Early Mass Transfer of Monocyclic Aromatics to Water Following Diluted Bitumen Spills in Freshwater Limnocorrals

During the initial days of a diluted bitumen (dilbit) spill, the monocyclic aromatic hydrocarbons benzene, toluene, ethylbenzene, and o,m,p-xylenes (BTEX) rapidly partition into air and water. Accurately characterizing the evaporation and dissolution trends of BTEX is essential for assessing potential environmental exposures. We investigated these processes following dilbit spills into limnocorrals in a boreal lake in Northwestern Ontario, with spill volumes ranging from 1.5 to 180 L, resulting in oil-to-water ratios from 1:71,000 to 1:500. BTEX concentrations in the water column peaked within 10–24 h and dropped below detection limits after 96 h. A mass transfer model, parametrized based on physical–chemical properties of the individual BTEX compounds and environmental conditions, accurately predicted BTEX fractionation and dissolution trends, with 29–86% of predictions within 3-fold of measured concentrations across all spill scenarios. This is the first report on the dissolution trends of BTEX following large-scale experimental dilbit spills in natural freshwater systems, which allowed for an important field evaluation of the model at a variety of different dilbit spill sizes.