Article pubs.acs.org/est
Estimates of Octanol−Water Partitioning for Thousands of Dissolved Organic Species in Oil Sands Process-Affected Water Kun Zhang, Alberto S. Pereira, and Jonathan W. Martin* Division of Analytical & Environmental Toxicology, Department of Laboratory Medicine & Pathology, University of Alberta, Edmonton, Alberta Canada, T6G 2G3 S Supporting Information *
ABSTRACT: In this study, the octanol−water distribution ratios (DOW, that is, apparent KOW at pH 8.4) of 2114 organic species in oil sands process-affected water were estimated by partitioning to polydimethylsiloxane (PDMS) coated stir bars and analysis by ultrahigh resolution orbitrap mass spectrometry in electrospray positive (+) and negative (−) ionization modes. At equilibrium, the majority of species in OSPW showed negligible partitioning to PDMS (i.e., DOW 0.1 μg kg−1) after exposure to OSPW (15 mg L−1 naphthenic acids) for 96 h. van den Heuvel et al. exposed yellow perch (Perca flavescens) in an experimental pond containing process-affected material for four months and found that naphthenic acids were not detectable in tissues ( 0 (Figure 2, blue box plots). This is perhaps not surprising, because organic chemicals that can be detected in negative ionization mode must have an acidic proton (e.g., carboxylic acid or phenolic functionality) and most are therefore likely present as anions in OSPW at the current pH and should have a correspondingly low propensity to partition to the hydrophobic PDMS material. Nevertheless, some of the naphthenic acids (O2−) had estimated log DOW’s ranging up to 2.0 (i.e., DOW up to 100). As shown in Figure 3A, carbon number and double-bond equivalents (DBE, i.e. a ring or double bond) showed significant effects on the estimated log DOW (ANCOVA, p < 0.05). There was a positive relationship between the number of carbon atoms in each naphthenic acid species and the estimated log DOW. There was also a trend with DBE whereby naphthenic acids with fewer DBEs showed higher estimated log DOW (Figure 3A). These findings demonstrate an important structure−activity relationship, and therefore emphasize the limitations of previous reports of naphthenic acid bioconcentration factors where only a single chemical species, or group averages, were reported. Nevertheless, in one study by van den Heuvel et al., the accumulation of C13H22O2 naphthenic acid in yellow perch (Perca f lavescens) was reported,9 and from their data the lipid-based bioconcentration factor was
