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Two screening tests of the "ready" biodegradability of isophthalic acid are available.

 

In the first (Lebertz, 1991a) isophthalic acid was tested for ready biodegradability according to the 1984 OECD 301B (Sturm Test) procedure, at concentrations of approximately 10 and 20 mg/L. The measured CO2 yield from IPA exceeded 60% of theoretical at both concentrations and the 60% threshold was crossed within the "10-day window", i.e. within 10 days of CO2 production reaching 10% of theoretical.

 

In the second (CITI, 1976), isophthalic acid (100 mg/L) was tested for biodegradability by the Chemicals Inspection and Testing Institute of Japan to fulfil the requirements of the Japanese Chemical Substances Control Law. A composite inoculum (applied at 30 mg suspended solids/L) originating from ten specified locations around Japan, not deliberately adapted to the test substance, fed with peptone and glucose prior to use and renewed at regular intervals (see OECD Guideline 301C 1984 and 1992 for details) was employed as standard practice at CITI for these investigations. An automated respirometer was used to make continuous measurements of biochemical oxygen demand (BOD) and recorded BOD was compared to the theoretical oxygen demand (ThOD) for IPA calculated assuming its complete mineralisation to terminal oxidation products. This comparison provides a measure of ultimate biodegradation. Measured BOD expressed as %ThOD reached 77.7% within 14 days in this study and further measurements indicated 85.3% ultimate degradation based on TOC removal (the "pass" criterion that applies to this parameter is 70%). Confirmatory indications are provided by specific analyses for the test substance using GC and UV-VIS spectrometric methods - these compound-specific techniques showed 100% and 96% loss of the parent test substance (primary degradation) and are consistent with the indications of ultimate biodegradation recorded in this study.

 

Both studies demonstrate that isophthalic acid is readily biodegradable and this result signifies that isophthalic acid will degrade rapidly and completely, without the formation of stable metabolites, under aerobic conditions in a variety environmental compartments (aquatic and terrestrial) and that extensive biodegradation may be anticipated in aerobic biological wastewater treatment processes. This (in addition to exposure considerations) obviates the need for studies of the degradation of isophthalic acid in water/sediment systems or in soil.

 

Based on its physico-chemical properties, isophthalic acid is expected to partition mainly toward the aqueous compartment during wastewater treatment and to be channelled predominantly toward aerobic biological (e.g. activated sludge) treatment. Nevertheless, a significant quantity may become associated with sludge solids during primary settlement or with waste activated sludge during secondary treatment and be directed toward thermophilic anaerobic digestion, which typically precedes the disposal of wastewater treatment sludges to land or alternatively by land-filling or incineration.

 

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 biodegradation under methanogenic conditions in digesting sludge (Battersby & Wilson, 1989, see Point 5.6). Since the screening method employed conservative conditions (a high test substance concentration and no other substrate feed, combined with a very low inoculum density) it may be assumed that phthalic acid will also 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 and phthalic acid are structural analogues, the same conclusions may be drawn for the behaviour of isophthalic acid during methanogenic sludge digestion.

 

Confirmation is provided by tests performed by Kleerebezem et al. (1999) to assess the amenability of IPA-laden process waste waters to anaerobic treatment. Half-lives for IPA dosed at ca. 310 mg/L to test systems inoculated from anaerobic treatment plants operated under three different regimes ranged from 74 to 156 days. These test results show that IPA is biodegradable under anaerobic, methanogenic conditions and it may be inferred that isophthalic acid is also likely to be degraded in other anaerobic environments, such as water-logged soils or sediments.

 

Isophthalic acid is not persistent (not P).

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