AUTC project number: MISC 8
Robert A. Perkins (UAF)
Alaska Department of Transportation & Public Facilities
ADOT&PF is responsible for many structures that incorporate wood pilings and other timber in Alaska waters. Most are treated with preservative to inhibit marine borers that will quickly destroy unprotected wood. Creosote is generally the most economical preservative and has been used for over a hundred years. Creosote contains many toxic chemicals and some governments and organizations are limiting its use. This project reviewed current science regarding use of creosoted wood in marine waters and the current regulatory matrix that controls its use, and developed recommendations for its use. Even with best management practices, polycyclic aromatic hydrocarbons (PAH) from new creosote timber will be transferred to the marine environment. Laboratory tests and field observations show that PAH chemicals slowly diffuse from the wood into the water column. The heavier PAH chemicals sink to the bottom directly, or adsorb to organic or inorganic moieties in the water and then sink, incorporating into the sediment. The lighter PAH chemicals are quickly volatilized and oxidized. Scientific observations of creosote behavior in meso-scale tests verify that the concentrations of PAH from marine piles in the water column are negligible after the first few weeks. The fate of PAH in the sediment depends on the oxygen status of the upper sediment layers. If the sediment is not anoxic, the PAH will be oxidized. With sufficient oxygen in the upper layers of sediment, the PAH concentration will initially rise, then decline. With timber treated according to best management practices, if the sediments are not anoxic and the surrounding waters are not stagnant, and the area is not already contaminated, creosote marine timbers are unlikely to have a significant long-term effect on the environment. Further, meso-scale testing indicated that effects were confined to a region close to the structures themselves.