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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Potassium cyanide is a chemical with an organic functional group (cyanide) and a metal (potassium), characteristics which affect its behavior in the environment.  The ECETOC Task Force determined that there are "no data" for a Koc value for potassium cyanide.  However, a Koc value has been estimated through QSAR modeling (KOCWIN version 2.00  in EPI Suite, U.S. Environmental Protection Agency). Potassium cyanide falls within the predictive domain of the model, based on its molecular weight and the inclusion of the cyanide/nitrile functional group in the training set of the model.  The model provides estimates of Koc by two methodologies; the estimated Koc presented here is based on the molecular connectivity index, which the user's guide for the model describes as "overall..is somewhat more accurate than the log Kow methodology", although the two estimates are not substantially different.  The predicted Koc value indicates that even when potassium cyanide is evaluated as free cyanide, the predicted partitioning to organic carbon is not substantial.  The results of an adsorption isotherm study (internal DuPont Co. report, 1993) produced higher estimates of a Koc value in the range of 434 to 1259; however, the study results may not account for cyanide losses attributable to volatilisation and complexation, and may overestimate the Koc value.  This is supported by the findings of Callaghan et al. (1997)  who stated that "(b)iological solids sorb cyanides, but as with the other sorbents, the amount thus bound is probably insignificant in comparison to the amounts volatilized or biodegraded." 

Key value for chemical safety assessment

Koc at 20 °C:
2.841

Additional information

The ECETOC JACC Report No. 53, "Cyanides of Hydrogen, Sodium and Potassium, and Acetone Cyanohydrin (CAS No. 74 -90 -8, 143 -33 -9, 151 -50 -8, and 75 -86 -5), September 2007, states that the Koc for sodium cyanide and potassium cyanide are "not applicable" to sodium cyanide and potassium cyanide, i.e., forms of cyanide that behave as inorganic compounds.

The range of Koc values from the 1993 DuPont study (> 434 - < 1259) include values below, near and above the approximate threshold Koc of 1000 indicative of immobility and strong sorption to soils or sediment. However, the methodology did not distinguish between adsorption of the sodium cyanide to soils and chemical reaction or complexation of the sodium cyanide with the soil. Callahan et al. (1979) as cited in the ECETOC JACC Report No. 53, stated that "HCN is not strongly partitioned into the sediments or suspended adsorbents, primarily due to its high solubility in water." Callahan et al. (1997) also state, "Biological solids sorb cyanides, but as with the other sorbents, the amount thus bound is probably insignificant in comparison to the amounts volatilized or biodegraded." Alesii and Fuller (1976), also as cited in ECETOC JACC Report No. 53, stated that cyanides are relatively mobile in the soil environment, indicating that absorption is unlikely to be significant in most aquatic environments. The QSAR modeling for sodium cyanide by the KOCWIN v2.0 QSAR modeling program predicts the Koc for sodium cyanide by removing the metal (Na) portion of the molecule, by two methods: Molecular Connectivity Index (MCI) and direct estimation from Kow; each method applies a correction factor for the cyanide/nitrile fragment, yielding estimated Koc values of 2.841 L/kg and 2.413 L/kg, respectively. These results suggest that even when sodium cyanide or potassium cyanide is evaluated as free cyanide, the predicted partitioning to organic carbon is not substantial.