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Administrative data

Link to relevant study record(s)

Description of key information

HCN is not strongly partitioned to sediment or suspended adsorbents, and is relatively mobile in moist soil environments.

Key value for chemical safety assessment

Additional information

The following is a summary from the ECETOC JACC Report, No. 53, 2007, in the absence of a specific Koc value and in lieu of writing individual endpoint study records on the publications covered in this review:

The fate of cyanides in soil is dependent on a number of chemical and biological processes such as redox conditions, pH, complexation or microbial degradation, based on comprehensive reviews of those processes including that published by Kjeldsen (1999). HCN is not strongly partitioned into the sediments or suspended adsorbents, primarily due to its high solubility in water (Callahan et al,1979).

Cyanides are relatively mobile in the soil environment (Alesii and Fuller, 1976). These authors reported that cyanide mobility is least where soils exhibit low pH, high concentrations of free iron oxides, and positively charged particles (e.g. kaolin, chlorite, gibbsite). Mobility is greatest at high pH, high concentrations of free CaCO3 (high negative charge) and low clay content.

Cruz et al (1974 cited by Callahan et al, 1979) studied the adsorption of HCN by montmorillonitic clays. The data showed that adsorption is fairly weak and is decreased by the presence of water. Thus, adsorption to montmorillonitic clays is probably not an important fate process in the aquatic environment (Callahan et al, 1979) or in soil. Free cyanide did not adsorb to goethite at different pHs (4 - 10), while potassium ferricyanide, K3[Fe(CN)6], adsorbed for 90% at pH 4.0 and 50% at pH 5 (Theis and West, 1986 cited by Murgatroyd et al, 1998). Cyanide ions are not strongly adsorbed or retained by soils (Murrmann and Koutz, 1972). The cyanide salts of most cations are soluble (except AgCN) but move only a short distance through soil before being biologically converted under aerobic conditions to nitrates (by microbial degradation to NH3, then conversion to NO3 -) or fixed by trace metals through complex formation. Under anaerobic conditions, cyanides denitrify to gaseous nitrogen compounds which enter the atmosphere. The cyanide ion is not involved in oxidation-reduction reactions (Murrmann and Koutz,1972).

In conclusion, HCN is not strongly partitioned into the sediments or suspended adsorbents, primarily due to its solubility in water. Cyanides are relatively mobile in the soil, indicating that adsorption is unlikely to be significant in most aquatic environments.