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Environmental fate & pathways

Additional information on environmental fate and behaviour

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additional information on environmental fate and behaviour
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Publication provides adequate experimental detail and the method employed was a precursor to the procedure adopted by the OECD as Guideline 311.
Reason / purpose:
reference to same study

Data source

Reference Type:

Materials and methods

Test guideline
equivalent or similar to
other: OECD 311: Anaerobic biodegradability of organic compounds in digested sludge by measurement of gas production
Principles of method if other than guideline:
Incubation for 60 days under strictly anaerobic, methanogenic conditions at 35 degrees C in the presence of a diluted inoculum taken from a sludge digester. Measurements made at regular intervals of headspace pressure and converted to cumulative net gas (CO2 + CH4) production (NGP). Biodegardation was calculated by expressing blank-corrected NGP as a percentage of the theoretical gas yield for the compound under test.
GLP compliance:
Type of study / information:
Conservative screening assessment (high test substance concentration (50 mg C/L) with no other substrate feed, low sludge solids density (2-3 mg dry solids/L)) of the potential for phthalic acid to undergo ultimate degradation (mineralisation) 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 mineralisation under the conditions of the test may be assumed to undergo complete degradation before digested sludges are applied to land. Phthalic acid (1,2-dicarboxylic acid) and terephthalic acid ( 1,4-dicarboxylic acid) are isomers and data relating to the anaerobic biodegradability of phthalic acid are expected to provide a reliable prediction of the behaviour of terephthalic acid under comparable test conditions.

Test material

Details on test material:
No specific information, test compounds (including phthalic acid) were obtained from either Aldrich or BDH and were of the highest purity available.

Results and discussion

Any other information on results incl. tables

The NGP obtained from triplicate vessels dosed with phthalic acid and incubated under methanogenic conditions (confirmed by GC analysis of headspace gas) was 135% +/- 7.5% of the theoretical yield. Phthalic acid was completely degraded within 4 weeks of incubation.

In the method applied by Battersby and Wilson to phthalic acid, the theoretical gas production (ThGP, based on an assumed ratio of CO2:CH4 formation) was calculated according to the Buswell equation, and by applying futher assumptions about the relative solubilities of the two gases in the aqueous test medium that may be influenced by test conditions. This applies particularly to CO2 in relation to pH. The inherent uncertainty of the reliability of these assumptions under the test conditions is discussed by Struijs and Stoltenkamp-Wouterse (1992): Anaerobic biodegradability: Results of a Dutch inter-laboratory excercise; RIVM report 719101 003. Nevertheless, the strong, positive NGP response >100% ThGP recorded for phthalic acid is indicative of extensive (complete) degradation.

Applicant's summary and conclusion

Phthalic acid was completely mineralised (converted to CH4 and CO2) within 4 weeks in a screening test designed to assess the potential of organic compounds to undergo degradation under methanogenic conditions in digesting sludge. Based on its close structural similarity to phthalic acid, terephthalic acid will also undergo complete and rapid mineralisation under comparable conditions.
Executive summary:

Phthalic acid was completely mineralised (converted to CH4 and CO2) within 4 weeks in a screening test designed to assess the potential of organic compounds to undergo degradation under methanogenic conditions in digesting sludge. Since the screening method employed conservative conditions (a high test substance concentration and no other substrate feed, combined with a very low inoculum density) the test may be considered to predict the fate of phthalic acid in wastewater sludge digesters under real operational conditions: it may be assumed that phthalic acid will undergo complete degradation during the full-scale digestion process. Consequently any phthalic acid that partitions 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 terephthalic acid and phthalic acid are isomers, terephthalic acid may be expected to undergo a similarly high degree of anaerobic biodegradation during methanogenic sludge digestion. Terephthalic acid is also likely to be degraded anaerobically in water-logged soils or sediments.