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Enhanced Sorption of PAHs in Natural-Fire-Impacted Sediments from Oriole Lake, California
Citation:
SULLIVAN, J., K. BOLLINGER, A. CAPRIO, M. G. CANTWELL, P. APPLEBY, J. KING, B. LIGOUIS, AND R. LOHMANN. Enhanced Sorption of PAHs in Natural-Fire-Impacted Sediments from Oriole Lake, California. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 45(7):2626-2633, (2011).
Impact/Purpose:
The fate of hydrophobic organic compounds (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), in sediments and soils depends largely on their sorption to solid phases. In urban/industrial sediments and soils, sorption is often dominated by anthropogenically derived eosorbents, such as soot, tar pitch, coal, or nonaqueous phase liquids (NAPL). Soot black carbon (BC) is formed by the condensation of small aromatic moieties in the gas phase of high-temperature combustion processes. Much less attention has been paid to the effect naturally produced charcoals and chars have on the sorption of HOCs in the field. Natural fires affect huge areas and have major impacts on land cover, atmospheric chemistry, and regional and global climate. The information in this article will be useful for scientists involved with assessing processes controlling the fate of organic compounds following combustion in the environment.
Description:
Surface sediment cores from Oriole Lake (CA) were analyzed for organic carbon (OC), black carbon (BC), and their δ13C isotope ratios. Sediments displayed high OC(20-25%) and increasing BC concentrations from ∼0.40% (in 1800 C.E.) to ∼0.60% dry weight (in 2000 C.E.). Petrographic analysis confirmed the presence of fire-derived carbonaceous particles/BC at ∼2% of total OC. Natural fires were the most likely cause of both elevated polycyclic aromatic hydrocarbon (PAH) concentrations and enhanced sorption in Oriole Lake sediments prior to 1850, consistent with their tree-ring-based fire history. In contrast to other PAHs, retene and perylene displayed decreasing concentrations during periods with natural fires, questioning their use as fire tracers. The occurrence of natural fires, however, did not result in elevated concentrations of black carbon or chars in the sediments. Only the 1912-2007 sediment layer contained anthropogenic particles, such as soot BC. In this layer, combining OC absorption with adsorption to soot BC (using a Freundlich coefficient n = 0.7) explained the observed sorption well. In the older layers, n needed to be 0.3 and 0.5 to explain the enhanced sorption to the sediments, indicating the importance of natural chars/inertinites in sorbing PAHs. For phenanthrene, values of n differed significantly between sorption to natural chars (0.1-0.4) and sorption to anthropogenic black carbon (>0.5), suggesting it could serve as an in situ probe of sorbents.