Deposition and persistence of polynuclear aromatic hydrocarbons after slash burning clear-cut sites in Oregon

Graduation date: 1983Research has been completed which identifies qualitatively and\ud quantitatively the deposition, persistence and fate of polynuclear\ud aromatic hydrocarbons (PNAH) on burned clear-cut sites in Oregon.\ud Eight PNAH were identified and quantified in post-burn litter samples\ud taken from four slash-burned sites. Deposition of lower\ud molecular weight, 3-4 ring compounds was considerably higher than\ud deposition of 5-7 ring compounds on all sites, with mean deposition\ud values ranging from 480 g/ha for phenanthrene to 5 g/ha for coronene.\ud PNAH levels were not appreciably higher in soil immediately after\ud burning, indicating that the bulk of PNAH production took place within\ud the litter, rather than the soil layer. Persistence studies indicated\ud that phenanthrene and fluoranthene, three and four ring\ud compounds, were gradually lost from litter, reaching concentrations\ud below detection limits (approximately 2 g/ha) less than two years\ud after burning. Higher molecular weight PNAH were considerably more\ud persistent in the litter, decreasing after five years approximately\ud to l9-23% of initial deposition. Movement into the top 2 cm of the\ud soil profile was more pronounced for the lower weight PNAH, but all\ud compounds appeared to equilibrate between litter and soil on the\ud basis of organic content within one year after burning. Differential\ud persistence and fate of PNAH on slash burn sites is explained by the\ud physical chemical characteristics of the compounds, such as solubility,\ud vapor pressure, and octanol-water partition coefficient