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<br />BIOLOGICAL REPORT 85(1.23)
<br />acrylonitrile, propionitrile, and suecinonitrile, are
<br />nitrile-containing materials of varying complexity
<br />and lability, and can liberate free and toxicologi-
<br />cally available amounts of cyanide. But the non-
<br />nitrileportion of the cyanogen molecule ma}~ exert
<br />an independent or interactive toxicity, causing a
<br />complex response.
<br />cyanates contain the OCN group. Inorganic
<br />cyanates that are formed industrially by the oxida-
<br />tion ofcyanidesalts hydrolyze in water to form am-
<br />monia and bicarbonate ion. Alkyl cyanates are
<br />insoluble in water and form cyanurates. Alkyl
<br />isocyanates contain the OCN radical, are formed
<br />from cyanates, and, like cyanates, are readily hy-
<br />drolyzed. Thiocyanates (SCN group) are formed
<br />from cyanides and sulfur-containing materials
<br />and are relatively stable.
<br />Total cyanides refers to al] cyanide-containing
<br />compounds, including simple and complex cya-
<br />nides, cyanoglycosides, and free cyanide. Total
<br />cyanides is a chemical measuremegt of free cya-
<br />nidepresent insolution or released by acidification
<br />or digestion. Only free cya nide is congidered to be a
<br />biologically meaningful expression of cyanide tox-
<br />icity. Under most circumstances, the concentra-
<br />tion of total cyanide will exceed that of HCN. In
<br />some waters, however, the total cyanide concen-
<br />tration may consist almost entirely offree cyanide,
<br />or it may contain cyanides that rgadi]y photo-
<br />decompose or dissociate to yield HCN, The relation
<br />between total cyanide and free cyanide in natural
<br />waters varies with recei~~ng-water conditions,
<br />type of cyanide compounds present, dggree ofexpo-
<br />sure to daylight, and presence of other chemical
<br />compounds.
<br />Hydrogen cyanide has frequently been associ-
<br />ated with the odor of bitter almonds (Ballantyne
<br />1983; Gee 1987). The threshold odor for olfactory
<br />detection of atmospheric HCN is 1 mgt, but the
<br />odor may not be detected for various reasons, in-
<br />cluding the presence of other odors and the fact
<br />that only 203 to 4030 of those tested cquld detect a
<br />cyanide odor.
<br />Analytical methods for determining free and
<br />bound cyanide and cyanogenic compounds in bio-
<br />logical materials are under revision. Current
<br />methods include chromatography; enzymic post-
<br />column cleavage; electrochemical detection; and
<br />ultraviolet, infrared, proton, and catbon-13 nu-
<br />clear magnetic resonance spectroscopies (Brimer
<br />19881. Proposed newer analytical methodologies
<br />include chemiluminescence (Wu et al. 1989);
<br />deproteinization techniques (Ivynitsky et al.
<br />1986); thin film dissociation coupled with prefer-
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<br />and is also one of the most toxic cyanide species, it
<br />is noteworthy that the toxicity of simple cyanides
<br />will not be affected measurably below pH 8.3.
<br />Acidification of dilute (milligrams per liter) cya-
<br />nide solutions will not intiate any greater release
<br />of HCI~r, but acidification of concentrated (grams
<br />per liter) solutions promotes HCN formation and
<br />release.
<br />Complex cyanides are compounds in which
<br />the cyanide anion is incorporated into a complex or
<br />complexes; these compounds are different in
<br />chemical and toxicologic properties from simple
<br />cyanides. In solution, the stabilit}~ of the cyanide
<br />complex varies with the type ofcation and the com-
<br />plex that it forms. Some of these are dissociable in
<br />weak acids to give free cyanide and a cation, while
<br />other complexes require much stronger acidic con-
<br />ditions for dissociation. The least-stable complex
<br />metallocyanidesincfude Zn(CN),2 , Cd(CN); ,and
<br />Cd(CN),2 ; moderate)y stable complexes include
<br />Cu(CN): , Cu(CN>a%, Ni(CN), 2 , and Ag(CN)s'; and
<br />the most stable complexes include Fe(CN)c'' and
<br />Co(CN)a''. The toxicity of complex cyanides is usu-
<br />ally related to their ability to release cyanide ions
<br />in solution, which then enter into an equilibrium
<br />with HCN; relatively small fluctuations in pH sig-
<br />nificantly affect their biocidal properties.
<br />cyanogen [(CN)sl is the simplest compound
<br />containing the cyanide group. cyanogen is an ex-
<br />tremely toxic, flammable gas that reacts slowly
<br />with water to form HCN, cyanic acid, and other
<br />compounds; it is rapidly degraded in the environ-
<br />ment. cyanogen and its halide derivations are
<br />comparable in toxicity to hydrogen cyanide.
<br />Nitrites are defined as organic compounds
<br />(RCN) containing the cyanide group. Cyanide
<br />bound to carbon as nitriles (other than as cyano-
<br />genic glycosides) are comparatively innocuous in
<br />the environment, and are low in chemical reac-
<br />tivity and are biodegradable. For simple mono-
<br />nitri]esthere is aclear progression, with more cya-
<br />nide being released as chain length increases. A
<br />similar pattern exists in dinitriles, but corres-
<br />ponding compounds require a longer carbon chain
<br />than mononitriles before free cyanide is produced.
<br />Based on studies with chicken liver homogenates
<br />(Davis 1981), mononitriles were more toxic than
<br />dinitriles, and within each group the order of toxi-
<br />cit}'was CH, > CxHs > C9H i > C,H9 > CsH n > C,H,:.
<br />Cyanohydrins [RzC(OH)CN] and cyanogenic
<br />glycosides [R~RzC(OR,)CN] are special classes of
<br />nitriles, in that under appropriate conditions they
<br />will decompose to HCN and cyanide ions. Cyano-
<br />gens (not to be confused with cyanogen), such as
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