Sensitivity of a Model Reptile, the Common Snapping Turtle (Chelydra serpentina), to In Ovo Exposure to 2,3,7,8‐Tetrachlorodibenzo‐p‐Dioxin and Other Dioxin‐Like Chemicals

Abstract

Reptiles represent the least-studied group of vertebrates with regards to ecotoxicology and no empirical toxicity data existed for dioxin-like chemicals (DLCs). This lack of toxicity data represents a significant uncertainty in ecological risk assessments of this taxon. Therefore, the present study assessed early-life sensitivity to select DLCs and developed relative potencies in the common snapping turtle (Chelydra serpentina) as a model reptile. Specifically, survival to hatch and incidence of pathologies were assessed in common snapping turtle exposed in ovo to serial concentrations of the prototypical reference congener 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and three other DLCs of environmental relevance, namely, 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 2,3,7,8-tetrachlorodibenzofuran (TCDF), and 3,3′,4,4′,5pentachlorobiphenyl (PCB 126). In ovo exposure to TCDD, PeCDF, TCDF, and PCB 126 caused a dose-dependent increase in early-life mortality, with median lethal doses (LD50s) of 14.9, 11.8, 29.6, and 185.9 pg/g-egg, respectively. Except for abnormal vasculature development, few pathologies were observed. Based on the measured LD50, common snapping turtle is more sensitive to TCDD in ovo than other species of oviparous vertebrates investigated to date. The potencies of PeCDF, TCDF, and PCB 126 relative to TCDD were 1.3, 0.5, and 0.08, respectively. These relative potencies are within an order of magnitude of World Health Organization (WHO) TCDD-equivalency factors (TEFs) for both mammals and birds supporting these TEFs as relevant for assessing ecological risk to reptiles. The great sensitivity to toxicities of the common snapping turtle, and potentially other species of reptiles, suggests a clear need for further investigation into the ecotoxicology of this taxon.

Reevaluation of 2,3,7,8‐Tetrachlorodibenzo‐p‐Dioxin Equivalency Factors for Dioxin‐Like Polychlorinated Dibenzo‐p‐Dioxins, Polychlorinated Dibenzofurans, and Polychlorinated Biphenyls for Fishes

“…This includes in vivo RePs for two salmonids with RePs of 0.003 and 0.005 and three sturgeons with RePs of 0.1, 0.08, and 0.07 (Supporting Information, Table S9). Further, RePs of PCB 126 have been measured for early life mortality in other oviparous vertebrates, including chicken with an ReP of 0.2 and common snapping turtle ( Chelydra serpentina ) with an ReP of 0.08 (Doering et al, 2022; Manning et al, 2012). These in vivo RePs of approximately 0.1 in three nonsalmonid species of fish, a bird, and a reptile provide evidence that RePs for PCB 126 in salmonids are much less than those in most other species and supports the notion that the WHO TEF for fishes based almost entirely on studies of salmonids underestimates the potency of PCB 126 by approximately 20‐fold.…”