Comparative sub-lethal effects of polybrominated diphenyl ethers following simulated maternal transfer and dietary exposure in two species of turtles

Abstract

Polybrominated diphenyl ethers (PBDEs) are contaminants of concern as their concentrations have been increasing in the environment in recent years. This project sought to determine the effects of embryonic and dietary exposure to two PBDE congeners (BDE-47 and BDE-99) on a suite of endpoints including development, growth, metabolic rate, behavior and thyroid function of embryonic, hatchling and juvenile red-eared slider turtles (<italic>Trachemys scripta elegans</italic>) and snapping turtles (<italic>Chelydra serpentina</italic>). Topical egg dosing was employed for embryonic exposures; transfer efficiencies across the red-eared slider eggshell were 25.82 % and 9.87 % for BDE-47 and -99 respectively whereas they were 31.30 % and 12.53 % across the snapping turtle eggshell. These transfer efficiencies were taken into account when topically dosing eggs in a subsequent exposure-response study of embryonic exposure to BDE-47. Sodium perchlorate was included as a positive control for thyroid disruption in the embryonic exposure study. Embryonic exposure to five concentrations of BDE-47 (target exposure range from 40 ng/g - 1000 ng/g ww) led to patterns of elevated standard metabolic rate in hatchlings of both species and increased liver weights in snapping turtles. No impacts were found on incubation time, hatching success or total glandular thyroxine (T₄) of the hatchlings. Embryonically exposed red-eared slider juveniles displayed delayed righting response behavior and both species showed patterns of reduced thyroid size and T₄ following exposure. Sodium perchlorate had significant impacts on survival, incubation time, volume of the external yolk and T₄ in the red-eared slider hatchlings. In snapping turtles, sodium perchlorate exposures led to impacts on hatching success, standard metabolic rate, liver and thyroid sizes, and T₄. A separate study of dietary exposure to BDE-47 and BDE-99 (2055 ng/g and 1425 ng/g respectively) over a six month period in both species revealed altered behavior and decreased T₄ in red-eared sliders and elevated standard metabolic rate in snapping turtles. Embryonic and dietary exposures to BDE-47 and -99 can elicit a suite of impacts potentially related to thyroid system function and are cause for concern, but the observed species specific differences in response require further investigation.