Branchial elimination of superhydrophobic organic compounds by rainbow trout (Oncorhynchus mykiss)

The branchial elimination of pentachloroethane and four congeneric polychlorinated biphenyls by rainbow trout was measured using a fish respirometer-metabolism chamber and an adsorption resin column. Branchial elimination was characterized by calculating a set of apparent in vivo blood:water partition coefficients (P_BW). Linear regression was performed on the logarithms of P_BW estimates and the logK_OW value for each compound to give the fitted equation: logP_BW=0.76·logK_OW-1.0 (r²=0.98). The linear nature of this relationship provides support for existing models of chemical flux at fish gills and suggests that a near equilibrium condition was established between chemical in venous blood entering the gills, including dissolved and bound forms, and dissolved chemical in expired branchial water. In vivo P_BW estimates were combined with P_BW values determined in vitro for a set of lower logK_OW compounds (Bertelson et al., Environ. Toxicol. Chem. 17 (1998) 1447-1455) to give the fitted relationship: logP_BW=0.73·logK_OW-0.88 (r²=0.98). The slope of this equation is consistent with the suggestion that chemical binding to non-lipid organic material contributes substantially to blood:water chemical partitioning. An equation based on the composition of trout blood (water content and the total amount of organic material) was then derived to predict blood:water partitioning for compounds with logK_OW values ranging from 0 to 8: logP_BW=log[(10^{0.73 logKow}·0.16)+0.84].