dimethyl 1,2-benzenedicarboxylate;reaction mass of: 1,2-dimethylpropylidene dihydroperoxide

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

GLP study according to protocol. The modified Strum test is not the best test setup for volatile substances. One of the degradation products is volatile and this could explain the spread in the duplicates. Even though this is an ommision in this study, still complete mineralization was measured in 3 out of 4 cases and this would not have been the case if a big part of the substances present was evaporated.

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source: The source of test organisms was activated sludge freshly obtained from a municipal sewage treatment plant: Waterschap de Maaskant', 's-Hertogenbosch, the Netherlands.
- Treatment: The sludge was kept under continuous aeration until further treatment. The concentration of suspended solids was 3.8 g/l in the concentrated sludge in experiment 1 and 3.7 g/l in the concentrated sludge in experiment 2 (information obtained from the municipal sewage treatment plant). Before use, the sludge was allowed to settle (30-90 minutes) and the liquid decanted for use as inoculum at the amount of 10 ml/l of mineral medium.

Duration of test (contact time):

29 d

Initial conc.:

ca. 22 mg/L

Based on:

test mat.

Initial conc.:

ca. 12 mg/L

Based on:

other: TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

- Test vessels: 2 litre all-glass brown coloured bottles.
- Milli-RO / Milli-Q water: Tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ionexchange cartridges (Milli-Q) (Millipore Corp., Bedford, Mass., USA).
- Stock solutions of mineral components:
A) 8.50 g KH2P04
21.75 g K2HP04
67.20 g Na2HP04.12H20
0.50 g NH4CI
dissolved in 1 I Milli-Q water, pH 7.4 ± 0.2
B) 22.50 g MgS04.7H20 dissolved in 1 I
Milli-Q water.
C) 36.40 g CaCI2.2H20 dissolved in 1 I Milli-Q water.
D) 0.25 g FeCI3.6H20 dissolved in 1 I Milli-Q water.
- Mineral medium: 1 I mineral medium contains: 10 ml of solution (A), 1 ml of solutions (B) to (D) and Milli-RO water.
- Barium hydroxide: 0.0125 M, stored in a sealed vessel to prevent absorption of CO2 from the air.
- CO2-free air: A mixture of oxygen (21 %) and nitrogen (79%) was led through a bottle, containing 0.5 - 1 litre 0.0125 M Ba(OH)2 solution to trap CO2 which might be present in small amounts. The CO2-free air was sparged through the scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 ml/min).

- Pre-incubation medium: Mineral components, Milli-RO water (ca. 80% total volume) and inoculum (1 % final volume) were added to each bottle. This mixture was aerated with CO2-free air overnight to purge the system of CO2.
- Type and no. of bottles:
Test suspension: containing test substance and inoculum (2 bottles).
Inoculum blank: containing only inoculum (2 bottles)
Positive control: containing reference substance (ca. 40 mg/I sodium acetate (Merck art. 1062680250, batch TA 820068 033), TOC= 12 mg/I) and inoculum (1 bottle).
Toxicity control: containing test substance, reference substance and inoculum (1 bottle).
- Preparation: The test substance and positive control were added to the bottles. The volumes of suspensions were made up to 2 litres with Milli-RO water, resulting in the mineral medium described before. Three CO2-absorbers (bottles filled with 100 mI 0.0125 M Ba(OH)2 were connected in series to the exit air line of each test bottle.
- Start of incubation: The test was started by bubbling CO2-free air through the solution at a rate of approximately 1-2 bubbles per second (ca. 30-100 ml/min).
- experimental CO2 production: The CO2 produced in each test bottle reacted with the barium hydroxide in the gas scrubbing bottle and precipitated out as barium carbonate. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCI.
- Measurements: Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until the 28th day. Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers was moved one position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series. Phenolphthalein was used as pH-indicator.
On the 28th day, the pH of the test suspensions was measured and 1 ml of concentrated HCI was added to each bottle. The bottles were aerated overnight to drive off CO2 present in the test suspension. The final titration was made on day 29.

Reference substance:

acetic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

44

Sampling time:

29 d

Remarks on result:

other: Experiment 1, bottle A

Parameter:

% degradation (CO2 evolution)

Value:

81

Sampling time:

29 d

Remarks on result:

other: experiment 1, bottle B

Parameter:

% degradation (CO2 evolution)

Value:

91

Sampling time:

29 d

Remarks on result:

other: Experiment 2, bottle A

Parameter:

% degradation (CO2 evolution)

Value:

62

Sampling time:

29 d

Remarks on result:

other: Experiment 2, bottle B

Details on results:

- pH:
Experiment 1: 7.6-8.3
Experiment 2: 7.4-7.8
- Test Temperature: 22 - 23 °C

In the toxicity control of both experiments more than 25% degradation occurred within 14 days (based on ThCO2). Therefore, the test substance was assumed to be not inhibitory on microbial activity.

Results with reference substance:

Results as expected

Validity criteria fulfilled:

no

Remarks:

The difference between the duplicates was >20% in both experiments

Interpretation of results:

readily biodegradable

Conclusions:

In both experiments the degradation was greater than 60%. Although the 10-day window criterium was not met,
This could be explained by formation of volatile substances which are not captured in this type of tests.
Expert judgement still classifies the test substance readily biodegradable.

Executive summary:

The subsatane was tested for its ready biodegradability in the carbon dioxide (CO2) evolution test (modified Sturm test) at approximately 44 mg per 2 Iitres, corresponding to 12 mg TOC/l.

The study procedure was based on EEC directive 92/69, C.4-C, December 1992, and OECD guideline No. 301 B July 17, 1992.

The Theoretical CO2 production (ThCO2) was calculated to be 2.01 mg CO2/mg.

For this project two experiments were performed.

Since the test substance was poorly soluble in water, weighed amounts were added to test bottles. The weighed amounts added to the test bottles in experiment 1 were: 44.1 mg to test substance bottle A, 43.8 mg to test substance bottle Band 44.4 mg to the toxicity control bottle. The weighed amounts added to the test bottles in experiment 2 were: 44.5 mg to test substance bottle A, 44.9 mg to test substance bottle Band 44.1 mg to the toxicity control bottle. 10 ml of milli-RO water was added to each weighing bottle and after vigorous shaking the resulting suspension was added quantitatively to the test medium. The test solutions were continuously stirred during the test.

Experiment 1: The relative degradation values calculated from the measurements performed during the test period revealed 44% degradation in test bottle A and 81% in test bottle B.

Experiment 2: The relative degradation values calculated from the measurements performed during the test period revealed 91% degradation in test bottle A and 62% in test bottle B.

In both experiments, biodegradation of the test substance of at least 60% was not reached within 10 days of biodegradation exceeding 10%. Thus, the criterion for ready biodegradability was not met. In the toxicity control of both experiments was found to be not inhibitory on microbial activity.

Except for the difference between the duplicate degradation values, all criteria for acceptability of the tests were met. Since the difference of duplicate degradation values was observed in both experiments and all other acceptability criteria were met, the difference was considered to be test substance related. Furthermore, the criterion for ready biodegradability (at least 60% degradation within 10 days of biodegradation exceeding 10%) was not met. Thus, the difference of duplicate values has no influence on the final conclusion (the criterion for ready biodegradability).

Reference 2

Endpoint:

biodegradation in water: screening tests

Type of information:

other: Expert statement

Adequacy of study:

other information

Reliability:

other: Expert statement

Interpretation of results:

readily biodegradable

Conclusions:

The biodegradability of Trigonox R-938 (main components are 67% dimethylphthalate and 29% methyl isopropyl ketone peroxide (peroxidic compounds)) has been assessed in a Sturm test (Notox, 2002). Biodegradation percentages ranging from 44 to 91 were found. Of the four replicates carried out only one replicate did not pass 60% at day 28. The curves of the replicates passing the 60% within 28 days did not meet the 10-day time window criterion. The time window concept is, however, only valid when single water-soluble chemical substances are studied. Trigonox R-938 is mixture of at least two substances i.e. dimethylphthalate and methyl isopropyl ketone peroxide.
Methyl isopropyl ketone peroxide dissolved in water is rapidly converted into methyl isopropyl ketone (2-methyl-3-butanone) at 20°C and neutral pH (environmental conditions). This decomposition product is volatile. The differences between the replicates of the Sturm test (Notox, 2002) may be explained with the volatility of the ketone. Volatile substances are lost with the air used to maintain aerobic conditions in the Sturm test vessels. The Sturm test is known to be unsuitable for volatile substances. The low Sturm test result (44% at day 28) should therefore be discarded.
Dimethylphthalate and the decomposition product of the peroxide are both classified as readily biodegradable. Dimethylphthalate was classified as readily biodegradable based on biodegradation percentages of 93 to 98 (EPA 2010). Methyl isopropyl ketone was degraded 85% in the Closed Bottle test (OECD 301D, a test suitable for volatile substance (Eastman, 2011).
Trigonox R-938 should be classified as readily biodegradable because of biodegradation results in excess of 60% in three replicates (no or limited loss of methyl isopropyl ketone) and the ready biodegradability of dimethylphthalate and methyl isopropyl ketone.

Eastman (2011) Safety Data Sheet Methyl isopropyl ketone (MIPK) Revision date 04/22/2011
Notox (2002) Determination of ready biodegradability: carbon dioxide (CO2) evolution test (modified Sturm test) with Trigonox R-938.
US EPA (2010) Screening-level hazard characterization; Phthalate esters category. page 18.

Executive summary:

The biodegradability of Trigonox R-938 (main components are 67% dimethylphthalate and 29% methyl isopropyl ketone peroxide (peroxidic compounds)) has been assessed in a Sturm test (Notox, 2002). Biodegradation percentages ranging from 44 to 91 were found. Of the four replicates carried out only one replicate did not pass 60% at day 28. The curves of the replicates passing the 60% within 28 days did not meet the 10-day time window criterion. The time window concept is, however, only valid when single water-soluble chemical substances are studied. Trigonox R-938 is mixture of at least two substances i.e. dimethylphthalate and methyl isopropyl ketone peroxide.

Methyl isopropyl ketone peroxide dissolved in water is rapidly converted into methyl isopropyl ketone (2-methyl-3-butanone) at 20°C and neutral pH (environmental conditions). This decomposition product is volatile. The differences between the replicates of the Sturm test (Notox, 2002) may be explained with the volatility of the ketone. Volatile substances are lost with the air used to maintain aerobic conditions in the Sturm test vessels. The Sturm test is known to be unsuitable for volatile substances. The low Sturm test result (44% at day 28) should therefore be discarded.

Dimethylphthalate and the decomposition product of the peroxide are both classified as readily biodegradable. Dimethylphthalate was classified as readily biodegradable based on biodegradation percentages of 93 to 98 (EPA 2010). Methyl isopropyl ketone was degraded 85% in the Closed Bottle test (OECD 301D, a test suitable for volatile substance (Eastman, 2011).

Trigonox R-938 should be classified as readily biodegradable because of biodegradation results in excess of 60% in three replicates (no or limited loss of methyl isopropyl ketone) and the ready biodegradability of dimethylphthalate and methyl isopropyl ketone.

Eastman (2011) Safety Data Sheet Methyl isopropyl ketone (MIPK) Revision date 04/22/2011

Notox (2002) Determination of ready biodegradability: carbon dioxide (CO2) evolution test (modified Sturm test) with Trigonox R-938.

US EPA (2010) Screening-level hazard characterization; Phthalate esters category. page 18.

Description of key information

MIPKP is mixture of at least two substances i.e. dimethylphthalate and methyl isopropyl ketone peroxide.

Methyl isopropyl ketone peroxide dissolved in water is rapidly converted into methyl isopropyl ketone (2-methyl-3-butanone) at 20°C and neutral pH (environmental conditions). This decomposition product is volatile.

Dimethylphthalate and the decomposition product of the peroxide are both classified as readily biodegradable. Dimethylphthalate was classified as readily biodegradable based on biodegradation percentages of 93 to 98 (EPA 2010). Methyl isopropyl ketone was degraded 85% in the Closed Bottle test (OECD 301D, a test suitable for volatile substance (Eastman, 2011).

MIPKP should be classified as readily biodegradable because of biodegradation results in excess of 60% in three replicates (no or limited loss of methyl isopropyl ketone) and the ready biodegradability of dimethylphthalate and methyl isopropyl ketone.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable