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<br />14 BIOlAG1CAL RaroaT 85(1.23)
<br />acrylonitriles(Egekezeand Oehme 1980; Purseret
<br />al. 1984; Becker 1985; Ballantyne 1987b).
<br />Polyacrylonitrile, for example, is used in fabrics,
<br />upholstery covers, paddings, and clothing; about
<br />50°v of the mass of the pol}•mer is theoretically
<br />available as HCA' under thermal decomposition
<br />(Purser et al. 1989; Homan 1987).
<br />Background Concentrations
<br />The reactivity of HCN, and its ability to con-
<br />dense with itself and other compounds, was prob-
<br />ablyresponsible for the prebiotic formation of the
<br />majority of biochemical compounds required for
<br />life (Marrs and Ballantyne 1987). Cyanide is now
<br />known to be present in a number of foodstuff' and
<br />forage plants, as a metabolite ofcertain drugs, and
<br />in various industrial pollutants; it also may be
<br />formed by the combustion of cyanide-releasing
<br />substances, such as plastics in airplane fires and
<br />tobacco in smoking (Robinson et al. 1985). Hydro-
<br />gen cyanide production may occur in hepato-
<br />pancreas of mussels, Mylilus edulis (Vennesland
<br />et a1.19816), in rat liver (Solomonson 1981), and in
<br />green and blue-green algae during nitrate metabo-
<br />lism (Leduc et al. 1982). Except for certain natu-
<br />rally occurring organic cyanide compounds in
<br />plants, itis uncommon to find c}•anide in foods con-
<br />sumed in the United States (EPA 1980).
<br />The cyanide anion is found in a variety of
<br />naturally occurring plant compounds as cyano-
<br />genic glycosides, glycosides, lathyrogenic com-
<br />pounds, indoleacetonitrile, and cyanopvridine al-
<br />kaloids. Plants that contain cyanogenic g]yco-
<br />sidesare potentially poisonous because bruising or
<br />incomplete cookie g can result in glycoside hydroly-
<br />sisand release of HCN (Towil] et al. 1978). Cyanide
<br />concentrations in cyanogenic plants are usual]}'
<br />-highest in ]eaves of young plants: 3evels drop rap-
<br />idly after pollination (Bieh] 1984). There are about
<br />-20 major cyanogenic glycosides, of which usually
<br />only one or two occur in any plant. They are syn-
<br />thesized from amino acids and sugars and are
<br />found in many economically important plants,
<br />such as sorghum, flax, lima bean, cassava, and
<br />many of the stone fruits (Table 2; Towil] et al. 1978;
<br />Shaw 1986). Cassava contains linamurin and
<br />lotaustralin, whereas the main cyanogenic
<br />glycoside in cereals is dhurrin; consumption of
<br />foods containing toxic cyanogens (primarily cas-
<br />sava) has been associated with death or mor-
<br />bidity-on an acute basis---0r goiter and tropical
<br />ataxic neuropathy on a chronic consumption basis
<br />lOkolie and Ugochukwu 1989). Cassava is a peren-
<br />nial shrub, native to the neotropics, grown for its
<br />tuberous starchy roots, and a traditional dietary
<br />staple oC many indigenous populations in
<br />Amazonia, especially the Tukanoan Indians in
<br />northwestern Amazonia (Dufour 1988). Cassava is
<br />one of the few food plants in which the cyanide con-
<br />tentmay create toxic problems. All varieties otcas-
<br />sava contain cyanogenic glycosides capable of
<br />liberating HCN, but amounts vary greatly depend-
<br />ing on variety and environmental conditions. Bit-
<br />ter cultivars of cassava provide over 70°'0 of the
<br />Tukanoan's Cood energy, appearing In the diet as
<br />bread, meal, a starch drink, and boiled cassava
<br />juice. The greatly elevated total cyanide content in
<br />bitter varieties (Table 2) may contain 5.1-13.4'i~. of
<br />the total as the toxic free cyanide (Dpfour 1988).
<br />The production of HCN by animals is almost
<br />exclusively restricted to various arthropods: 7 of
<br />about 3,000 species of centipedes; 46 of 2,500 spe-
<br />cies of polydesmid millipedes; and 10 of 750,000
<br />species otinsects, including 3 species of beetles, 4
<br />moths, and 3 butterflies (Duffey 1981). Milli-
<br />pedes-which are eaten frequently by toads and
<br />starlings-secrete cyanide for defensive purposes
<br />in repelling predators; in zygaenid moths, cyanide
<br />seems to be localized in eggs (Tablle 2; Duffey
<br />1981).
<br />Cyanide concentrations in fish from streams
<br />that were deliberately poisoned with cyanide
<br />ranged between 10 and 100 µg total cyanide per
<br />kilogram whole body fresh weight fFW; Wiley
<br />1984). Total cyanide concentrations in gill tissues
<br />of salmonids under widely varying conditions of
<br />temperature, nominal water concentrations, and
<br />duration of exposure ranged from about 30 µg/kg
<br />FR' to >7,000 µglkg (Holden and Marsden 1964).
<br />Unpoisoned fish usually contained <1 µg/kg FW in
<br />gills, although values up to 50 µg/kg occurred occa-
<br />sional]}•. Lowest cyanide concentrations in gills oc-
<br />curred at elevated (summer) water temperatures;
<br />at lower temperatures, survival was greater and
<br />residues were higher (Holden and Marsden 1964).
<br />Fish retrieved from cyanide-poisoned environ-
<br />ments,dead oralive, can probably be consumed by
<br />humans because muscle cyanide residues were
<br />considered to be low (i.e., <1.000 mg/kg FW; Leduc
<br />1954 ~.
<br />Cyanide pollution is likely to occur in many
<br />places, ranging from industrialized urban areas to
<br />gold mines in the western United States and
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