Acute toxicity and tissue concentrations of 6PPD-quinone in Arctic grayling (Thymallus arcticus, Thymallinae)

Studies of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPDQ) toxicity have identified sensitive and resistant species within the subfamily Salmoninae, but thus far fewer than 10 species, all in two genera (Oncorhynchus and Salvelinus), have shown sensitivity in experiments. The Arctic grayling (Thymallus arcticus, Salmonidae, Thymallinae) was extirpated from its range in the Great Lakes region of the United States, but because of the importance of this species to the Native American tribes of Michigan, a reintroduction effort is underway. Because high 6PPDQ concentrations have been found in Great Lakes tributaries, it is important to understand if this species is at risk from 6PPDQ exposure. Using standard methods with flow-through exposures to provide stable 6PPDQ concentrations, we exposed Arctic grayling at 3 weeks after swim-up to a series of 6PPDQ concentrations for 96 hr, evaluating mortality and measuring tissue concentrations of 6PPDQ in surviving and dying fish. We observed that grayling were sensitive to 6PPDQ, with 24- and 96-hr median lethal concentrations of 5,136 and 3,137 ng/L, respectively. Tissue concentrations were much higher than those observed in other sensitive salmonines in previous studies. While this is only the third genus found to be sensitive to 6PPDQ leading to acute lethality and the first species outside of Salmoninae, the median lethal concentrations determined for the Arctic grayling exposed in this study are at 6PPDQ water concentrations unlikely to be encountered in situ.