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Environmental fate & pathways

Biodegradation in soil

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biodegradation in soil
Type of information:
experimental study
Adequacy of study:
supporting study
3 (not reliable)
Rationale for reliability incl. deficiencies:
significant methodological deficiencies
The analysis was based on absorbance in the bulk supernatant at a selected wavelength. Therefore, this study is not reliable based on potential interference and lack of extraction.

Data source

Reference Type:
Report date:

Materials and methods

Test guideline
no guideline available
Principles of method if other than guideline:
Test solution contained substituted benzenes as the sole carbon source. Inoculum was Niagara silt loam. The UV absorbance of the centrifuged supernatant aliquot was monitored up to 64 days for cleavage of benzene ring (cleavage results in loss of UV absorbance).
GLP compliance:
Test type:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Details on test material:
No details provided in the publication.

Study design

Oxygen conditions:
Soil classification:
other: Niagara silt loam
Details on soil characteristics:
1 ml of a 1% suspension used to inoculate 40 ml test substance solution
Details on experimental conditions:
25 µg/ml of test substance tested over 64 day period.

The procedure employed, essentially the same as that used earlier with the chlorophenols and chlorophenoxy-alkanoic acids, relies upon the loss of ultraviolet absorbancy when the benzene ring is cleaved by microorganisms derived from soil inoculum. The solution contained the test compound as the sole carbon source to support microbial proliferation and had, in addition to the aromatic compound, 1.6 grams of K2-HPO4, 0.40 gram of KH2PO4, 0.50 gram of NH4NO3, 0.20 gram of MgSO4•7H2O, 25 mg. of CaCl2•2H2O, 2.3 mg. of FeCl3•6H2O and 1000 ml of distilled water.

Forty-milliliter aliquots of the medium were placed in 4-oz. screw-cap bottles, 45 mm diameter x 80 mm high, and these were inoculated with 1.0 ml of a 1% suspension of Niagara silt loam. A parallel series of reaction vessels was set up identical to the first, except that each bottle also contained 8 mg of HgCl2 and 5 x 10-7 M Tween 80. Readings were made on these flasks at the same time intervals. Another series identical to the first was set up to determine if the chemicals at the concentrations employed were toxic to the microflora; these vessels received glucose to a final concentration of 1%, and the growth in the tubes was recorded visually. The bottles were incubated in the dark at 25 °C.

At intervals of 3 to 6 hours and at 1, 2, 4, 8, 16, 32, and 64 days after inoculation, the solutions were mixed, an aliquot was removed, and the suspension was centrifuged 10 minutes at 825 x G. The absorbancy of the supernatant was read at the selected wavelength against the supernatant from the reaction vessel containing a soil-medium mixture free of the chemical, but incubated in an identical fashion. The liquid and the soil residue were returned to the bottles and incubated further. Readings were made on the Beckman spectrophotometer, Model DU. All reaction vessels were set up in duplicate, and absorbancies measured on the replicates at each sampling period.

Results and discussion

Half-life / dissipation time of parent compound
> 64 d
Remarks on result:
other: Neither of the phenylenediamine isomers (ortho and meta) exhibited ring cleavage within 64 days.
Details on results:
Neither of the phenylenediamine isomers (ortho and meta) exhibited ring cleavage within 64 days.

Most of the substituted anilines were not suitable substrates under the test conditions. The resistance of the anilines was rather surprising because amino compounds are universal cellular constituents, by contrast with nitro, chloro, and sulfonate compounds. Seven of the 15 anisoles were also largely inert when exposed to the mixed soil population, but six of the seven contained either a nitro or an amino substituent.

Applicant's summary and conclusion

Neither of the phenylenediamine isomers (ortho and meta) exhibited ring cleavage within 64 days.
Executive summary:

The rate of degradation of mono- and disubstituted benzenes (approx. 80 substances) by soil microorganisms was determined by a spectrophotometric technique. Chloro, sulfonate, and nitro groups retarded the rate of biodegradation whereas carboxyl and phenolic hydroxyl groups favored decomposition of the substituted benzenes. The meta isomer was commonly the most resistant to attack by soil microorganisms, but the ortho isomer was the most resistant for certain classes of compounds.


The loss of UV absorbance was not observed over the 64 day period for ortho and meta phenylenediamine indicating slow decomposition under the test conditions.

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