Wood-preserving chemicals

Wood-preserving chemicals

1 Wood-preserving chemicals 1.1 Introduction This chapter describes the chemicals that are used in the preservation of wood. The chapter is followed b...

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1 Wood-preserving chemicals 1.1 Introduction This chapter describes the chemicals that are used in the preservation of wood. The chapter is followed by a discussion of pressure-treated wood manufacturing technologies. An understanding of both the toxic nature of chemicals used and manufacturing steps is critical to identifying and responsibly managing the many forms of pollution and waste generated in the production of treated wood products. As described in later chapters, a wood-treating plant generates both fugitive and point sources of pollution. While many of these are better managed today, historically the industry has been among the worst polluters, leaving toxic legacies that are likely to be a concern for present and future generations. The industry overall has lagged in adopting good housekeeping and source reduction practices that have been available for more than 70 years. Much of this can be attributed to an industry structure that is historically based on small fragmented business units and enterprises. The USA almost stands as an island unto itself with the industry’s continued dependence on creosote coal tars, pentachlorophenol, and arsenicals. While these chemicals unquestionably provide superior product performance as pesticides designed to kill, they bring with them negative impacts to workers, neighboring communities, and the environment. For more than 30 years the National Institute of Occupational Safety and Health (NIOSH, 1977a) and the Occupational Safety and Health Administration (OSHA, 1978) have labeled creosote as a dangerous chemical that is linked to cancer. The US Environmental Protection Agency (EPA, 1984) has defined creosote, pentachlorophenol, and arsenical treating formulations as chemicals that are potential carcinogens. Austria, India, Indonesia, New Zealand, Sweden, Switzerland, the EU/EEA member states, and Belize are among the international community that have banned, or placed severe restrictions on, the use of pentachlorophenol because of its link to carcinogenicity and the fact that the product contains dioxins. Both New York and New Jersey have banned all use of creosote in treated wood manufacturing as of 2008. There is overwhelming consensus from the scientific community and governmental organizations that the chemicals used by the US wood-preserving industry are dangerous and cancer causing. Companies that continue to use such chemicals have an obligation to employ the best available technologies and practices that eliminate these materials from entering into the air and into surface water run-off that may enter into receiving bodies or pass through communities, and from contaminating groundwater.

Handbook of Pollution Prevention and Cleaner Production Vol. 2 Copyright Ó 2010 by Elsevier Inc. All rights reserved.


Handbook of Pollution Prevention and Cleaner Production

1.2 Wood types and products The feedstock material used by the industry sector is wood, of which there are several varieties. Primary types of wood exploited by the industry are Douglas fir, southern pine, oak, and mixed hardwood. The products made to service the rail industry are crossties, switches (switch ties), pilings, poles, crossarms, lumber and timber, and fence posts. A crosstie is also referred to as a railroad tie or a tie. The British call a railroad tie a sleeper. It is one of the cross-braces that support the rails on a railway track. Figure 1.1 shows a stack of crossties as they are typically bundled for shipment to a customer. Rail tracks are used on railways which, together with switches, guide trains without the need for steering. The tracks consist of two parallel steel rails, which are laid upon sleepers (crossties) that are embedded in ballast to form the railroad track. The rail is fastened to the ties with spikes, lag screws, bolts, or clips such as Pandrol clips. Figure 1.2 shows crossties arranged in a track. On average, about 3000 railroad ties are used per mile of track. A rail profile is a hot rolled steel profile of a specific shape or cross-section (an asymmetrical I-beam) designed for use as the primary component of railway track. Railway rails are subject to very high stresses and have to be constructed of very-high-quality steel. Minor flaws in the steel that pose no problems in reinforcing rods for buildings can, however, lead to broken rails and dangerous derailments when used on railway tracks. The rails represent a substantial fraction of the cost of a railway line. Only a small number of rail sizes are made by the steelworks at one time, so a railway must select the nearest suitable size. Worn, heavy rail from a mainline is often reclaimed and downgraded for reuse on a branchline, siding or yard.

Figure 1.1 Stack of creosote-treated railroad ties.

Wood-preserving chemicals


Figure 1.2 Railroad ties comprising a section of track.

Track ballast forms the trackbed upon which railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track structure. This also serves to hold the track in place as the trains roll by. It is typically made of crushed stone, although ballast has sometimes consisted of other, less suitable materials. The term ‘‘ballast’’ comes from a nautical term for the stones used to stabilize a ship. Good-quality track ballast is made of crushed natural rock with particles between 28 and 50 mm in diameter; a high proportion of particles finer than this will reduce its drainage properties, and a high proportion of larger particles result in the load on the ties being distributed improperly. Angular stones are preferable to naturally rounded ones, as these interlock with each other, inhibiting track movement. Soft materials such as limestone are not particularly suitable, as they tend to degrade under load when wet, causing deterioration of the line; granite, although expensive, is one of the best materials in this regard (Ellis, 2006). Usually, a baseplate (i.e. a tie plate) is used between the rail and wood sleepers, to spread the load of the rail over a larger area of the sleeper. Sometimes spikes are driven through a hole in the baseplate to hold the rail, while at other times the baseplates are spiked or screwed to the sleeper and the rails clipped to the baseplate. Tie plates add to the stability of track, lengthen the life of wood ties, and provide uniform wear on the rail head. Tie plates are available in single- or double-shoulder design (see Figure 1.3). Steel rails can carry heavier loads than any other material. Railroad ties spread the load from the rails over the ground and also serve to hold the rails a fixed distance apart (the gauge). Ties are laid across the ballast at intervals of about two feet (roughly 3000 ties per mile). The rails are then laid atop the ties, perpendicular to them. If the ties


Handbook of Pollution Prevention and Cleaner Production

Figure 1.3 Examples of tie plates.

are wood, tie plates are then set atop the ties on the rail flange, and then spikes or bolts are driven through the tie plates into the ties to clamp down the rails. Historically, US railroads have used driven rail spikes to hold the rail to the tie, while European railways favor square-headed bolts that are screwed into the wood. For concrete ties, steel clips (e.g. the Pandrol clip) are used to fasten the rails. After this is done, additional ballast is then added to fill the spaces between and around the ties to anchor them in place. The ties serve as anchors and spacers for the rails, while providing a slight amount of give to accommodate weather and settling. The ties are ‘‘floating’’ in the top of the ballast. Failure of a single tie is generally insignificant to the usability and safety of the rails. Rails lie somewhat freely in tie plates and sliding movement of the rail through the plate is possible, leading to creeping rails or misaligned or unevenly spaced ties. To prevent this, anchors are placed transversely under the rail at each side of the tie to prevent slippage of the rail and the tie relative to each other. The tie anchor is usually a spring-loaded clip placed with a hammer blow (driven) or with a special lever (wrench). Wood is a versatile and effective material for use as a crosstie. However, the key properties of wood will vary with class of wood type. In order to allow for the potential use of a broad range of wood types, the wood tie properties need to be considered in terms of the categories of wood. The material properties noted herein are based on a collection of data reported from various sources on the Web and are consistent with those presented in the Manual for Railway Engineering of the American Railway Engineering and Maintenance of Way Association (AREMA, 2007). Table 1.1 provides wood property values using the following parameters: 1. Dimensions are for a standard main line wood crosstie and are based on the AREMA specification that allows a ¼-inch reduction in width and depth. The unit of measure is inches. 2. Volume is defined as the total amount of space occupied by the crosstie and is calculated based on the dimensions shown. The unit of measure is cubic feet. 3. Density is mass per unit volume and is based on reported values derived from the testing of small clear specimens of wood using ASTM procedure D-143 and US Forest Service data. Actual whole tie values may differ. The unit of measure is pounds per cubic foot.

1. Dimensions Length (in) Width (in) Depth (in)

Nominal 102 9 7

2. Volume (ft3)


Northern mixed hardwoods

Southern mixed hardwoods

Southern yellow pine


Douglas fir

102 8.75 6.75

102 8.75 6.75

102 8.75 6.75

102 8.75 6.75

102 8.75 6.75

102 8.75 6.75


3. Density (pcf) (lb/ft3)


3.49 65.3

3.49 58.9

3.49 62.1

3.49 53.4

3.49 59.7

4. Weight (lb)







5. Moment of inertia (in4)













6. Section modulus (in3) 7. Modulus of elasticity (MOE)





8. Modulus of rupture (MOR) (psi)







Janka Ball





9. Rail seat compression test (psi) 10. Material surface hardness test (lb) 11. Static bending strength (in-kips) 12. Stiffness; load/deflection (in) 13. Single tie lateral push test (lb)

0.165 1950

0.157 1900


















0.212 1800


0.134 1850

0.187 1700

Wood-preserving chemicals

Table 1.1 Typical material and tie strength properties

0.125 1800



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4. Weight is the density multiplied by the volume. The unit of measure is pounds. 5. Moment of inertia (MOI) is a measure of the rectangular shape of the crosstie and is calculated around its neutral axis calculated based on the defined dimensions and a rectangular cross-section. The unit of measure is inches4. 6. Section modulus is a measure of the shape of the crosstie and is calculated by dividing the MOI by the greatest distance of the section from the neutral axis, calculated from dimensions and rectangular cross-section. The unit of measure is inches3. 7. Modulus of elasticity (MOE) is the rate of change of unit stress with respect to unit strain under uniaxial loading within the proportional (or elastic) limits of the material. This parameter is a measure of the stiffness of the crosstie, i.e. the relationship between load (stress) and deflection (strain). Values are average reported ones derived from testing of small clear specimens of wood using ASTM procedure D-143 and US Forest Service data. Actual whole tie values may differ. Unit of measure is pounds per square inch. 8. Modulus of rupture (MOR) is a measure of the maximum load-carrying capacity or strength of the crosstie and is defined as the stress at which the material breaks or ruptures (based on the assumption that the material is elastic until rupture occurs). Reported values are those derived from testing of small clear specimens of wood using ASTM procedure D-143 and US Forest Service data. Actual whole tie values may differ. The unit of measure is pounds per square inch. 9. The rail seat compression test is a measure of the crushing strength or load-carrying capacity of the crosstie at the rail seat (under the tie plate) and is defined as load per unit area at which compression of the wood occurs. The unit of measure is pounds per square inch. 10. The material surface hardness (Janka Ball) test is a measure of the surface hardness of the crosstie and is defined as load necessary to push a two-inch-diameter steel ball 0.25 inches into the tie surface. The unit of measure is pounds. 11. Static bending strength is a measure of the strength of the crosstie and is based on a load/deflection test carried out to failure of the wood material (test similar to C-stiffness load/deflection test). The unit of measure is inch-kips. 12. C-stiffness load/deflection is a measure of the flexibility of the crosstie and is based on a load deflection test in which a load of 10,000 lb is applied to the center of the crosstie, which is supported from below at two points 60 inches apart. The deflection is measured. The unit of measure is inches. 13. The single-tie lateral push test is a measure of the lateral resistance of a single crosstie in ballasted track and is representative of the relative resistance of the track to lateral movement in the ballast. Values are based on field tests taken by the US Department of Transportation and are based on ‘‘minimum’’ value for consolidated track adjusted to account for differences in density (weight) of the different crosstie wood materials. The unit of measure is pounds.

1.3 Chemicals used in preservation 1.3.1

Coal-tar creosote

Coal-tar creosote is a brownish black/yellowish dark green oily liquid with a characteristic sharp odor, obtained by the fractional distillation of crude coal tars. The approximate distillation range is 200–400 C as reported in

Wood-preserving chemicals


Table 1.2 General properties of creosote Property



Coal-tar creosote, creosote oil, coal-tar oil, creosote P1

CAS nos.

8001-58-9; 90640-80-5 (anthracene oil); 61789-28-4

Molecular mass

Variable (complex mixture of hydrocarbons)

Boiling range

~200–400 C


1.00–1.17 g/cm3 at 25 C


4–14 mm2/s at 40 C

Flash point

Above 66 C

Ignition temperature

500 C

Octanol/water partition coefficient (log Kow)


Solubility in organic solvents

Miscible with many organic solvents

Solubility in water

Slightly soluble/immiscible

the general public literature. Table 1.2 summarizes the general properties of creosote. The chemical composition of creosotes is influenced by the origin of the coal and also by the nature of the distilling process. This means that creosote components are rarely consistent in their type and concentration. According to the US EPA there are six major classes of compounds in creosote (Willeitner and Dieter, 1984; US EPA, 1987): 



aromatic hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs (nonheterocyclic PAHs can constitute up to 90% of creosote by weight), and benzene, toluene, ethylbenzene and xylene compounds (known collectively as BTEX); tar acids/phenolics, including phenols, cresols, xylenols, and naphthols (tar acids, 1–3 weight %; phenolics, 2–17 weight %); tar bases/nitrogen-containing heterocycles, including pyridines, quinolines, benzoquinolines, acridines, indolines, and carbazoles (tar bases, 1–3 weight %; nitrogencontaining heterocycles, 4.4–8.2 weight %); aromatic amines, such as aniline, aminonaphthalenes, diphenylamines, aminofluorenes, and aminophenanthrenes, cyano-PAHs, benzacridine, and its methylsubstituted congeners; sulfur-containing heterocycles, including benzothiophenes and their derivatives (1–3 weight %); oxygen-containing heterocycles, including dibenzofurans (5–7.5 weight %).

Table 1.3 provides chemical analyses of several coal-tar creosotes as reported by the US EPA, including the source data that were assembled in the reporting.


Table 1.3 Chemical analyses of coal-tar creosotesa Chemical analysis (weight %)b

Aromatic hydrocarbons Indene Biphenyl

Tar acids/phenolics Phenol o-Cresol m-, p-Cresol 2,4-Dimethylphenol Naphthols











0.6 1.3

0.43 1.45

0.87 4.1

1.3/3.0* 0.9*/1.7 1.2*/2.8 2.0*/2.3


13–18 12–17 12.0

7.6 0.9c 2.1c

9.0*/14.7 7.3/10.0* 2.3/3.0* 21* 3.0* 2.0* 4.0* 7.6/10.0* 7.0/8.5* 1.0/2.0*

3.1 3.1

9.0 7–9

8.3c 5.2c

12.32 3.29 7.51 3.42 0.15 12.51 5.03

11.4 8.87 11.5 5.16 0.1 5.86 6.33



16.9c 8.2d

10.21 0.45 0.9

6.7 0.54 0.8



12.9 2.2 4.5 1.6 0.2 5.8 4.6 3.1 11.2 3.1 1.7

2–3 1–5

7.5c 5.3c

4.6 3.7 2.2 0.5 0.22 0.5–1.0 0.2 0.2 0.1

4.41 2.0

2.27 1.13

0.2–2.2 0.1–1.5



0.21 <0.1

<0.05 <0.05

0.24 0.10 0.24 0.12 0.12


0.24 0.2 0.6 0.48


3.0 5.6

5.9 3.4 2.2 3.4


1 0.43c




2.31 0.59


Handbook of Pollution Prevention and Cleaner Production

PAHs Naphthalene 1-Methylnaphthalene 2-Methylnaphthalene Dimethylnaphthalenes Acenaphthylene Acenaphthene Fluorene Methylfluorenes Phenanthrene Methylphenanthrenes Anthracene Methylanthracenes Fluoranthene Pyrene Benzofluorenes Benz[a]anthracene Benzo[k]fluoranthene Chrysene Benzo[a]pyrene Benzo[e]pyrene Perylene




2d 2.0d 0.7d 4d 0.3d 3.9d 2d 2.8d 3.1d 2d

0.59 0.18 0.29

0.58 0.30 0.05

0.89 0.59 0.5










0.4 1.0

0.3 0.78

0.5 0.73


3.7 23.1

<0.1 6.14

<0.1 5.59

Aromatic amines Aniline Sulfur-containing heterocycles Benzothiophene Dibenzothiophene Oxygen-containing heterocycles/furans Benzofuran Dibenzofuran Other unspecified components





Wood-preserving chemicals

Tar bases/nitrogen-containing heterocycles Indole Quinoline Isoquinoline Benzoquinoline Methylbenzoquinoline Carbazole Methylcarbazoles Benzocarbazoles Dibenzocarbazoles Acridine


Adapted from Heikkila¨ (2001). Key: (A) From Lorenz and Gjovik (1972); with asterisk (*) from a literature survey; without asterisk, our own measurements of main components in an AWPA standard creosote. (B) From Nestler (1974); six creosotes, four unspecified, and two fulfilled the US federal specifications I and III. (C) From Andersson et al. (1983); Rudling and Rosen (1983); creosote used in the impregnation of railway ties. (D) From Wright et al. (1985). (E) From ITC (1990); AWPA standard creosote P1 (AWPA P1). (F) From Nylund et al. (1992); sample of German creosote; about 85 compounds were identified. (G) From Nylund et al. (1992); sample of former Soviet creosote; about 85 compounds were identified. (H) From Schirmberg (1980); three different creosote samples, all fulfilling the British standard BS 144/73/2. c Concentration in PAH fraction. d Concentration in nitrogen compound fraction. b



Handbook of Pollution Prevention and Cleaner Production

Creosotes used in wood preservation are classified according to national/ international standards in terms of specifications – e.g. American Wood Preservers’ Association (AWPA) standards P1 and P2 and the Western European Institute for Wood Preservation creosote grades A, B, and C. Prior to 1994, creosote could contain up to 20% phenolic compounds; in 1994, however, this was limited to 3% (EC, 1994). In recent years, legislation in many countries has required that the benzo[a]pyrene content of creosote be reduced. The EU (European Committee for Standardization, 2000) finalized a standard on classification and methods of testing for creosotes. European industry uses only creosote grades B and C with a benzo[a]pyrene content lower than 50 mg/kg (0.005 weight %) and, for grade C, lower volatile compounds (European Committee for Standardization, 2000). In contrast, the USA has been protective of this industry and has allowed lax requirements for coal-tar creosote. Coal-tar creosote (CAS 8001-58-9) is the most common form of creosote used in the workplace. It is referred to by the EPA as simply ‘‘creosote’’. It is a thick, oily liquid that is typically amber to black in color, and is a distillation product of coal tar. It has a burning, caustic taste. Coal-tar creosote is the most widely used wood preservative in the USA. It is used as a wood preservative and waterproofing agent for log homes, railroad ties, telephone poles, marine pilings, and fence posts. It is also a restricted-use pesticide, and is used as an animal and bird repellant, insecticide, animal dip, fungicide, and a pharmaceutical agent for the treatment of psoriasis. Because of its lethal properties, both Canada and the European Union have restricted its use and are moving towards a total ban of the product. There are approximately 300 chemicals that constitute the major compositional mix in coal-tar creosote; however, there can be up to 10,000 different chemicals in all within a typical mixture. Common synonyms are creosote (coal tar); AWPA #1; brick oil; coal creosote; coal-tar creosote; coal-tar oil (DOT); creosote (wood); creosote oil; creosote P1; creosotum; cresylic creosote; dead oil; heavy oil; liquid pitch oil; naphthalene oil; preserv-o-sote; RCRA Waste number U051; sakresote 100; tar oil; UN 1136 (DOT); and wash oil. Coal tar (CAS 8007-45-2) and coal-tar pitch (CAS 67996-93-2) are the byproducts of the high-temperature treatment of coal to make coke or natural gas. These chemical products are usually thick, black or dark brown liquids or semisolids with a naphthalene-like odor. Coal tar has a sharp, burning taste. Because of its dangerous properties both Canada and the European Union have banned the product. Coal-tar creosotes, coal tar, and coal-tar pitch are similar in composition, with the major chemicals in them that can cause harmful health effects being PAHs, phenol, and cresols. Approximately 75–85% or more of the coal tar mixture is comprised of PAHs. Coal-tar pitch is a residue produced during the distillation of coal tar and is distinct from coal tars and coal-tar creosotes. The pitch is a shiny, dark brown to black residue containing PAHs and methyl and polymethyl derivatives along

Wood-preserving chemicals


with heteronuclear components. Properties of PAHs are reported on the OSHA website (http://www.osha.gov/dts/sltc/methods/organic/org058/org058.html). The International Agency for Research on Cancer (IARC, 1987) defines coaltar creosote as ‘‘the fractions or blends of fractions specifically used for timber preservation’’. The US EPA simply refers to this mixture as ‘‘creosote’’. Bedient et al. (1984) have reported that mixture composition varies across production lots and manufacturers, but that an average composition contains about 85% PAHs and 2–17% phenolic compounds. The National Institute for Occupational Safety and Health (NIOSH, 1977b) defines coal-tar pitch as the tar distillation residue produced from coking. This means that the grade of pitch can vary significantly since distillation conditions such as residence time and temperature have first-order effects on the composition of the pitch. The product is comprised mainly of condensed ring aromatics, which includes two- to six-ring systems, along with minor components of phenolics and aromatic nitrogen bases. Weyand et al. (1991) and Guillen et al. (1992) have shown that the number of chemical components in coal-tar pitch is of the order of many thousands. Since commercial creosote mixtures come from different sources, which rely on different distillation parameters as well as sources of coal, one may expect that the creosote components are inconsistent in type and concentration. Weyand et al. reported two- to 20-fold differences in concentrations of several PAHs from a study of four coal tars. The IARC has determined that coal-tar creosote is a probable human carcinogen. The US EPA has determined that coal-tar creosote is a probable human carcinogen, and that coal-tar pitch is a confirmed human carcinogen. The EPA classified coal-tar creosote as a carcinogen in the 1992 Toxics Release Inventory (TRI). Skin cancer and cancer of the scrotum have resulted from longterm exposure to low levels of these chemicals, especially through direct contact with skin during wood treatment or manufacture of coal-tar-creosote-treated products, or in coke or natural gas factories. Cancer of the scrotum in chimney sweeps has been associated with prolonged skin exposure to soot and coal-tar creosote. Eating food or drinking water contaminated with a high level of creosotes causes a burning in the mouth and throat, as well as stomach pains. Brief exposure to large amounts of coal-tar creosote can result in a rash or severe irritation of the skin, chemical burns of the surfaces of the eye, convulsions, mental confusion, kidney or liver problems, unconsciousness, or even death. Longer exposure to lower levels of coal-tar creosote, coal tar, or coal-tar pitch by direct contact with skin or by exposure to the vapors from these mixtures can also result in sun sensitivity causing damage to skin in the forms of reddening, blistering, or peeling. Longer exposures to the vapors of the creosotes, coal tar, or coal-tar pitch can also cause irritation of the respiratory tract. The NIOSH recommended exposure limits (RELs) are time-weighted average (TWA) concentrations for up to a 10-hour working day during a 40-hour working week. A short-term exposure limit (STEL) is designated by ‘‘ST’’


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preceding the value; unless noted otherwise, the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a working day. A ceiling REL is designated by ‘‘C’’ preceding the value. Any substance that the NIOSH considers to be a potential occupational carcinogen is designated by the notation ‘‘Ca’’. The OSHA permissible exposure limits (PELs) are reported in Tables Z-1, Z-2, and Z-3 of the OSHA General Industry Air Contaminants Standard (29 CFR 1910.1000). Unless noted otherwise, PELs are TWA concentrations that must not be exceeded during any 8-hour work shift of a 40-hour working week. An STEL is designated by ‘‘ST’’ (short term) preceding the value and is measured over a 15-minute period unless noted otherwise. OSHA ceiling concentrations (designated by ‘‘C’’ preceding the value) must not be exceeded during any part of the working day; if instantaneous monitoring is not feasible, the ceiling must be assessed as a 15-minute TWA exposure. In addition, there are a number of substances from Table Z-2 (beryllium, ethylene dibromide, etc.) that have PEL ceiling values that must not be exceeded except for specified excursions. For example, a ‘‘5-minute maximum peak in any 2 hours’’ means that a 5-minute exposure above the ceiling value, but never above the maximum peak, is allowed in any 2 hours during an 8-hour working day. Because creosote and coal-tar products have such a broad composition of dangerous chemicals, a safe exposure level to the generic chemical itself is meaningless. From an inhalation exposure standpoint, the concern is for harmful PAHs. Benzo[a]pyrene is an example of one of these PAHs. It is one of the most studied of these hydrocarbons, and it is a ‘‘fingerprint’’ chemical for detecting the presence of PAHs. The benzo[a]pyrene content of coal tar is between 0.1% and 1% and it contributes to the serious potential health effects for employees exposed to emissions. Four other examples of PAH chemicals are anthracene, phenanthrene, pyrene, and carbazole, all of which are major components in creosote. PAHs are regulated by both the OSHA and EPA. Because these agencies regulate PAHs under slightly different definitions in relation to sources of emission, they refer to them by different names. The OSHA refers to them as coal-tar pitch volatiles (CTPVs) because, by definition, they come from both coke ovens and coal tar, which is derived from the coking process. The EPA calls them coke oven emissions (COEs), which by definition only relates to emissions from coke ovens. Both agencies, however, are referring to the same group of chemicals, including those of particular concern, the PAHs. The term CTPV (COE) is understood to mean ‘‘benzene-soluble fraction’’ and is therefore a measure of the presence of anthracene, benzo[a]pyrene, phenanthrene, acridine, chrysene, and pyrene (i.e. the benzene-soluble fraction is the sum of those components collected in a sample and determined to be soluble in benzene). CTPVs or COEs from hot industrial processes volatilize and then condense from coal or hot tar as soon as they contact normal (ambient) air temperature. CTPVs evaporate from the surface of hot coal tar during tar-processing

Wood-preserving chemicals


operations. COEs (including PAHs) escape at coke ovens during coal charging (filling an oven), coking, and coke pushing (removal of coke room an oven). In the case of wood-treating plants, CTPVs escape from treating cylinders when the wood product is removed after the treating cycle. The vapor pressure of CTPVs and COEs is so low at normal temperature that they are treated as particulate matter. Because they are particles, they can be removed from the air by particulate filters when process temperatures are near ambient. The standards to bear in mind are:    

OSHA General Industry PEL – 0.2 mg/m3 OSHA Construction Industry PEL – 0.2 mg/m3 TWA ACGIH threshold limit value (TLV) – 0.2 mg/m3 TWA; Appendix A1 (Confirmed Human Carcinogen) NIOSH REL – 0.1 mg/m3 TWA; Cyclohexane Extractable Fraction, Potential Carcinogen.

Standard procedures and analytical methods are provided by the OSHA (for recommended detailed analytical and sampling procedures, go to http://www. osha.gov/dts/sltc/methods/organic/org058/org058.html). In the OSHA sampling method, air samples are collected by drawing known amounts of air through cassettes containing glass fiber filters (GFFs). The filters are analyzed by extracting benzene and gravimetrically determining the benzene-soluble fraction (BSF). If the BSF exceeds the appropriate PEL, then the sample is analyzed by high-performance liquid chromatography (HPLC) with a fluorescence (mL) or ultraviolet (UV) detector to determine the presence of selected PAHs. The following are OSHA-recommended target concentrations that should not be exceeded in the workplace environment:       

0.20 0.15 8.88 0.79 9.00 3.27 2.49


mg/m3 for coal-tar pitch volatiles (PEL) mg/m3 for coke oven emissions (PEL) mg/m3 (1.22 ppm) for phenanthrene mg/m3 (0.11 ppm) for anthracene mg/m3 (1.09 ppm) for pyrene mg/m3 (0.35 ppm) for chrysene mg/m3 (0.24 ppm) for benzo[a]pyrene.


Pentachlorophenol (commonly referred to as PCP or Penta; CAS 87-86-5) is a chlorinated hydrocarbon. Its molecular structure is that of a phenol group with five chlorine atoms. Pentachlorophenol (C6HCl5O) is a synthetic fungicide that is part of the organochloride family. It has historically been used as a pesticide, herbicide, and wood preservative chemical. A major use of PCP has been as a wood preservative for power line and telephone poles, cross-arms and fence posts. PCP was first produced in the 1930s and has been marketed under various names, including Santophen, Pentachlorol, Chlorophen, Chlon, Dowicide 7, Pentacon, Penwar, Sinituho and Penta. It is available in two forms, PCP itself or


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as the sodium salt of PCP, which dissolves readily in water. In the past, it has been used as a herbicide, insecticide, fungicide, algaecide, disinfectant and as an ingredient in antifouling paint, and in some agricultural seed applications (for nonfood uses), leather, masonry, wood preservation, cooling tower water, rope, and in paper mill systems. Common synonyms are: penta-ate; pentachlorophenate sodium; pentachlorophenol, sodium salt; pentachlorophenoxy sodium; pentaphenate; phenol, pentachloro-, sodium derivative monohydrate; sodium PCP; sodium pentachlorophenate; sodium pentachlorophenolate; and sodium pentachlorophenoxide. The standard AWPA P8 defines the properties of pentachlorophenol preservative. Pentachlorophenol solutions for wood preservation contain no less than 95% chlorinated phenols, as determined by titration of hydroxyl and calculated as pentachlorophenol. The performance of pentachlorophenol and the properties of the treated wood are influenced by the properties of the solvent used. The AWPA P9 standard defines solvents and formulations for organic preservative systems. A commercial process using pentachlorophenol dissolved in liquid petroleum gas (LPG) was introduced in 1961, but later research showed that field performance of PCP/LPG systems was inferior to that of PCP systems. Thus, PCP/LPG systems are no longer used. The heavy petroleum solvent included in AWPA P9 Type A is recommended as preferable for maximum protection, particularly when wood treated with pentachlorophenol is used in contact with the ground. The heavy oils remain in the wood for a long time and do not usually provide a clean or paintable surface. Pentachlorophenol in AWPA P9, Type E solvent (dispersion in water), is only approved for above ground use in lumber, timber, bridge ties, mine ties, and plywood for southern pines, coastal Douglas fir, and redwood. In the pressure process method of preserving wood, the wood is placed in a pressure-treating vessel, where it is immersed in PCP and then subjected to applied pressure. In the nonpressure process method, PCP is applied by spraying, brushing, dipping, and soaking. Utility companies save millions of dollars in replacement poles, because the life of these poles increases from approximately 7 years for an untreated pole to about 35 years for a preservative-treated pole using this chemical. In some instances we have learned that wood-treating facilities in the past have added PCP to creosote production runs on an intermittent basis when fungicide problems have occurred. PCP is highly toxic and carcinogenic. These factors are almost intuitive when one considers the synthesis route. PCP can be produced by the chlorination of phenol in the presence of catalyst (anhydrous aluminum or ferric chloride) and a temperature of up to approximately 191 C. This process results in a product that is only 84% and 90% pure. During the process several contaminants, including other polychlorinated phenols, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, are produced. These impurities are more toxic than the PCP itself. The World Health Organization (http://www.inchem.org/documents/ehc/ehc/ ehc71.htm#SectionNumber:2.1) notes many more impurities in technical PCP,

Wood-preserving chemicals


depending on the manufacturing method. Among these are chlorophenols, particularly isomeric tetrachlorophenols, and several microcontaminants, mainly polychlorodibenzodioxins (PCDDs), polychlorodibenzofurans (PCDFs), polychlorodiphenyl ethers, polychlorophenoxyphenols, chlorinated cyclohexenons and cyclohexadienons, hexachlorobenzene, and polychlorinated biphenyls (PCBs). Table 1.4 provides PCP compositional data compiled and reported by the World Health Organization. The quality of PCP depends on the source and date of manufacture. Furthermore, analytical results may be extremely variable, particularly with regard to earlier results, which should be considered with caution. Some early studies from the 1970s report chlorinated 2-hydroxydiphenyl ethers, which may be converted to dioxins during gas chromatography, thus giving a false indication of a higher level of PCDDs. Unlike these ‘‘predioxins’’, other isomers are not direct precursors of dioxins, and are labeled ‘‘isopredioxins’’ in early studies. The toxicity of PCDDs and PCDFs depends both on the number and the position of chlorine substituents. Thus a precise characterization of PCP impurities is essential. The presence of highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-T4CDD) has been confirmed once in commercial PCP samples at concentrations up to 1100 ng/kg. The higher polychlorinated dibenzodioxins and dibenzofurans are more characteristic of PCP products. Hexachlorodibenzo-p-dioxin (H6CDD), which is considered highly toxic and carcinogenic, has been reported by the World Bank Organization (WBO) at levels of 0.03–35 mg/kg. Also octachlorodibenzop-dioxin (OCDD) is present in relatively high amounts in unpurified technical PCP. The identification of 2-bromo-3,4,5,6-tetrachlorophenol as a major contaminant in some commercial PCP samples (ca. 0.1%) has been reported. The thermal decomposition of PCP or Na-PCP results in significant amounts of PCDDs and PCDFs, depending on the thermolytic conditions. Pyrolysis of alkali metal salts of PCP at temperatures above 300 C results in the condensation of two molecules to produce OCDD. PCP itself forms traces of OCDD only on prolonged heating in bulk and at temperatures above 200 C. Beginning in 1984, the US EPA recommended restricted use of PCP. The following are EPA-approved precautions:  

Logs treated with pentachlorophenol should not be used for log homes. Wood treated with pentachlorophenol should not be used where it will be in frequent or prolonged contact with bare skin (for example, chairs and other outdoor furniture), unless an effective sealer has been applied. Pentachlorophenol-treated wood should not be used in residential, industrial, or commercial interiors except for laminated beams or building components that are in ground contact and are subject to decay or insect infestation, and where two coats of an appropriate sealer are applied. Sealers may be applied at the installation site. Wood treated with pentachlorophenol should not be used in the interiors of farm buildings where there may be direct contact with domestic animals or livestock that may crib (bite) or lick the wood.

Technical RhonePoulenc (86%)

104,000 <1000 ns

ns ns ns

50,000 20 ns

70,000 ns 70,000

<0.05 ns <0.5 <0.5 <1.0

<0.05 ns 1 6.5 15

<0.2 <0.2 9 235 250

<0.001 ns 3.5 130 600

<0.01 ns 5 150 600

ns ns 30 80 80

ns ns <0.5 <0.5 <0.5

ns ns 3.4 1.8 <1.0

<0.2 <0.2 39 280 230

ns 0.2 10 60 150

ns ns ns ns ns







Technical Dow (88.4%)

Technical Dow (98%)

Technical Dow (90.4%)

30,000 ns ns

44,000 <1000 62,000

2700 500 5000

Dibenzo-p-dioxins (mg/kg PCP) TetrachloroPentachloroHexachloroHeptachloroOctachloro-

<0.1 <0.1 8 520 1380

<0.05 ns 4 125 2500

Dibenzofurans (mg/kg PCP) TetrachloroPentachloroHexachloroHeptachloroOctachloro-

<4 40 90 400 260



Handbook of Pollution Prevention and Cleaner Production

Technical Dow (ns)

Technical Dyn. Nobel (87%)

Technical Monsanto (84.6%) Phenols (mg/kg PCP) TetrachloroTrichloroHigher chlorinated phenoxyphenols


Table 1.4 WBO-reported impurities (mg/kg PCP) in different technical PCP products

Wood-preserving chemicals




In interiors of farm buildings where domestic animals or livestock are unlikely to crib (bite) or lick the wood, pentachlorophenol-treated wood may be used for building components that are in ground contact and are subject to decay or insect infestation, and where two coats of an appropriate sealer are applied. Sealers may be applied at the installation site. Do not use pentachlorophenol-treated wood for farrowing or brooding facilities. Do not use treated wood under circumstances where the preservative may become a component of food or animal feed. Examples of such sites would be structures or containers for storing silage or food. Do not use treated wood for cutting boards or countertops. Only treated wood that is visibly clean and free of surface residue should be used for patios, decks, and walkways. Do not use treated wood for construction of those portions of beehives that may come into contact with the honey. Pentachlorophenol-treated wood should not be used where it may come into direct or indirect contact with public drinking water, except for uses involving incidental contact such as docks and bridges. Do not use pentachlorophenol-treated wood where it may come into direct or indirect contact with drinking water for domestic animals or livestock, except for uses involving incidental contact such as docks and bridges.

The following are OSHA safe exposure limits:    

PEL – 0.5 mg/m3 (skin) PEL TWA – 0.5 mg/m3 (skin) ACGIH TLV – 0.5 mg/m3 TWA (skin); Appendix A3 (Confirmed Animal Carcinogen with Unknown Relevance to Humans) NIOSH REL – 0.5 mg/m3 TWA (skin).

According to the United Nations Environment Programme (UNEP, 1991/1996) extensive use of PCP to treat wood, and to a lesser extent use in homes and gardens, together with its physical characteristics, indicate that there is likely to be widespread human exposure occurring partially through skin contact, but mainly through inhalation, which is the most dangerous route of exposure to PCP. The UNDP has reported that this has been confirmed by many reports of its occurrence in the general environment and its presence in body fluids, both in the general population and in exposed workers. Airborne levels of PCP production and woodpreservation facilities have ranged from several mg/m3 to more than 300 mg/m3 in some work areas. Domestic use, such as indoor application of wood preservatives and paints based on PCP or PCP-treated wood or indoor wood panels or boards, has historically led to high concentrations in the indoor atmosphere. Pentachlorophenol is not listed under the Pesticide Safety Directorate as being authorized for use in the UK. The primary UK legislation controlling pesticides is the Food and Environmental Protection Act (FEPA 1985 – as amended) and the Control of Pesticides Regulations (COPR 1986) made under this act. The UK legislation implementing the relevant EU Directive on releases to water is found in the ‘‘Surface Waters (Dangerous Substances) (Classification) Regulations, 1997 (SI 1997/2560)’’. It is also controlled under the UK Pollution Prevention


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and Control Regulations. Pentachlorophenol is also regulated under EC Council Directive 76/769/EEC relating to restrictions on the marketing and use of dangerous substances and preparations, Council Directive EC 76/464/EEC on the discharge of certain dangerous substances to the aquatic environment, 96/61/ EEC on integrated pollution prevention and control, and EC Directive 76/464: ‘‘Pollution of the aquatic environment by dangerous substances’’ (plus daughter directives); it is also on the list of 11 substances under review as potential ‘‘priority hazardous substances’’ under the proposed Water Framework Directive. Directive 86/280/EEC sets limit values on the discharge of pentachlorophenol to water. It is a UK ‘‘Red List’’ pollutant, the presence of which in the environment is of particular concern. Internationally it is listed as a substance for priority action on its control under the OSPAR and Helsinki Conventions. The US EPA is reassessing PCP as part of its re-registration program for older pesticides. Federal law directs EPA to periodically re-evaluate older pesticides to ensure that they continue to meet current safety standards. Pentachlorophenol was one of the most widely used biocides in the USA before regulatory actions to cancel and restrict certain nonwood-preservative uses of pentachlorophenol in 1987. Pentachlorophenol is a standardized oil-borne preservative listed in the AWPA Book of Standards under P8, Section 1. It now has no registered residential uses. The production of pentachlorophenol for wood preservation began on an experimental basis in the 1930s. In 1947 nearly 3200 metric tons of pentachlorophenol were reported to have been used in the USA by the commercial woodpreserving industry. Before the 1987 Federal Register Notice that canceled and restricted certain nonwood uses, pentachlorophenol was registered for use as a herbicide, defoliant, mossicide, and as a disinfectant. As of 2002, approximately 11 million pounds of pentachlorophenol were produced (http://www.epa. gov/pesticides/factsheets/chemicals/pentachlorophenol_main.htm).


Inorganic arsenicals

Inorganic arsenicals are those wood-preserving chemicals that contain arsenic. Arsenic is a naturally occurring semi-metallic element with an atomic weight of 74.92. Pure arsenic (which is rarely found in nature) exists in three allotropic forms: yellow (alpha), black (beta), and gray (gamma). Many inorganic arsenic compounds are found in the environment, frequently occurring as the sulfide form in complex minerals containing copper, lead, iron, nickel, cobalt, and other metals. Arsenic compounds occur in trivalent and pentavalent forms; common trivalent forms are arsenic trioxide and sodium arsenite, and common pentavalent forms are arsenic pentoxide and the various arsenates. Arsenic and arsenic compounds occur in crystalline, powder, amorphous, or vitreous forms. Elemental arsenic has a specific gravity of 5.73, sublimes at 613 C, and has a very low vapor pressure of 1 mmHg at 373 C. Many of the inorganic arsenic compounds occur as white, odorless solids with specific gravities ranging from about 1.9 to more than 5. Arsenic trioxide, the most common arsenic compound in commerce, melts at 312 C and boils at 465 C (ATSDR, 2000). In water,

Wood-preserving chemicals


elemental arsenic is insoluble, calcium arsenate and arsenites are sparingly soluble, and arsenic trioxide, arsenic pentoxide, and other arsenicals are soluble. Arsenic pentoxide, potassium arsenite, and the sodium salts are soluble in ethanol. Arsenic, arsenic pentoxide, arsenic trioxide, the calcium arsenites, lead arsenate, and potassium arsenate are soluble in various acids. When heated to decomposition, arsenic compounds emit toxic arsenic fumes. The end-use distribution of inorganic arsenic compounds in the USA has varied over the years. Inorganic arsenic compounds were widely used as pesticides from the mid-1800s to the mid-1900s and were used in medicine until the 1970s, primarily for treatment of leukemia, psoriasis, and asthma. By the mid1970s, arsenic use shifted from pesticides to wood preservatives, and by 1980 wood preservatives were the primary use. Since about the mid-1990s, arsenic trioxide used in wood preservation has accounted for 86–90% of total USA arsenic consumption. Wood treated with chromated copper arsenate (CCA), known as ‘‘pressure-treated wood’’, has been used widely to protect utility poles, building lumber, and foundations from decay and insect attack. Wood preservatives are expected to remain the major domestic use for arsenic; however, a voluntary phase-out of CCA for certain residential uses (e.g. in wood for decks, play structures, fencing, and boardwalks) that went into effect on 31 December 2003 will reduce this use of arsenic. CCA will continue to be used in wood products for industrial use. The USA is the world’s leading consumer of arsenic; however, arsenic has not been produced in the USA since 1985, when production of 2200 metric tons (4.9 million pounds) was reported. All arsenic metal and compounds consumed in the USA now are imported. Before 1985, US arsenic production varied widely, reaching a peak of 24,800 metric tons (54.7 million pounds) in 1944. Average annual production was 12,200 metric tons (26.9 million pounds) from 1935 to 1959 and 5100 metric tons (11.2 million pounds) from 1960 to 1985. US imports of arsenic and arsenic compounds increased as production decreased, with annual averages of about 8300 metric tons (18.3 million pounds) from 1935 to 1959, 11,300 metric tons (24.9 million pounds) from 1960 to 1985, and 23,300 metric tons (51.4 million pounds) from 1986 to 2002. Annual exports reached a peak of 4200 metric tons (9.3 million pounds) in 1941, but since 1985 have ranged from 36 to 1350 metric tons (79,000 to 3 million pounds). Arsenic imports are mainly in the form of arsenic trioxide; arsenic metal generally accounts for about 3–5% of imports. Inorganic arsenic compounds are known human carcinogens. Epidemiological studies and case reports of humans exposed to arsenic compounds for medical treatment, in drinking water, or occupationally have demonstrated that exposure to inorganic arsenic compounds increases the risk of cancer. Cancer tissue sites include the skin, lung, digestive tract, liver, bladder, kidney, and lymphatic and hematopoietic systems (organs and tissues involved in the production of blood). Skin cancer has been reported in individuals exposed to arsenic for therapeutic reasons, sometimes in combination with other cancers, such as angiosarcoma (blood-vessel tumors) of the liver, intestinal and bladder


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cancer, and meningioma (tumors of the membranes covering the central nervous system); however, only skin cancer has been clearly associated with medical use of arsenic in epidemiological studies (http://ntp.niehs.nih.gov/ntp/roc/eleventh/ profiles/s015arse.pdf).


Water-borne preservatives

Water-borne preservatives are used when cleanliness and paintability of the treated wood are required. Several formulations involving combinations of copper, chromium, and arsenic have shown high resistance to leaching and good performance in service. Water-borne preservatives are included in specifications for items such as lumber, timber, posts, building foundations, poles, and piling. Historically they have been used extensively by the railroad industry and for general construction markets. The AWPA has reported that dual treatment (water-borne copper-containing salt preservatives followed by creosote) is possibly the most effective method of protecting wood against all types of marine borers. The AWPA standards have recognized this process as well as the treatment of marine piles with high retention levels of ammoniacal copper arsanate (ACA), ammoniacal copper zinc arsenate (ACZA), or chromated copper arsenate (CCA). Water-borne preservatives leave the wood surface comparatively clean, paintable, and free from objectionable odor. CCA and acid copper chromate (ACC) must be used at low treating temperatures (38–66 C (100–150 F)) because they are unstable at higher temperatures. Because water is added to the wood in the treatment process, the wood must be dried after treatment to the required moisture content for the end use intended. As already noted, inorganic arsenicals are a restricted-use pesticide. Standard wood preservatives used in water solution include ACC, ACZA, and CCA (Types A and C). Other preservatives in AWPA P5 include alkylammonium compound (AAC) and inorganic boron. Water-borne wood preservatives, without arsenic or chromium, include ammoniacal copper quat (ACQ) (Types B and D), copper bis(dimethyldithiocarbarmate) (CDDC), ammoniacal copper citrate (CC), and copper azole Type A (CBA-A), for above ground use only. The following is a brief description of the major water-borne preservatives: 

Acid copper chromate (ACC). This contains 31.8% copper oxide and 68.2% chromium trioxide (AWPA P5). The solid, paste, liquid concentrate, or treating solution can be made of copper sulfate, potassium dichromate, or sodium dichromate. Use of ACC is generally limited to cooling towers that cannot allow arsenic leachate in cooling water. Ammoniacal copper zinc arsenate (ACZA). This is used in the USA but not in Canada. It is commonly used on the West coast for the treatment of Douglas fir. Wood heated with ACZA performs and has characteristics similar to those of wood treated with CCA. ACZA contains approximately 50% copper oxide, 25% zinc oxide, and 25% arsenic pentoxide dissolved in a solution of ammonia in water (AWPA P5). The weight of ammonia is at least 1.38 times the weight of copper oxide.

Wood-preserving chemicals



To aid in solution, ammonium bicarbonate is added (at least equal to 0.92 times the weight of copper oxide). A similar formulation, ammoniacal copper arsenate (ACA), is used in Canada. Chromated copper arsenate (CCA). Type A is only being used by a few treaters in California. CCA Type A is high in chromium. Service data on treated poles, posts, and stakes installed in the USA since 1938 have shown that CCA Type A provides excellent protection against decay fungi and termites. CCA Type B (I-33) is a formulation whose commercial use in the USA started in 1964, but it is no longer used in significant quantities. CCA Type B is high in arsenic and has been commercially used in Sweden since 1950. CCA Type C (Wolmanmently) is the most common formulation of CCA being used. Type C composition was selected by AWPA technical committees to encourage a single standard for CCA preservatives. Ammoniacal copper quat (ACQ). There are basically two types of ACQ preservatives (AWA P5): Type B (ACWB; ammoniacal) and Type D (ACWD; amine-based). ACQ is used for many of the same applications as are ACZA and CCA, but it is not recommended for use in salt water. ACFB, the ammoniacal formulation, is better able to penetrate difficult-to-treat species such as Douglas fir and it provides a more uniform surface appearance. Copper bis(dimethyldithiocarbamate) (CDDC). This is a reaction product formed in wood as a result of the dual treatment of two separate treating solutions. The first treating solution contains a maximum of 5% bivalent copper–ethanolamine (2aminoethanol), and the second treating solution contains a minimum of 2.5% sodium dimethyldithiocarbamate. Ammoniacal copper citrate (CC). This has 62.3% copper as copper oxide and 35.8% citric acid dissolved in a solution of ammonia in water (AWPA P5). Copper azole Type A (CBA-A). This has 49% copper as Cu, 49% boron as boric acid, and 2% azole as tebuconazole dissolved in a solution of ethanolamine in water (AWPA P5). Inorganic boron (borax/boric acid). Borate preservatives are readily soluble in water, are highly leachable, and should only be used above ground where the wood is protected from wetting. They are effective against decay, termites, beetles, and carpenter ants. Borates are odorless and can be sprayed, brushed, or injected. They will diffuse into wood that is wet. Borates are widely used for log homes, natural wood finishes, and hardwood pallets. Compounds are derived from the mineral sodium borate, which is the same material used in laundry additives.


Other wood-preserving chemicals

Copper naphthenate Copper naphthenate is an organometallic compound that is a dark-green liquid imparting this color to the wood. Weathering turns the color of the treated wood to light brown after several months of exposure. The wood may vary from light brown to chocolate brown if heat is used during treatment of the wood. The AWPA P8 standard defines the properties of copper naphthenate, and AWPA P9 covers the solvents and formulations for organic preservative systems. Copper naphthenate has been used commercially since the 1940s for many wood products. It is a reaction product of copper salts and naphthenic acids,


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which are usually obtained as by-products in petroleum refining. Copper naphthenate is not a restricted-use pesticide but is handled as an industrial pesticide. It may be used for superficial treatment, such as by brushing with solutions with a copper content of 1–2%.

Chlorothalonil Chlorothalonil (CTL; tetrachloroisophthalonitrile) is an organic biocide that is used to a limited extent for mold control in CCA-treated wood (AWPA P8). It is effective against wood decay fungi and wood-destroying insects. The CTL has limited solubility in organic solvents and very low solubility in water, but it exhibits good stability and leach resistance in wood. The solvent used in the formulation of the preservative is AWPA P9 Type A.

Chlorothalonil/chlorpyrifos Chlorothalonil/chlorpyrifos (CWCPF) is a preservative system composed of two active ingredients (AWPA P8). The ratio of the two components depends upon the retention specified. Chlorothalonil is an effective fungicide, and chlorpyrifos is very effective against insect attack. The solvent used for formulation of this preservative is specified in AWPA P9.

Oxine copper (copper-8-quinolinolate) Oxine copper (copper-8-quinolinolate) is an organometallic compound. The formulation consists of at least 10% copper-8-quinolinolate, 10% nickel-2ethylhexanoate, and 80% inert ingredients (AWPA P8). It is used as a standalone preservative for above-ground use for sapstain and mold control and is also used for pressure treating. A water-soluble form can be made but the solution is corrosive to metals. Oxine copper solutions are greenish brown, odorless, toxic to both wood decay fungi and insects, and are reported to have a low toxicity to humans and animals. Because of its low toxicity to humans and animals, oxine copper is the only EPA-registered preservative permitted by the US Food and Drug Administration for treatment of wood used in direct contact with food. Some examples of its uses in wood are commercial refrigeration units, fruit and vegetable baskets and boxes, and water tanks. Oxine copper solutions have also been used on nonwood materials, such as webbing, cordage, cloth, leather, and plastics.

Zinc naphthenate Zinc naphthenate is similar to copper naphthenate but is less effective in preventing decay from wood-destroying fungi and mildew. It is light colored and does not impart the characteristic greenish color of copper naphthenate, but it does impart an odor. Water-borne and solvent-borne formulations are available.

Wood-preserving chemicals


Zinc naphthenate is not used for pressure treating and is not intended as a standalone preservative.

Bis(tri-n-butyltin) oxide Bis(tri-n-butyltin) oxide, commonly called TBTO, is a colorless to slightly yellow organotin compound. It is soluble in many organic solvents but insoluble in water. It is not used for pressure treating or as a stand-alone preservative for inground use. TBTO concentrate contains at least 95% bis(tri-n-butyltin) oxide by weight and 38.2–40.1% tin (AWPA P8). This preservative has lower toxicity, causes less skin irritation, and has better paintability than does pentachlorophenol, but it is not effective against decay when used in ground contact. TBTO is recommended only for above-ground use, such as millwork. It has been used as a marine antifoulant, but this use has been almost eliminated because of the environmental impact of tin on shellfish.

3-Iodo-2-propynyl butyl carbamate 3-Iodo-2-propynyl butyl carbamate (IPBC) is a preservative intended for nonstructural, above-ground use only (e.g. millwork). It is not used for pressuretreating applications such as decks. The IPBC preservative is included as the primary fungicide in several water-repellent/preservative formulations under the trade name Polyphase and marketed by retail stores. It is not an effective insecticide. Water-borne and solvent-borne formulations are available. Some formulations yield an odorless, treated product that can be painted if dried after treatment. IPBC is also being used in combination with didecyldimethylammonium chloride in a sapstain-mold formulation (NP-I). IPBC contains 97% 3-iodo2-propynyl butyl carbamate, with a minimum of 43.4% iodine (AWPA P8).

Alkylammonium compound Alkylammonium compound (AAC) or didecyldimethylammonium chloride (DDAC) is a compound that is effective against wood decay fungi and insects. It is soluble in both organic solvents and water, and is stable in wood. It is used as a component of ammoniacal copper quat (ACQ; a water-borne preservative) for above-ground and ground contact and is a component of NP-1 for sapstain and mold control.

Propiconazole Propiconazole is an organic triazole biocide that is effective against wood decay fungi but not against insects (AWPA P8). It is soluble in some organic solvents. It has low solubility in water and is stable and leach resistant in wood. It is currently used for above-ground and sapstain control application in Europe and Canada. Solvents used in the formulation of the preservative are specified in either AWPA P9 Type C or Type F.


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4,5-Dichloro-2-N-octyl-4-isothiazolin-3-one This is a biocide that is effective against wood decay fungi and insects. It is soluble in organic solvents but not in water, and is stable and leach resistant in wood. This biocide is not currently being used as a wood preservative. The solvent used in the formulation of the preservative is specified in AWPA P9 Type C.

Tebuconazole Tebuconazole (TEB) is an organic triazole biocide that is effective against wood decay fungi. It is soluble in organic solvents but not in water, and it is stable and leach resistant in wood. Currently, TEB has no commercial application at present. The solvents used in the formulation of this preservative are specified in either AWPA P9 Type C or Type F.

Chlorpyrifos Chlorpyrifos (CPF) is a preservative (see AWPA P8) that is very effective against insect attack but not fungal attack. If fungal attack is a concern, then CPF should be combined with an appropriate fungicide, such as chlorothalonil/chlorpyrifos or IPBC/chlorpyrifos.

Water-repellent and nonpressure treatments Water-repellent preservatives retard the ingress of water when wood is exposed above ground. Preservatives help reduce dimensional changes in the wood as a result of moisture changes when the wood is exposed to rainwater or dampness for short periods. As with any wood preservative, the effectiveness in protecting wood against decay and insects depends upon the retention and penetration obtained. Preservatives are most often applied using nonpressure treatment like brushing, soaking, or dipping. Since the focus of this section of the volume is on pressure-treated wood, we only discuss this in passing. Preservative systems containing water-repellent components are sold under various trade names. Many are sold to the public for household and farm use. Federal specification TT-W-572 stipulates that such preservatives be dissolved in volatile solvents, such as mineral spirits, and do not cause appreciable swelling of the wood. The preservative chemicals in Federal specification TT-W-572 may be one of the following:    

not less than 5% pentachlorophenol; not less than 1% copper in the form of copper naphthenate; not less than 2% copper in the form of copper naphthenate for tropical environments; not less than 0.045% copper in the form of oxine copper for uses when foodstuffs will be in contact with the treated wood.

Wood-preserving chemicals


References American Railway Engineering and Maintenance of Way Association (AREMA), 2007. Manual for Railway Engineering, Chapter 30, Section 30-A-1. Andersson, K., Levin, J.O., Nilsson, C.A., 1983. Sampling and analysis of particulate and gaseous polycyclic aromatic hydrocarbons from coal tar sources in the working environment. Chemosphere 12, 197–207. ATSDR, 2000. ‘‘Toxicological Profile for Arsenic’’. NTIS Accession No. PB2000108021. Atlanta, GA: Agency for Toxic Substances and Disease Registry. pp. 466. Bedient, P.B., Rodgers, A.C., Bouvette, T.C., et al., 1984. Groundwater Quality at a Creosote Waste Site. Groundwater 22, 318–329. EC, 1994. European Parliament and Council Directive 94/60/EC of 20 December 1994, amending for the 14th time Directive 76/769/EEC on the approximation of the laws, regulations and administrative provisions of the Member States relating to restrictions on the marketing and use of certain dangerous substances and preparations. Official Journal of the European Communities. L365:1. Ellis, I., 2006. Ellis’ British Railway Engineering Encyclopedia. Available at Lulu.com. European Committee for Standardization, 2000. Derivates from coal pyrolysis d coal tar based oils: Creosotes d specifications and test methods. Brussels, European Committee for Standardization, pp. 1–11 (Project Reference 00317007 prEN 14998; CEN/TC 317/WG2). Guillen, M.D., Iglesias, M.J., Dominguez, A., et al., 1992. Polynuclear Aromatic Hydrocarbon Retention Indices on SE-54 Stationary Phase of the Volatile Components of a Coal Tar Pitch: Relationships between Chromatographic Retention and Thermal Reactivity. Journal of Chromatography. 591, 287–295. Heikkila¨, P. 2001. Respiratory and dermal exposure to creosote [Dissertation]. Kuopio, University of Kuopio (Kuopio University Publications C. Natural and Environmental Sciences 120). Available at http://www.uku.fi/vaitokset/2001/. International Agency for Research on Cancer (IARC), 1987. Monographs on the Evaluation of Carcinogenic Risk to Humans. Supplement 7, Vols 1–47. IARC, World Health Organization. ITC, 1990. Information about coal-tar creosote for wood preservation. Prepared by Tar Industries Services (TIS) for International Tar Conference, Paris, March, pp. 1–79. Lorenz, L.F., Gjovik, L.R., 1972. Analysing creosote by gas chromatography: relationship to creosote specifications. Proceedings of the Annual Meeting of the American Wood-Preservers’ Association 68, 32–42. National Institute of Occupational Safety and Health (NIOSH), 1977a. Criteria for a Recommended Standard – Occupational Exposure to Coal Tar Products. NIOSH, Washington, DC, September. National Institute of Occupational Safety and Health (NIOSH), 1977b. Criteria for Recommended Standard: Occupational Exposure to Coal Tar Products, NIOSH-78– 107. SRI International for US Department of Health and Human Services, NIOSH, Cincinnati, OH. Nestler, F.M., 1974. Characterization of wood-preserving coal-tar creosote by gas – liquid chromatography. Analytical Chemistry 46, 46–53. Nylund, L., Heikkila¨, P., Hameila, M., Pyy, L., Linnainmaa, K., Sorsa, M., 1992. Genotoxic effects and chemical compositions of four creosotes. Mutation Research 265, 223–236.


Handbook of Pollution Prevention and Cleaner Production

Occupational Safety and Health Administration (OSHA), 1978. Occupational Guidelines for Coal Tar Pitch Volatiles. OSHA, Washington, DC, September. Rudling, J., Rosen, G. 1983. Kemiska ha¨lsorisker vid tra¨impregnering II. Stockholm, Arbetarskyddsstyrelsen (Report No. Underso¨kningsrapport 1983:11) [cited in Heikkila¨, 2001]. Schirmberg, R., 1980. [The concentration of polycyclic aromatic compounds in some creosotes.] Analytical report to the Finnish Wood Preservers’ Association. Helsinki, Finnish Institute of Occupational Health (in Finnish) [cited in Heikkila¨, 2001]. United Nations Environment Programme (UNEP), 1991/1996. Joint FAO/UNEP Programme for the Operation of Prior Informed Consent. Food and Agriculture Organization of the United Nations, UNEP, Rome/Geneva, 1991, amended 1996. US Environmental Protection Agency (EPA), 1984. Wood Preservative Pesticides: Creosote, Pentachlorophenol and Inorganic Arsenicals, Position Document 4. EPA, Washington, DC, July. US Environmental Protection Agency (EPA), 1987. Weyand, E.H., Wu, Y., Patel, S., et al., 1991. Urinary Excretion and DNA Binding of Caol Tay B6C3FI Mice Following Ingestion. Chemical Research and Toxicology 4 (4), 466–473. Willeitner, H., Dieter, H., 1984. Steinkohlenteero¨l. Holz als Roh- und Werkstoff 42, 223–231. Wright, C.W., Later, D.W., Wilson, B.W., 1985. Comparative chemical analysis of commercial creosotes and solvent refined coaldII. Materials by high resolution gas chromatography. Journal of High Resolution Chromatography, & Chromatography Communications 8, 283–289.