C8-C26 branched and linear hydrocarbons – Distillates

Biodegradation in water: screening tests

Description of key information

OECD 301F: 68% biodegradation after 28 days (on the basis of oxygen consumption), conclusion: readily biodegradable. The test item failed to meet the 10-Day window validation criterion. However, in accordance with the Revised Introduction to the OECD Guidelines for Testing of Chemicals, Section 3, Paragraph 43 (Page 8), if testing on a complex mixture is performed, and it is anticipated that a sequential biodegradation of the individual structures takes place, then the 10-Day window should not be applied to interpret the results of the test. Based on chemical analysis, 94% removal of test item was observed over the test period. 

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The key ready biodegradation study is a recently conducted test performed with Distillates (Fischer-Tropsch), C8-26 – branched and linear, in accordance with OECD 301F (manometric respirometry) and in compliance with GLP (Mead, 2014). The substance was introduced into test flasks by first adsorbing 50 mg onto glass-fibre filter paper supported on aluminium foil prior to addition into the test vessel. The test substance concentration was 100 mg/l. A glass-fibre filter paper supported on aluminium foil was also added to each control and reference item vessel to maintain consistency between these vessels and the test item vessels. The system consisted of a sample flask sealed by a sensor head/CO₂trap immersed in a temperature controlled water bath. The inoculum was non-adapted activated sludge sampled from a municipal waste water treatment plant treating predominantly domestic sewage. Assessment of biodegradation was made by oxygen consumption and chemical analysis using gas chromatography.

At the end of the 28 day test period, the test substance had attained 68% biodegradation on the basis of oxygen consumption and the substance was therefore considered to be readily biodegradable. Based on chemical analysis, 94% removal of test item was observed over the test period.

 

Battersby and Bumpus (2001) report results of OECD 301 F tests performed on two samples of Distillates, (Fischer-Tropsch), C8-26 – branched and linear (sample nomenclature in the test report SMDS-1 and SMDS-2; no further information available about sample characteristics or composition, though it is stated that both samples contained an antioxidant additive). The substances were introduced on to glass-fibre filter paper suspended over foil; the paper and foil were both added to the flask. The test substance concentration was 30 mg C/l. For neither method is there any indication of steps being taken to minimise or prevent evaporation during test substance loading or during the test. The inoculum was non-adapted activated sludge sampled from a municipal waste water treatment plant treating predominantly domestic sewage. The concentration of sludge in the test system was 30 mg as dry solids/l. Assessment of biodegradation in both tests was made by oxygen consumption analysis only. At the end of the 28 day test period, high levels of degradation were achieved for both samples: Based on fraction of the theoretical oxygen demand (ThOD), SMDS-2 reached 75% removal and the 10-day window criterion was met. SMDS-1 reached 74% removal, rapidly biodegradable but for this sample the 10-day window was not met. By comparison, the same study also reported a result of 60% ThOD in 28 days for an ultra low sulfur diesel fuel (ULSD), and values in the range 59% – 68% removal for blends of the SMDS samples with ULSD. The study concludes that one of the two samples of SMDS (Distillates (Fischer-Tropsch), C8-26-branched and linear) is readily biodegradable meeting the 10-day window; the other sample fails the 10-day window criteria by a small margin. The plotted degradation levels over time demonstrate a relatively smooth ongoing increase in degradation.

The ready biodegradability of a comparable product (Sasol SPDTM Diesel) has been studied using the manometric respirometry method, OECD 301F (Albertus and Phillips, 2005). The composition is not discussed in the study report but an average carbon number of C13 is evident in the ThOD calculation. The substance was loaded onto glass fibre filter papers and added to the test flasks. The test substance concentration was ca. 27 mg/l. There is no indication of steps being taken to minimise or prevent evaporation during test substance loading or during the test. The inoculum was ‘return-water’ containing microorganisms sampled from a waste water treatment plant dedicated to treat only domestic sewage. The concentration of sludge in the test system was not stated but it is reported that the oxygen uptake of the inoculum blank was within the acceptable range. The progress of biodegradation was monitored via O₂uptake only. At the end of the 28 day test period, based on fraction of the theoretical oxygen demand (ThOD), greater than 75% removal was achieved and the 10-day window criterion was met. Validity criteria were reported to be met. The raw data were not presented in the report.

A study of the ready biodegradation of Distillates (Fischer-Tropsch), C8-26-branched and linear has been conducted (Xue Han, 2009a). The study was conducted in accordance with OECD Guideline 301B. In this study two alternative methods were used to introduce the test substance into the test system. In test 1, the substance was adsorbed on to silica gel. The test substance concentration was 16.4 mg C/l. In test 2, the substance was introduced on to glass-fibre filter paper suspended over foil; the paper and foil were both added to the flask. The test substance concentration was 15.3 mg C/l. For neither method is there any indication of steps being taken to minimise or prevent evaporation during test substance loading or during the test. The inoculum was non-adapted activated sludge sampled from a municipal waste water treatment plant treating predominantly domestic sewage. The concentration of inoculum in the test system was 30 mg suspended solids/l. The study determined, as far as possible, the absence of inhibition of microorganisms by the test substance. Assessment of biodegradation in both tests was made by CO₂analysis only. At the end of the 28 d test period, 8.4% degradation was reported for test 1 and 39.5% in test 2. The kinetics show clearly that a plateau was reached early in both tests followed by increasing degradation late in the test (for test 2 in particular a significant increase in percent degradation is seen between days 25 – 28). This is suggestive of rapid degradation of some constituents with a lag period for others. In view of the use of CO₂analysis only, it is not possible to interpret the results further than this or discriminate between constituents. The increased surface area available in the test system associated with the presence of the filter paper may have played a role in the higher degradation levels achieved in test 2. The study was conducted in accordance with GLP. Whilst there is not strong evidence that the test had significant methodological deficiencies, the result showing such low degradation is surprising for this carbon chain range, conflicting with findings in other tests with similar samples, and casts significant doubt on this study, which is therefore disregarded for the present purpose. Distillates (Fischer-Tropsch), C8-26-branched and linear was not readily biodegradable in this study.

To investigate and further clarify the results of the first OECD 301B study (Xue Han 2009), a further OECD 301B test was performed in compliance with GLP, with additional chemical analysis (Bayliss, 2014). The test item, at a concentration of 10 mg Carbon/L, was exposed to activated sewage sludge microorganisms with mineral medium in sealed culture vessels in the dark at 21±1°C for 28 days. As with Test 2 in the Xue Han study, test material was introduced to the test vessels by first adsorbing to glass fibre filter paper. The test substance attained 44% degradation in 28 days on the basis of CO₂evolution; 0% degradation was observed in abiotic control vessels. However, chemical analysis of the biotic and abiotic test preparations by gas chromatography showed measured test concentrations of less than the limit of quantitation of the analytical method employed at Day 29. The results of chemical analysis indicate significant loss of test material through abiotic processes, for example evaporative loss due to aeration of test vessels. It is therefore considered that the OECD 301B method is not appropriate for this test substance and the results of the first OECD 301B study (Xue Han 2009) should be disregarded. The same applies to the following OECD 301B study with the related substance GTL Kerosine ("C8 -C16"):

A biodegradation test has been performed using Kerosine (Fischer-Tropsch), full range, C8-16-branched and linear (Zhang, 2009). The study was conducted in accordance with OECD Guideline 301B. The test substance was introduced into the test system by being adsorbed on to silica gel. The test substance concentration was 15.5 and 15.9 mg C/l in the two tests. There is no indication of steps being taken to minimise or prevent evaporation during test substance loading or during the test. The inoculum was non-adapted activated sludge sampled from a municipal waste water treatment plant treating predominantly domestic sewage. The concentration of inoculum in the test system was 30 mg suspended solids/l. The study determined, as far as possible, the absence of inhibition of micro-organisms by the test substance. Assessment of biodegradation in both tests was made by CO₂analysis only. At the end of the 28 d test period, 14.25% degradation was reported. The kinetics appear to show that the degradation proceeded smoothly with a short period of slightly increased degradation in the final days of the test. In view of the use of CO₂analysis only, it is not possible to interpret the results further than this or discriminate between constituents. The study was conducted in accordance with GLP. Whilst there is not strong evidence that the test had significant methodological deficiencies, the result showing such low degradation is surprising for this carbon chain range, conflicting with findings in other tests with similar samples, and casts significant doubt on this study, which is therefore disregarded for the present purpose. Kerosine (Fischer-Tropsch), full range, C8-16-branched and linear was not readily biodegradable in this study. However, additional analysis performed in a more recent study (Bayliss, 2014) indicates that this test method is not suitable for the test material and the results can be disregarded, as discussed above.

Information on related substances (CAS 64742 -47 -8 and CAS 64742 -48 -9), which might be also used to conclude that the substance is readily biodegradable:

Test type: ready biodegradability activated sludge, domestic (adaptation not specified) OECD Guideline 301F (Ready Biodegradability – Manometric Respirometry)	% Degradation of test substance:   68-70% (O2consumption)	2 (reliable with restrictions) Supporting study read-across from supporting substance (structural analogue or surrogate) Test material: C11-15 n- and iso-alkanes (52%) and C10-15 cycloalkanes (46%)  (CAS: 64742-47-8)	Battersby, Bumpus and Eagle, 1997a
Test type: ready biodegradability activated sludge, domestic (adaptation not specified) OECD Guideline 301F (Ready Biodegradability – Manometric Respirometry)	% Degradation of test substance:   80% after 28 d (O2consumption)	2 (reliable with restrictions) Supporting study read-across from supporting substance (structural analogue or surrogate) Test material: C9-13 n- and iso-alkanes (60%) and C9-11 cycloalkanes (38%) (CAS: 64742-48-9)	Battersby, Bumpus and Eagle, 1997b

A study of ready biodegradability of C11-15 n- and iso-alkanes (52%) and C10-15 cycloalkanes (46%) is available (Battersby, Bumpus and Eagle, 1997a). The tested substance lies within the carbon number range for GTL Gasoil, but some of the longer chain constituents are not represented in the substance used in this test. This method uses the guideline method OECD 301F (manometric respirometry) and is compliant with GLP. The inoculum is municipal WWTP sludge pre-conditioned with filtration and aeration. Alongside the test substance, a positive control, inhibition control and blank were tested. Due to low solubility the test substance (18 µL/L, equivalent to 14 mg/l) was loaded by injection into the test vessels below the surface, with magnetic stirring. The test report does not refer to any visible phase separation. The test substance was degraded by approx. 68-70% after 28 d based on oxygen uptake, but only ca. 48% degradation within the 10-day window occurred. The validity criterion relating to variation between replicates was not met; this was ascribed in the study report to insolubility / volatility of test substance, and assumed not to impact the interpretation. The kinetics display a short initial lag phase; a plateau was not reached by the end of the test. The test substance was considered readily biodegradable not meeting the 10-day window.

A study of ready biodegradability of C9-13 n- and iso-alkanes (60%) and C9-11 cycloalkanes (38%) is available (Battersby, Bumpus and Eagle, 1997b). The test substance lies within the carbon number range for GTL Gasoil, but some of the longer chain constituents are not represented in the substance used in this test. This method uses the guideline method OECD 301F (manometric respirometry) and is compliant with GLP. The inoculum is municipal WWTP sludge pre-conditioned with filtration and aeration. Alongside the test substance, a positive control, inhibition control and blank were tested. Due to low solubility the test substance (19 µl/l , equivalent to 15 mg/l) was loaded by injection into the test vessels below the surface, with magnetic stirring. The test report does not refer to any visible phase separation. The test substance was degraded by approx. 80% after 28 days based on oxygen uptake, but only ca. 52% degradation within the 10-day window occurred. The validity criteria were met. The kinetics display a short initial lag phase; a plateau was not reached by the end of the test. The test substance was considered readily biodegradable not meeting the 10-day window.