Environmental concentrations of tire rubber-derived 6PPD-quinone alter CNS function in zebrafish larvae

N-(1,3-Dimethylbutyl)-N & PRIME;-phenyl-p-phenylenediamine quinone (6PPD-quinone) is a degradation product of 6PPD, an antioxidant widely used in rubber tires. 6PPD-quinone enters aquatic ecosystems through urban stormwater runoff and has been identified as the chemical behind the urban runoff mortality syndrome in coho salmon. However, the available data suggest that the acute effects of 6PPD-quinone are restricted to a few salmonid species and that the en-vironmental levels of this chemical should be safe for most fish. In this study, larvae of a tolerant fish species, Danio rerio, were exposed to three environmental concentrations of 6PPD-quinone for only 24 h, and the effects on explor-atory behavior, escape response, nonassociative learning (habituation), neurotransmitter profile, wake/sleep cycle, circadian rhythm, heart rate and oxygen consumption rate were analyzed. Exposure to the two lowest concentrations of 6PPD-quinone resulted in altered exploratory behavior and habituation, an effect consistent with some of the ob-served changes in the neurotransmitter profile, including increased levels of acetylcholine, norepinephrine, epineph-rine and serotonin. Moreover, exposure to the highest concentration tested altered the wake/sleep cycle and the expression of per1a, per3 and cry3a, circadian clock genes involved in the negative feedback loop. Finally, a positive chronotropic effect of 6PPD-quinone was observed in the hearts of the exposed fish. The results of this study emphasize the need for further studies analyzing the effects of 6PPD-quinone in tolerant fish species.

Automated summary

N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine quinone (6PPD-quinone) is a degradation product of 6PPD, widely used in rubber tires. It enters aquatic ecosystems through urban stormwater runoff and has been identified as the cause behind urban runoff mortality syndrome in coho salmon. This study exposed larvae of a tolerant fish species, Danio rerio, to different concentrations of 6PPD-quinone and analyzed its effects on various behaviors, neurotransmitter profile, circadian rhythm, heart rate, and oxygen consumption rate. The results showed that exposure to 6PPD-quinone led to altered behavior, neurotransmitter levels, circadian rhythm, and heart rate, emphasizing the need for further studies on the effects of this chemical.