title: Concentration dependence of biotransformation in fish liver S9: Optimizing substrate concentrations to estimate hepatic clearance for bioaccumulation assessment.
abstract: In vitro bioassays to estimate biotransformation rate constants of contaminants in fish are currently being investigated to improve bioaccumulation assessments of hydrophobic contaminants. The present study investigates the relationship between chemical substrate concentration and in vitro biotransformation rate of 4 environmental contaminants (9-methylanthracene, pyrene, chrysene, and benzo[a]pyrene) in rainbow trout (Oncorhynchus mykiss) liver S9 fractions and methods to determine maximum first-order biotransformation rate constants. Substrate depletion experiments using a series of initial substrate concentrations showed that in vitro biotransformation rates exhibit strong concentration dependence, consistent with a Michaelis-Menten kinetic model. The results indicate that depletion rate constants measured at initial substrate concentrations of 1 μM (a current convention) could underestimate the in vitro biotransformation potential and may cause bioconcentration factors to be overestimated if in vitro biotransformation rates are used to assess bioconcentration factors in fish. Depletion rate constants measured using thin-film sorbent dosing experiments were not statistically different from the maximum depletion rate constants derived using a series of solvent delivery-based depletion experiments for 3 of the 4 test chemicals. Multiple solvent delivery-based depletion experiments at a range of initial concentrations are recommended for determining the concentration dependence of in vitro biotransformation rates in fish liver fractions, whereas a single sorbent phase dosing experiment may be able to provide reasonable approximations of maximum depletion rates of very hydrophobic substances.
authors.affiliation: Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Justin C
authors.initials: JC
authors.lastname: Lo
authors.affiliation: School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Gayatri N
authors.initials: GN
authors.lastname: Allard
authors.affiliation: School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: S Victoria
authors.initials: SV
authors.lastname: Otton
authors.affiliation: Department of Statistics and Actuarial Science, Simon Fraser University, Surrey, British Columbia, Canada.
authors.forename: David A
authors.initials: DA
authors.lastname: Campbell
authors.affiliation: Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.|School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Frank A P C
authors.initials: FA
authors.lastname: Gobas
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000032:analysis / Q000378:metabolism; D001564:Benzo(a)pyrene / Q000032:analysis / Q000378:metabolism; D001711:Biotransformation; D002911:Chrysenes / Q000032:analysis / Q000378:metabolism; D004785:Environmental Pollutants / Q000032:analysis* / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008110:Liver Extracts / Q000378:metabolism; D008954:Models, Biological; D017686:Oncorhynchus mykiss / Q000378:metabolism*
chemical_list: D000873:Anthracenes; D002911:Chrysenes; D004785:Environmental Pollutants; D008110:Liver Extracts; C031180:chrysene; D001564:Benzo(a)pyrene; C046962:9-methylanthracene
keywords: Bioaccumulation; Biotransformation; Fish; Hydrophobic chemicals; In vitro