Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:14:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 14 (pt 1/9)
Character Range: 2333329–2336301

14             Cyanide (free)

14.1          General
Several comprehensive reviews of cyanide in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (ATSDR 2006; WHO 2004 and 2011; RIVM 2001; DEFRA & EA 2002; NICNAS 2010). The following provides a summary of the key aspects of cyanide that are relevant to the derivation of a soil HIL.

Cyanide is a chemical group consisting of one atom of carbon connected to one atom of nitrogen by three molecular bonds. Cyanides can both occur naturally or be man-made and many are powerful and rapid-acting poisons. Hydrogen cyanide and the simple cyanide salts (sodium cyanide and potassium cyanide) are common examples of cyanide compounds. Certain bacteria, fungi, and algae can produce cyanide. In certain plant foods, including almonds, millet sprouts, lima beans, soy, spinach, bamboo shoots and cassava roots (which are a major source of food in tropical countries), cyanides occur naturally as part of sugars or other naturally-occurring compounds (ATSDR 2006).

Cyanide in soil and water predominantly comes from industrial processes. Major sources of cyanide in water includes discharges from metal mining processes, organic chemical industries, iron and steel plants or manufacturers, and publicly owned wastewater treatment facilities. Other cyanide sources include vehicle exhaust, releases from certain chemical industries, burning of municipal waste, and use of cyanide-containing pesticides. Much smaller amounts of cyanide may enter water through stormwater runoff where road salts containing cyanides are used.

Cyanide can be present in soil as cyanide complexes, free cyanide or as the gas hydrogen cyanide. The behaviour of cyanide is complex and the potential for free cyanide to be present should include some consideration of the former source. Review of cyanide in soil from a range of sources (RIVM 2001) identified little free cyanide (or hydrogen cyanide gas) present at former manufactured gasworks sites (with most cyanide in the form of Prussian blue), little free cyanide associated with former metallurgic and photographic industry wastes (where most cyanide present is complexed) and other waste materials.

The lifetime of dumped free cyanide and simple cyanides at high or low concentrations in the soil is limited. At high concentrations, leaching and emanation of free cyanide is dominant initially, together with the formation of metal hexacyanide complexes, generally with iron and/or manganese. Later and/or at low concentrations, free cyanide is reduced by biochemical breakdown. Little free cyanide is liberated from cyanide complexes found in soil (RIVM 2001).

14.2          Previous HIL
The derivation of the previous HIL (HIL A = 250 mg/kg) for cyanide is presented by Turczynowicz (1993) and NEPC (1999). In summary, the HIL was derived on the basis of the following:
    * Background intakes of