Frequent Questions

Does the maximum contaminant level goal (MCLG) and maximum contaminant level (MCL) for cyanide apply to free or total cyanide?

The MCLG and MCL for cyanide apply to free cyanide.  EPA determined that only free cyanides should be regulated because these are the species of health concern due to their bioavailability and toxicity.  EPA has approved test methods that test for total cyanide to be used as a screening tool.  If total cyanide is above the MCL then the analysis for free cyanide would be required to determine whether there is an exceedance of the MCL.  (57 FR 31776, 31786; July 17, 1992)
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