N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone, also known as 6PPD quinone, was recently identified as a toxic chemical that causes acute mortality in coho salmon following exposure to urban runoff. Despite its potential occurrence in receiving waters worldwide, there is no information about the toxicity of 6PPD quinone to other aquatic species. In this study, to assess the aquatic toxicity of 6PPD quinone to freshwater fish and crustacean species, we performed standardized 48−96 h acute toxicity tests of 6PPD quinone with four species (Danio rerio, Oryzias latipes, Daphnia magna, and Hyalella azteca). In contrast to the high toxicity observed in coho salmon in a previous study (24 h LC 50 of 0.79 μg/L), 6PPD quinone did not exhibit acute lethal toxicity to any species at its maximum water solubility. The absence of acute lethality of 6PPD quinone to tested species indicates that the urban runoff toxicity observed for the species can be attributed to other chemicals. The observed large discrepancy in toxicity (by a factor of ∼100) might be due to the specific toxicity of 6PPD quinone to coho salmon. Further research is needed to reveal the underlying mechanisms of the observed difference, which will be useful for both urban runoff management and aquatic toxicology.

-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 (LC 50 ) 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 (ILC 50 ) 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 ILC 50 values for S. leucomaenis pluvius. These results suggest that species sensitivity differences might be affected by toxicodynamic factors as well as toxicokinetics.

The sediment-water interface of spiked-sediment toxicity tests is a complex exposure system, where multiple uptake pathways exist for benthic organisms. The freely dissolved concentration (C free ) in sediment pore water has been proposed as a relevant exposure metric to hydrophobic organic contaminants (HOCs) in this system. C free , however, has rarely been measured in spiked-sediment toxicity tests. In this study, we first developed a direct immersion SPME method for measuring C free in overlying and pore water in a sediment test using polydimethylsiloxane (PDMS)-coated glass fibers, resulting in sensitive and repeatable in situ measurements of HOCs. Then, we measured This article is protected by copyright. All rights reserved. Accepted ArticleC free and total dissolved concentrations (C diss ) in the sediment test systems with the freshwater amphipod Hyalella azteca, thoroughly evaluated the temporal and spatial profiles of four HOCs (phenanthrene, pyrene, benzo[a]pyrene, and chlorpyrifos). Furthermore, we examined the relationship between the measured concentrations and the lethality of H. azteca. We found that the test system was far from an equilibrium state for all four chemicals tested, where C diss in overlying water changed over the test duration and a vertical C free gradient existed at the sediment-water interface. C diss was larger than C free by a factor of 170-220 in pore water for benzo[a]pyrene due to the strong binding to dissolved organic carbon. The comparison of the median lethal concentrations (LC50) of chlorpyrifos in the sediment test and those in water-only tests indicates that C free in pore water was the most representative indicator for toxicity of this chemical. The method and findings presented in this work warrant further research on the chemical transport mechanisms and the actual exposure in sediment tests using different chemicals, sediments, and test species.

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