Triethyl citrate

Toxicity to microorganisms

Administrative data

Endpoint:

toxicity to microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non GLP, non-OECD guideline, followed U.S. FDA guidelines (1987), and standard ASTM, FDA, EPA or equivalent soil and compost biodegradation tests.

Data source

Reference

Reference Type:

grey literature

Title:

Unnamed

Year:

2000

Report date:

2000

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: U.S. FDA guideline (1987)

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: ASTM D 5988 (ASTM, 1999)

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: EPA OPPTS 835.3300 (Soil Biodegradation)

Test guideline 4

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 307 (Aerobic and Anaerobic transformation in soil)

Test guideline 5

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD B CO2 Evolution

Principles of method if other than guideline:

The soil and compost biodegradation studies were performed according to U.S. Food & Drug Administration guidelines (1987), ASTM and EPA guidelines.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Triethyl citrate

EC Number:

201-070-7

EC Name:

Triethyl citrate

Cas Number:

77-93-0

Molecular formula:

C12H20O7

IUPAC Name:

triethyl citrate

Constituent 2

Reference substance name:

TEC

IUPAC Name:

TEC

Test material form:

not specified

Sampling and analysis

Analytical monitoring:

not specified

Test solutions

Vehicle:

no

Test organisms

Test organisms (species):

other: Standard laboratory soil mix per (McCassie et al., 1991)

Details on inoculum:

Soil Properties: A standard laboratory soil mix was prepared according to McCassie et. al., 1991. The soil mix was adjusted to 60% of its water holding capacity (WHC) and preincubated for 48 h to eliminate the flush of CO2 that normally accompanies the rewetting of a soil.

Study design

Limit test:

no

Total exposure duration:

42 d

Test conditions

Test temperature:

30 ± 1°C

Nominal and measured concentrations:

1,530 mg TEC/kg soil, 3,070 mg TEC/kg soil, 6,130 mg TEC/kg soil, 11,500 mg TEC/kg soil, 23, 000 mg TEC/kg soil

Reference substance (positive control):

yes

Remarks:

Microcrystalline cellulose

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

42 d

Dose descriptor:

NOEC

Effect conc.:

160 other: mg C/50 g soil

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: lack of inhibition of degradation

Remarks on result:

other: This substrate loading concentration of 160 mg C/50 g soil is equivalent to 3.2 mg C/g soil, and is the highest test concentration within the recommended range of substrate loading concentrations (≤ 5 mg C/g soil) that resulted in no inhibition.

Effect concentrations 2

Duration:

42 d

Dose descriptor:

NOEC

Effect conc.:

5 480 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: lack of inhibition of degradation

Remarks on result:

other: The NOEC was based on a soil concentration of 6130 mg/kg of the substance (derived from the experimental substrate loading concentration of 160 mg C/50 g soil, carbon as 52.17% of the substance MW, and Kd = 0.1192).

Any other information on results incl. tables

Aerobic biodegradation of triethyl citrate in standard laboratory soil mix was determined using laboratory bioreactors. The time required to achieve 50% mineralisation (t₅₀) increased as the TEC concentration in the soil increased. At all test concentrations, the net mineralization of the TEC was greater than that of the positive control (cellulose). The TEC half-lives were calculated as 6.6 d at 40 mg TEC-C/50 g soil which corresponds to 1,530 mg TEC/kg soil based on 52.17% carbon; 7.1 d at 80 mg TEC-C/50 g soil which corresponds to 3,070 mg TEC/kg soil; 9.4 d at 160 mg TEC-C/50 g soil which corresponds to 6,130 mg TEC/kg soil; 19.8 d at 300 mg TEC-C/50 g soil which corresponds to 11,500 mg TEC/kg soil; 43.0 d at 600 mg TEC-C/50 g soil which corresponds to 23,000 mg TEC/kg soil. 

Aerobic soil biodegradation of TEC met or exceeded pass levels defined by ASTM, FDA, EPA guidelines and OECD guidelines. The conversion of TEC-C into CO₂ exceeded 50% ThCO₂within the 64 -day time limit set by the equivalent FDA soil biodegradation test (U.S. FDA, 1987) and 60% ThCO₂ within the time limits set by the equivalent ASTM methods (ASTM, 1999) (≤180 days) and U.S. EPA methods (U.S. EPA, 1998) (≤64 days). 

At the substrate loading concentrations in the range recommended by the FDA and U.S. EPA tests (OPPTS 835.3110 Ready Biodegradability test - U.S. EPA, 1998) of ≤ 5 mg substrate–C/g (i.e., includes test concentrations up to and including 160 mg C/50 g soil , the conversion of substrate-C into CO₂ exceeded 60% ThCO2 within a 10 -14 day window following the lag period. At this concentration of 160 mg C/50 g soil, the half-life was reported as 9.4 days and the T₆₀ as 12.7 days. These results indicate that TEC can be considered readily biodegradable (U.S. EPA, 1998).  Therefore, the substrate loading concentration of 160 mg C/50 g soil may be considered the NOEC(soil). The NOEC(soil) is the basis for calculating the NOEC(water) and NOEC(soilds) in sewage sludge.

Calculation of the NOEC(water) and NOEC(soilds):

160 mg C/50 g soil = 3.2 mg C/g soil = 3200 mg C/kg soil.

Based on a substance molecular weight of 276.29, and a chemical formula of C₁₂H₂₀O₇, carbon constitutes 52.17% of the substance molecular weight. Therefore, 3200 mg C/kg soil = 6130 mg TEC/kg soil.

The soil-water partition coefficient (K_d) of the substance was determined from the adsorption coefficient (K_oc) of 5.959 L/kg and the default fraction organic carbon content in soil (f_oc = 0.02), based on the relationship K_d = K_oc* f_oc, so that K_d = 5.959 * 0.02 = 0.1192 L/kg.

Assuming that the soil NOEC of 6130 mg/kg in soil (6130 ppm) indicates a non-inhibitory concentration for both the soild and aqueous compartments in sewage sludge,

the K_d was then used to predict the partitioning bewteen the solid and aqueous compartments as the concentration in solid (C_s) and the concentration in water (C_aq), based on the relationship K_d = C_s/C_aq. Thus, C_s = 650 mg/kg and C_aq = 5480 mg/L is consistent with the K_d of 0.1192 L/kg. The NOEC(water) is equivalent to the C_aq and is thus 5480 mg/L; the NOEC(solids) is equivalent to C_s and is thus 650 mg/kg.

Applicant's summary and conclusion

Validity criteria fulfilled:

not specified

Conclusions:

Results of the aerobic soil and compost biodegradation tests demonstrated that TEC met or exceeded biodegradation “pass levels” defined in ASTM, FDA and U.S. EPA guidelines. Most importantly, at low concentrations, most representative of those likely to occur through the designed use of TEC in consumer products, the half-life (t50) was calculated to be within the range of one to three weeks. The soil concentration of 6,130 mg TEC/kg soil can be considered a NOEC for microorganisms.