Life stage, chorion, and hatchery origin differences in the toxicity of 6PPDQ to coho salmon

Several salmonid species die from acute exposure to 2-((4-methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione (6PPDQ)—a ubiquitous pollutant that enters waterways via roadway runoff. Coho salmon ( Oncorhynchus kisutch) is the most sensitive species. Toxicity has been characterized for some coho life stages, but differences in study design and source populations between studies diminish comparability of life stage sensitivity. Coho were exposed to 6PPDQ at five distinct life stages (embryos, alevins, fry, parr, and adults) and as alevins from two different hatcheries; results were characterized by measures of sublethal morphological and behavioral effects, survival analysis, and concentration response analysis. Exposures during embryo development significantly altered morphology and caused post-hatch mortality and differences in phototaxis. Dechorionated embryos were vulnerable to 6PPDQ, with increased mortality relative to intact embryos. Embryos did not die in acute exposures, but 24 h LC 50 s were 689 ng/L for alevin, 239 ng/L for fry, and 71 ng/L for parr. Adults were as sensitive as parr. Alevins from different hatcheries had similar sensitivity. These findings reshape understanding of 6PPDQ toxicity to early life stage coho and reveal novel sublethal effects.