The stability of some metal EDTA, DTPA and DOTA complexes: Application as tracers in groundwater studies

Abstract

Studies of the stability of various metal EDTA, DTPA and DOTA complexes in order to evaluate their applicability as non-sorbing tracers have been performed. In laboratory tests, the stability generally increases for the individual metal ions in the EDTA<DTPA<DOTA order. For most metal ions, the same trend can be observed for the thermodynamic stability constants. In the in situ experiment, various metal EDTA tracers were used in very low concentrations; YbEDTA-, for example had a breakthrough and recovery which were very similar to the non-sorbing tracers used. According to the extremely low tracers concentrations used, thermodynamic data indicate that all metal EDTA tracers should have been decomplexed as a result of the competition with the naturally occurring cations in the groundwater. This was not found, which indicates that the decomplexation rate and sorption mechanism are important in estimating the applicability of the metal complexes as tracers. The DOTA complexes of elements in the middle of the lanthanide series have indicated high stability in the laboratory tests and therefore appear to be good candidates as non-sorbing tracers. However, in contrary to the metal EDTA tracers, the DOTA complexes of La 3+ and Lu 3+ seemed to be slightly delayed in the in situ experiment.

Heavy metals extractability in a soil amended with sewage sludge

“…This Cr behavior in DTPA solutions is due to Cr solubility, which decreases above pH 4, with complete precipitation above pH 5.5 (Alloway, 1995). Another reason could be the slow kinetics for the formation of Cr-DTPA complexes (Byegård et al, 1999). In soil columns experiments, Cr was found to leach out faster by organic acids as compared with DTPA (Wasay et al, 2001).…”

“…Studies on diffusive gradients in thin films (Ernstberger et al, 2005) showed that Zn and Cd presented higher extraction rates than Ni. The present study shows that, while Zn (k = 0.020 ε -1 ) and Cd (k = 0.026 ε ) needed some more extractions to get near the amount extracted at Ct 15 .…”

“…The present study shows that, while Zn (k = 0.020 ε -1 ) and Cd (k = 0.026 ε ) needed some more extractions to get near the amount extracted at Ct 15 . This behavior is clearly related to the differences in metal binding strength to the surfaces of soil particles (Ernstberger et al, 2005;Fangueiro et al, 2005) or, for Cr, slow dissolution of mineral phases.…”

“…So far, there has not been a satisfactory protocol that fully gauges the extent and rates to which metals can be released from soil particles (Zhang et al, 2001). The fate, transport, and bioavailability of heavy metals in soils are dependent on the extent and rate the metals may be desorbed at the soil colloid-extractant interfaces especially in those soils amended with sewage sludge (Zhang et al, 2001;Ernstberger et al, 2005;Shirvani et al, 2007).…”

Chelating Agents in the Environment

“…EDTA is also used in nuclear reactor decontamination and waste processing (58,59). EDTA has recently been suggested for use as a groundwater tracer (60 …”