2,3,7,8-TETRACHLORODIBENZO-PARA-DIOXIN (TCDD) TOXICITY DURING EARLY LIFE STAGE DEVELOPMENT OF LAKE TROUT (SALVELINUS-NAMAYCUSH)

Lake trout (Salvelinus namaycush) eggs containing [H-3]TCDD concentrations from 0 to 302 parts per trillion (ppt) were observed through the fry stage for TCDD metabolism, elimination, and toxicity. All radioactive residues extracted from eggs and sac fry were due to TCDD; no metabolites were detected. [H-3]TCDD was not eliminated from eggs and sac fry, but was rapidly eliminated from fry (t1/2, 35-37 d). Hatchability was less at egg TCDD concentrations greater-than-or-equal-to 226 ppt; however, the greatest TCDD-related mortality occurred during the sac fry stage. In all TCDD groups (34-302 ppt), sac fry that died developed subcutaneous yolk sac edema prior to death, resembling blue-sac disease. The development of yolk sac edema preceded sac fry mortality, and the severity of edema varied directly with cumulative mortality. Based on TCDD concentrations in the egg resulting from a 48-h exposure, the no observable adverse effect level (NOAEL) for mortality was 34 ppt and the lowest observable adverse effect level (LOAEL) was 55 ppt. The TCDD concentration in eggs that caused 50% mortality above control at swim-up (LD50) was 65 ppt. Lake trout sac fry exposed as eggs are more sensitive to the lethal effects of TCDD than any mammalian, avian, or fish species investigated thus far.