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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
Study period:
August 2001 to May 2002
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was conducted following a modification of a standard guideline without deviations from the protocol, but it was not conducted under GLP guidelines and oxygen consumption was not reported.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 304 A (Inherent Biodegradability in Soil)
Deviations:
no
GLP compliance:
no
Test type:
laboratory
Oxygen conditions:
aerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
silt loam
% Org. C:
>= 1.5 - <= 2.2
pH:
>= 5.2 - <= 6.9
Soil no.:
#2
Soil type:
silt loam
% Org. C:
>= 1.5 - <= 2.2
pH:
>= 5.2 - <= 6.9
Details on soil characteristics:
Mean nutrient levels for nitrogen (N), potassium (K) and phosphate (PO4) as measured over several years and seasons were 626 (N), 760(K), and 442 (PO4).
Soil No.:
#1
Duration:
61 d
Soil No.:
#2
Duration:
61 d
Soil No.:
#1
Initial conc.:
2 000 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
2 000 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Soil No.:
#1
Temp.:
Approximately 20 degrees C
Microbial biomass:
Approximately 10E5 microbial cells per gm soil dw
Soil No.:
#2
Temp.:
Approximately 20 degrees C
Microbial biomass:
Approximately 10E5 microbial cells per gm soil dw
Details on experimental conditions:
The method applied to assess biodegradability in soil was based on a modification of the OECD 301F Ready Biodegradability Manometric Respirometry Test that measures oxygen consumption. The test procedure evaluates the ready biodegradability of a test substance as mediated by microorganisms. The consumption of oxygen is determined by measuring the quantity of oxygen (produced electrolytically) required to maintain constant gas volume in the respirometer flask, or from the change in volume or pressure (or a combination of the two) in the apparatus. Evolved carbon dioxide is absorbed in a solution of 10 N sodium hydroxide (NaOH). The amount of oxygen taken up by the microbial population during biodegradation of the test substance (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of theoretical oxygen demand (ThOD). ThOD was calculated using the equations referenced in the OECD 301F test. The apparatus used is an electrolytic respirometer, manufactured by Co-ordinated Environmental Service (Kent, England). The system is based on a proven oxygen generating process coupled to a sensitive manometric cell. The sample is placed in a sample flask, which is then sealed by a manometric cell/CO2 trap and immersed in a temperature stabilized water bath. As the biodegradation process progresses, the microorganisms consume O2 converting it to CO2 during aerobic respiration. The CO2 produced is absorbed by a solution of 10N NaOH in the CO2 trap, which causes a net reduction in gas pressure within the sample flask. This pressure reduction is detected by the manometric cell and triggers the electrolytic process. The electrolytic process generates oxygen, which restores the pressure in the sample flask. The duration of the electrolyzing current is proportional to the amount of oxygen supplied to the microorganisms.

The test substance was evaluated in triplicate test systems. To correct for the endogenous respiration of the soil, triplicate blank systems were similarly prepared. The soil flasks for these studies were specially designed respirometer flasks, each containing approximately 60g of a soil and substance. The respirometer soil flask is basically a glass cylinder with a threaded connection designed to attach to the respirometer manifold. The dimensions of the flask are approximately 4 in (h) x 2 in. (dia).

Triplicate test systems for each substance were prepared by weighing five grams of air-dried soil into tared glass bottles, adding (by weight) the appropriate amount of test or positive control substance to the dried soil and mixing thoroughly with a glass rod. The remaining mass of pre-weighed soil was then added to the test system and the contents were then again mixed thoroughly with the glass rod. The amounts of substance and soil necessary to achieve a 2000 mg/Kg concentration were calculated and added based on soil dry weight. The glass rod was left in the test system to prevent loss of any substance or soil particles adhered to the rod surface. To correct for the endogenous respiration of the soil, triplicate blank systems were also prepared by combining 5 grams air-dried soil and 60 grams of the moisturized soil (on a dry weight basis). The soils were adjusted to 60% of water holding capacity (WHC) before the start of each study.

Two sequential studies using silty loam soil were conducted to determine the repeatability of the results, in addition to the effect on microbial activity due to an extended soil storage time of approximately four months. In addition, the reproducibility of the O2 measurements were evaluated by using two different respirometer systems in the second study.
Soil No.:
#1
% Degr.:
61.2
Parameter:
O2 consumption
Sampling time:
61 d
Soil No.:
#2
% Degr.:
62.6
Parameter:
O2 consumption
Sampling time:
61 d
Soil No.:
#2
% Degr.:
59.7
Parameter:
O2 consumption
Sampling time:
61 d
Soil No.:
#1
DT50:
45 d
Type:
(pseudo-)first order (= half-life)
Temp.:
ca. 20 °C
Soil No.:
#2
DT50:
43 d
Type:
(pseudo-)first order (= half-life)
Temp.:
ca. 20 °C
Soil No.:
#2
DT50:
46 d
Type:
(pseudo-)first order (= half-life)
Temp.:
ca. 20 °C
Transformation products:
not measured
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Residues:
not measured
Results with reference substance:
The positive control, rapeseed oil, results were as follows:

Soil Biodegradation
(#) (% on day 61)
1 66.8, 61.9 (two sets of controls)
2 66.7
Conclusions:
Hydrocarbons, C11-C14, n-alkanes, isoalkanes, cyclics, <2% aromatics, biodegraded to a great extent (>60%) in a silt loam soil at a rate comparable to the control, rapeseed oil (62 to 67%), within a two month test period as measured in respirometric oxygen consumption tests. The half-life, based on three tests was 45 days. This extent was replicated in two separate studies.
Executive summary:

The objective of this work was to evaluate the biodegradability of the test substance using an experimental design based on modifications of standard OECD test guidelines. Two studies were conducted to assess the extent of ultimate biodegradability of the test substance in comparison to the positive control, rapeseed oil. Rapeseed oil is considered to be rapidly biodegradable and is used as the positive control for the ASTM Standard Test Method for Determining Aerobic Aquatic Biodegradation of Lubricants and/or their Components (ASTM Designation: D5864-95). Additionally, rapeseed oil performance is considered to satisfy criteria for test validity as it degraded to at least 50% in 64 days as recommended for a positive control substance in the standard U.S. Food and Drug Administration Environmental Assessment Technical Handbook (1987), test method 3.12 for inherent biodegradation in soil. The test substance biodegraded to a great extent (>60%) in a silt loam soil at a rate comparable to the control, rapeseed oil (62 to 67%), within a two month test period as measured in respirometric oxygen consumption tests. The half-life, based on three tests was 45 days. The results were consistent between two separate studies and suggest that the test substance can biodegrade in terrestrial habitats rapidly and to a great extent. The control and test substances were tested at a relatively high concentration, 2000 mg/Kg.

Description of key information

In accordance with column 2 of REACH Annex IX, the simulation testing on ultimate degradation in soil does not need to be conducted as the normal paraffinic substances representative of C9-C14 Aliphatics (less than 2% aromatic) are readily biodegradable. However, data is available from a Guideline (OECD 304 A) study conducted on Hydrocarbons, C11 -C14, n-alkanes, isoalkanes, cyclics, <2% aromatics and is presented below.

Hydrocarbons, C11-C14, n-alkanes, isoalkanes, cyclics, <2% aromatics, biodegraded to a great extent (>60%) in a silt loam soil at a rate comparable to the control, rapeseed oil (62 to 67%), within a two month test period as measured in respirometric oxygen consumption tests. The half-life, based on three tests was 45 days. This extent was replicated in two separate studies. These data are used as read-across data to Tetradecane.

Key value for chemical safety assessment

Additional information

In accordance with column 2 of REACH Annex IX, the simulation testing on ultimate degradation in soil does not need to be conducted as the normal paraffinic substances representative of C9-C14 Aliphatics (less than 2% aromatic) are readily biodegradable. However, data is available from a Guideline (OECD 304 A) study conducted on Hydrocarbons, C11 -C14, n-alkanes, isoalkanes, cyclics, <2% aromatics and is presented below.

Hydrocarbons, C11-C14, n-alkanes, isoalkanes, cyclics, <2% aromatics, biodegraded to a great extent (>60%) in a silt loam soil at a rate comparable to the control, rapeseed oil (62 to 67%), within a two month test period as measured in respirometric oxygen consumption tests. The half-life, based on three tests was 45 days. This extent was replicated in two separate studies. These data are used as read-across data to Tetradecane.