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Environmental fate & pathways

Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Although a GLP study performed according to the 1984 OECD 301B Guideline the purity was not reported.
Justification for type of information:
The test substance rapidly hydrolyses to isophthalic acid (IPA) and IPA is structurally similar to terephthalic acid (TPA). Therefore, studies with IPA and TPA are being used to fulfil this data requirement. Additional documentation, provided within the IUCLID Assessment Reports section, supports the read-across approach.
Reason / purpose for cross-reference:
read-across: supporting information
according to guideline
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
(performed according to the original 1984 version of the guideline ("Modified Sturm Test"), current at the time of testing)
(The current OECD 301B (1992) recommends a single concentration and has introduced the concept of the 10-day window, but the test procedure is fundamentally the same as the 1984 version).
GLP compliance:
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Prior to use the activated sludge from the sewage plant (Frankfurt/M. -Niederrad) was washed twice with mineral nutrient medium to eliminate organic components and poisons from the sludge. After resuspension with mineral nutrient medium to the original volume the sludge was aerated for 4 hours. It was then homogenized in a waring blender at medium speed for 2 minutes and then settled for about 30 minutes. The supernatant was filtered through a coarse filter paper the first 200 mL being discarded. The filtrate was used as inoculum (1% of the final volume of the test solution).
Duration of test (contact time):
14 d
Initial conc.:
10.19 mg/L
Based on:
test mat.
Initial conc.:
20.07 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
The test solutions contained in a total volume of 3500 mL: 35 mL of the inoculum, 14 mL of the ferrichloride solution, 3.5 mL of the magnesium sulphate solution, 3.5 mL of the calcium chloride solution, 7 mL of the phosphate mixture solution and 3.5 mL of the ammonium sulphate solution. The test solution was made up to a final volume of 3500 mL with ultrapure water (Millipore, Milli 0). A stock solution with the test material could not be prepared in aqua bidest. due to poor water solubility. For this reason 35.65 mg and 70.25 mg of the test material were weighed into small glass tubes previously cleaned by treatment with acetone, rinsed with demineralised water, and dried at 104°C. The glass tubes with the test material were given together into the test solutions at the starting point of the test. At the same time one blank without any test substance but with inoculation and one reference (Na-Benzoate) with 20 mg TOC (Total Organic Carbon) per litre were run in parallel. Before starting the test, the mineral salt solution with inoculation but without test substance was aerated with CO2 - free air for 24 h in order to purge the system of CO2. Within this study the solutions with the test material were stirred by means of magnetic stirrers in order to distribute the test substance in a way that it was dissolved at the maximum solubility.

The test substance and inoculum were incubated at 22.0 to 23.5°C. CO2 released from the test material was trapped as BaCO3 using a trap system. The degradation was followed by CO2 analysis. After reference to blank control (test solution with inoculation but without any test material), the total amount of CO2 produced by the test substance was determined for the test period and calculated as a percentage of the total CO2 that the test substance, based on its carbon content, could have theoretically produced (%TCO2).
Reference substance:
benzoic acid, sodium salt
20 mg/L TOC/L
Test performance:
The poor water solubility of the test material did not appear to affect the performance of the test.
% degradation (CO2 evolution)
Sampling time:
14 d
Remarks on result:
other: 10 mg/L test substance, based on measurements made on day 16 after the inoculum was killed by acidification on day 14.
% degradation (CO2 evolution)
Sampling time:
14 d
Remarks on result:
other: 20 mg/L test substance, based on measurements made on day 16 after the inoculum was killed by acidification on day 14.
% degradation (CO2 evolution)
> 60
Sampling time:
5 d
Remarks on result:
other: Both 10 & 20 mg/L test solutions. 60% degradation occurred within the 10-day window.
Details on results:
The temperature range during the test was 22.0 to 23.5°C (mean 22.7 ± s = 0.33°C).
Results with reference substance:
Na-Benzoate was degraded at 84% within 6d (final titration at 7d = 1 day after acidification), indicating
that the conditions of the test were met.
Validity criteria fulfilled:
Interpretation of results:
readily biodegradable
The study and the conclusions which are drawn from it fulfil the quality criteria (validity, reliability, repeatability).
Terephthalic acid is readily biodegradable.
Executive summary:

Terephthalic 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 TPA 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. Terephthalic acid is therefore considered to be readily biodegradable.

Description of key information

The substance and other members of the category are all readily biodegradable. Therefore, no additional information on degradation and simulation tests in soil or sediments is required according to REACH regulation. However, additional data on biodegradation in anaerobic sewage sludge are available and presented here for the sake of completeness. A study by Kleerebezem et al. (1999) showed that time to degrade 50% of isophthalic and terephthalic acid was 74 and 55 days, respectively, in a completely stirred reactor using digested sewage sludge.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information