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Diss Factsheets

Ecotoxicological information

Toxicity to soil microorganisms

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Administrative data

toxicity to soil microorganisms
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted specific principles, acceptable for assessment.
Justification for type of information:
The source and the target substances share structural similarities with common functional groups, esters, and side chains varying in their lenght. Moreover, the side chains are chemically simple structures which have no structural alerts for toxicity and which are closely related to substances of known low toxicity.

Data source

Reference Type:
Triglyceride degradation in soil
Hita, C. et al.
Bibliographic source:
Org. Geochem 25(1-2): 19-28

Materials and methods

Principles of method if other than guideline:
No guidelines was followed.
The degradation of the model molecule (pure tristearin) was investigated in three different soil types, to determine the behavior of fatty wastes.
GLP compliance:
not specified

Test material

Constituent 1
Reference substance name:
Glycerol tristearate
EC Number:
EC Name:
Glycerol tristearate
Cas Number:
propane-1,2,3-triyl trioctadecanoate
Details on test material:
- Name of test material (as cited in study report): tristearin
- Analytical purity: no data

Sampling and analysis

Analytical monitoring:

Test substrate

Details on preparation and application of test substrate:
- Method: The three soil samples were first sieved (<2mm), adjusted to 2/3 of the water-holding capacity of each respective soil and then weighed into 750 cm3 flasks in portions calculated to correspond to 100 g o.d. soil. The soils were subsequently supplemented with a pure triglyceride.

Test organisms

Test organisms (inoculum):

Study design

Total exposure duration:
4 wk

Test conditions

Test temperature:
Details on test conditions:
- Test container: flask
- Amount of soil: 100 g
- No. of replicates per concentration: yes, 3 replicates
- No. of replicates per control: yes, 3 replicates

Nominal and measured concentrations:
0.2% (wt/wt)

Results and discussion

Effect concentrations
Key result
4 wk
Dose descriptor:
other: hydrolisis of the trigliceride
Effect conc.:
ca. 0.2 other: %
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
other: biodegradation of the test material
Remarks on result:
other: increased activity of soil microorganisms

Any other information on results incl. tables

The results show that, due to the soil supplementation with tristearin, free fatty acids were produced. After soil microflora adaption, these compounds are utilized as they are freed by enzymatic hydrolysis. A part of the of the monocarboxyclic acids is probably oxidized to form di-, keto- and hydroxyl-acids. Contrary the acid fractions evolution, the amounts of the neutral fractions increased between 1 and 4 weeks in the supplemental soils. This is due to the increase of the quantity of alcohols and polar neutral compounds. Bio-oxidation processes seem to be more efficient after 4 weeks. After 1 week also a low decrease, compared to the controls, in the amounts of hydrocarbons consecutive to a low increase of the ester fractions.

Main result of the monoacid fractions analysis was the rapid formation of stearic acid in considerable amounts. This result showed that an intense hydrolysis reaction with specific lipase of tristearin had occurred after the soil supplementation. The investigations of ester fractions showed that new alkanoic acids (methyl stearate, ethyl stearate, and propyl stearate), not determined in the controls, were generated in the supplemented soils. Among other processes the following hypothesis to explain the formation of these compounds were proposed:

1.      Bioesterification of a part of the free stearic acid, released by an enzymatic hydrolysis reaction

2.      Alcoholysis of the triglyceride to form esters, directly

3.      And/or direct formation of these compounds from tristearin with C-C and C-O bond cleavages

Applicant's summary and conclusion

Validity criteria fulfilled:
To study the fate of fatty wastes left by food industries in the soil, tristearin was chosen as a model molecular marker and its biodegradation followed in different types of soil in a laboratory experiment. Samples of three soils (controls and treatments) were incubated for periods of 1–4 weeks, at 20°C. A significant disappearance of total free lipids was observed. A detailed study of different lipid classes showed an increased activity by soil microorganisms. This resulted in the oxidation and hydrolysis of the added component, producing free stearic acid and esters (methyl stearate, ethyl stearate and propyl stearate). After 4 weeks, the amounts of these compounds decreased. They are certainly intermediate components in the biodegradation processes of triglycerides. The use of this pathway for the elimination of fatty wastes in soil seems to be all the more important as it is known that fatty acids, mono/diglycerides and glycerol are removed more easily than triglycerides.