A Critical Review: 2,3,7,8 –Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) Effects on Gonad Development in Bivalve Mollusks

Abstract

Bivalve mollusks are equally sensitive to 2,3,7,8-tetrachlorodibenzo-p-dioxin's (2,3,7,8-TCDD) effect on gonad development, embryonic development, and epithelial lesion occurrence as higher vertebrates. 2,3,7,8-TCDD alters normal development of reproductive organs and early development in bivalve mollusks at 2 to 20 pg/g wet weight. In both Crassostria virginica and Mya arenaria, 2,3,7,8-TCDD preferentially accumulates into the gonads. The sensitivity of gonad maturation is likely due to disruption of cross-talk between highly conserved steroid, insulin, and metabolic pathways involved in gonad differentiation. The altered gonad development and decreased veliger larval survival can partially explain the lack of self-sustaining bivalve populations in 2,3,7,8-TCDD contaminated estuaries.

Key Words:

• 2,3,7,8-TCDD
• bivalve
• mollusks
• reproductive toxicity

ACKNOWLEDGEMENTS

These studies were supported from grants from the NIEHS (ES07148) and NJDEP and NJ Agricultural Experiment Station (NJ01201). We would like to also thank Dr. Tim Kubiak (US Fish and Wildlife Service) for his insightful comments on the manuscript.

This paper was developed from a presentation given at the symposium on “Common Effects Endpoints for Persistent Toxic Substances in Human and Ecological Epidemiology” at the 2007 Society of Environmental Toxicology and Chemistry (SETAC) annual meeting.

Notes

^aLesion prevalence taken from Brown (39).

^bValues within the table are the percent lesion and the values in () are the number with lesions compared to number of animals with this organ.

^aValues in the table mean and standard deviation, and

∗ indicates significant difference from Day 1 value.

^bFive animals were sampled at each time point, with the exceptions of Day 21 and 28 for gavage and day 21 for injection where 4 animals were sampled.

^aValues in the table are per cent of recovered 2,3,7,8-TCDD equivalents. The values in parenthesis are total recovered 2,3,7,8-TCDD equivalents.

^aPlus (+) or negative (−) signs indicate whether the effect was observed in laboratory controlled studies. ND indicates the endpoint was not evaluated. The value in () are doses resulting in significant differences from controls