Cyanide

Cyanide
Cyanides are one of the most toxic of all chemicals towards fish and great care has to be taken to avoid discharging untreated Cyanide wastes into rivers and streams. Such toxic wastes may arise from electroplating and case-hardening processes and also metal cleaning.
Cyanides can be present as 'free cyanide' as HCN or simple complexes ie Sodium, Potassium, Zinc, Copper and Cadmium Cyanide. Heavy metals like iron and nickel form tight complexes with Cyanide which can only be broken down by distillation.