| Abstrakt: |
An in-depth biodegradation test program was executed on the hexadentate ligand Ethylene Diamine Di Succinate (EDDS). The EDDS structure contains 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 ethylene diamine with maleic anhydride) and on the single [S,S]-and [R,R]-isomers. Biodegradation screening of the 14C-labelled EDDS isomer mixture in a Batch Activated Sludge (BAS) test with various inocula revealed incomplete mineralization, up to ca. 65 % after 28 days. N-(2-aminoethyl) aspartic acid (AEAA), probably the d-isomer, was identified as the major portion of the 14C-material remaining in solution. Further testing revealed that the [S,S]-isomer is rapidly. and completely mineralized in all test systems. Bycontrast, [R,R]-EDDS remained undegraded in a Sturm (OECD, 301B) test, but was very slowly biotransformed into the recalcitrant metabolite AEAA in a BAS test. The [S,R]/[R,S] form undergoes biotransformation to AEAA in both high and low biomass systems. In a sewage treatmentsimulation test (OECD 303) the steady state DOC removal of mixture-EDDS in a CAS test was limited to 25--35%, even after extensive pre-acclimation, while the [S,S]-isomer achieved nearly complete removal (96%). This study illustrates the importance stereospecificity may haveon the biodegradation and metabolite formation of a chemical. A biodegradation scheme for the different EDDS stereoisomers is proposed. [ABSTRACT FROM AUTHOR] |
Full Text from ScienceDirect