Photodegradation of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine disuccinic acid (EDDS) within natural UV radiation range

The rate of photodegradation of two chelating agents, ethylenediaminetetraa cetic acid (EDTA) and an isomeric mixture of ethylenediamine disuccinic aci d (EDDS), was analysed in humic lake water and in distilled water using exp osure to sunlight, and in the laboratory using lamps emitting UV radiation in the range 315-400 nm. Degradation was studied using Fe(III) complexes an d sodium salts of chelates. Fe(III) complexes were illuminated at pH 3.1 an d 6.5. The results demonstrated that the rate of photodegradation of Fe(III )-EDTA and Fe(III)-EDDS complexes seems to be pH dependent. In the laborato ry experiments degradation occurred much faster when the original pH was 3. 1 rather than 6.5. The photodegradation of the isomeric mixture of EDDS was markedly faster than the degradation of EDTA both in the laboratory and fi eld experiments, and both in humic and distilled water. The results indicat ed that in natural waters photodegradation of EDDS is independent of initia l speciation of EDDS, while degradation of EDTA is dependent on its existen ce as Fe(III)-EDTA species. (C) 2001 Elsevier Science Ltd. All rights reser ved.