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<br />U <br /> <br />~I <br /> <br /> <br />1 <br /> <br /> <br /> <br />rainbow trout (McGeach}'and Leduc 19881; higher <br />resistance to cyanide correlated with higher activ- <br />ity induced b}• exercise and higher temperatures, <br />suggesting a faster detoxification rate or higher <br />oxidative and anaerobic metabolisms. Low levels <br />of cyanide that were harmful when applied con- <br />stantly ma}• be harmless under seasonal or other <br />variations that allow the organism to recover and <br />detoxify (Leduc 1981). Acclimatization by fish to <br />low sublethal levels of cyanide through continuous <br />exposure might enhance their resistance to poten- <br />tially lethal concentrations (Leduc 1961, 1984), <br />but studies with Atlantic salmon and rainbow <br />trout indicate otherwise. Prior acclimatization of <br />Atlantic salmon smolts to cyanide increased their <br />resistance only slightly to lethal concentrations <br />(Alabaster et al. 1983 ).Juvenile rainbow trout pre- <br />viously exposed to low sublethal concentrations <br />showed a marked reduction in fat synthesis and <br />swimming performance when challenged with <br />higher cyanide doses; effects were most pro- <br />nounced at low water temperatures (Kovacs and <br />Leduc 1982a). Experimental evidence is lacking on <br />exposure to lethal concentrations after prior expo- <br />sure to high sublethal concentrations; some inves- <br />tigatorspredict decreased resistance (Leduc 1984 ), <br />and others increased survival (Towill et al. 1976). <br />Birds <br />CYANIDE 29 <br />First signs of cyanide toxicosis in sensitive <br />birds appeared between 0.5 and 5 min after e::po- <br />sure, and included panting, eye blinking, saliva- <br />tion, and lethargy (Wiemeyer et al. 1986). In <br />more-resistant species, such as domestic chickens, <br />signs of toxicosis began 10 min after exposure. At <br />higher doses, breathing in al] spe©es tested be- <br />came increasingly deep and labored, followed by <br />gasping and shallow intermittent breathing. <br />Death usually followed in 15-30 min, although <br />birds alive at 60 min frequently recovered <br />(W iemeyer et al. 1986 ). The rapid recovery of some <br />birds exposed to cyanide may be due to the rapid <br />metabolism of cyanide to thiocyanate and its sub- <br />sequent excretion. Species sensitivity to cyanide <br />was not related to body size but seemed to be asso- <br />ciated with diet (Wieme}•er et al. 1986). Birds that <br />feed predominantl}• on flesh, such as vultures, kes- <br />trels, and owls, were more sensitive Lo cyanide <br />than were species that feed mainly oh plant mate- <br />rial-with the possible exception of rltallard (Arras <br />platyrhynchos)---as judged by acute oral LD50 val- <br />ues (Table 4). <br />Table 4. Cyanide effects on selected .species of birds. <br /> <br />1 <br /> <br />1 <br /> <br /> <br /> <br />Species, dose, and other <br />variables Effects Reference° <br />Mallard, Anne plalyrhynchos <br />Single oral dose of NaCN <br />0.53 mg CN/kg body weight (BW ), eyuivalent to <br />1.1 mg CN/kg B1~' (2.0 mg NaCN/I:g BW ( <br />127 mg CN/kg BW i•?.4 mg NaCN/kg BW) <br />1.43 mg CN/kg Elt' (2.; mg NaCN/hg BWl <br />Turkey vulture, Cathartes aara <br />Single oral dose of 19.1 mg CN/kg BN' <br />equivalent to 36 mg NaCN/kg BW <br />Single oral dose of 19.1 mg CN7i:g BVJ, <br />equivalent to 36 m;: NaCN/I:g BW <br />No deaths <br />About 6S dead <br />About 33 x dead <br />LD50; 959c confidence interval <br />(C.1.1 of 2.2 and 3.2 mg NaCN/kg BW <br />Up to 60 ~ of the cyanide in <br />blood was present as free <br />cyanide and the remainder as <br />bound cyanide <br />Average time to death .cas <br />about 19 min and ranged <br />between 6 and 41 min; cyamde <br />residues postmortem, in mg <br />CN/kg fresh we~eht (FN'), were <br />6. ~ in blood (Max. 21) and <br />0.6 in liver (Max. 2.R) <br />7 <br />W <br /> <br />