Wood preservation facilities, creosote: chapter D-3

3. Environmental Effects

Creosote is a mixture of 200-250 identifiable substances; of these, 85% are PAHs (6). Therefore, the following environmental effects are based on the potential effects of PAHs on the environment. In general, Polycyclic Aromatic Hydrocarbon (PAH)s become increasingly less soluble in water with an increasing number of benzenoid or other rings, and with increasing molecular weight. PAHs from creosote mixture have little solubility in water.

PAHs have a low degree of volatility and photo-oxidation appears to be an important dissipation pathway for PAHs in the environment. However, the photo-oxidized products are persistent in air, water and soils and are bioaccumulative (6).

PAHs are a group of complex hydrocarbons composed of two or more fused aromatic (benzenoid) rings. Differences in the structure and size of individual PAHs result in substantial variability in the physical and chemical properties of these substances (10).

3.1 Aquatic Toxicity

Aquatic organisms may be adversely affected by exposure to elevated levels of PAHs in sediments, freshwater or marine environment.

The fate and behavior of PAHs in aquatic systems is influenced by a number of physical, chemical and biological processes. While some of these processes, such as photo-oxidation, hydrolysis, biotransformation, biodegradation and mineralization, result in the transformation of PAHs into other substances, other physical processes, such as adsorption, desorption, solubilization, volatilzation, resuspension and bioaccumulation, are responsible for the cycling of these substances throughout the aquatic environment (10).

Although there are no water quality objectives or standards specifically for creosote, water quality criteria do exist for some component compounds or indicators of creosote (10, 11, 12, 13, 14, 15). These criteria are summarized in Table 4. The Canadian Council of Ministers of the Environment (CCME)’ Canadian Water Quality Guidelines for the Protection of Aquatic Life has guidelines for 19 specific polycyclic aromatic hydrocarbons (PAHs), but there is insufficient information on PAHs in the marine environment at this time (12).

The PAHs listed in Section 2 are highly to very highly toxic to freshwater and saltwater fish and invertebrates, with anthracene and fluoranthene being the most toxic PAHs in the water column (6).

Canadian limits for PAHs in aquatic environments are accessible on the CCME website under the Canadian Environmental Quality Guidelines Summary Table.

Table 3 presents the regulatory limits for creosote components in natural water bodies.

Provincial guidelines are applicable and should be consulted. Provincial guidelines may differ from or be more specific than national guidelines. Provincial regulations may require additional measures that may enhance, but not reduce, protection.

3.2 Air Pollution

Air pollution from wood preservation is usually specific to some process within the plant and rarely is an issue outside the facility. Creosote can emit vapours of PAHs once applied to wood products. A few PAHs like acenaphthene, fluorene, phenanthrene, anthracene and fluoranthene show a degree of volatility from wood surfaces. More volatility has been observed at higher temperatures (30°C) and less at lower temperatures (4°C). As much as 85% of PAHs still remain on the wood surface at lower temperatures. Half-lives for volatility of these components are between 6 months and one year. Volatilization also does not appear to be a dissipation pathway for PAHs in the environment. (6)

Air pollution from wood preservative facilities can be generated as vapour/gas, aerosols and/or contaminated dust, especially where the creosote is heated and is open to ambient air.

Section 4 addresses the potential health effects of exposure to air pollution from wood preservatives. Air pollution should be considered when evaluations of potential chemical discharges are made in Section 5.

3.3 Soil Contamination

PAHs are found in environmental samples almost always as complex mixtures. Any possible approach for dealing with environmental risks of mixtures involves a number of trade-offs in terms of the ability of the approach to account for compositional variability across sites; toxicological variability across different taxa and soil types; and the possibility of non-additive effects (synergistic or antagonistic interactions, for example) of individual constituents in the mixture (16).

A study from Debruyn et al. (2007), suggests that Mycobacteria could be capable of degrading high molecular weight PAHs. This may be an eventual avenue to attenuate the effects of PAHs on contaminated sites (17).

The CCME has developed the Canadian Soil Quality Guidelines for the Protection of Environmental and Human Health. Developing soil quality guidelines for PAHs is particularly challenging because there is likely to be more than one toxicological mode of action in an exposed organism. There is no single final soil quality guideline (SQG_f) for any of the PAHs that will protect both human and environmental health. The reader is encouraged to read the detailed scientific rationale for the development of these PAH soil quality guidelines to better understand the inherent assumptions and limitations (16).

Alkyl-substituted PAHs, in particular, are common constituents of petrogenic (petroleum-derived) PAH mixtures. Too little is currently known about the environmental fate and toxicity (either for humans or various other living organisms) to enable development of Canadian soil quality guidelines for alkyl-PAHs (16).

Soil contamination can be an issue at wood preservation facilities if no effective measures are in place. Contaminated soil can be spread by vehicles and wind, but it will mostly migrate into runoff water and can potentially contaminate drinking water or surface water. The design and operational recommendations presented in Sections 7 and 8 contain measures to minimize soil contamination.

Certain information can be found in various CCME publications:

Canadian Soil Quality Guidelines

Additional general information on PAH is available.