BIODEGRADATION OF [S,S], [R,R] AND MIXED STEREOISOMERS OF ETHYLENE DIAMINE DISUCCINIC ACID (EDDS), A TRANSITION-METAL CHELATOR

An in-depth biodegradation test program was executed on the hexadentat e ligand Ethylene Diamine Di Succinate (EDDS). The EDDS structure cont ains two chiral carbon atoms, and has three stereoisomers ([R,R],[R,S] /[S,R],[S,S]). Our research has focused on the isomer mixture (i.e. 25 %[S,S], 25%[R,R]; 50%[S,R]/[R,S], as produced from the reaction of eth ylene diamine with maleic anhydride) and on the single [S,S]- and [R,R ]-isomers. Biodegradation screening of the C-14-labelled EDDS isomer m ixture in a Batch Activated Sludge (BAS) test with various inocula rev ealed incomplete mineralization, up to ca. 65 % after 28 days. N-(2-am inoethyl) aspartic acid (AEAA), probably the d-isomer, was identified as the major portion of the C-14-material remaining in solution. Furth er testing revealed that the [S,S]-isomer is rapidly and completely mi neralized in all test systems. By contrast, [R,R]-EDDS remained undegr aded in a Sturm (OECD 301B) test, but was very slowly biotransformed i nto the recalcitrant metabolite AEAA in a BAS test. The [S,R]/[R,S] fo rm undergoes biotransformation to AEAA in both high and low biomass sy stems. In a sewage treatment simulation test (OECD 303) the steady sta te DOC removal of mixture-EDDS in a CAS test was limited to 25-35 %, e ven after extensive pre-acclimation, while the [S,S]-isomer achieved n early complete removal (96%). This study illustrates the importance st ereospecificity may have on the biodegradation and metabolite formatio n of a chemical. A biodegradation scheme for the different EDDS stereo isomers is proposed. (C) 1997 Elsevier Science Ltd.