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Biodegradation in water and sediment: simulation tests

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Description of key information

A study of biodegradation in surface water/sediment was conducted according to OECD Guideline 309.
Primary degradation of [14C]1,3 EVB and [14C]1,4 DVB to more polar [14C]degradation products occurred in surface water and surface water/sediment mixtures with half-lives ranging from 3.8 to 31.4 days over the test concentration range of 50 to 1500 µg/L.
Mineralization of [14C]1,3 EVB to14CO2 reached 19.8  and 67.7% of applied radioactivity within 49 days at 50 and 500 µg/L, respectively, in the presence of sediment while mineralization was limited in surface water alone (3%). Little mineralization of [14C]1,4 DVB(<1%) occurred in the reaction mixtures under the conditions of the test.
The half-lives for the parent compounds 1,3-EVB and 1,4-DVB are less than the criteria for persistence in surface water (i.e. 40 days in fresh water). Inspection of the tables in the study report listing metabolites as a percentage of applied radioactivity at each sampling point illustrates an overall progression of multiple metabolites to shorter HPLC retention times over time. In the reverse-phase HPLC assay used in the study, shorter retention times correlate with more polar, water soluble metabolites. The progression to shorter retention times indicates that these metabolites themselves are not persistent, but rather continue to degrade to simpler, more polar compounds.
Efforts were made to structurally characterize transformation products formed during aerobic mineralization of DVB-55 in surface water that represented >10% of the administered radioactive dose. Selected samples were subjected to analysis by GC/MS and LC/MS by Electrospray Ionization in the positive and negative ionization modes (ESI (+/-)), Atmospheric Pressure Chemical Ionization (APCI (+/-)), and Atmospheric Pressure Photo Ionization (APPI). Due to the insufficient amount of mass of the unknown(s), no conclusive identification could be made from the analysis results generated in this study.

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Additional information

The study was conducted to evaluate the rate and extent of degradation of a14C-labeled test substance and its components in surface water-sediment systems. Radiolabelled 1,4 divinylbenzene, ([14C] 1,4 DVB) and 1,3 ethylvinylbenzene ([14C] 1,3 EVB), chosen as representative components of DVB-55, were used to determine both primary degradation and mineralization kinetics and allowed for the detection of any stable degradation products formed at >10% yield. Incubation of the non-labeled components of DVB-55 with the [14C] 1,3 EVB in selected reaction mixtures was used to evaluate the impact of the isomers on the degradation kinetics of the radiolabeled test material.

Primary degradation of [14C]1,3 EVB and [14C]1,4 DVB to more polar [14C] degradation products occurred in surface water and surface water/sediment mixtures with half-lives ranging from 3.8 to 31.4 days over the test concentration range of 50 to 1500µg/L. Half-lives for the test materials were shorter in the presence of sediment, likely due to higher concentrations of microorganisms associated with sediments. 

Mineralization of [14C]1,3 EVB to 14CO2 reached 19.8 and 67.7% within 49 days at 50 and 500 µg/L, respectively, in the presence of sediment while mineralization was limited in surface water alone (3%). In the presence of non-labeled DVB-55, the half-life of 50 µg/L [14C]1,3 EVB in water/sediment mixtures increased from 17.4 to 34.3 days and mineralization to 14CO2 was limited (<1%). Little mineralization of [14C]1,4 DVB (<1%) occurred in the reaction mixtures under the conditions of the test. 

The half-lives for the parent compounds 1,3-EVB and 1,4-DVB are less than the criteria for persistence in surface water (i.e. 40 days in fresh water).  Inspection of the tables in the study report listingmetabolites as a percentage of applied radioactivity at each sampling point illustrates an overall progression of multiple metabolites to shorter HPLC retention times over time.  In the reverse-phase HPLC assay used in the study, shorter retention times correlate with more polar, water soluble metabolites.  The progression to shorter retention times indicates that these metabolites themselves are not persistent, but rather continue to degrade to simpler, more polar compounds.

 

Efforts were made to structurally characterize transformation products formed during aerobic mineralization of DVB-55 in surface water that represented >10% of the administered radioactive dose. Selected samples were subjected to analysis by GC/MS and LC/MS by Electrospray Ionization in the positive and negative ionization modes (ESI (+/-)), Atmospheric Pressure Chemical Ionization (APCI (+/-)), and Atmospheric Pressure Photo Ionization (APPI). Due to the insufficient amount of mass of the unknown(s), no conclusive identification could be made from the analysis results generated in this study.

 

Attempts to identify the metabolites using a variety of analytical techniques were unsuccessful due to insufficient amounts of the unknowns available for characterization.