Sublethal toxicity assessments of 7PPD-quinone and 77PD-quinone in zebrafish embryos and sac-fry

High salmonid toxicity of 6PPD-quinone, a transformation product of the tire antioxidant 6PPD, has accelerated the search for safer tire alternatives. We evaluated the toxicity of the quinone transformation products of two candidate alternatives, 7PPD-quinone (7PPD-Q) and 77PD-quinone (77PD-Q), in zebrafish (Danio rerio) early life stages. Embryos and sac-fry were exposed to these chemicals under OECD Test Guideline 212 conditions. Endpoints included 8-day survival, hatching, heartbeat, eye and head sizes, body length, morphological deformities, and yolk-sac pigmentation. The results showed that no 8-day lethality occurred for either chemical up to 2000 µg L^-1. 7PPD-Q produced significant, concentration-related reductions in hatching success (2000 µg L^-1), eye (≥1000 µg L^-1) and head sizes (≥500 µg L^-1), and yolk-sac pigmentation (≥500 µg L^-1). By contrast, 77PD-Q significantly reduced pigmentation only (≥1000 µg L^-1). Neither chemical produced concentration-dependent changes in heartbeat, overt malformations, or body length. These results indicate that early-life zebrafish are far less sensitive to these PPD-quinones than coho salmon (Oncorhynchus kisutch). Given the high observed effect concentrations, which approached or exceeded the predicted water solubility limits, developmental risk of 7PPD-Q and 77PD-Q to zebrafish appears low.