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1 <br /> <br /> <br /> <br />1 <br /> <br />1 <br /> <br />1 <br />1 <br />t <br />I' <br />r <br /> <br />J <br />t <br /> <br />c <br />u <br />d <br />n <br />c <br />ui <br />u <br />z <br />a <br />O <br />LL <br />0: <br />W <br />a <br />w <br />H <br />a <br />w <br />100 <br />BO <br />sD <br />70 <br />60 <br />50 <br />4D <br />70 <br />20 <br />t0 <br />FREE CYANIDE, in ug/L <br />hepatic damage. Exposure of fish for 9 days to 10 <br />µg HCN/L was suftcient to induce extensive <br />necrosis in the liver, although gill tissue showed no <br />damage. Intensification of liver histopathology <br />was evident at dosages of 20 and 30 µg HCN/L and <br />exposure periods up to 18 days (Leduc 1984). Cya- <br />nide has a strong, immediate, and long-lasting in- <br />hibitory effect on the swimming ability of fish <br />(Leduc 1984). Free cyanide concentrations as low <br />as 10 µg/L can rapidly and irreversibly impair the <br />swimming ability of salmonids in well-aerated <br />water (Doudoroff 1976). Osmoregulatory distur- <br />bancesrecorded at 10 µg HCN/L may affect migra- <br />tory patterns, feeding, and predator avoidance <br />(Leduc et al. 1982; Leduc 1984). In general, fish ex- <br />perience asignificant reduction in relative per- <br />formance (based on osmoregulation, growth, <br />swimming, and spermatogenesis) at 10 µg HCN/L, <br />and although fish can sun~ve indefinitely at 30 µg <br />HCI~T/L in the laboratory, the different physiologi- <br />cal requirements necessary to survive in nature <br />could not be met (Leduc 1978, 1981; Leduc et al. <br />1982; Figure). Increased predation by green sun- <br />fish (Lepomis cyancllus) on fathead minnows <br />(Pimephales promefas) was noted at sublethal con- <br />centrations of HCN, but it was uncertain if fat- <br />heads became easier pre}• or if green sunfish had <br />greater appetites (Smith et al. 1979). <br />Sodium cyanide has stimulatory e}Tects on <br />oxygen-sensitive receptors in ]ungi-ish, amphibi- <br />ans, reptiles, birds, and mammals (Smatresk <br />CYANIDE 27 <br />Figure. Summary of lethal and sub- <br />lethal effects of free cyanide on fresh- <br />water fish. Modifigd from Leduc et al. <br />(1982). <br />1986). Facultative and aquatic air breathers ap- <br />pear to rely on air breathing when external <br />chemoreceptors are stimulated, whereas obligate <br />air-breathing fish are more responsive to internal <br />stimuli (Smatresk 1986). Gill ventilation fre- <br />quency of longnose gar (Lepisosteus osseus), for ex- <br />ample, was little affected by external cyanide <br />application, but responded strongly when cyanide <br />was administered internally by injection <br />(Smatresk 1986). Cyanide, like fiany other chemi- <br />cals, can stimulate growth of filth during exposure <br />to low sublethal levels. This phenomenon, referred <br />to as hormesis, is little understood and warrants <br />additional research (Leduc 1984). <br />The observed toxicity to aquatic life of simple <br />and complex cyanides was attributed almost en- <br />tirely to molecular (undissoci~ted) HCN derived <br />from ionization, dissociation, and photodecomposi- <br />tion of cyanide-containing compounds. The toxic- <br />ity of the cyanide ion, CN-, which is a minor <br />component of free cyanide (HCN + CN-) in waters <br />that are not exceptionally alkaline is of little im- <br />portance (Doudoroff 1976; Towill et a1.1978; Smith <br />et al. 1979; EPA 1980). The acute toxicity of stable <br />silver cyanide and cuprocyanidp complex anions is <br />much less than that of molecular HCN, but is nev- <br />erthelessimportant; these ion8 can be the princi- <br />pal toxicants, even in some very dilute solutions. <br />The much lower toxicities of the terrocyanide and <br />ferricyanide complexions-which are of high sta- <br />bilitybut subject to extensive and rapid photolysis, <br />10 20 70 40 50 lOD 150 <br />