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