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<br />18 BIOLOGICAL REPORT 85(1.23)
<br />low in winter owing to dilution by high runoff, but
<br />peaked in summer because of cyanide production
<br />by plants (Leduc 1984). Cyanides do not seem to
<br />persist in aquatic environments. In small, cold
<br />oligotrophic lakes treated with 1 mg NaCN/L,
<br />acute toxicity was negligible within 40 days. In
<br />warm shallow ponds, toxicity disappeared within 4
<br />days after application of 1 mg I~'aCN/L. In rivers
<br />and streams, toxicity rapidly disappeared on dilu-
<br />tion (Leduc 1984). Cyanide was not detectable in
<br />water and sediments of Yellowknife Ba}', Canada,
<br />between 1974 and 1976, although the bay receives
<br />liquid effluents containing cyanides from an oper-
<br />ating gold mine. Nondetection was attributed to
<br />rapid oxidation (Moore 1981). Several factors con-
<br />tribute to the rapid disappearance of cyanide from
<br />water. Bacteria and protozoans ma}' degrade cya-
<br />nide by converting it to carbon dioxide and ammo-
<br />nia. Chlorination of water supplies can result in
<br />conversion to cyanate (EPA 19801. An alkaline pH
<br />favors oxidation by chlorine, and an acidic pH fa-
<br />vors volatilization of HCN into the atmosphere
<br />(EPA 1980).
<br />Persistence in Water, Soil,
<br />and Air
<br />In µ^ater, cyanides occur as Tree hydrocyanic
<br />acid, simple cyanides, easily degradable complex
<br />cyanides such as Zn(CN)s, and sparingly decom-
<br />posable complex cyanides of iron and cobalt; com-
<br />plex nickel and copper cyanides are intermediate
<br />between the easily decomposable and sparingly
<br />degradable compounds (Towill et al. 1978). Cya-
<br />nide has relatively low persistence in surface wa-
<br />ters under normal conditions but may persist Tor
<br />extended periods in groundwater (Way 198]1.
<br />Volatilization is the dwttinant mechanism for re-
<br />moval of free cyanide from concentrated solutions
<br />and is most effective under conditions of high tem-
<br />peratures,high dissolved oxygen levels, and at in-
<br />creased concentrations of atmospheric carbon
<br />dioxide (Leduc et al. 1982: Simovic and Snodgrass
<br />19851. Loss of simple cyanides from the water col-
<br />umn is primarily through sedimentation, micro-
<br />bial degradation, and volatilization (Leduc et al.
<br />1952; Alarrs and Ballanttime 1987). V~'ater-soluble
<br />strong complexes, such as ferricyanides and fer-
<br />rocvanides, do not release free cyanide unless ex-
<br />posed to ultraviolet light. Thus, sunlight may lead
<br />to cyanide formation in wastes containing iron-
<br />cyanidecomplexes (Towill et al. 1978; Leduc et al.
<br />1982: Simovic and Snodgrass 1985; Marrs attd Bal-
<br />lantyne 1987).
<br />Alkaline chlorination of wastewaters is one of
<br />the most widely used methods of treating cyanide
<br />wastes. In this process, cyanogen chloride, (CNCll
<br />is formed, which at alkaline pH is hydrolyzed to
<br />the cyanate ion (CNO-). If free chlorine is present,
<br />CNO' can be further oxidized (Way 1~i81; Leduc et
<br />al. 1982; Simovic and Snodgrass 1986; Marrs and
<br />Ballantyne 1987). Other methods used in cyanide
<br />waste management incl • ie ]agoonirtg far natural
<br />degradation, evaporatiu.. exposure to ultraviolet
<br />radiation, aldehyde treatment, ozoniaation, acidi-
<br />fication-volatilization-reneutralization, ion ex-
<br />change, activated carbon absorption, electrolytic
<br />decomposition, catalytic oxidation, and biological
<br />treatment with cyanide-metabolizing bacteria
<br />(Towill et al. 1978; EPA 1980; Way 1981; Marrs
<br />and Ballantyne 1987). In the case of Canadian
<br />gold-mining operations, the primary treatment for
<br />cyanide removal is to retain gold mill wastewaters
<br />in impoundments for several days to months; re-
<br />moval occurs through volatilization, phot.o-
<br />degradation, chemical oxidation, and, to a lesser
<br />extent, microbial oxidation. Microbial oxidation of
<br />cyanide is not significant in mine tailing ponds,
<br />which typically have pH >10, a low dumber of mi-
<br />croorganisms,low nutrient levels, large quiescent
<br />zones, and cyanide concentrations >10 mg/L
<br />(Simovic and Snodgrass 1985).
<br />Cyanide seldom remains biologically avail-
<br />able in soils because it is either comp~exed by trace
<br />metals, metabolized by various microorganisms, or
<br />lost through volatilization (Towill et al. 1978;
<br />Marrs and Ballantyne 1987). Cyanide ions are not
<br />strongly adsorbed or retained on soils, and leach-
<br />ing into the surrounding ground water will prob-
<br />ablyoccur. Under aerobic conditions, cyanide salts
<br />in the soil are microbially degraded to nitrites or
<br />form complexes with trace metals. Under anaero-
<br />bicconditions, cyanides denitrify to gaseous nitro-
<br />gen compounds that enter the atmosphere.
<br />Volatile cyanides occur only occasionally in
<br />the atmosphere, due largely to emissions from
<br />plating plants, fumigation, and other special op-
<br />erations (Towill et al. 1978). Under normal condi-
<br />tions cyanide has relatively low persistence in air,
<br />usuallybetween 30 days and 1 year (Way 1981), al-
<br />though some atmospheric HCN may persist for up
<br />to 11 years (Marrs and Ballantyne 1Q87). Data are
<br />lacking on the distribution and transformation of
<br />cyanide in the atmosphere (Towill et al. 19781 and
<br />should be acyuired.
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