Inventory and Emission Factors of Creosote, Polycyclic Aromatic

Inventory, emission factors, and total yearly emissions of creosote, PAH, and phenols from the Swiss railway network were determined based on the anal...
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Environ. Sci. Technol. 2000, 34, 4766-4772

Inventory and Emission Factors of Creosote, Polycyclic Aromatic Hydrocarbons (PAH), and Phenols from Railroad Ties Treated with Creosote MARTIN KOHLER,* TINA KU ¨ NNIGER, PETER SCHMID, ERIKA GUJER, ROWENA CROCKETT, AND MAX WOLFENSBERGER Swiss Federal Laboratories for Materials Testing and Research (EMPA), Department of Organic Chemistry, U ¨ berlandstrasse 129, CH-8600 Du ¨ bendorf, Switzerland

Inventory, emission factors, and total yearly emissions of creosote, PAH, and phenols from the Swiss railway network were determined based on the analysis of cross sections of selected railroad ties which were in use for up to 46 years. Approximately 9 million wooden railroad ties are installed in Switzerland, each being treated with roughly 15 kg of creosote. During the service time of a typical railroad tie of 20-30 years, about 5 kg of creosote are emitted, corresponding to an emission factor of 208 mg/ (m2 × day). PAH emissions occur as emissions of the volatile 2- and 3-ring PAH (such as naphthalene, acenaphthylene, acenaphthene, anthracene, fluorene, phenanthrene; boiling point up to 340 °C). PAH emissions for an average railroad tie were found to be about 0.5 kg (sum of 16 EPAPAH), corresponding to an emission factor of 20.3 mg/(m2 × day). Emissions of phenolic compounds were determined to be in the range of 10 g for each tie, corresponding to an emission factor of 0.58 mg/(m2 × day). According to our study, about 1710 t of creosote components are being emitted by the ties of the Swiss railway network, every year. Based on the values reported above, yearly emissions of 2- and 3-ring EPA-PAH add up to 139 t. Cumulated emissions of phenolic compounds are in the order of 4 t per year.

Introduction Polycyclic aromatic hydrocarbons (PAH) are ubiquitous environmental pollutants. There are many known sources of PAH such as furnaces, internal combustion engines, industrial processes e.g. carbon anode and graphite production as well as the use of coal tar based products e.g. creosote. From the point of view of emission control, assessment of the relative contributions to the total emission of the various sources of PAH is a key issue. Although wood treated with creosote represents a significant inventory of PAH, surprisingly few studies exist that report quantitative data on emissions of PAH from this particular source. An ecological assessment of railway ties carried out at EMPA (1) as well as ongoing work at the Swiss Agency for the Environment, Forests and Landscape (BUWAL) on the assessment of * Corresponding author phone: +41 1 823 4334; fax: +41 1 823 4041; e-mail: [email protected]. 4766

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sources of PAH on a European level (Oslo and Paris Conventions, OSPARCOM (2)) gave rise to this study, designed to obtain data on emissions of PAH from railroad ties treated with creosote. Creosote is manufactured by distillation of coal tar and contains up to 85% of polycyclic aromatic hydrocarbons (3). Between 20 and 40% of the total weight of a typical creosote can be attributed to the 16 PAH defined as priority pollutants by the United States Environmental Protection Agency (EPA). Levels of benzo[a]pyrene in conventional creosotes are in the range of several hundred ppm; however, creosotes with contents of benzo[a]pyrene down to 5 ppm can be produced by current technology (4). Specifications for creosote products were issued by various institutions such as the WesternEuropean Institute for Wood Preservation (WEI standards WEI-A, WEI-B, and WEI-C (5)) and the American Wood Preservers' Association (AWPA Standards P1/P13 and P2 (6)). For regulations on the use of creosote issued by the European Community see ref 7. Presently, approximately 9 million wooden railroad ties are in service in Switzerland; this accounts for 43% of the ties installed. In addition to creosoted ties made from beech and oak wood, sectional steel ties (35%) and prestressed concrete ties (22%) are used. Since untreated wood is destroyed within a few years, wooden railroad ties are treated with creosote. This procedure is still regarded as the best option for this purpose (high protection level, low cost of treatment, electrical insulator). The vacuum-pressure treating process for creosote impregnation of wood was patented by Bethell in the United Kingdom in 1839. Today, a variety of optimized methods for vacuum-pressure treatment are applied (Bethell, Ru ¨ pping, Lowry) (8). In Switzerland, wooden railroad ties are replaced after an average service time of 26 years, mostly due to mechanical stress. Based on the numbers given above, about 346000 ties treated with creosote need to be replaced every year. Currently, most of these ties are reused for construction purposes. Considering the high surface concentrations of benzo[a]pyrene and other carcinogens found in used ties (9), policies for disposal and recycling of railroad ties (indoor use, gardens, public areas, playgrounds) were established (7). Various attempts were made in the past to assess the quantification of PAH emissions from wood treated with creosote, either laboratory experiments (3) or long-term outdoor studies (10-14) on treated wood. Based on emission factors determined by laboratory measurements of PAH emissions from planks of Yellow Pine painted with creosote, Gevao and Jones (3) estimated the annual U.K. emissions for acenaphthene, fluorene, phenanthrene, anthracene, and fluoranthene from freshly treated wood to be 100 t. Studies based on leaching experiments on railroad ties (leaching from milled wood and leaching from full tie sections) were published by Cooper et al. (15). A “standard shower test” for freshly treated wood was developed in The Netherlands, which specifies a maximum leaching limit of 2500 mg PAH (sum of 21 species) per m3 treated wood (16). In an extensive field study on creosote emissions from railroad ties by Petrowitz and co-workers (10, 11), more than 600 railroad ties were treated with creosote, selected according to their creosote content, and installed at a site near Monrovia (Liberia). Other field studies include long-term studies on poles treated with creosote being exposed for several decades (12-14), indicating loss of the low boiling PAH by evaporation and partial transfer of the high boiling PAH into the surrounding soil. 10.1021/es000103h CCC: $19.00

 2000 American Chemical Society Published on Web 10/12/2000

FIGURE 1. Obtaining representative wood samples from railroad ties. In this study, we performed a retrospective analysis of a set of railroad ties being in service between 0 and 46 years. Emission factors were determined by analysis and comparison of the concentrations of creosote, PAH, and phenolic compounds in cross sections of selected railroad ties.

Experimental Section Samples. A set of 6 railroad ties at ages of 0.5, 1, 6, 19, 32, and 46 years made from beech and oak wood was selected in cooperation with the Swiss Federal Railways and industry. From each tie, three slices (3 × 24 × 16 cm) at 1/10, 1/3, and 1/2 of the length were cut. From each slice, a strip (3 × 3 × 16 cm) was cut, which was divided into 8 pieces (3 × 3 × 2 cm), representing a cross section from the top to the bottom of the railroad tie (layers 1-8, see Figure 1). From each level, shavings (thickness 0.25 mm) of the three corresponding pieces were combined, resulting in 8 samples from each tie (total 48 samples from 6 ties). Extraction and Analysis. Creosote content and boiling range as well as concentration of PAH and phenols were determined from the residual creosote extracted from the 48 samples. The shavings (5 g) were spiked with 100 µg of acenaphthene-d10 (extraction recovery standard) and extracted with 200 mL of a mixture of 8 parts toluene and 2 parts methanol for 4 h (reflux). This procedure was optimized previously and was shown to yield quantitative extraction. The extract was filtered, and the volume was adjusted to 250 mL at room temperature. The creosote content was determined gravimetrically by evaporation of 50 mL of the extract at a temperature of 50 °C and a pressure of 20 mbar. The boiling range of the extracted creosote was measured by gas chromatography (SimDis, simulated distillation, according to DIN 51435) and given as a set of temperatures indicating evaporation of 10%, 50%, 90%, and 98% of the sample. The results obtained by the SimDis method were successfully validated by comparison with thermogravimetrical analysis (TGA) of 3 standard creosote samples. Concentrations of the 16 PAH defined as priority pollutants by the U.S. Environmental Protection Agency (16 EPA-PAH) were determined by gas chromatography/high-resolution mass spectrometry using deuterated internal standards by the following procedure: 100 µL of the toluene/methanol extract and 100 µL of internal standard were put on a silica gel column (4 × 30 mm, 250 mg silica gel 60, deactivated with 10% water, conditioned with 5 mL of cyclohexane) and

eluted with 10 mL of cyclohexane. As an internal standard, 100 µL of a solution of naphthalene-d8 (5 ng/µL), anthracened10 (2 ng/µL), chrysene-d12 (2 ng/µL), perylene-d12 (0.2 ng/ µL), and benzo[ghi]perylene-d12 (0.02 ng/µL) in cyclohexane was used. After reduction of the volume of the filtered samples from 10 mL to 100 µL (series A), 5 µL of each sample was diluted with 200 µL of cyclohexane (series B). Due to the high concentration differences of the individual PAH in creosote, the diluted sample (series B) was used to quantify the 2- and 3-ring PAH, whereas the concentrated sample (series A) was taken to quantify the 4- to 6-ring PAH. Immediately before analysis, all samples were spiked with 10 µL syringe standard (2 ng/µL pyrene-d10, cleanup recovery). High-resolution gas chromatography (MEGA 2 HRGC, Fisons) was performed on capillary columns (20 m × 0.3 mm, stationary phase PS086, film thickness 0.15 µm, carrier gas hydrogen at 40 kPa, oncolumn injection). PAH and internal standards were detected on a high-resolution mass spectrometer (MAT 95, Finnigan) in MID-mode (multiple ion detection) at a mass resolution of 10000. The method was validated by analysis of a certified reference standard (NIST SRM1647), and the error was found to be within 20% of the specified values. The content of total phenolic compounds was determined with UV/vis spectrophotometry according to ASTM 1783-91 (4-aminoantipyrin method).

Results and Discussion Creosote - Properties and Composition. Until 1994, the Swiss Federal Railways installed railroad ties treated with creosote according to the WEI-A standard. This standard corresponds to the creosote which was used for many decades for the treatment of railroad ties in Europe (boiling range 210-450 °C, benzo[a]pyrene content lower than 500 ppm). During the past decade, creosotes corresponding to WEI-B and WEI-C have been developed. Benzo[a]pyrene contents below 50 ppm were achieved for creosotes according to the WEI-B standard, which contains less high boiling components (boiling range 210-400 °C). Railroad ties treated with creosote according to WEI-B were installed between 1994 and 1997. Further improvement was made by the introduction of creosote according to WEI-C (4), containing lower amounts of the most volatile components (boiling range 250-400 °C, benzo[a]pyrene contents below 50 ppm). Starting from 1998, the Swiss Federal Railways exclusively installed ties treated with creosote according to WEI-C. VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. PAH Contents [ppm ) mg/kg] of Commercial Creosotes and Carbolineum Samples contents in [ppm] naphthalene acenaphthylene acenaphthene anthracene fluorene phenanthrene benz[a]anthracene chrysene fluoranthene pyrene benzo[a]pyrene benzo[b]fluoranthene benzo[k]fluoranthene dibenz[a,h]anthracene benzo[ghi]perylene indeno[1,2,3-cd]pyrene sum EPA-PAH [%]

creosote T1 creosote T4 carbolineum creosote T2 creosote T5 creosote T7 creosote T3 creosote T6 creosote T8 (WEI-A) (WEI-A) T9 (WEI-B) (WEI-B) (WEI-B) (WEI-C) (WEI-C) (WEI-C) 9500 7 9500 9000 19000 68000 380 340 55000 31000 160 96 67 16 45 40 20

27000 1700 30000 8000 43000 84000 250 120 100000 88000 3 3 4 1 1 2 39

16000 80 46000 8200 42000 48000 950 620 62000 46000 56 56 50 7 14 16 27

6900 110 61000 5500 48000 49000 62 43 60000 41000 15 14 14 3 5 6 27

15000 3700 43000 7000 58000 76000 130 63 100000 83000 2 3 3 1 2 2 39

52000 800 110000 7100 73000 71000 95 55 77000 42000 14 11 11 5 7 7 43

3800 27 27000 14000 46000 120000 39 19 120000 87000 15 13 15 6 5 5 42

12000 140 27000 10000 35000 91000 210 96 120000 100000 2 2 2 1 1 1 41

7400 43 21000 7700 34000 49000 350 170 69000 59000 9 8 10 3 4 5 25

FIGURE 2. PAH profiles [ppm ) mg/kg] of two creosotes according to WEI-A and WEI-C standards. PAH contents and boiling range of 9 commercially available creosote samples were determined (see Table 1). The concentration range of the PAH varies between 1 ppm and more than 100000 ppm. Between 20 and 40% of the total weight of a typical creosote is represented by the sum of the 16 EPA-PAH. Levels of benzo[a]pyrene detected vary between 2 and 160 ppm. Good correlation between the upper limit of the boiling range and the content of benzo[a]pyrene was found for all products (data not shown). The various types of creosotes could be distinguished easily by boiling range analysis (SimDis and TGA). Generally, the larger the number of aromatic rings in the chemical structure of a PAH, the lower are solubility (in water) and volatility. Figure 2 shows typical PAH-profiles of commercially available creosotes (WEI-A and WEI-C). The standard creosote (WEI-A) contains significantly higher amounts of 5- to 6-ring PAH (due to its high upper boiling range limit) than the new WEI-C variety, which contains also lower amounts of naphthalene, but higher amounts of the 3- and some 4-ring PAH (medium boiling range). Railroad Ties - Inventory and Emissions. Standards established by the Swiss Federal Railways several decades 4768

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ago request a creosote content of 160 kg/m3 for beech wood and 60 kg/m3 for oak wood ties. With permeable timbers such as beech wood, which accounts for about 80% of the railroad ties in service in Switzerland, complete penetration of large size timbers can be obtained. Due to the structure of wood, local concentrations of creosote decrease from the outside toward the center of the railroad tie. Oak wood, however, can only be penetrated to a depth of a few cm by standard vacuum-pressure treatment. Creosote - Inventory and Emissions. Knowledge of the original creosote content (160 kg/m3 for beech wood and 60 kg/m3 for oak wood ties) as well as the typical distribution patterns of creosote in new and in used railroad ties is crucial to determine emissions of creosote and PAH by comparison of railroad ties of different ages. In Figure 3, the creosote contents across a new and a used railroad tie are shown. Creosote contents of 27.9% in the top and 24.6% in the bottom layers were measured in the new railroad tie (sample S1). In the center, contents of 15.5 and 16% were found. For the used railroad tie (sample S5), the concentrations of creosote in the center were almost the same (15.9 and 16.5%), but concentrations at the outside were down at 12.6 to 13.9%.

amounts of creosote during the service time of each railroad tie were calculated for each of the eight layers. The results are shown in Table 2. Quantities of emitted creosote increase with increasing age up to 5 kg. Emitted quantities of creosote of beech and oak wood ties are both in the order of 5 kg, regardless of the type of wood. Railroad ties made from oak wood contain considerably less creosote than ties made from beech wood. The creosote, however, is concentrated within the outer layers (2-4 cm) where significant emission takes place. The fact that low volatile components are enriched in the outer layers may be used to estimate the amount of creosote being emitted. For the railroad tie sample S5, the increase of the benzo[a]pyrene concentration corresponds to a reduction of the original creosote content by 29%. A reduction of the original creosote content by 34% was determined using the method based on the standard concentration profile.

FIGURE 3. Distribution of creosote in a new and used railroad tie as a function of depth. Each bar represents 2 cm of the cross section of the tie (black bars represent top and bottom layers). This inversion of the concentration profile upon exposure has already been described by Petrowitz and co-workers (10, 11). The authors report, that immediately after treatment, the concentration of creosote to a depth of 2 cm was found to be about 25 to 35% higher than at a depth of 8-10 cm. Losses of creosote observed were 8% after 2 years, 18% after 5 years, and 27% after 10 years service time. Concentration profiles can be used to estimate the amount of creosote being emitted, based on the assumption that the concentration of creosote in the center remains unchanged. Standard concentration profiles for beech and oak wood railroad ties were defined, representing typical creosote concentrations after treatment. These standard profiles were compared to the concentrations of creosote determined in railroad ties of different ages. From this comparison, emitted

Creosote is a complex mixture containing polycyclic aromatic hydrocarbons as well as monocyclic aromatic compounds including phenols and heterocyclic compounds. The range of water solubility and volatility of these species is enormous. Therefore, emissions will consist mainly of components with high volatility and high water solubility. Data obtained by analysis of the boiling range of the creosote extracted from various layers support this point. Results of a boiling range analysis of the creosote extracted from a new and from a railroad tie in service for 32 years are given in Figure 4. On the outermost layers (black bars) of the used railroad tie (sample S5), the upper limit of the boiling range is significantly increased, demonstrating that creosote components of high volatility have been emitted exclusively from the outermost layers. This effect could not be seen either for new railroad ties (sample S1) nor for railroad ties being in service up to 6 years (data not shown). Based on the boiling range analysis, the properties of the creosotes used for vacuum-treatment of these two railroad tie samples can be determined. The boiling range limits for the new railroad tie (creosote according to WEI-C) are around 275 °C (10%) and 460 °C (98%), whereas the boiling range limits for the used railroad tie (32 years old, creosote according to WEI-A) are between 225 °C and 510 °C, clearly reflecting the differences in the boiling range of the two different creosote products. Results obtained from the outermost layers of the railroad

TABLE 2. Description of Railroad Tie Samples and Summary of Results railroad tie sample

S1

S2

S3

S4

S5

S6

age [years] type of wood origina creosote type creosote emissions emission [%] emission [kg] PAH contents (extract) naphthalene [ppm] benzo[a]pyrene [ppm] PAH emissions naphthalene [g] acenaphthylene [g] acenaphthene [g] anthracene [g] fluorene [g] phenanthrene [g] total PAH emissions [g] toxicity equivalents TEQ [g] phenols in extract [%] emissions of phenols [g]

0.5 beech Corbat sa WEI-C

1 beech VFT WEI-A

6 beech VFT WEI-A

19 oak SBB WEI-A

32 beech SBB WEI-A

46 oak SBB WEI-A

3 0.4

19 2.9

10 1.5

93 5.3

34 5.1

88 5.0

3830 6

13860 386

20850 425

22000b 1980b

29100 814

11900b 1480b

4.9 0.0 18.2 2.7 12.7 109.8 148.3 0.241 0.16 0.6

39.7 0.0 42.1 18.6 70.7 272.0 443.1 1.07 0.06 1.3

30.6 0.0 0.0 14.5 0.0 147.9 193 0.364 0.13 1.7

c c c c c c c c 0.77b 10.6

127.8 0.4 229.4 23.9 117.4 0.0 498.9 0.714 0.26 14.3

c c c c c c c c 0.73b 10.0

a Corbat sa, Vendlincourt, Switzerland; VFT AG, Hahnau, Germany; SBB Swiss Federal Railways, Bern, Switzerland. b Mean values from the extract from layers 1 and 8 (oak wood). c No data on PAH emissions (oak wood).

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FIGURE 4. Boiling range of creosote extracts of a new and a used railroad tie as a function of depth. Each bar represents 2 cm of the cross section of the tie (black bars represent top and bottom layers).

FIGURE 5. PAH concentrations [ppm ) mg/kg] in creosote extracted from a used railroad tie. Each bar represents 2 cm of the cross section of the tie (black bars represent top and bottom layers). ties made of oak wood (ages 19 and 46 years) show upper boiling range limits between 540 and 560 °C as expected for creosote according to WEI-A. PAH - Inventory and Emissions. The distribution of the individual PAH in creosote extracted from used ties was found to be different from that found for commercially available creosote samples. Concentrations of 4- to 6-ring PAH in the extracts from all used railroad ties were significantly higher than in the creosote samples according to WEI-A. In a beech wood railroad tie being in service for 32 years (sample S5) concentrations of benzo[a]pyrene of 1122 and 954 ppm were found in the outermost layers. The highest benzo[a]pyrene concentrations were detected in creosote extracted from an oak wood railroad tie (sample S4, 19 years old), containing 1892 ppm in the top and 2061 ppm benzo[a]pyrene in the bottom layer. High concentrations of benzo[a]pyrene found in used railroad ties were also reported by Rotard and Mailahn (9), who measured levels of benzo[a]pyrene between 1830 4770

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and 10490 ppm in creosote extracted from used railroad ties collected from various playgrounds (corresponding to contents of 183 and 1573 ppm in wood). From the concentration profiles of the individual PAH across the railroad ties, emissions of 2- and 3-ring PAH could be unambiguously detected. This is demonstrated in Figure 5, showing the concentration profiles of all 16 EPA-PAH for a railroad tie being in service for 32 years (sample S5). For naphthalene, acenaphthene, and fluorene, concentrations in the top and bottom layers (black bars) are significantly lower than in the inner layers (white bars). On the other hand, concentrations of benz[a,h]anthracene, fluoranthene, pyrene, chrysene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, dibenz[a,h]anthracene, benzo[ghi]perylene, and indeno[1, 2, 3-cd]pyrene are all significantly higher in the top and bottom layers than in the inner layers. One can go one step further and compare top (leftmost bar in each group) and bottom (rightmost bar in each group) of

the railroad tie. In all cases, the concentrations of the volatile PAH are lower on the top side, whereas the concentrations of the less volatile PAH are increased compared to the bottom side. The same trend is reflected by the boiling range data shown in Figure 4. Thus, it can be concluded that the major part of the emissions take place at the top side, induced by sun radiation, rain, and wind. Decreased concentrations of naphthalene, methylnaphthalenes, fluorene, and methylfluorenes in creosote extracted from used ties were also reported by Petrowitz and co-workers (10, 11). Cooper and co-workers (15) also found significantly different distribution of PAH constituents in creosote extracted from ties removed from service compared to new creosote. With the exception of naphthalene, the volatile components of creosote such as quinoline, 2-methylnaphthalenes, acenaphthene, and dibenzofuran were more highly represented in the new creosote, and preferential loss of the more volatile and water soluble components was observed. To quantify the amounts of each of the 16 EPA-PAH emitted by each railroad tie, a simple and robust procedure was defined (profile analysis). As confirmed by analysis of the new railroad tie S1, the content of creosote is a function of the depth of the respective layer. However, concentrations of all individual PAH species in the creosote extracts across the profile of a new railroad tie were found to be equal at the time of creosote treatment. Once a railroad tie is installed in the track, the amount of creosote within the outermost layers starts to decrease. The concentrations of the 2- and 3-ring PAH in these layers decrease as well, while the relative concentrations of the 5- to 6-ring PAH increase with increasing exposure time. Emissions of each of the 16 EPAPAH can be calculated from the difference between the amount of each PAH in each layer at the time the railroad tie was vacuum-treated (estimated data) and the amount of the same PAH at the end of the service time (measured data). To estimate the PAH content at the time of vacuumtreatment, the creosote concentrations at the time of treatment in each layer were estimated using the standard concentration profile. The amounts of each PAH in each layer at the time of treatment can then be calculated from the amount of creosote and its composition at that time. Since virtually no emission takes place from the center of the railroad tie (as showed by the boiling range analysis, see Figure 4), the composition of the innermost layers can be taken to represent the composition of the original creosote (conservative estimate). Since this estimate can only be made for railroad ties made of beech wood of sufficient age, the most reliable estimates for the quantities of PAH emitted can be made based on the beech wood railroad tie aged 32 years. As shown in Table 2, the total amount of PAH emitted from this tie is in the order of about 0.5 kg (sum of 16 EPAPAH). The total estimated EPA-PAH emissions rise with increasing age of the ties from 148.3 g (sample S1, age 0.5 years) up to 498.9 g (sample S5, age 32 years). Emissions of 4- to 6-ring PAH could not be detected applying this method. Expressed in toxicity equivalents (TEQ) according to Nisbeth and LaGoy (17), emissions are in the order of 1 g TEQ for each tie (see also refs 18 and 19). Alternatively, an upper limit for the PAH emissions can be estimated by the amount of creosote being emitted. An average railroad tie (beech or oak) emits about 5 kg of creosote during its service time. Based on our measurements, the sum of the 16 EPA-PAH accounts for about 20% of the total weight of a typical creosote (WEI-A), resulting in an upper emission limit of about 1 kg. Since low boiling creosote components such as aromatics and methylnaphthalenes are emitted preferentially, the total amount of the 16 EPA-PAH being emitted has to be below this upper limit of 1 kg. Phenols - Inventory and Emissions. Typical concentrations of phenolic compounds between 0.06 and 0.77% were

measured in the creosote extracted from beech wood ties. Emissions were assessed using the same method which was applied for the determination of PAH emissions. Again, lower concentrations of phenols were found in the outermost levels of the railroad ties. Total emissions were calculated to be in the order of 10 g within 32 years using the profile analysis method. Emission Factors for Creosote, PAH, and Phenols. Emission factors were calculated based on the emitted amounts of creosote, PAH, and phenols and on age and dimensions of the railroad ties probed (20). Based on sample S5 (age 32 years, surface 2.1 m2), emission factors of 208 mg/(m2 × day) for creosote, 0.58 mg/(m2 × day) for phenols, and 20.3 mg/(m2 × day) for 2- and 3-ring PAH were calculated. Gevao and Jones (3) report mean total PAH fluxes for five PAH (acenaphthene, fluorene, phenanthrene, anthracene, and fluoranthene) from creosote treated wood between 2.57 ( 1.52 mg/(m2 × day) at 4 °C and 29.5 ( 6.1 mg/(m2 × day) at 30 °C. OSPARCOM (2) reports emission factors for 10 PAH (naphthalene, anthracene, phenanthrene, fluoranthene, benz[a]anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[a]perylene, and indeno[1,2,3-cd]pyrene) of creosote treated wood (2). The mean total flux given is 5994 × 10-6 kg/(m2 × year) into the soil (reported to be 2/3 of the total amount). This figure corresponds to a total flux (soil and air) of 24.6 mg/(m2 × day). Based on an estimated number of 9 million wooden railroad ties and the average content of creosote for each tie based on the standard concentration profiles for beech and oak wood, the cumulated inventory of creosote in the Swiss railway network is estimated to 116000 t. Considering the composition of a typical creosote, this amount corresponds to a naphthalene inventory of 1100 t and to an inventory of benzo[a]pyrene of 18 t. The inventory of the 16 EPA-PAH adds up to 23400 t. The same estimate made for the total inventory of phenolic compounds leads to an amount of 232 t. According to our study, about 1710 t of creosote components are being emitted by the ties of the Swiss railway network, every year. Based on the values reported above, yearly emissions of 2- and 3-ring EPA-PAH add up to 139 t. Cumulated emissions of phenolic compounds are in the order of 4 t per year.

Acknowledgments This work has been funded by the Swiss Agency for the Environment, Forests and Landscape (BUWAL) and by the Swiss Federal Laboratories for Materials Testing and Research (EMPA). The authors thank N. Heeb, P. Mattrel, C. Seiler, and M. Zennegg (EMPA Organic Chemistry Department) as well as K. Richter and D. Heer (EMPA Wood Department) and A. Zanier (EMPA Department of Motor Fuels/Combustibles) for support and discussions. U. von Arx, S. Joss, and A. Weber (BUWAL) are acknowledged for helpful discussions. Support (railroad tie and creosote samples) from the Swiss Federal Railways and from industry (Corbat sa, Vendlincourt, Switzerland; VFT AG, Castrop-Rauxel, and Hahnau, Germany; Cindu Chemicals, Uithoorn, The Netherlands) is gratefully acknowledged.

Literature Cited (1) Ku ¨ nniger, T.; Richter, K. EMPA Research Report 115/38; Swiss Federal Laboratories for Materials Testing and Research, 1998. (2) Oslo and Paris Conventions for the Prevention of Marine Pollution, Working Group on Diffuse Sources (DIFF). PAH Emission Factors with Procedural Guidance for the Submission of PAH Emission Data; Norway, DIFF 97/7/3-E(L), Cadiz, 30.93.10.96, 1996. (3) Gevao, B.; Jones, K. C. Environ. Sci. Technol. 1998, 32, 640-646. (4) Boenigk, W. Holz-Zentralblatt 1996, 122(23), 1. (5) Western-European Institute for Wood Preservation; Alle´e Hofter-Vleest 5, boıˆte 4, B-1070 Bruxelles. VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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Received for review May 17, 2000. Revised manuscript received August 7, 2000. Accepted August 29, 2000. ES000103H