| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1998 Concern about skewed sex ratios and female-female pairings among endangered roseate terns (Sterna dougallii) on Bird Island in Buzzards Bay, Massachusetts prompted studies with common terns from the same site as a surrogate species. Over seventy percent (11115) of male common tern embryos sampled from this site in 1993 had testes containing areas of ovarian cortical tissue (ovotestes), suggesting that terns may be affected by endocrine-disrupting contaminants. These terns are exposed to non-ortho PCBs which bind to the aryl hydrocarbon receptor (AhR), and lower chlorinated PCBs, hydroxymetabolites of which bind to the estrogen receptor. Our objectives were to document the presence of ovotestes in common tern embryos from Bird Island and Nauset, a reference site, in 1994, and to determine the relationship between environmental contaminants and ovotestes development, as well as other health-related effects. Pipping tern embryo gonads were examined histologically, and yolk sacs were extracted and analyzed for PCBs and chlorinated pesticides. Extracts also were analyzed for dioxin equivalents (TCDD-EQs) using a chick embryo hepatocyte (CEH) bioassay. Total PCBs were significantly higher in Bird Island tern embryos (mean 114, range 17- 663 ugig lipid) than Nauset (mean 35, range 8- i 78 ugig lipid); but were variable at both sites. Total PCBs were highly correlated with TCDD-EQs. Tern hepatic EROD activity was relatively insensitive to induction; only when TCDD-EQs were above 82 ± 26 ng/g lipid were EROD activities elevated. Levels of organic pesticides were below levels thought to be of toxicological significance. The percentage of male tern embryos with ovotestes at Nauset (60%) and Bird Island (78%) was high and not significantly different; ovotestes in terns from both sites ranged in severity from absent (1) to intersex ...
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