Acute Toxicity of 4-HDPA and 6PPDQ, transformation products of 6PPD, to early instars of the mayfly, Neocloeon triangulifer

Abstract Our analysis of water samples collected during a rain event from two urban rivers in the Greater Toronto Area, Ontario, Canada indicated that selected transformation products (TPs) of the tire antioxidant, 6PPD, including 6PPD-quinone (6PPDQ) and 4-hydroxydiphenylamine (4-HDPA) were present at concentrations >1 µg/L. In acute (96-h) toxicity tests with aquatic larvae of the mayfly, Neocloeon triangulifer, 6PPDQ did not cause mortalities at the highest test concentration, which was just below the limit of solubility. In toxicity tests with 4-HDPA, a calculated 96-h LC50 of 339 µg/L is above environmentally relevant concentrations. However, in toxicity tests with 6PPD, there was evidence that the degradation of this tire wear compound produced unknown TPs that caused mortalities in exposed mayfly larvae. Additional work could identify other TPs of 6PPD that could be a hazard to aquatic invertebrates exposed to tire wear compounds transported into surface waters from transportation corridors.