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

The present study assessed the stability of uncomplexed DTPA and Fe(III)-DT PA over 24 h, under experimental conditions similar to those previously use d to assess the aquatic toxicity of DTPA and Fe(III)-DTPA (MS synthetic med ium, 20 degrees C; wet laboratory water (WLW), 25 degrees C). DTPA was meas ured using ion-interaction reversed-phase liquid chromatography at 0 h (t(0 )) and 24 h (t(24)). DTPA consistently eluted at approximately 3.3 min. Act ual DTPA concentrations corresponded well with nominal concentrations, just ifying the use of nominal concentrations for previous ecotoxicological bioa ssays. There was no significant degradation of DTPA either when uncomplexed or ferric-complexed, over 24 h (P > 0.05). In addition, there was no diffe rence 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 deg radation. However, the presence of what appeared to be a degradation produc t 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. (C) 1999 Elsevier Science Ltd. All rights reserved.