title: Effect of carboxylic acid content on the acute toxicity of oil sands naphthenic acids.
abstract: Fractions of methylated naphthenic acids (NAs) isolated from oil sands process-affected waterwere collected utilizing Kugelrohr distillation and analyzed by proton nuclear magnetic resonance (1H NMR) spectroscopy. 1H NMR analysis revealed that the ratio of methyl ester hydrogen atoms to remaining aliphatic hydrogen atoms increased from 0.130 to 0.214, from the lowest to the greatest molecular weight (MW) fractions, respectively, indicating that the carboxylic acid content increased with greater MW. Acute toxicity assays with exposure to monocarboxyl NA-like surrogates demonstrated that toxicity increased with increasing MW (D. magna LC50 values of 10 +/- 1.3 mM and 0.59 +/- 0.20 mM for the respective lowest and highest MW NA-like surrogates); however, with the addition of a second carboxylic acid moiety, the toxicity was significantly reduced (D. magna LC50 values of 10 +/- 1.3 mM and 27 +/- 2.2 mM forthe respective monocarboxyl and dicarboxyl NA-like surrogates of similar MW). Increased carboxylic acid content within NA structures of higher MW decreases hydrophobicity and, consequently, offers a plausible explanation as to why lower MW NAs in oil sands process-affected water are more toxic than the greater MW NAs.
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, ON, Canada. rafrank@uwaterloo.ca
authors.forename: Richard A
authors.initials: RA
authors.lastname: Frank
authors.forename: Katharina
authors.initials: K
authors.lastname: Fischer
authors.forename: Richard
authors.initials: R
authors.lastname: Kavanagh
authors.forename: B Kent
authors.initials: BK
authors.lastname: Burnison
authors.forename: Gilles
authors.initials: G
authors.lastname: Arsenault
authors.forename: John V
authors.initials: JV
authors.lastname: Headley
authors.forename: Kerry M
authors.initials: KM
authors.lastname: Peru
authors.forename: Glen
authors.initials: G
authors.lastname: Van Der Kraak
authors.forename: Keith R
authors.initials: KR
authors.lastname: Solomon
mesh_terms: D048908:Aliivibrio fischeri / Q000187:drug effects; D000818:Animals; D002264:Carboxylic Acids / Q000032:analysis* / Q000737:chemistry / Q000633:toxicity; D016001:Confidence Intervals; D003621:Daphnia / Q000187:drug effects; D004952:Esters; D008163:Luminescent Measurements; D009682:Magnetic Resonance Spectroscopy; D009821:Oils / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D023382:Toxicity Tests, Acute
chemical_list: D002264:Carboxylic Acids; D004952:Esters; D009821:Oils; D012822:Silicon Dioxide; C046170:naphthenic acid