Environmental fate of EDTA and DTPA.

EDTA can be extremely persistent in WWTP and also in natural waters; DTPA seems more biodegradable. However, the biodegradability of DTPA might be of negligible significance as EDTA, and in some cases also DTPA, are generally found in the receiving waters of many industrial areas, thus being classified as one of the major organic pollutants discharged in waters. The photochemical degradation of Fe(III) complexes of these compounds is documented, but the extent to which these results can be applied to natural waters is not clear. There exist still some uncertainties in the chemical speciation, adsorption, overall degradation, and ultimately the eutrophication effect of EDTA and especially of DTPA. It can be inferred that EDTA can affect the essential and nonessential metal balance in natural waters as well as in aquatic organisms, even in the long term. The estimation of the chemical speciation of EDTA and DTPA in natural waters is a challenging task because of of the complexicity of the system and should be based not only on equilibrium calculations but also on direct analytical determinations of diverse metal species. Unfortunately, analytical methods for speciation studies at environmentally relevant concentrations are not available. Also, monitoring of EDTA or DTPA in sediments and solid particles has not been initiated. EDTA and DTPA are not expected to be acutely toxic to aquatic organisms. On the other hand, in natural waters, several compounds affect organisms simultaneously. Therefore, EDTA and DTPA can contribute to the aquatic toxicity at significantly lower concentration than those determined by short-term toxicity tests. Also, more studies should be directed to estimating chronic effects, including the possible imbalance of body calcium in animals and other organisms. EDTA and DTPA can certainly desorb heavy metals bound to sediments and also prevent heavy metal sedimentation, thus increasing their cycle in water. However, these metal complexes are not expected to be as bioavailable as a free metal ions. Taken together, EDTA and DTPA, being persistent compounds, contribute to the general chemicalization of the aquatic environment. They can also cause several indirect and, under extreme circumstances, direct effects in the aquatic environment. Thus, their release into natural waters should be minimized wherever possible.