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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil: simulation testing
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is readily biodegradable
Endpoint:
biodegradation in soil, other
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
1. HYPOTHESIS FOR THE CATEGORY APPROACH
The hypothesis is that the category members have similar structures and properties (very rapid biodegradability), which are consistent across the category (Scenario 6 in the RAAF). The consistency of this property across the category is discussed in the endpoint summary.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Please refer to the test material identity information within each endpoint study record and to the endpoint summary. The source chemicals and the target chemical are linear aliphatic alcohols which are members of the long chain linear aliphatic alcohol Category.

The long chain linear aliphatic alcohol Category has at its centre an homologous series of increasing carbon chain length alcohols. The category members are structurally very similar. They are all primary aliphatic alcohols with no other functional groups. The category members are linear or contain a single short-chain side-branch at the 2-position in the alkyl chain, which does not significantly affect the properties (‘essentially linear’). The category members have saturated alkyl chains or contain a small proportion of naturally-occurring unsaturation(s) which does not significantly affect the properties. The branched and unsaturated structures are considered to have such similar properties that their inclusion in the category is well justified.
Impurities: Linear and/or ‘essentially linear’ long chain aliphatic alcohols of other chain lengths may be present. These are not expected to contribute significantly to the properties in respect of this endpoint due to consistent properties (see point 3).
There are no impurities present at or above 1% which are not category members or which would affect the properties of the substance.

3. CATEGORY JUSTIFICATION
The category members are structurally very similar (see point 2) and are biochemically very similar. The metabolic synthesis and degradation pathways are well established. This Category is associated with a consistency and predictability in the physicochemical, environmental, and toxicological property data across its members.

The consistency of observations in this property across the range of chain lengths covered by this Category is described in the Endpoint Summary and in the Category Report attached in Section 13.

In this registration, the information requirement is based on read-across from members of the category with shorter chain length and similar chemical properties, for which there would be an expectation of consistency in behaviour.

4. DATA MATRIX
A data matrix for the C6-24 alcohols Category is attached in Section 13.
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Soil No.:
#1
% Degr.:
100
Parameter:
test mat. analysis
Sampling time:
24 h
Remarks on result:
other: C10
Soil No.:
#2
% Degr.:
100
Parameter:
test mat. analysis
Sampling time:
24 h
Remarks on result:
other: C10
Soil No.:
#3
% Degr.:
100
Parameter:
test mat. analysis
Sampling time:
24 h
Remarks on result:
other: C10
% Degr.:
87
Parameter:
O2 consumption
Sampling time:
28 d
Remarks on result:
other: C14-C18
Soil No.:
#1
DT50:
>= 0.5 - <= 1 h
Type:
not specified
Temp.:
>= 19.1 - <= 21.6 °C
Remarks on result:
other: C10
Soil No.:
#2
DT50:
>= 1 - <= 2 h
Type:
not specified
Temp.:
>= 19.1 - <= 21.6 °C
Remarks on result:
other: C10
Soil No.:
#3
DT50:
>= 0.25 - <= 0.5 h
Type:
not specified
Temp.:
>= 19.1 - <= 21.6 °C
Remarks on result:
other: C10
Transformation products:
yes
Remarks:
C10
No.:
#1

Description of key information

Significant technical difficulties were encountered during method development for a recent study of adsorption/desorption (OECD 106, Wildlife, 2015) of the structurally analogous alcohol, decan-1-ol (CAS 112-30-1), using natural standard soils, in that it was not possible to detect sufficient substance and establish equilibrium in non-sterilised soil samples. During method development in preparation for this study, the laboratory reported that after equilibration with soils for 15-minute to 24-hour periods, decan-1-ol dosed into the test vessels was partly or completely transformed into a more polar product, which was clearly distinguishable from the starting material as clear and well separated peaks in the chromatograms. The rate of transformation depends on the soil type. Only after a very short (5-minute) equilibration the parent material remained intact (personal communication, 8 January 2015 from Wildlife International laboratory). Half-lives were not explicitly derived, but chromatograms presented would indicate the half-life of decan-1-ol in the soil test samples was approximately 30 min - 1 hour (silt loam soil); 1 - 2 hours (loamy sand), and 15 - 30 minutes (clay loam). Following sterilisation of the soil samples by autoclaving, the substance remained adequately stable for a 2-hour period, therefore the instability can be attributed to biodegradation of the substance by soil microbiota. The polar degradation product is most likely the corresponding carboxylic acid, though it was not definitively identified. The chromatograms show that decan-1-ol was effectively fully removed in all four soil types by the 24 h time point (in the case of 2 of the soil types, within 2 hours). Similar degradation can be expected for docosan-1-ol.

Key value for chemical safety assessment

Half-life in soil:
3 d
at the temperature of:
12 °C

Additional information

In accordance with Column 2 of REACH Annex IX, the full soil simulation test (required in Section 9.2.1.3) does not need to be conducted as the substance is readily biodegradable, and has been shown to be very rapidly degraded in non sterilised standard soils as part of method development for the soil adsorption study.

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols

The data available regarding persistence in soil are limited. A commercial multi-constituent substance (CAS 68155-00-0 (C14-18 and C16-18 unsaturated) and CAS 68002-94-8 (C16-18 and C18 unsaturated)) was found to be readily biodegradable in a reliable OECD 301D study using a non-standard inoculum; garden soil microorganisms (Borner, 1999). A recent and reliable study of adsorption and desorption using the batch equilibrium method (in compliance with OECD 106 and GLP) has been conducted with decan-1-ol.