Migration of polycyclic aromatic hydrocarbons from creosote-treated roundwood in soil under controlled laboratory conditions

Abstract

Creosote is used as a wood preservative in a variety of terrestrial and aquatic environments, and some of its components can be detrimental to ecosystem function at high enough concentrations. Therefore, it is important to quantify chemical migration from creosote-treated commodities to better understand their impact. This work measures the migration of 16 polycyclic aromatic hydrocarbons (PAHs) from creosote-treated southern pine and Douglas-fir roundwood posts set in soil contact in barrels under controlled laboratory conditions. Experiments were carried out in soils with both low and high organic matter (OM) content. PAH content was measured in soil over a 32-month period at two distances from the post surface (76 and 152 mm) and at three different depths from the surface (0–15 cm, 15–30 cm, and 30–46 cm). PAH concentration varied widely among the 16 different compounds measured, but generally PAHs with four or fewer rings were more abundant and more frequently found than larger five-ringed PAHs across sample types. It was difficult to identify clear patterns in PAH migration by distance from wood and depth from soil surface because levels were generally low (below 0.4 PPM), and the data was highly variable, which eliminated the possibility of differentiating means statistically in most cases. In many cases, PAH levels found in controls that contained untreated wood were similar to levels found in control soil that contained treated wood, indicating some PAHs found could originate from the soil or surrounding environment. The clearest trend found was that high OM soils much more frequently contained measurable levels of the different PAHs, which is likely due to the known affinity PAHs have for OM. This work provides some methodological insight into studying PAH migration in soils that can help explain PAH migration patterns in soils with different proportions of OM. It also shows that without wetting with liquid water or other physical disturbances faced by wood in service, PAH migration from creosote-treated wood into soil is minimal.