Uncovering spatially resolved 6PPDQ metabolism in rainbow trout fry with nano-DESI mass spectrometry imaging

N-(1,3-Dimethylbutyl)-N’-phenyl-p-phenylenediamine quinone (6PPDQ) is an emerging tire-derived contaminant that poses a critical environmental risk to select salmonids. However, the mechanisms of 6PPDQ toxicity are currently unresolved. While species-specific metabolomic effects of 6PPDQ exposure have been explored, to our knowledge no studies have investigated the in situ spatial distribution of 6PPDQ and 6PPDQ biotransformation products in salmonids. Herein, we employ nanospray desorption electrospray ionization (nano-DESI) mass spectrometry imaging (MSI) to visualize 6PPDQ metabolism in 6-week post-hatch rainbow trout fry exposed to a 0.61 μg/L timeweighted concentration of 6PPDQ for 96 hours, as well as control fry. These data provide the first spatial mapping of 6PPDQ metabolism in fishes. 6PPDQ was not observed in any fish tissues; however, the primary 6PPDQ biotransformation product, hydroxylated 6PPDQ, was found to localize in the liver and gut of exposed fry. Additionally, interrogation of non-targeted nano-DESI spatial metabolomics revealed an accumulation of free fatty acids in the central nervous system of exposed fry. Overall, this study uncovers spatially resolved 6PPDQ metabolism in exposed fishes and explores the disparate localization of endogenous metabolites disrupted by 6PPDQ exposure.