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PT13 Aquatic Ecotoxicology I
(PT177) Biotransformation effects on the bioconcentration and toxicity of pentachlorobenzene (PCBZ) in Hyalella azteca.
Lee, J-H1, Landrum, P1, 1 Great Lake Environmental Research Labortory, NOAA, Ann Arbor, MI, USA
ABSTRACT- To investigate the influence of biotransformation on the bioconcentration and toxicity of pentachlorobenzene (PCBZ) in H. azteca, inhibition experiments were conducted for 10 d using the biotransformation inhibitor, piperonyl butoxide (PBO). Previously, no biotransformation of PCBZ by H. azteca was detected, because metabolites were not found in the body residue. Here, the bioconcentration factor increased with increasing water concentration and the values were larger in the presence of PBO. These data suggested that PCBZ was biotransformed into easily eliminated metabolites. Using a toxicokinetic model with first-order elimination of PCBZ and Michaelis-Menten biotransformation routes, the maximum reaction rates in the presence and the absence of PBO were estimated to be 89.5±22.6 and 64.2±20.3 mol kg-1 h-1, saturation rate constants were 486±216 and 507±211 mol kg-1, respectively when the elimination rate constant was 0.009 h-1. The uptake clearance rate was 63.9±8.7 L kg-1 h-1. Mortality by PCBZ in the presence of PBO was greater than in the absence of PBO. The differences in mortality tended to be magnified with decreasing PCBZ water concentration. These results made the median lethal concentration (LC50(t)) in the presence of PBO smaller than LC50(t) in the absence of PBO. In addition, co-exposure to PBO and PCBZ increased the mean lethal residue (MLR50(t)) values for a given exposure concentration but decreased the median lethal time. As a result, MLR50(t) in the presence of PBO was not significantly different from MLR50(t) in the absence of PBO. An unexpected result based on a first-order toxicokinetic model was a steeper slope of MLR50(t) than the slope of LC50(t) versus time in the toxicity curve (a plot of log LC50(t) or MLR50(t) vs. log time). The above results were not explained by PBO concentration, but by the differences in toxicokinetic parameters with and without PBO.
Key words: pentachlorobenzene, biotransformation, Hyalella azteca, damage assessment model
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