N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone, also known as 6PPD-quinone (6PPD-Q), was recently identified as the toxic chemical that causes acute mortality in coho salmon following exposure to urban road runoff. Subsequent studies found that there were large differences in sensitivity to 6PPD-Q (>100-fold) even among salmonid species. Here we performed 96 h acute toxicity tests of 6PPD-Q with three salmonid species (Salvelinus leucomaenis pluvius, Salvelinus curilus, and Oncorhynchus masou masou) and found that 6PPD-Q was lethally toxic to S. leucomaenis pluvius with a 24 h median lethal concentration (LC50) of 0.51 μg/L but not to the other two species at environmentally relevant concentrations (<3.8 μg/L). In addition, we measured the concentrations of 6PPD-Q and the suspected monohydroxylated metabolite in brain and gill tissues for the three species. The median internal lethal concentrations (ILC50) of 6PPD-Q were estimated to be 4.0 μg/kg of wet weight in brain and 6.2 μg/kg of wet weight in gill for S. leucomaenis pluvius, while the tissue concentrations of 6PPD-Q in the other two surviving species exceeded the ILC50 values for S. leucomaenis pluvius. These results suggest that species sensitivity differences might be affected by toxicodynamic factors as well as toxicokinetics.
Hiki et al. (Mon,) studied this question.