ASSESSMENT OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN INDUCED SAC FRY MORTALITY IN LAKE TROUT (SALVELINUS-NAMAYCUSH) FROM DIFFERENT REGIONS OF THE GREAT-LAKES

Background levels of TCDD toxic equivalents (TEs) in lake trout (Salve linus namaycush) eggs (calculated using fish-specific toxicity equival ency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs), dib enzofurans (PCDFs), and biphenyls (PCBs)) were higher for two location s in Lake Ontario than Lake Superior and a hatchery (10.5-10.9 versus 0.3 and 0.05 pg TE/g egg). Despite the higher contamination of Lake On tario eggs, sac fry mortality was uniformly low for all eggs. This is consistent with TCDD toxicity equivalence concentrations (TECs) of all eggs being less than the TCDD no observable adverse effect level (NOA EL) for Lake Superior lake trout sac fry mortality (34 pg TCDD/g egg). Eggs exposed in the laboratory to [H-3]TCDD and maintained at either 8 or 8-3-8 degrees C had similar sac fry mortalities. For all sources of eggs, [3H]TCDD-induced sac fry mortality was associated with blue s ac disease, which was not affected by water temperature, and resulted in similar LD(50) values (42-72 pg[H-3]TCDD/g egg). Thus, lack of sac fry mortality in wild Lake Ontario lake trout eggs was not caused by l ack of responsiveness to TCDD but rather was attributable to egg TECs being below the TCDD NOAEL for sac fry mortality.