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Ecotoxicological information

Toxicity to soil microorganisms

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Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Study period:
No data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Meets generally accepted scientific standards, well documented and acceptable for assessment. However there are deviations from standardised protocols which include the duration of the test, the test medium and the temperature but these are considered to be acceptable.
Reason / purpose for cross-reference:
reference to same study
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test)
Deviations:
yes
Remarks:
1) Test temperature is 25 °C whereas the OECD Guideline requires 20 °C +/- 2 °C, although this is not thought to compromise the results. 2) The duration is 40 days whereas the OECD Guideline duration is 28 days. But measurements were taken at 24 h
GLP compliance:
not specified
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 100 ppm and 1000 ppm
- Sampling method: 4-NP was analysed using gas chromatography with FID detection.
Vehicle:
yes
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: Reconstituted soil was used comprising a mixture of mature sewage sludge compost (1/3 d.m.) and sandstone (2/3 d.m.). The compost made from a mixture of digested sludge and sawdust was provided by the Sieg-Roche (canton de Vaud, Switzerland) pilot plant after 9 months of maturation (Hubert, 1985) and was mixed with a Permian sandstone without calcium carbonate from the Vosges massif (France).

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: Technical grade nonylphenol was dissolved in ethanol at 0.4 ml/g spiked compost. The dissolved substances were mixed with part of the compost (4 g d.m.) and the ethanol was left to evaporate. The spiked compost was then mixed thoroughly in an incubation cell with the rest of the 60 g sample (16 g d.m. compost + 40 g d.m. sandstone).

VEHICLE:
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): Ethanol
- Evaporation of vehicle before use: Yes
Test organisms (inoculum):
other: Aged compost and sandstone mix
Total exposure duration:
40 d
Test temperature:
25 degrees C
Moisture:
51% field water holding capacity (WHC) was adjusted to 60% WHC
Details on test conditions:
TEST SYSTEM
- Test container (type, material, size): Incubation cell in a multipurpose assembly incubator (Parr and Smith 1969).
- No. of replicates per concentration: 1
- No. of replicates per vehicle control: 1

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): Reconstituted soil was used comprising a mixture of mature sewage sludge compost (1/3 d.m.) and sandstone (2/3 d.m.). The compost made from a mixture of digested sludge and sawdust was provided by the Sieg-Roche (canton de Vaud, Switzerland) pilot plant after 9 months of maturation (Hubert, 1985) and was mixed with a Permian sandstone without calcium carbonate from the Vosges massif (France).
- Soil texture of the sandstone
- % sand: 75%
- % silt: 12%
- % clay: 13%
- pH (in water): 6.80 (mixed soil)
- C:N ratio: 20 (mixed soil)
Total P: 1% (mixed soil)
- Maximum water holding capacity (in % dry weight): 51% WHC of mixed soil and adjusted to 60% WHC for the test
- Cation exchange capacity (mmol/kg): 22.1 meq/100g of the mixed soil

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Respiration (CO2 evolution)

VEHICLE CONTROL PERFORMED: yes

POST-TREATMENT
On removal from the incubator, the replicates were mixed thoroughly and half the quantity was freeze-dried. After freeze-drying three samples off each treatment were analysed for residula nonylphenol. Only 4-nonylphenol concentrations were measured.
Nominal and measured concentrations:
Nominal concentrations of 0, 100 ppm and 1000 ppm.
Reference substance (positive control):
no
Duration:
40 d
Dose descriptor:
NOEC
Effect conc.:
100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
respiration rate
Remarks on result:
other: 4.7 to 1657.0
Details on results:
No data
Results with reference substance (positive control):
No data
Reported statistics and error estimates:
Results were interpreted using Student's t-test and one-way analysis of variance (F-test) where P<0.05 was considered to be significant.

Evolution of biomass ATP was also measured in this study but was not significantly different among the three treatments. After an initial increase in ATP content, concentrations stabilised around 400 ng/g in the control and 100ppm treatments. However, in the 1000ppm treatment a progressive decrease in ATP content was observed from the 5th day onwards. The diffrence between values on days 10 and 40 were significant (t<0.01) suggesting that nonylphenol does have a sudden lethal action on global biomass since the ATP content directly reflects the active soil biomass. It does not however reveal qualitative changes in the microflora. The biomass-ATP measure may also be insufficiently sensitive to show fine but significant biomass fluctuations. No microbial counts were possible in this study.

Validity criteria fulfilled:
yes
Conclusions:
Respiration started at the same rate (37 ug C/g organic C per h) in all three treatments. CO2 evolution did not differ significantly between the 100 ppm samples and the controls, which is taken as the NOEC. In contrast, in the 1000 ppm samples, CO2 evolution was significantly depressed by the 4th day (F<0.05), although an EC50 is not available.
Executive summary:

In a 40-day chronic toxicity study, soil microbes were exposed at control (with ethanol) and two test concentrations of 100 and 1000 ppm nonylphenol. The NOEC based on carbon respiration was 100 mg nonylphenol/kg. Based on the results of this study, nonylphenol would not be considered to have adverse effects on soil microbial respiration at 100 mg/kg, although some reduction in soil microbial respiration may be seen at 1g/kg.

This study is classified as acceptable and is similar in methodology to the requirements of the OECD Guideline 217 (2000) Soil Microorganisms: Carbon Transformation Test.

Endpoint:
toxicity to soil microorganisms
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
In accordance with Regulation (EC) 1907/2006 Annex XI (1.5) and the relevant ECHA guidance documents, the substances detailed in the table below are grouped for the purposes of read across to reduce the need for unnecessary repeat testing on the basis that the substances are similar on the basis of a common functional groups.
Reason / purpose for cross-reference:
read-across source
Vehicle:
yes
Duration:
40 d
Dose descriptor:
NOEC
Effect conc.:
100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
respiration rate
Remarks on result:
other: 4.7 to 1657.0
Details on results:
No data
Results with reference substance (positive control):
No data
Reported statistics and error estimates:
Results were interpreted using Student's t-test and one-way analysis of variance (F-test) where P<0.05 was considered to be significant.

Evolution of biomass ATP was also measured in this study but was not significantly different among the three treatments. After an initial increase in ATP content, concentrations stabilised around 400 ng/g in the control and 100ppm treatments. However, in the 1000ppm treatment a progressive decrease in ATP content was observed from the 5th day onwards. The diffrence between values on days 10 and 40 were significant (t<0.01) suggesting that nonylphenol does have a sudden lethal action on global biomass since the ATP content directly reflects the active soil biomass. It does not however reveal qualitative changes in the microflora. The biomass-ATP measure may also be insufficiently sensitive to show fine but significant biomass fluctuations. No microbial counts were possible in this study.

Executive summary:

The read across for 4-tert-octylphenol (CAS: 140-66-9); is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of Toxicity to soil microorganisms. Based on the information available for the read across substances, the substance is expected to be toxic to soil microorganisms.

Description of key information

One study was available for the soil microbial endpoint (Annex IX, Endpoint 9.4.2 Effects on Soil Microorganisms).  The study by Trocme et al., (1989) presents a long-term carbon transformation test by soil microorganisms in the presence of nonylphenol where a NOEC of 100 mg nonylphenol/kg can be derived.

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
100 mg/kg soil dw

Additional information

There was one reliable toxicity study relating to soil microorganisms where a 40-day test based on microbial respiration by measuring carbon transformation provided a NOEC of 100 mg nonylphenol/kg (Trocme et al., 1989). This is the Key Study although this result is the only one available. There are some deviations from the standard OECD 217 Guideline but these are not thought to undermine the study. In contrast to the standard test protocol, the test duration is far greater (at 40 days) which would traditionally lead to a more sensitive toxicity value. The fact that there was no evidence of toxicity at 100 mg/kg when compared to the control, suggests that this study is more protective of this endpoint than a standard OECD study. This study indicates that soil microorganisms are less sensitive to nonylphenol than soil invertebrates but may be more sensitive than terrestrial plants. These data are considered to be suitable for use in the octylphenol risk assessment.