Stability of DTPA and iron(III)-DTPA under laboratory ecotoxicological conditions

The present study assessed the stability of uncomplexed DTPA and Fe(III)-DTPA over 24 h, under experimental conditions similar to those previously used to assess the aquatic toxicity of DTPA and Fe(III)-DTPA (MS synthetic medium, 20°C; wet laboratory water (WLW), 25°C). DTPA was measured using ion-interaction reversed-phase liquid chromatography at 0 h (t0) and 24 h (t24). DTPA consistently eluted at approximately 3.3 min. Actual DTPA concentrations corresponded well with nominal concentrations, justifying the use of nominal concentrations for previous ecotoxicological bioassays. There was no significant degradation of DTPA either when uncomplexed or ferric-complexed, over 24 h (P>0.05). In addition, there was no difference in DTPA and Fe(III)-DTPA degradation between MS synthetic medium and WLW (P>0.05). Therefore, the previously reported decrease in DTPA toxicity, when complexed with iron was concluded not to be due to enhanced DTPA degradation. However, the presence of what appeared to be a degradation product in all Fe(III)-DTPA samples after 24 h, indicated that DTPA might be more susceptible to degradation when complexed with iron, as reported by other researchers.