Toxicokinetics of polybrominated diphenyl ethers across life stages in the northern leopard frog (Lithobates pipiens)

Abstract

Polybrominated diphenyl ethers (PBDEs), a class of flame retardants, are bioaccumulative toxins that can biomagnify in food webs. However, little is known about the toxicokinetics of total and congener-specific BDEs in lower vertebrates. The authors exposed northern leopard frog (Lithobates (Rana) pipiens) tadpoles to diets containing DE-71 (a pentabromodiphenyl ether mixture (0 ng/g as control, 71.4 ng/g, and 634 DE-71 ng/g wet mass)) for 50 d, followed by a period of depuration during which they were fed only undosed (control) food. After 28 d, tadpoles eliminated over 94% of the ΣPBDEs from their tissues (t½ = 5.9 ± 1.9 d) with no significant differences in elimination rates for the predominant congeners. Elimination of BDE-99 was independent of dose, indicating first-order kinetics. It did not fit a biexponential model significantly better than a monoexponential model, indicating single-compartment elimination. To compare developmental life-stage kinetics following larval exposure, the authors collected individuals at the beginning and end of metamorphosis and at 70 d postmetamorphosis. During metamorphosis, total-body residues per individual did not significantly change, implying little to no elimination. After 70 d, juvenile frogs eliminated 89.7% of the ΣPBDEs from their tissues, and BDE-47 was eliminated at a faster rate (t½ = 17.3 d) than BDE-99 and BDE-100 (t½ = 63.0 d and 69.3 d, respectively). Because the kinetics of PBDEs in L. pipiens differed among life stages, developmental life stage-especially for species that undergo metamorphosis-should be considered when determining the toxicity of persistent organic pollutants.

Immunomodulation in Post-metamorphic Northern Leopard Frogs,Lithobates pipiens, Following Larval Exposure to Polybrominated Diphenyl Ether

“…3,12 Specifically, tadpoles fed concurrently in our facility on two of the same diets described above (71.4 and 634 ng PBDE/g) had body burden residues of 46.3 and 632.4 ng PBDE/g tissue, respectively, after feeding for 50 days. 43 The fertilized embryos obtained from Nasco are offspring of field-collected adult males and females from southeastern Minnesota and Wisconsin, such that we expect the tadpoles in our study to be to representative of natural populations. However, information regarding genetic relatedness within and/or across batches was not provided by the supplier, so as a precaution batches of tadpoles were not mixed and each batch was replicated twice at each treatment level.…”

“…In order to provide proper nutrition, crickets were dusted with calcium and vitamins prior to being fed to the froglets. The depuration of contaminant levels during this period (e.g., ref 43) Seven weeks post-metamorphosis, frogs were intraperitoneal (i.p.) injected with 25 μL of the antigen [keyhole limpet hemocyanin (2 mg KLH/25 mL PBS)] and Titer Max Gold (Sigma), an adjuvant previously used in L. pipiens and known to stimulate antibody production.…”

Contaminant and Environmental Influences on Thyroid Hormone Action in Amphibian Metamorphosis

“…PBDEs are widely disseminated throughout invertebrates, vertebrates, sediments, and diverse environments, including Arctic marine biota (72). PBDEs can readily accumulate and magnify within trophic levels (114). Mammalian biotransformation of PBDEs to hydroxylated metabolites by cytochrome P450 enzymes result in products that are more toxic than the parent congeners.…”

“…The elimination of PDBEs following depuration was studied in R. pipiens tadpoles that had consumed environmentally-relevant concentrations of DE-71 for 50 days at Gosner stage 25. Following 28 days of depuration, tadpoles had removed more than 94% of PBDE congeners from their bodies (114). The ability to eliminate PBDEs from tissues can vary according to life stage.…”

“…The ability to eliminate PBDEs from tissues can vary according to life stage. Metamorphosing frogs (Gosner stage 42–46) were unable to eliminate PBDEs following depuration, however, juvenile frogs eliminated 89.7% of PBDEs over a 70 day depuration (114). Wild R. limnocharis adult frogs found proximal to contaminated e-waste recycling sites similarly showed reduced PBDE levels following 54 days of depuration (116).…”