Assessing taste and visual perception of Mn(II) and Mn(IV)

Abstract

The US Environmental Protection Agency secondary maximum contaminant level (SMCL) for manganese (Mn) is 0.05 mg/L, reportedly because of bitter metallic taste, black–brown particles in water, and black–brown discoloration of fixtures and laundry. This study revisited visual and taste thresholds for Mn(II) and Mn(IV) using one‐in‐five, one‐in‐three, and triangle tests for concentrations from 0.005–506 mg/L. Results showed that Mn(II) and Mn(IV) do not taste significantly different from distilled water at 0.05 mg/L Mn. The population taste threshold for Mn(II) from manganese sulfate is > 1,000 times the SMCL; the threshold concentration is 75–100 mg/L Mn(II) and likely is influenced by both sulfate and Mn(II) taste contribution. Aqueous Mn(II) is colorless at 0.05 mg/L and remains visually undetectable at concentrations as high as 506 mg/L; Mn(IV) is visually detectable in water at concentrations as low as 0.005 mg/L. Findings suggest that consumers cannot detect Mn(II) concentrations above the SMCL by taste or sight and that bitter and metallic descriptors for 0.05 mg/L Mn are unwarranted.