Isotopic Fingerprints of Iron–Cyanide Complexes in the Environment

Tracing the origin of iron–cyanide complexes in the environment is important because these compounds are potentially toxic. We determined the stable isotopic compositions of cyanide-carbon (C_CN) and cyanide-nitrogen (N_CN) in 127 contaminated solids and 11 samples of contaminated groundwater from coal carbonization sites, blast furnace operations, and commercial cyanide applications. Coal-carbonization-related cyanides had unique high mean δ¹³C_CN values of −10.5 ± 3.5‰ for the solids and −16.1 ± 1.2‰ for the groundwater samples, while the values for blast furnace sludge (−26.9 ± 1.5‰), commercial cyanides (−26.0 ± 3.0‰), and their corresponding groundwaters were significantly lower. Determination of δ¹³C_CN is a promising tool for identifying the source of cyanide contamination. However, for coal carbonization sites, historical research into the manufacturing process is necessary because a nonconventional gas works site exhibited exceptionally low δ¹³C_CN values of −22.7 ± 1.7‰. The δ¹⁵N_CN values for samples related to coal carbonization and blast furnaces overlapped within a range of +0.1 to +10.3‰, but very high δ¹⁵N_CN values seemed to be indicative for a cyanide source in the blast furnace. In contrast, commercial cyanides tend to have lower δ¹⁵N_CN values of −5.6 to +1.9‰ in solids and −0.5 to +3.0‰ in the groundwater.