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Environmental fate & pathways

Biodegradation in soil

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Reference
Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
no guideline followed
Principles of method if other than guideline:
Study investigating the degradation of branched 4-nonylphenol isomers in a rice paddy soil under oxic conditions over 58 days.
GLP compliance:
not specified
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
other: gleyic hydragric anthrosol
% Clay:
46.7
% Silt:
37.9
% Sand:
15.4
% Org. C:
2.5
pH:
6.31
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location: rice paddy soil collected from the Changshu Experimental Station of the Chinese Academy of Sciences in Jiangsu Province, China
- Collection procedures: not stated
- Soil preparation (e.g., 2 mm sieved; air dried etc.): The soil was air dried, sieved through 2 mm and stored at room temperature shortly before use.
Soil No.:
#1
Duration:
58 d
Soil No.:
#1
Initial conc.:
59.6 other: µmol/kg soil dw
Based on:
other: mixture of 5 nonylphenol isomers (4 branched and 1 linear)
Soil No.:
#1
Initial conc.:
ca. 12 other: µmol/kg soil dw
Based on:
other: of each isomer
Soil No.:
#1
Initial conc.:
3.7 other: MBq/kg soil dw
Based on:
other: mixture of 5 nonylphenol isomers (4 branched and 1 linear)
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
20 ± 1 °C
Humidity:
70% of the max water-holding capacity
Details on experimental conditions:
EXPERIMENTAL DESIGN
- Soil condition: air dried
- Soil (g/replicate): 5 g
- No. of replication treatments: 54
- Test apparatus (Type/material/volume): Serum flask
- Details of traps for CO2 and organic volatile, if any: The 14CO2 released from the soil was absorbed by 1.0 mL of NaOH (1 M) contained in one 6mL vial, which was suspended from the bottom of the stopper.

Test material application
- Volume of test solution used/treatment: A stock solution of a mixture of five 4-NP isomers (14C-4- NP111, 4-NP112, 13C-4-NP38, 4-NP65, and 4-NP1) was prepared in methanol at a concentration of 16.6 μmol/mL with a molar ratio of the five isomers in the mixture at about 1:1:1:1:1 (each
isomer at about 3.3 mmol/L). About 18 μL of the stock solution of the 4-NP isomer mixture was added with a microsyringe to 0.2 g of soil.
- Application method (e.g. applied on surface, homogeneous mixing etc.): The soil was mixed and transferred into a 100 mL serum flask containing 4.8 g of soil. The whole soil was then thoroughly mixed and kept overnight to evaporate the methanol solvent. The homogeneity of the 4-NP distribution within the soil was proved by determining the radioactivity of soil subsamples (0.02-0.05 g) from the flask
- Is the co-solvent evaporated: yes

Experimental conditions (in addition to defined fields):
- Continuous darkness: Yes

Other details, if any:

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions:
- Evidence that an/aerobic conditions were maintained during the experiment (e.g. redox potential):
Key result
Soil No.:
#1
DT50:
2.1 - 10.3 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: mean DT50 of the 4 branched isomers
Transformation products:
not specified
Details on transformation products:
One metabolite of 14C-4-NP111 was found in the active soil, but no metabolite was detected in the sterilized soil. The metabolite had a higher Rf value (0.75) on TLC than that of the parent 14C-4-NP111 (0.38), indicating that the metabolite was less polar than 4-NP111.
Evaporation of parent compound:
no
Volatile metabolites:
no
Residues:
yes
Details on results:
TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): no

NON-EXTRACTABLE RESIDUES
- % of applied amount at end of study period: 3.3 - 24.4 %

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: about 5%

Isomer-Specific Degradation of 4-NP Isomers in Soil

The five (four branched and one linear) 4-NP isomers degraded at different rates in the active rice paddy soil during 58 days of incubation under oxic conditions. The k ranged from 0.09 to 0.58 day-1 with the following increasing order: 4-NP1 (0.58 day1) > 4-NP38 (0.38 day1) > 4-NP65 (0.13 day1) > 4-NP112 (0.10 day1) > 4-NP111 (0.09 day1), showing that the linear isomer 4-NP1 degraded most rapidly in the soil (t1/2 = 1.4 days), while the branched 4-NP111, the main component of tNP mixtures was degraded considerably more slowly (t1/2 = 10.3 days). The observed higher recalcitrance of the branched 4-NP isomers than 4-NP1 can be attributed to the alkyl chain structure at the benzene ring. The branched isomers have a quaternary α-C on the alkyl chain, and this structure is regarded resistant to ω- and β-oxidation. The length of the side chain at α-C seems to be the most important factor for their degradation. The three isomers with an ethyl side chain at α-C (4-NP111, 4-NP112, 4-NP65) showed a longer t1/2 than 4-NP38 with two methyl side chains at α-C. The branch number of the alkyl chain also seems to be a factor affecting isomer degradation. The isomers with an alkyl side chain branched at two positions (such as 4-NP111 at α-C and γ-C and 4-NP112 at α-C and δ-C) exhibited a longer t1/2 than isomer 4-NP65 with only one branch at α-C.

Mineralization and Bound-Residue Formation of 4-NP111

Good recoveries of radioactivity (96107%) of the experiments, suggesting that the volatility of 14C-4-NP111 was negligible in the soil. The mineralization of 14C-4-NP111 in the rice paddy soil was low (about 5% of the initially applied 14C within 58 days) and did not have a lag phase (Figure 2), indicating that microorganisms in the soil did not need an apparent adaptation time for mineralizing 4-NP111. In the sterilized soil less than 0.5% of 14C-4-NP111 was mineralized, indicating that the mineralization of 14C- 4-NP111 in the active soil was attributable to microbial activity. During incubation of 58 days in the soil, the extractable radioactivity decreased to 38.3% of the initial radioactivity whereas the bound radioactivity increased rapidly to 31.1% within the beginning 5 days and to 54.4% at the end of the incubation. Comparing the degradation of 4-NP isomers in the active and sterilized soils, it can be concluded that formation of the bound residues was apparently related to the microbial activity. Formation of bound residues is regarded as a consequence of aging processes of organic pollutants in soil, for which the main mechanisms are sorption and diffusion.

Fractionation of Bound Residues of 4-NP111

The bound residues of 14C-4-NP111 in the soil were fractionated according to their alkaline solubility into fulvic acids, humic acids, and humin. Most of the bound radioactivity was located in the humin fraction, already amounting to >84% after incubation for 5 days. The humin-bound residues increased during incubation and accounted for 96% of the total bound residues at the end of incubation.

Executive summary:

Using 14C- and 13C-ring-labeling, degradation of five p-nonylphenol (4-NP) isomers including four branched (4-NP38, 4-NP65, 4-NP111, and 4-NP112) and one linear (4-NP1) isomers in a rice paddy soil was studied under oxic conditions. Degradation followed an availability-adjusted first-order kinetics with the decreasing order of half-life 4-NP111 (10.3 days) > 4-NP112 (8.4 days) > 4-NP65 (5.8 days) > 4-NP38 (2.1 days) > 4-NP1 (1.4 days). One metabolite of 4-NP111 with less polarity than the parent compound occurred rapidly and remained stable in the soil. At the end of incubation (58 days), bound residues of 4-NP111 amounted to 54% of the initially applied radioactivity and resided almost exclusively in the humin fraction of soil organic matter, in which chemically humin-bound residues increased over incubation.

Description of key information

DisT50 = 2.1 - 10.3 days for different branched 4-nonylphenol isomers (read across).

Key value for chemical safety assessment

Additional information

Since no simulation studies assessing the biodegradability of Benzaldehyde, 2-hydroxy-5-nonyl, oxime, branched (CAS 174333-80-3) in soil are available, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances, a read-across to Phenol,4-nonyl-,branched (CAS 84852-15-3) was conducted , which is a secondary component and structurally similar to the main component of the substance. The only structural difference between the source substance and the target substance is the lack of an aldoxime group at the phenol ring of the molecule. The read across is justified by similarity of structure and functional groups and accordingly similar physico-chemical properties, which is expected to result in similar environmental behavior and fate (see table and Analogue justification document attached).

Substance

Benzaldehyde, 2-hydroxy-5-nonyl, oxime, branched

Phenol, 4-nonyl, branched*

CAS number

174333-80-3

84852-15-3

Structure

see attachment (chapter 6.1)

 see attachment (chapter 6.1)

Molecular formula

C16O2NH25

C15H24O

Molecular weight

~ 263 g/mole

~ 220.35 g/mole

PC parameter

 

 

Water solubility

0.4 mg/L (EU method A.6)

5.7 mg/L (ASTM E 1148-02)

Partition coefficient

5.5 (EU method A.8)

5.4 (OECD 117)

Vapour pressure

0.37 Pa at 20 °C (OECD 104)

~1 Pa at 20 °C (ASTM-D 2879)

Environmental fate

 

 

Biodegradability

0 % in 28 days (OECD 302c)

non-adapted inoculum:

0 % in 28 days (OECD 301B)

 

adapted inoculum:

48.2-62 % in 28 days (OECD 301B)

Adsorption [log KOC]

3.7 (OECD 121)

4.35 - 5.69 (EPA OTS 796.2750)

Hydrolysis

not relevant

Ecotoxicology

 

 

Short-term toxicity to fish

[96h-LC50]

1.1 mg/L (EU method C.1)

0.05 – 0.22 mg/L (different methods)

Long-term toxicity to aquatic invertebrates

[NOEC]

0.005 mg/L (OECD 210)

0.006 mg/L (ASTM E 1241-05)

Short-term toxicity to aquatic invertebrates

[48h-EC50]

2.7 mg/L (EU method C.2)

0.08 – 0.14 mg/L (different methods)

Long-term toxicity to aquatic invertebrates

[21d-NOEC]

0.189 mg/L (OECD 211)

0.024 - 0.116 mg/L (different methods)

Short-term toxicity to algae

[72h-EC50]

36.3 mg/L (OECD 201)

0.33 - 1.3 mg/L (different methods)

Long-term toxicity to algae

[72h-NOEC/EC10]

14.9 mg/L (OECD 201)

0.5 mg/L (Algal growth inhibition test according to UBA 1984)

Toxicity to microorganisms

[EC50]

200.4 mg/L (OECD 209)

950 mg/L (OECD 209)

* Data were taken from Phenol, 4-nonyl-,branched (CAS 84852-15-3) dossier published on the ECHA data base

 

Several soil - simulation studies with 4-nonylphenol are available in the literature. However, only one focused on different branched nonylphenol isomers. Shan et al. (2011) studied the degradation of five p-nonylphenol (4-NP) isomers including four branched (4-NP38, 4-NP65, 4-NP111, and 4-NP112) and one linear (4-NP1) isomers in a rice paddy soil using 14C- and 13C-ring-labelled nonylphenol. Degradation followed availability-adjusted first-order kinetics with the decreasing order of half-life 4-NP111 (10.3 days) > 4-NP112 (8.4 days) > 4-NP65 (5.8 days) > 4-NP38 (2.1 days) > 4-NP1 (1.4 days). One metabolite of 4-NP111 with less polarity than the parent compound occurred rapidly and remained stable in the soil. At the end of incubation (58 days), bound residues of 4-NP111 amounted to 54% of the initially applied radioactivity and resided almost exclusively in the humin fraction of soil organic matter, in which chemically humin-bound residues increased over incubation.

In conclusion, branched nonylphenol is mineralized slowly but integrated into organic matter rapidly in soil. Based on the reasons given above this conclusion is also considered to be true for Benzaldehyde, 2-hydroxy-5-nonyl, oxime, branched (CAS 174333-80-3).