Wood preservation facilities, 2013 technical recommendations: chapter 3

3. Overview of Preservative Properties

The commercial preservatives used in Canada have a long history of success in preserving a large variety of wood products. Each preservative is effective in preventing wood deterioration, and each one has physical and chemical properties that make it suitable for one or more specific products. No one preservative is considered suitable for all possible product applications; each has found a niche of preferential use.

The preservatives in use have a range of physical, chemical and toxicological characteristics that determine their potential for causing harm and, therefore, the best modes of handling them during operation.

3.1 Toxicity, Hazards and Risks

A substance will be considered for scientific assessment if federal, provincial or international programs have identified it as potentially harmful to the environment or human health.

A substance is considered toxic if, after rigorous scientific assessment and based on a decision taken under federal programs, it either conforms or is equivalent to “toxic” as defined in the Canadian Environmental Protection Act, 1999 (CEPA 1999) (16).

Under section 64 of CEPA 1999, a substance is considered to be toxic if it is entering or may enter the environment in a quantity or concentration or under conditions that

1. have or may have an immediate or long-term harmful effect on the environment or its biological diversity;
2. constitute or may constitute a danger to the environment on which life depends; or
3. constitute or may constitute a danger in Canada to human life or health (16).

In most wood preservatives, the active ingredients are combined with other substances--most commonly solvents. These preservative formulations may exhibit different physical and toxicological properties than the undiluted preservative (active ingredients in their pure form). This factor needs to be taken into account when proposing recommendations for proper designs and operational practices.

3.2 Human Health Concerns

Wood preservatives can be harmful to humans if not properly handled. The exposure routes by which they can enter the human body are inhalation (vapour, dust, aerosol, etc.), ingestion (solid, liquid), ocular exposure and through the skin (vapour, liquid, solid). Exposure limits are given for individual preservatives in Part II - Preservative-specific Information and Recommendations. Such limits are usually also contained in the material safety data sheets (MSDS) issued by chemical manufacturers.

Plant operators should obtain references to or copies of relevant MSDS from their preservative supplier and must follow the requirements written on the pesticide label.

3.3 Environmental Concerns

The properties of a preservative chemical or formulation are also important in determining its environmental fate and its potential for contaminating the treatment facility and other sites. A preservative can enter the environment in many ways, such as by spillage or leaching, as effluent, or through air emission. Subsequently it may be subject to a wide variety of processes that may eliminate it from the environment completely, modify it into breakdown products that are more or less harmful, or transfer it to another environmental medium (17, 18).

The main physical-chemical properties that determine the movement of a chemical in the environment (17) are as follows:

• solubility in water and in organic solvents;
• vapour pressure;
• adsorption/desorption in soil or sediment;
• stability;
• partition coefficient between octanol and water; and
• reactivity with co-contaminants and soil microbes.