 10 polychlorinat ed 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 ar omatic 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.ncasi 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

Dibenzofuran

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 th e 10 polychlorinated dibenzofurans listed in Table 1. Thus, the molecule dibenzofuran is not the same as pol ychlorinated dibenzofurans or PCDFs, and has its own CAS No. (132-64-9). In fact, wikipedia ( http://en.wikipedia.org/ wiki/Dibenzofuran ) makes specific mention of the following inaccurate characterization:

“ Dibenzofurans can also inaccurately refer to polychlorin ated dibenzofurans (PCDFs), a family of organic compounds with one or several of the hydrog ens in the dibenzofuran structure replaced by chlorines. For example, 2,3,7,8-tetrachloro dibenzof uran (TCDF) has chlorine atoms substituted for each of the 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 together a re often inaccurately
called dioxins.”ncasi March 7, 2013

3 2,3,7,8-Tetrachlorodibenzofuran

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 concen tration in one RR sample treated with creosote was measured at ~ 900 ppm, this compound is just an organi c and should not be confused with dioxins or furans, which are clearly multiple chlorine-substitute d forms of dibenzofurans 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 creosote application or creosote manufacture?

As discussed earlier, dibenzofuran is neither a chlo rinated dioxin nor a chlorinated furan, and the terms “dioxins” or “PCDD/Fs” are specifically reserved for 17 specific chlorinated dioxins and furans each with its own CAS numbers. EPA also requested informati on on whether “dioxins” can be formed either during the manufacture of creosote (mainly from coal ta r) itself or during the application of creosote to railroad ties (for preservation).

The second aspect, viz., the potential for dioxin formati on during the application process of creosote to railroad ties, can be readily dismissed as reaction me chanisms other than some form of combustion or the bleaching of pulp with chlorine have never been repor ted. Trace levels of dioxins, especially the octachlorinated types (OCDD and OCDF), are ubiquitous in nature. Trace amounts (mainly OCDFs) havencasi March 7, 2013

4 been detected in ground and river water, and ev en 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 a nd re-deposited on the forest floor, is generally assumed to be origin
of these OCDD/Fs in nature.

There is also no evidence in published literatu re on PCDD/F formation during the manufacture of creosote. Creosote applied to railroad ties is ma nufactured 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 th e context of pentachlorophenol (PCP) that is also used by wood preservers besides creosote. Dioxins are believed to be a common impurity in commercial-grade
PCP ( http://www.epa.gov/region4/superfund/sit es/npl/florida/amercreopenfl.html

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