Isophthalic acid

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

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

Reliability:

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.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1989

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 311: Anaerobic biodegradability of organic compounds in digested sludge by measurement of gas production

Deviations:

not applicable

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). Biodegradation was calculated by expressing blank-corrected NGP as a percentage of the theoretical gas yield for the compound under test.

GLP compliance:

no

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 isophthalic acid ( 1,3-dicarboxylic acid) are structural analogues and data relating to the anaerobic biodegradability of phthalic acid are expected to provide a reliable prediction of the behaviour of isophthalic acid under comparable test conditions.

Test material

Test material information

Constituent 1

Reference substance name:

Phthalic acid

EC Number:

201-873-2

EC Name:

Phthalic acid

Cas Number:

88-99-3

IUPAC Name:

phthalic acid

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.

Phthalic acid (benzene-1,2-dicarboxylic acid) is a structural analogue of isophthalic acid (benzene-1,3-dicarboxylic acid). Both compounds comprise a single benzene ring with two carboxyl substituents. Since these substances have identical molecular weights and differ only in the location of attachment of one of the two identical functional substituents to the benzene ring, the read-across from phthalic acid to isophthalic acid is considered justified.

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.

Applicant's summary and conclusion

Conclusions:

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, isophthalic 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 and more favourable 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 isophthalic acid (benzene-1,3 -dicarboxylic acid) and phthalic acid (benzene-1,2 -dicarboxylic acid) are structural analogues, the same conclusions may be drawn for the behaviour of isophthalic acid during methanogenic sludge digestion.