Lab Matters Spring 2018 | Page 29

environmental health Cyanide: Forms of Cyanide Tips for Cyanide Testing: • Is generally known to be toxic • Free cyanide: Cyanide ion (CN ) and hydrogen cyanide in water (HCN,). Also called “simple cyanide.” - • Is non-carcinogenic and doesn’t bioaccumulate so there isn’t a need to detect cyanide at trace concentrations. • Has acute health effects. The US Safe Drinking Water Act maximum contaminant level goal and the maximum contaminant level (MCL) have always been the same: 200 µg/L as free cyanide (i.e., CN - and HCN). • Has a lethal dose: about 4 mg/Kg. It would take about 525 L of water at the MCL to drink the median lethal dose, LD50. methods (Figure 1). The deionized water went through the MWRA drinking water treatment process (ammonia, hypochlorite, elevated pH and alkalinity) and was then tested using the prescribed cyanide preservation and testing procedure (dechlorination with ascorbic acid or thiosulfate and then raising the pH with sodium hydroxide (NaOH)). The dechlorination and NaOH, along with the sample matrix, cause free cyanide to form. However, US EPA has