C8-C26 branched and linear hydrocarbons – Distillates

Biodegradation in water and sediment: simulation tests

Description of key information

In accordance with column 2 of REACH Annex IX, the simulation testing on ultimate degradation in surface waters does not need to be conducted as the substance is highly insoluble in water. 
The following results of experimental studies on biodegradation in water for related substances might be used as supporting information: 
- 60-62 % degr. after 28 d (BOD) [two separate OECD 306 tests; read-across from supporting substance 'C10-C20 n-, iso-paraffins']
- 62.8 % degr. after 28 d (BOD) [OECD 306; read-across from supporting substance 'GTL C14-17 n-paraffins']

Additional information

In accordance with column 2 of REACH Annex IX, the simulation testing on ultimate degradation in surface waters does not need to be conducted as the substance is highly insoluble in water.

No ready biodegradability tests in seawater are available for GTL Diesel; the following data for related products (CAS 848301-67-7 and CAS 90622-45-0) might be used as supporting information:

Method	Results	Remarks	Reference
Test type: ready biodegradability seawater OECD Guideline 306	% Degradation of test substance:   60% after 28 d (BOD)	2 (reliable with restrictions) weight of evidence read-across from supporting substance (structural analogue or surrogate) Test material: C10-C20 n-, iso-paraffins (CAS: 848301-67-7)	Ward and Boeri, 2004
Test type: ready biodegradability seawater OECD Guideline 306	% Degradation of test substance:   62% after 28 d (BOD)	2 (reliable with restrictions) weight of evidence read-across from supporting substance (structural analogue or surrogate) Test material: C10-C20 n-, iso-paraffins (CAS: 848301-67-7)	Drake, 2005
Test type: ready biodegradability seawater OECD Guideline 306	% Degradation of test substance:   62.8% after 28 d (BOD)	2 (reliable with restrictions) weight of evidence read-across from supporting substance (structural analogue or surrogate) Test material:GTL C14-17 n-paraffins (CAS: 90622-45-0)	Drake, 1999

The biodegradability of 'C10-C20 n-, iso- paraffins' in seawater has been assessed in a study compliant with OECD 306 closed bottle test (Ward and Boeri, 2004). The test substance lies within the carbon number range for GTL Gasoil, but some of the longer chain constituents of GTL Gasoil are not represented in the substance used in this test. The study is not in compliance with GLP. The natural seawater medium was sourced from the Atlantic Ocean at Marblehead, Massachusetts. It was aerated, stored for <24 h and was filtered just before the test. Analytical determination of the unfiltered water is presented in the report and confirms TOC not detectable (LOD 2 mg/l). Due to its low solubility, the test substance was loaded into the test vessels by dosing onto Polysorb to give an effective concentration of 2 mg/l. Positive control (sodium benzoate), toxicity control (test substance co-dosed with sodium benzoate), carrier control (polysorb) and seawater blanks were used. The study used eight replicates of each test system; duplicate sampling and analysis at each time period. In this study the test substance reached 60% degradation in 28 days (based on BOD). Kinetics show steady biodegradation. The 10-day window was not met. Achievement of >60% removal is indicative that the substance can be expected to meet the criteria for ready biodegradability, so this result indicates a substance on that threshold. Validity criteria for the test were met.

A second OECD 306 seawater closed bottle test is available for an equivalent substance 'C10-C20 n- ,iso-paraffins' (Drake, 2005). The test substance lies within the carbon number range for Distillates, but some of the longer chain constituents are not represented in the substance used in this test. In this GLP-compliant test the sample has been tested in a study which has deviations from the guideline methodology, and important information and raw data missing from the test report. The seawater medium was sourced from Burnham-on-Crouch estuary (which has no industrial or river outputs). Suspended solids were removed by hydro-cyclone and settlement. The TOC content of the medium is not reported. The test substance preparation involved dilution of a stock solution in deionised water. Due to low solubility, a solubilising agent (Igepal CA-360; concentration equivalent to 0.5 mg/l in test vessels) was used to emulsify the test substance in the stock. The use of such an agent is not discussed in the guideline and represents a deviation. A control at the same concentration was included in the test, as well as a positive control (sodium acetate). Test substance loading is equivalent to 1 g/l in the stock solution, and subsequent dilutions are not clearly described, although a final dosing of 2.0 mg/L was reported in the summary. Without the raw data results, it is not possible for the reviewer to assess how the use of surfactant might have affected the test, however Igepal CA-360 (2-[2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethoxy]ethanol) is not expected to be rapidly biodegradable and so it should not in theory have significantly enhanced biodegradation of the test substance. Degradation of 62% (based on BOD) occurred during the 28 day test. Raw data are not presented. Kinetics show steady biodegradation. The 10-day window was not met, but this is not strictly a criterion for this type of study. Achievement of >60% removal is indicative that the substance can be expected to meet the criteria for ready biodegradability. Validity criteria for the test were reported to be met.

A seawater closed bottle test (OECD 306) is available for the related substance GTL C14-17 n-paraffins (Drake, 1999). The test substance lies within the carbon number range for Distillates, but some of the short and long chain constituents are not represented in the substance used in this test, and the substance name suggests that branched and cyclic constituents would only be present at low levels. In this GLP-compliant test the sample has been tested in a study which has deviations from the guideline methodology, and important information and raw data missing from the test report. The seawater medium was sourced from Burnham-on-Crouch estuary (which reportedly has no industrial or river outputs). Suspended solids were removed by hydro-cyclone and settlement. TOC content of the medium is not reported. The test substance preparation involved dilution of a stock solution in deionised water. Due to low solubility, a solubilising agent (non-ionic surfactant, Synperonic OP8; concentration equivalent to 1.0 mg/l in test vessels) was used to emulsify the test substance in the stock. The use of surfactant is not discussed in the guideline and represents a deviation. A surfactant control at the same concentration was included in the test, as well as positive control (sodium acetate). Test substance loading is equivalent to 2.0 mg/l in the test vessels. Without the raw data results, it is not possible for the reviewer to assess how the use of surfactant might have affected the test, however Synperonic OP8 (understood to be 2-[2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethoxy]ethanol) is not expected to be rapidly biodegradable and so it should not in theory have significantly enhanced biodegradation of the test substance. Degradation of 62.8% (based on BOD) occurred during the
28-day test. Raw data are not presented. Kinetics show steady biodegradation. The 10-day window was not met, but this is not strictly a criterion for this type of study. Achievement of >60% removal is indicative that the substance can be expected to meet the criteria for ready biodegradability. Validity criteria for the test were reported to be met.

CONCAWE (Lampi, 2010) have reported some experimental half-life data from a range of sources in fresh and marine water test systems. Many of the data are taken from EMBSI (2009), not described in detail and not available for review (see Letinskiet al. below). This is just part of a wider PBT assessment and validation exercise which is discussed in the environmental fate report (PFA, 2011b). The discussion reports that “degradation of iso-paraffins is influenced negatively by increased branching of the molecule, because complex branching hinders the initial oxidation and the subsequent lipid catabolism of the hydrocarbon molecules (Prince and Walters 2007).”

A poster (Letinskiet al., undated) summarises a novel testing method in which biodegradation in natural seawater is assessed for multi-constituent test substances. This may be the study EMBSI (2009) referenced in Lampi 2010 above, which was not available for review. Up to 35 individual constituents of low solubility (including linear and cyclic aliphatic hydrocarbons and aromatics; the carbon number range is not stated) were tested in a single test system using this method. The test substance mixtures were loaded using a passive dosing system via elution through a solution in silicone oil coated onto the surface of a tube. The individual test substances are in this way loaded below their respective water solubilities and the analytical recovery is indicated to be good. The test duration was 192 days. The objective of the study was to examine primary degradation, which was analysed by a solid phase micro-extraction technique and GC-MSD. Results are then compared vs predicted half-life using BIOHCWIN (refer to 4.1.2.1.2) There are a number of significant uncertainties in the study as described, which is necessarily brief given the format of a poster. The results show significant variability and scatter. It is not apparent how or whether it was truly possible to differentiate between primary degradation products of specific loaded compounds. Most importantly, the possibility of acclimation within the test system is readily apparent, and this is not discussed. The study is considered to be reliable, though the results are not necessarily meaningful for exposure assessment purposes for individual constituents. In respect of the aliphatic substance categories tested, the study drew the conclusion that BIOHCWIN is a conservative method for predicting biodegradation of hydrocarbons.