AN EGG INJECTION METHOD FOR ASSESSING EARLY LIFE STAGE MORTALITY OF POLYCHLORINATED DIBENZO-PARA-DIOXINS, DIBENZOFURANS, AND BIPHENYLS IN RAINBOW-TROUT, (ONCORHYNCHUS-MYKISS)

To characterize the risk that polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) pose to salmonid early life stage survival, we developed a method to expose rainbow trout (Oncorhynchus mykiss) eggs to graded doses of PCDD, PCDF, and PCB congeners, using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as a prototype. Rainbow trout eggs were injected 24-50 h post-fertilization with 0.2-mu-l of 50 mM phosphatidylcholine (PC) liposomes (control) or 0.2-mu-l of 5-7 graded doses of TCDD incorporated into 50 mM PC liposomes. Injection volume never exceeded 0.6% egg volume. Immediately following injection, the injection site was sealed with Super glue(R), resulting in 92-97% of TCDD dose retained by the egg. Following both egg injection and waterborne egg exposure, TCDD toxicity in rainbow trout was manifested by half-hatching mortality but predominantly by sac fry mortality associated with hemorrhages, pericardial edema, and yolk sac edema. TCDD LD50s, following injection and waterborne exposure of rainbow trout eggs, were 421 (331-489) and 439 (346-519) pg TCDD/g egg (LD50, 95% fiducial limits), respectively. As in rainbow trout, TCDD toxicity in lake trout (Salvelinus namaycush) following the same two routes of exposure was manifested by half-hatching mortality but predominantly by sac fry mortality preceded by hemorrhages and yolk sac edema. LD50s, based on the dose of TCDD in lake trout eggs, were 47 (21-65) and 65 (60-71) pg/g following injection and waterborne exposure, respectively. The egg injection method is ideal for assessing the relationship between early life stage mortality in rainbow trout and graded egg doses of individual PCDD, PCDF, or PCB congeners.