Cyanides and thiocyanates

Cyanides occur in many effluents generated by industry [40], particularly metal finishing and metal treatment. The oxidation of cyanide is achieved by both electrochemical and chemical methods. Commercial electro- 

LI Direct oxidation. The electrochemical oxidation of cyanide in an alkaline environment is believed to proceed according to the following reactions  

The cyanogen formed can then undergo alkaline hydrolysis to cyanate (CN)2 + 20H CN + CNO + H2O At high pH, cyanide oxidation could result in cyanate directly  

2 Indirect oxidation. The indirect oxidation of cyanide is primarily based on the oxidation of chloride ions to produce hypochlorite. In practice the cyanide feed solution can be dosed with sodium chloride as a saturated solution and passed continuously through the cell. The indirect processes is said to have several potential advantages over direct oxidation, which include a lower cell voltage, through the increased conductivity, fast chemical reaction and lower overvoltages and reduced wear with platinum or DSA type coated electrodes. Energy consumptions are quoted at around 4-10 kWh kg cyanide. 

The treatment of cyanates and thiocyanates can generally use technology identical with that for cyanides. In the treatment of thiocyanate at 

---

Copperil) cyanide. CuCN (and copperil) thiocyanate), are similarly obtained as white precipitates on adding cyanide and thiocyanate ions (not in excess) respectively to copper(II) salts ... 

Silver nitrate is used volumetrically to estimate chloride, bromide, cyanide and thiocyanate ions. Potassium chromate or fluorescein is used as an indicator. 

Cadmium Hydroxide. Cd(OH)2 [21041-95-2] is best prepared by addition of cadmium nitrate solution to a boiling solution of sodium or potassium hydroxide. The crystals adopt the layered stmcture of Cdl2 there is contact between hydroxide ions of adjacent layers. Cd(OH)2 can be dehydrated to the oxide by gende heating to 200°C it absorbs CO2 from the air forming the basic carbonate. It is soluble ia dilute acids and solutions of ammonium ions, ferric chloride, alkah haUdes, cyanides, and thiocyanates forming complex ions. 

Although it is moot whether carbon monoxide, cyanide, and thiocyanate should be included as organic compounds, brief comments on their biodegradation are summarized. 

LEED has also been used to study the adsorption of halide ions, cyanide and thiocyanate ions, and organic molecules on single-crystal metal surfaces. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

Sanner T, Rivedal E. 1985. Tests with the Syrian hamster embryo (SHE) cell transformation assay. In Ashby J, de Serres FJ, et al., eds. Progress in mutation research. Vol. 5. Evaluation of short-term tests for carcinogens. Amsterdam, The Netherlands Elsevier Science Publishers, 665-671. Sato M, Ishizu S, Momotuni H. 1975. [Determination of acrylonitrile, cyanide and thiocyanate in blood and urine.] Jap J Ind Health 17 99-105. (Japanese). 

Cailleux, A., J.F. Subra, P. Riberi, E. Tuchais, A. Premel-Cabic, and P. Allain. 1988. Cyanide and thiocyanate blood levels in patients with renal failure or respiratory disease. Jour. Medic. 19 345-351. 

Philbrick, D.J., J.B. Hopkins, D.C. Hill, J.C. Alexander, and R.G. Thomson. 1979. Effects of prolonged cyanide and thiocyanate feeding in rats. Jour. Toxicol. Environ. Health 5 579-592. 

Methaemoglobin forming compounds should be used cautiously in victims suffering from concurrent carbon monoxide poisoning or hypoxia. The second approach calls for provision of additional sulfur groups to enhance the detoxification of cyanide and thiocyanate by endogenous rhodanese this comes about by giving sodium thiosulphate. 

Several studies provided data on blood and urine concentrations of cyanide and thiocyanate following occupational exposures at low concentrations. These values are generally similar to those of smokers who have not been occupationally exposed to HCN. Whole-blood cyanide concentrations during... 

Maehly, A.C. and A.Swensson. 1970. Cyanide and thiocyanate levels in blood and urine of workers with low-grade exposure to cyanide. Int. Arch. Arbeitsmed. 27 195-209. 

Vesey, C.J., P.V.Cole, P.J.Simpson. 1976. Cyanide and thiocyanate concentrations following sodium nitroprusside infusion in man. Br. J. Anaes. 48 651-660. 

Blood and urine levels of cyanide and thiocyanate can be measured, and small amounts of these compounds are always detectable in blood and urine. We do not know the exact cyanide exposure levels linked with high levels of cyanide or thiocyanate in body fluids. Harmful effects can occur when blood levels of cyanide are higher than 0.2 parts per billion (ppb), but some... 

Facilities in each state that manufactured or processed hydrogen cyanide in 1992, the range of the maximum amounts stored on site, and the types of production or use activities (e.g., production for sale or on-site use in processing) are shown in Table 4-1 (TRI93 1995). The information in Table 4-1 is derived from the Toxics Release Inventory (TRI). The TRI data should be used with caution since only certain types of facilities are required to report. This is not an exhaustive list. No information is available in the TRI database for other cyanide and thiocyanate compounds in this profde because these compounds are not included under SARA, Title III and, therefore, are not among the chemicals that facilities are required to report (EPA 1993g). 

Several studies document the biodegradation of mixtures of cyanides and thiocyanate in waste waters (e g., Boucabeille et al. 1994b Mudder and Whitlock 1984 Paruchuri et al. 1990 Shivaraman et al. 

The values reported for environmental levels of cyanide and thiocyanate must be interpreted with caution. Methods for the analysis of cyanide and thiocyanate have many interferences. In addition, samples containing cyanide and/or thiocyanate may not be stable if the samples are not carefully preserved. It should be noted that the amounts of cyanide or thiocyanate found by chemical analysis are not necessarily the amounts that are bioavailable. 

Table 5-3. Cyanide and Thiocyanate Concentrations ( jg/mL)a in Smokers and Nonsmokers... 

Reliable monitoring data for the levels of cyanide and thiocyanate in contaminated media at hazardous waste sites are needed so that the information obtained on levels of cyanide and thiocyanate in the environment can be used in combination with the known body burdens of cyanide and thiocyanate to assess the potential risk of adverse health effects in populations living in the vicinity of hazardous waste sites. Also, there is a need for data relating to exposure levels of cassava eaters in the United States. 

Exposure Levels in Humans. The levels of cyanide and thiocyanate in various human tissues and body fluids of both control and occupationally exposed groups and of smokers and nonsmokers are available (see Sections 2.3.4, 2.6.1, and 5.5). The levels of these chemicals in humans consuming foods containing cyanogenic materials also are available. 

Methods for Determining Biomarkers of Exposure and Effect. Besides environmental exposure, exposure to cyanide can also occur from consumption of cyanide-containing food, metabolism of certain drugs, and smoking cigarettes. Since so many factors can influence cyanide exposure, the exact correlation between cyanide concentrations in the body and its level in the environment has not been made. Therefore, measuring cyanide and/or thiocyanate levels in blood and urine cannot be used as a biomarker for exposure to low cyanide concentrations. Analytical methods of required sensitivity and reliability to detect cyanide and thiocyanate in blood, plasma, and urine of both unexposed and exposed persons are available (see Table 6-1 and Table 6-3). Further studies determining biomarkers for exposure to low cyanide concentrations would be useful. 

ASTM. 1994b. Standard test methods for cyanide in water- Automated method for total cyanide, dissociable cyanide and thiocyanate. Annual book of ASTM standards. Vol. 11.02 Water(II). American Association for the Testing ofMaterials. Philadelphia, PA. 102-111. 

---