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Environmental fate & pathways

Additional information on environmental fate and behaviour

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Administrative data

Endpoint:
additional information on environmental fate and behaviour
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Publication provides adequate experimental detail and describes lab-scale simulations of the anaerobic sludge digestion process.

Data source

Reference
Reference Type:
publication
Title:
Behaviour of phthalic acid esters during batch anaerobic digestion of sudge
Author:
Ziogou, K., Kirk, W.W. and Lester, J.N.
Year:
1989
Bibliographic source:
Water Research 23 (6), pp743-748. Publ.: Elsevier

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
Determination the degradability and rate of biodegradability of dimethyl pthalate during the anaerobic digestion of STP sludges.
GLP compliance:
no
Type of study / information:
Assessments of the fate of dimethyl phthalate acid to undergo degradation under methanogenic conditions employed in the anaerobic digestion of wastewater treatment sludges. Anaerobic digestion typically precedes the disposal of wastewater treatment sludges on soil; compounds that show a high potential for degradation under the conditions of the test may be assumed to undergo complete degradation before digested sludges are applied to land. Dimethyl phthalate (1,2-dicarboxylic acid, dimethyl ester) and dimethyl terephthalate ( 1,4-dicarboxylic acid, dimethyl ester) are isomers and data relating to the anaerobic biodegradability of dimethyl phthalate are expected to provide a reliable prediction of the behaviour of dimethyl terephthalate under comparable test conditions.

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Dimethyl phthalate (>99%) was obtained from Aldrich.

Results and discussion

Any other information on results incl. tables

In the type 1 test DMP was degraded without a lag phase and >90% removal was observed within 8 days. Degradation also occurred in the treatment amended with 0.5% (w/v) sodium azide, but not in the autoclaved abiotic control. This confirmed that the removal of DMP was the result of a biological rather than a physico-chemical process and suggested either that the sodium azide added as a metabolic inhibitor was present at too low a concentration to be effective or that microbial enzymes present in the sludge remained active in spite of the inhibitor addition.

Similarly rapid degradation of DMP was also observed in the type 2 test and the findings were fitted to zero- and first-order kinetic models. The first-order model gave the better fit and the first-order rate constant and half-life determined for DMP in anaerobic digester sludge were 8.9E-3 and 78 hours, respectively.

It should be noted that these findings relate to analytical measurements of concentrations of the parent molecule (the same method was applied to five other, related phthalate compounds in the investigations reported by Ziogou et al.); they therefore indicate primary biodegradation (a structural transformation of the phthalate moiety) but not necessarily ultimate degradation - complete mineralisation to the terminal products CO2 and CH4. Further evidence of the ultimate anaerobic biodegradation potential of phthalic acid (and hence DMP) is provided by Battersby and Wilson (1989) (see the following summary).

Applicant's summary and conclusion

Conclusions:
Dimethyl phthalate was rapidly degraded in anaerobic digester sludge: >90% removal occurred in 8 days. Based on its close structural similarity to dimethyl phthalate, dimethyl terephthalate will also undergo rapid degradation under comparable conditions.
Executive summary:

Dimethyl phthalate was biodegraded by >90% in 8 days in a series of tests designed to simulate conditions in anaerobic sludge digesters at STPs. The relatively small fraction of dimethyl phthalate that may partition to wastewater treatment sludge solids (either primary sludge and/or surplus activated sludge) may be expected to be completely degraded before the digested product becomes available for application to soil. Since dimethyl phthalate and dimethyl terephthalate are isomers, dimethyl terephthalate may be expected to undergo a similarly high degree of anaerobic biodegradation during methanogenic sludge digestion. Dimethyl terephthalate is also likley to be degraded anaerobically in water-logged soils or sediments.