PARENT SESSION
PT2 - Endocrine Disruption
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P555) Influence of 3-Methylcholanthrene Co-exposure on Tributyltin Induced Reproductive Effects and Imposex Development in Ilyanassa obsoleta.
McClellan-Green, Patricia*,1,2, 1 North Carolina State University, Department of Environmental and Molecular Toxicology, Raleigh, NC, USA2 Duke University, Division of Coastal Systems Science and Policy, Nicholas School of the Environment and Earth Sciences, Beaufort, NC, USA
ABSTRACT- Populations of the neogastropod Ilyanassa obsoleta that are exposed to high levels of tributyltin (TBT) exhibit a significant increase in the development of imposex. Previous studies in our laboratory have shown that ~50% of female Ilyanassa exposed to 20 ng/l TBT developed a penis or penis stub (Oberdorster et. al., 1998). Further studies have shown that the co-occurrence of other environmental compounds plays a significant role in the development of imposex characteristics and reproductive capacity of these organisms. Ilyanassa obsoleta were collected from a clean site. The snails were acclimated in the laboratory for several weeks then randomly separated into one of five treatment groups. All snails were exposed to 20 ng/l TBT plus increasing concentrations of 3-methylcholanthrene (3-MC), i.e., 0, 2.5, 5, 7.5, or 10 nM 3-MC. Snails were sampled at 10, 20, 30 and 45 day intervals. The snails were removed from their shells, sexed and judged for imposex. Snails exposed to TBT and 3-MC during the winter months (February-March) were also judged for imposex rates and the number of egg capsules produced by each female determined. Results indicate that exposure to increasing concentrations of 3-MC causes a significant reduction in imposex development in TBT exposed snails. Analysis of TBT concentration in the co-exposed snails did not show an effect by 3-MC on the uptake rate of TBT. Attempts to determine whether debutylation of the TBT played a role in reduced imposex induction were unsuccessful due to the presence of a co-eluting contaminant. Furthermore, breeding female Ilyanassa exposed to 20 ng/l TBT produced significantly fewer egg capsules per female than control or 3-MC exposed snails. In addition, animals exposed to both TBT +3-MC, produced more egg capsules per female. This indicated that the co-administration of 3-MC protected the snails from the effects of TBT exposure. Possible explanations for the protective effect of 3-MC include increased P450 activity capable of metabolizing TBT, a partial competition for binding to enzymes carrying out the metabolic function or an increase in the enzyme activities necessary for the production of neuropeptide or steroid hormones.
Key words: endocrine, imposex, reproduction, mixture