Pentachlorophenol (PCP) in wood treatment
1.Introduction Wood is a hard, fibrous structural tissue found in the stems and roots of trees and other woody plants. It has been used for thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees or it is defined more broadly to include the same type of tissue elsewhere such as in the roots of trees or shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves. It also mediates the transfer of water and nutrients to the leaves and other growing tissues. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber. The Earth contains about one trillion tonnes of wood, which grows at a rate of 10 billion tonnes per year. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 1991, approximately 3.5 billion cubic meters of wood were harvested. Dominant uses were for furniture and building construction. The wood-preserving industry treats lumber with various chemicals to protect against insect damage and decay. Chemically preserved wood is used in products for outdoor use such as railway ties, fencing, telephone poles, exterior plywood panels, and outdoor decks. The industry has operated in our country for over 100 years, with sites often having operated for decades. Spills from the treatment process have left many of these sites heavily contaminated with the chemicals used to preserve wood. Just a few preserving chemicals have been widely used by the industry. The oldest preservative process treats wood with creosote, a tarry liquid derived from coal. Pentachlorophenol (PCP) became widely used as a preservative after 1950, although its purchase and use is now restricted. Metal salts made from chromium, copper, arsenic, or zinc (e.g., chromated copper arsenate [CCA]) are now the most frequently used preservatives. Pentachlorophenol (PCP) has been used for many years as a preservative in the wood treatment industry. It is a manufactured substance not occurring naturally in the environment. PCP was formerly one of the most heavily used pesticides in the world. Today its purchase and use is restricted to certified applicators, and it is used industrially as a wood preservative for power line poles, fence posts, etc. Before restriction, PCP was widely used as a wood preservative. It is made by only one company in the United States. Pure PCP is a white crystalline material, but the commercial grade form usually found atwaste sites is dark gray to brown.

2.General characterization of the product

Pentachlorophenol (PCP) is an organochlorine compound used as a pesticide and a disinfectant. First produced in the 1930s, it is marketed under many trade names. It can be found in two forms: PCP itself or as the sodium salt of PCP, which dissolves easily in water.

Figure 1 – Pentaclorophenol structure

Pentachlorophenol (PCP) was introduced in the 1930's as a preservative for timber and lumber. It still is used extensively for that purpose as well as in a wide variety of agricultural and industrial applications as fungicide, bactericide, herbicide, molluscicide, algicide, and insecticide (especially against wood—boring insects). Although the use level has declined somewhat in recent xears, present production worldwide is estimated to be about 50,000 metric tons (5 x lO kg) per year. PCP residues occur widely in man and his environment. For example, PCP was detected in over 80% of urine specimens analyzed during a US Environmental Protection Agency survey of both occupationally exposed workers and the general public. Although PCP, itself is among the more toxic chemicals available to the public, the technical product contains neutral impurities which could prove to be more hazardous. Certain isomers of hexa— and heptachlorodibenzo—p--dioxin and chlorodibenzofurans have high acute and chronic toxicity and their physical and chemical properties differ markedly from those of the phenols. A wide variety of analytical methods have become available for analytical detection and measurement of PCP and its related compounds. They reveal that while the chlorophenols are readily susceptible to breakdown through both biological and abiotic processes, the chlorinated impurities generally are more stable in the environment (Sections 3 and 4). For these reasons, PCP is closely regulated in several nations, and the US Environmental Protection Agency took action in 1978 to limit registered uses in the United States. However, the chemical remains one of the most effective, available, and inexpensive agents against the microbial and insect-caused destruction of property, especially in tropical climates, and the perception of its persistence, human exposure, or environmental hazard by one society can differ markedly from that in others. 3.Chemichal and phisycal properties Pentachlorophenol is used in the phenol form (PCP), as salts (commonly NaPCP), or as esters (laurate or acetate). The chemical and physical properties of the derivatives cannot be assumed to be identical to those of PCP itself in quantitative or even qualitiative terms, but comparatively little is known about them. Most of the following discussion refers to technical PCP.

As with any phenol, the hydroxyl group of PCP takes part in nucleophilic reactions (e.g.,it forms esters with organic and inorganic acids and ethers with alkylating agents such as methyl iodide or diazomethane). Electron withdrawal by the ring—chlorines causes PCP to be unusually acidic {PKA 4.70 in water, roughly comparable to propionic acid, PKA 4.9] and a relatively weak nucleophile, while stabilizing its salts (sodium pentachloro— phenate is a stable item of commerce). Although the high degree of chlorination makes the aromatic ring sufficiently electropositive to form stable charge—transfer complexes with electron donors, the ring chlorines are as resistant to nucleophilic displacement (e.g by hydroxide ions) under normal conditions as those of the chlorinated aromatic hydrocarbons. Some common physical properties of PCP and NaPCP are summarized in Table 1. The pure substances are white crystalline solids, while the commercial material generally is seen as tan or gray flakes. Pure anhydrous PCP melts near 190°C (its monohydrate melts at 174°C), but technical products may melt at 187—189° or less due to impurities; PCP salts are high—melting. Detailed physical properties are given by Carswell and Nason.

Table 1 - Selected physical properties of PCP

4.Manufactural methodes The most commonly used method for PCP production in clandestine labs is based on the Bruylants reaction, that is displacement of an alpha-amino nitrile by an organometallic reagent. The general outline of this reaction is shown in Scheme I. There are two steps: preparation of a nitrile intermediate (PCC), and reaction of this intermediate with a grignard reagent. The PCC intermediate can be synthesized through several routes, two of which are illustrated here. A typical clandestine batch operation might be run on a 3 to 5 molar scale, and is usually limited by the amount of piperidine to be employed (usually a maximum of 500 gm).

Scheme 1 – Synthesis of PCP using a nitrile intermediate In recent years, part of the technical PCP has been commercially purified by distillation

at the factory, a process which reduces the levels of neutral impurities considerably (Table 2), but the extent to which the purified product is used is proprietary information.

Table 2 - Typical composition of PCP

With the variety of routes and conditions of manufacture, and the large number of manufacturers, the quality of PCP could be expected to vary significantly with source and date of manufacture. The impurities formed during manufacture presently provide the most controversial aspect of PCP use. 5.Process description Wood preserving using PCP employs either a pressure process (Figure 2) or a thermal process (Figure 3) to impregnate the wood with the preservative chemical. In the first instance, hydraulic pressure is used to force the preservative into the wood. In the second instance, the effects of heating and cooling are used to induce preservative movement into the wood. However, before the wood can be preserved, it must be seasoned or dried to ensure that preservative penetration requirements can be met. Seasoning or drying may be done by air seasoning or kiln drying, and, at pressure treatment plants, by either Boulton drying or steam conditioning. In these two processes a combination of heat and vacuum is used to remove moisture from the wood in the pressure retort. PCP can be purchased in liquid solution, dry flake or block form. The PCP solution used for wood preservation is typically dissolved in a petroleum solvent and contains between 5 and 10% technical-grade PCP by weight. The pressure-treatment process is carried out in horizontal pressure retorts or cylinders. Properly seasoned wood is placed in the retort and then the retort door is sealed. If the Rueping process is used, the retort is first pressurized with air. The retort is then filled with the preservative chemical while maintaining the initial air pressure in the retort by bleeding air through a vent line into the preservative tank. If the Lowery process is used, the retort is filled with oil while atmospheric pressure is maintained in the vessel. When the retort is full of preservative the pressure is increased until the desired injection has been achieved. The maximum allowable pressure is 200 psi (1,380 kPa). The pressure is then reduced and, if desired, the temperature of the oil can be quickly raised to create an expansion bath. The preservative is then returned to the preservative tank. A vacuum is then applied to the retort to recover excess preservative from the cells of the wood. After the recovered preservative is pumped from the retort a final steam bath may be applied. After the retort has been drained the door is opened and the treated wood is removed from the retort. Quality control testing is then completed and the material is either shipped or moved to storage to await shipment.

Figure 2 - Flow Diagram - Wood Preservation Using Pentachlorophenol Pressure Process

The thermal-treating process is carried out in open tanks. In some cases the full length of the wood member is immersed in the preservative, while in other cases only the butt end of the material is treated. The seasoned wood is placed in the thermal-treating chamber and the tanks are filled with hot preservative. After completion of the hot-bath period, the hot preservative is either replaced by cold preservative (cold bath) or the preservative in the tank is allowed to cool (cooling bath). This cycle may be repeated if required. A final expansion bath with hot preservative may be applied. The oil is then removed from the tanks and the treated wood is taken out. Quality control testing is then completed and the material is either shipped or moved to storage to await shipment.

Figure 3 - Flow Diagram - Wood Preservation Using Pentachlorophenol Thermal Process

At a facility used for wood preservation using PCP, the probable NPRI reportable substances are shown in Table 2.

Compound

CAS Registry Number1

Criteria air contaminants (including oxides of nitrogen (expressed as NOx), sulphur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOCs), total particulate matter (TPM), particulate matter with a diameter = 2.5 microns (PM2.5), and particulate matter with a diameter = 10 microns (PM10)) Hexachlorobenzene2 Polychlorinated dibenzo-p-dioxins and Polychlorinated dibenzofurans2

Refer to the Canada Gazette Part I Notice for the year being reported.

118-74-1

*

Table 2 - Probable Reportable Substances with CAS Numbers-Preservation Facilities Using Pentachlorophenol

1 CAS Registry Number denotes the Chemical Abstracts Service Registry Number, as appropriate 2 This class of substances is restricted to certain congeners. Consult the Canada Gazette Part I Notice for the year being reported for the relevant list of congeners. * No single CAS number applies to their NPRI listing.

6.Health and Environmental Impact – Risk Assessment

Pentachlorophenol (PCP) is very toxic, persistent and bioaccumulates in organisms. PCP is classified as “Toxic in humans in contact with skin and if swallowed” (R24/25) and as “Very toxic by inhalation” (R26). Damages have been recorded in the cardiovascular system, blood and liver when inhaled by humans. Tests on animals have shown that PCP has impacts on the immune system and central nervous system. It has also been classified as a carcinogen. Additionally, PCP is very toxic to many fish species. Pentachlorophenol is persistent in the environment and bioaccumulates in organisms. Decomposition of the sodium salt in PCP (NaPCP) into PCP and bioaccumulation depends heavily on pH value. The substance is classified as “Very toxic to aquatic organisms and may cause long-term adverse effects in the aquatic environment” (R50/53). The EU strategy for endocrine-disrupting substances covers, among other things, the preparation of a candidate list of potential endocrine-disrupting substances, which are to be prioritised for further investigation of endocrine-disrupting properties. PCP is included in Category 1 on this list. Category 1 comprises substances where there is more or less extensive documentation of endocrine-disrupting effects in living animals and which therefore should be prioritised for further study of these effects. 7.Alternatives PCP is currently not used in Norwegian manufacturing. For impregnation of wood products, there are several satisfactory alternatives. Wood products that do not need impregnation can be used, or other impregnation agents or other surface treatment less hazardous to health and the environment can be used. It is also possible to use other materials such as steel (which can be recovered), fibreglass, cement/concrete which has a lifetime that is almost twice as long as PCP-processed wood. Furthermore, such materials do not need the level of maintenance as impregnated wood, and do not need to be processed as hazardous waste. PCP is used in yarn and textiles to reduce mould and insects. There are alternative chemicals less hazardous to health and the environment, which have similar effects on mould and insects. Denmark has regulated PCP in products, which shows that it is possible to cover this need with alternative means.

8.Conclusions and Summary Report on an Environmental Life Cycle Assessment of PCP Less Energy & Resource Use: Treated wood utility poles require less total energy, less fossil fuel, and less water than concrete, galvanized steel, and fiber-reinforced composite utility poles. • Lower Environmental Impacts: Treated wood utility poles have lower environmental impacts than concrete, steel, and fiber-reinforced composite utility poles in five of the six impact indicator categories assessed: anthropogenic greenhouse gas, total greenhouse gas, • Decreases Greenhouse Gas Levels: Treated wood utility poles lower greenhouse gas levels in the atmosphere while concrete, galvanized steel, and fiber-reinforced composite utility poles increase greenhouse gas levels in the atmosphere. • Offsets Fossil Fuel Use: Improved reuse of pentachlorophenol-treated utility poles for energy recovery will further reduce greenhouse gas levels in the atmosphere, while offsetting the use of fossil fuel energy.

Figure 4 - Impact indicator comparison (normalized to pentachlorophenol-treated utility pole = 1.0)

Impact indicator values for the cradle-to-grave life cycle of pentachlorophenol-treated utility poles were normalized to one (1.0), with concrete, galvanized steel, and fiberreinforced composite utility pole impact indicator values being a multiple of one (if larger) or a fraction of one (if smaller). The normalized results are provided in Figure 1. The carbon embodied in wood products, such as utility poles, is removed from the atmosphere during growth, stored for decades while the product is in use, and can be used for beneficial energy recovery at disposition. This temporary storage of carbon in the wood product reduces atmospheric levels of CO2 because the service life of the pole exceeds the time required for tree growth.

Final conclusions:   



PCP is a priority hazardous substance, and national goals have been established for phasing it out. Documentation shows that PCP has serious effects on health and the environment, and it has been detected in the environment. Products with PCP also contribute to emissions of dioxins and furans, which have serious effects on health and the environment. The proposed regulation will fill this gap in the current regulation of PCP. Their physical and chemical properties differ from those of PCP; although they, too, can be degraded by light and are adsorbed strongly, little is known about their environmental persistence and fate. They may be expected to bioconcentrate, be only slowly metabolized by animals or microorganisms, and accumulate in the livers of animals; however, although PCP has been sought (and found) in a variety of environmental situations, similar data on PCP impurities nd conversion products are almost nonexistent. In addition, dioxins are known to be generated from PCP photochemically, by burning of treated wood, and via the corresponding predioxins, but any contribution of these sources to human exposure has not been evaluated.

Recomandations:

The following recommendations are intended to implement three general objectives:    The exposure of humans and economic animals to PCP and its impurities must be defined andminimized. The indiscriminate use of PCP products (e.g., most home uses) should be limited, in favorof essential uses. The quality of technical PCP should be improved.

1. A worldwide survey of PCP production and use patterns should be established by an international agency in order to better define environmental inputs and potential exposure. 2. Further efforts to define PCI' impurities should be encouraged, authentic standards of the major toxic impurities made available through commercial channels, and methods for their specific determination simplified and standardized to permit more extensive analysis. 3. Commercial PCP from a wide range of identified existing sources should be analyzed for specific neutral impurities, including toxic dioxin and dibenzofuran isomers, and such analyses should become routine by manufacturers to provide a basis for estimating chronic health hazards and improving the quality of specific PCP products. 4. Commerically purified PCP and technical PCP should be compared and evaluated in relation to possible hazards under recommended conditions of use, rather than by composition only, to determine the desirability of purification in relation to the increased costs. 5. The chemistry of impurity formation during PCP production should be investigated in relation to possible improvement of the manufacturing processes, as an alternative to postmanufacture purification.

6. The presence of the chlorinated dioxins and other chlorophenyl ethers and their conversion products should be verified in man and animals and then surveyed in relation to possible sources of exposure. 7. The presence and fate of PCP and its impurities should be determined in sediments, air, water, and treated products under conditions of normal use in order to relate their persistence or movement to potential human exposure. 8. The presence of PCP and its metabolites in human urine and blood should be verified their levels monitored, and the sources specifically identified with the purpose of controlling them.