Somatic and gastrointestinal in vivo biotransformation rates of hydrophobic chemicals in fish

Abstract

To improve current bioaccumulation assessment methods, a methodology is developed, applied, and investigated for measuring in vivo biotransformation rates of hydrophobic organic substances in the body (soma) and gastrointestinal tract of the fish. The method resembles the Organisation for Economic Co-operation and Development (OECD) 305 dietary bioaccumulation test but includes reference chemicals to determine both somatic and gastrointestinal biotransformation rates of test chemicals. Somatic biotransformation rate constants for the test chemicals ranged between 0 d(-1) and 0.38 (standard error [SE] 0.03)/d(-1) . Gastrointestinal biotransformation rate constants varied from 0 d(-1) to 46 (SE 7) d(-1) . Gastrointestinal biotransformation contributed more to the overall biotransformation in fish than somatic biotransformation for all test substances but 1. Results suggest that biomagnification tests can reveal the full extent of biotransformation in fish. The common presumption that the liver is the main site of biotransformation may not apply to many substances exposed through the diet. The results suggest that the application of quantitative structure-activity relationships (QSARs) for somatic biotransformation rates and hepatic in vitro models to assess the effect of biotransformation on bioaccumulation can underestimate biotransformation rates and overestimate the biomagnification potential of chemicals that are biotransformed in the gastrointestinal tract. With some modifications, the OECD 305 test can generate somatic and gastrointestinal biotransformation data to develop biotransformation QSARs and test in vitro-in vivo biotransformation extrapolation methods.

Assimilation efficiency of sediment-bound PCBs ingested by fish impacted by strong sorption

“…Previous work by Gobas et al reviewed empirical measurements of assimilation efficiency in the literature and concluded that dietary assimilation efficiency is initially independent of log K OW and starts decreasing at log K OW of 6 for a range of hydrophobic organic chemicals because of reduced bioavailability and steric hindrance in crossing biological membranes. The values predicted by the Gobas et al and Lo et al models are plotted in Figure B. In these nonlinear models, assimilation efficiency (α) is presented as α = (2 + 3 × 10 −7 × K OW ) −1 and α = (1.9 + 5.6 × 10 −9 x K OW ) −1 , respectively.…”

“…The values predicted by the Gobas et al model were derived by fitting a nonlinear correlation to empirical data from various fish species that may not have the cap ability to predict variations in fish species, feeding rate, and diet type and quality, as well as food concentration. Using the relationship derived from one species and size (rainbow trout) by Lo et al led to improved predictions (1– R 2 = 0.51) compared with the relationship derived for multiple species and sizes by Gobas et al .…”

“…( A ) Mass of polychlorinated biphenyls (PCBs) in the W (worm) diet, fish tissue, gut tissue, and gut content, and ( B ) assimilation efficiency of different PCBs in the W diet as a function of log K OW and their comparison with literature values. The lines in ( B ) represent the assimilation efficiency‐log K OW correlations developed by Gobas et al and Lo et al . Error bars represent standard error.…”

Deriving bioconcentration factors and somatic biotransformation rates from dietary bioaccumulation and depuration tests

“…The average feeding rate was 0.012 ± 0.002 g dry food/g wet fish/d, and the growth dilution rate constant for the test fish was 0.0066 ± 0.0012 d −1 and 0.0066 ± 0.0015 d −1 for the control fish. That study involved simultaneous dietary exposure to 7 reference chemicals (i.e., 1,2,4,5‐tetrachlorobenzene; pentachlorobenzene [PCBz]; hexachlorobenzene [HCBz]: 2,2′,5,5′‐PCB [PCB 52]; 2,2′,4,4′,6,6′‐PCB [PCB 155]; 2,2′,4,4′,5,5′‐PCB [PCB 153]; and 2,2′,3,3′,4,4′,5′,5′,6,6′‐PCB [PCB 209]), which were assumed not to be biotransformed significantly, and 8 test chemicals (i.e., 1,2,3,4‐tetramethyl benzene; β‐hexachlorocyclohexane [β‐HCH]; trans‐decalin; 9‐methylanthracene; chrysene; hexylcyclohexane; 2,6‐dimethyldecane; and benzo[ a ]pyrene), which were expected to be biotransformed. The authors measured depuration rate constants over a period of 114 d and used linear regression of the natural logarithm of the concentrations of the test and reference chemicals versus time to determine the depuration rate constant for the reference and test chemicals.…”

Comparison of laboratory-derived biomagnification factors for hexachlorobenzene in common carp conducted under 9 test conditions

“…The endpoint in this new test is the biomagnification factor (BMF), which is considered to be a meaningful measure of the potential for a chemical to undergo dietary biomagnification in the environment [5,6]. However, there are as yet limited experimental BMF data, and many researchers and regulators are still trying to identify appropriate strategies for assessing the bioaccumulation potential of chemicals using dietary exposure tests [10][11][12][13][14]. However, there are as yet limited experimental BMF data, and many researchers and regulators are still trying to identify appropriate strategies for assessing the bioaccumulation potential of chemicals using dietary exposure tests [10][11][12][13][14].…”