Potential Effects of Contaminants on Fraser River Sockeye Salmon

tetrachlorodibenz<strong>of</strong>urans (T4CDF)]. Mehrle et al. (1988) exposed rainbow trout fry toT4CDD and T4CDF in water for a period <strong>of</strong> 28 days, and observed fish through a 28-day depuration period. After 56 days, significant mortality (45%) was observed in-1trout with maximum tissue residue levels <strong>of</strong> 0.99 ìg T4CDDkg BW. Twenty-twopercent mortality was observed after 56 days in fish that had a maximum tissue residue-1 -1level <strong>of</strong> 11.9 ìg T4CDFkg BW (or 1.19 ìg TEQkg BW) in their tissues (Mehrle etal. 1988).The results <strong>of</strong> egg injection studies appear to confirm the results <strong>of</strong> investigations inwhich test organisms were exposed to T4CDD in the water column. Walker et al.(1992) reported that the survival <strong>of</strong> rainbow trout alevins was greatly reduced (i.e., by-1> 60%) when eggs were injected with a dose <strong>of</strong> 0.437 ìg T4CDDkg egg. A median-1lethal dose (LD 50) <strong>of</strong> 0.421 ìgkg egg was reported in this study. Similarly,significant mortality during the hatching to swim-up stage was observed when rainbow-1 -1trout eggs were injected with a dose <strong>of</strong> 8.0 ìg T4CDFkg egg (or 0.8 ìg TEQkgegg; Walker and Peterson 1991). Median lethal doses (LD 50) <strong>of</strong> other PCDD and-1PCDF congeners ranged from 0.099 ìg TEQkg egg for 1,2,3,4,7,8-H6CDF to-10.367 ìgTEQkg egg for 1,2,3,7,8-P5CDF in this study.Single dose exposures (via intraperitoneal injection) <strong>of</strong> T4CDD have also resulted inadverse biological effects in juvenile rainbow trout. For example, Spitsbergen et al.(1988) reported that growth rates were significantly reduced up to 80 days following-1administration <strong>of</strong> a single dose <strong>of</strong> 5 ìgkg BW <strong>of</strong> T4CDD to rainbow troutfingerlings. Extreme mortality (90%) was observed following administration <strong>of</strong>-125 ìgkg BW in this study. While mortality generally follows exposure to high doses<strong>of</strong> T4CDD, more subtle effects have been observed at lower dosage rates. In juvenile-1rainbow trout, administration <strong>of</strong> doses as low as 0.03 ìgkg BW resulted in theaccumulation <strong>of</strong> erythrocytes in the spleen after 21 or 42 days (van der Weiden et al.1992). Haemorrhages in the skin and fins <strong>of</strong> these fish were evident at a higher dosage-1rate (0.3 ìgkg BW); significant mortality (20%) was only observed at ten times this-1exposure level (3.06 ìgkg BW; van der Weiden et al. 1992).The available data indicate that lake trout are one <strong>of</strong> the most sensitive species <strong>of</strong>freshwater fish. Walker et al. (1992) injected lake trout eggs with doses <strong>of</strong> T4CDD <strong>of</strong>-1up to 0.103 ìgkg BW and monitored survival during incubation (i.e., to swim-up).The results <strong>of</strong> this study indicate that small incremental changes in exposure levels canhave very significant effects on survival rates. The LD 50 <strong>of</strong> T4CDD, considering-1survival from hatching to swim-up, was 0.047 ìgkg egg for this species. Similarly,89