Dibutyl phthalate

Biodegradation in water and sediment: simulation tests

Administrative data

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1984

Report date:

1983

Materials and methods

Test material

Test material information

Specific details on test material used for the study:

Commerical samples of 14 PAEs were supplied by U.S. manufacturers for testing. If more than one manufacturer produced the individual PAE, the PAE product provided was an equal proportion blend. Before testing, the PAEs were analyzed to confirm that they were within commercial specification limits.

Study design

Duration of test (contact time):

28 d

Results and discussion

% Degradation

% Degradation 1

Key result

% Degr.:

ca. 5

Parameter:

CO2 evolution

Sampling time:

2.5 d

% Degradation 2

Key result

% Degr.:

ca. 15

Parameter:

CO2 evolution

Sampling time:

6.5 d

% Degradation 3

Key result

% Degr.:

ca. 17

Parameter:

CO2 evolution

Sampling time:

9 d

% Degradation 4

Key result

% Degr.:

ca. 23

Parameter:

CO2 evolution

Sampling time:

13.5 d

% Degradation 5

Key result

% Degr.:

ca. 40

Parameter:

CO2 evolution

Sampling time:

20.5 d

% Degradation 6

Key result

% Degr.:

ca. 57

Parameter:

CO2 evolution

Sampling time:

28 d

Half-life of parent compound / 50% disappearance time (DT50)

DT50:

ca. 15.4 d

Any other information on results incl. tables

The CO2 evolution data, estimated rate constants and halflife, and percentages of primary degradation for the PAEs and glucose tested in sets 1 through 4 are presented in Table 1. It was originally intended to run all of the PAEs in three sets; however, both of the blank units in set 3 developed leaks to the atmosphere, which resulted in high levels of BaCO3 precipitation. As a result, a fourth set was run in which CO2 evolution data were collected, as in the previous sets, but in which specific PAE analysis was conducted only at the end of the test on the contents of the triplicate CO2 evolution flasks.

In general, all of the PAEs were biodegraded rapidly as measured by loss of the parent molecule (primary biodegradation) and percentage of CO2 evolution (ultimate biodegradation). The primary biodegradation at 28 days was >99%, except for DBP, BBP, and DTDP, which were 68 to >99%, 59 to 89%, and >50%, respectively. Similar conclusions could be reached from the ultimate biodegradation data. All of the PAEs tested with pQoled acclimated inoculum had >50% theoretical CO2 evolution at day 28 with the exception of BBP and DTDP, which were 43 and 37%, respectively. However, BBP and DTDP were still degrading at day 28. The 95% confidence limits indicate that many of the differences between the mean ultimate biodegradation and rate constant values are not statistically significant.

Variation in CO2 evolution values among the triplicates or duplicates for each PAE and glucose in the sets can be examined by expressing the standard deviation as a percentage of the mean values obtained from the individual runs in a set. At day 28, the standard deviations of CO2 evolution data ranged between +/-2 and +/-37% of the respective means. At day 28, the mean and median of the standard deviations were ±12 and ±5%, respectively. The ratio between the highest and lowest individual CO2 evolution value among duplicates or triplicates on day 28 ranged between 1.0 and 2.1 and

averaged 1.3. This indicates that individual values for a chemical varied by no more than about twofold. The rate constant data were more variable. The range, mean, and median of the standard deviations (expressed as a percentage of the mean) were 2 to 57, 21, and 14.5%, respectively. The ratio between the highest and lowest individual rate constant amohg duplicates or triplicates ranged between 1.0 and 2.9 and averaged 1.6, indicating that the individual rate constants for a chemical varied about twofold on the average. All of the individual CO2 and rate constant values for a chemical in a set were within two standard deviations of the set mean calculated for that chemical, indicating that outlying data points were absent.

Applicant's summary and conclusion

Conclusions:

Biodegradation of DBP after 28 days was ca. 57%.

Executive summary:

An acclimated shake flask CO2 evolution test was used to study the biodegradability of 14 commercial phthalate esters that are commonly used as plasticizers. Both CO2 evolution (ultimate biodegradation) and

loss of parent phthalate esters (primary biodegradation) were measured.