Measurement of cyanide in urban snowmelt and runoff

Ferrocyanide compounds enter the environment as anti-caking additives to road salts. In illuminated aquatic environments, the salts dissociate and form toxic free cyanide, which can then be lost through volatilization. The most common techniques for analysis of cyanide in environmental samples measure total and free (generally weak-acid dissociable, WAD) cyanide species. Cyanide has been detected in urban snow and winter runoff, but its potential impact in aquatic environments is not well understood. Between 2007 and 2009, cyanide was measured in parking lot runoff after deicer application, runoff from an urban snow disposal site and stormwater ponds. Parking lot runoff concentrations were highest, with 42% of samples displaying WAD cyanide and 97% containing total cyanide at concentrations higher than the method detection limit (MDL) of 0.01 mg/L. Smaller proportions of snow disposal site runoff and stormwater pond samples displayed WAD and total cyanide levels above the MDLs. Since the MDLs achieved were higher than guideline levels, the actual number of exceedances could not be determined. While this study indicates that cyanide in road salts poses a potential risk to the aquatic environment, it also highlights the need for more sensitive analytical techniques for such samples.