Superfund Research Program

Environmental Fate of Azo Dyes and Related Products

Project Leader: M. Wilson Tabor (University of Cincinnati Medical Center)
Grant Number: P42ES004908
Funding Period: 1995 - 2001

Project-Specific Links

Final Progress Reports

Year:   1999 

A reverse phase HPLC method using photodiode array detection was developed to monitor the abiotic degradation of azo dyes. Dyes AO7, AO8, AO10, AR14, AR18 and AR88 were examined. This laboratory system for abiotic treatment was a modified Clemmenson reduction, employing zinc as an electron donor, producing redox potentials comparable to reported values of anaerobic sediments: an E₀ of –240V as compared to –240V to –22V for 12 different sites. AO7 was shown to abiotically degrade into sulfanilic acid (quantitated via HPLC analysis) and 1-amino-2-naphthol (not measured). AO8, AR18 and AO10 were degraded in reactions that followed pseudo first order kinetics, as determined by HPLC with products not identified. AR14 was degraded in the laboratory system through multiple mechanisms with no intermediates or products being identified. AR88 degradation was not significant at the low concentration measurable in our HPLC system. AO7 and the other dyes, with the exception of AR88 and AR14, have similar rate constants and probably undergo similar reactions. Due to the similarity between the laboratory conditions and environmental conditions, these azo dyes are likely to be degraded abiotically in anoxic environments with a half-life of 3 to 6 days. Aggregation apppeared to be a major factor interfering with abiotic degradation at high concentrations of several dyes; aggregation and/or adsorption to sediments and biomass could be the other possible fates for AR88, even at low concentrations in anoxic environmental sediments.