Naphtha (Fischer-Tropsch), light, C4-10-branched and linear

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: scientifically acceptable method

Justification for type of information:

QSAR prediction: migrated from IUCLID 5.6

Qualifier:

no guideline required

Principles of method if other than guideline:

For the estimation/calculation the percentages by weight and the mean percentages of branching have been used to determine a composition of a typical sample of the substance 'Naphtha (Fischer-Tropsch), light, C4-C10 - branched and linear'. This composition has been used as the basis for modelling biodegradability.

GLP compliance:

no

Remarks:

not applicable (estimated by calculation)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
not applicable

Oxygen conditions:

other: not applicable (QSAR)

Inoculum or test system:

other: not applicable (QSAR)

Details on inoculum:

not applicable (QSAR)

Duration of test (contact time):

ca. 28 d

Parameter followed for biodegradation estimation:

other: Calculation of "ready biodegradability"

Details on study design:

not applicable (QSAR)

Reference substance:

other: not applicable (QSAR)

Preliminary study:

not applicable (QSAR)

Test performance:

not applicable (QSAR)

Parameter:

other: calculation

Value:

> 60

Sampling time:

28 d

Remarks on result:

other: 67.5% of test substance is predicted to be readily biodegradable and passing the 10-day window ; 22.5% of test substance is predicted to be readily biodegradable but not passing the 10-day window and 10% would be inherently biodegradable.

Details on results:

The biodegradability of the chemical components of the substance has been predicted in accordance with the methods described in 'Principles of method if other than guideline'. The results of applying these methods to a typical composition show that 67.5% of the mass of the substance would be considered readily biodegradable, passing the 10-day window (RB10), 22.5% would be readily biodegradable not passing the 10-day window (RBN) and 10% would be inherently biodegradable (INH).

Results with reference substance:

not applicable (QSAR)

Validity criteria fulfilled:

not applicable

Interpretation of results:

readily biodegradable

Conclusions:

A reasonable conclusion that can be drawn is that, Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear, should be considered to be readily biodegradable. The substance would therefore be classed 'readily biodegradable'.
Test data found in the literature support this conclusion: Biodegradation studies are available for two related substances. Biodegradation studies of Naphtha (petroleum), hydrotreated light (CAS No. 64742-49-0) reported 89% and 98% degraded in 28 days. The study was conducted to OECD Guideline 301F (CEFIC-HSPA 2002). A biodegradation study of Naphtha (petroleum), hydrotreated heavy (CAS No. 64742-48-9 reported 10% degraded in 28 days. This was a closed bottle study, not appropriate to poorly soluble substances (Exxon Biomedical Sciences, Inc.1988).
Moreover, measured data for representative individual components, e.g. hexane (confidential IUCLID), 2-methylpentane (confidential IUCLID), 2-methylbutane (Solano-Serena, 2000) and n-decane (Verschueren, 1983; Wakeham, 1986) are also in agreement with the degradabilities that have been assigned when predicting the biodegradability of the substance. It should be noted that the original study reports have not been reviewed.

Executive summary:

QSAR calculations were performed to estimate the biodegradability of the test substance. A reasonable conclusion that can be drawn is that, Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear, should be considered to be readily biodegradable.

Test data found in the literature support this conclusion: Biodegradation studies are available for two related substances. Biodegradation studies of Naphtha (petroleum), hydrotreated light (CAS No. 64742-49-0) reported 89% and 98% degraded in 28 days. The study was conducted to OECD Guideline 301F (CEFIC-HSPA 2002). A biodegradation study of Naphtha (petroleum), hydrotreated heavy (CAS No. 64742-48-9 reported 10% degraded in 28 days. This was a closed bottle study, not appropriate to poorly soluble substances (Exxon Biomedical Sciences, Inc.1988). Moreover, measured data for representative individual components, e.g. hexane (confidential IUCLID), 2-methylpentane (confidential IUCLID), 2-methylbutane (Solano-Serena, 2000) and n-decane (Verschueren, 1983; Wakeham, 1986) are also in agreement with the degradabilities that have been assigned when predicting the biodegradability of the substance. It should be noted that the original study reports have not been reviewed.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH

The rational for the analogue approach is the high structural similarity between source and target substance. Both substances, ‘Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear’ and ‘Naphtha (petroleum), hydrotreated light’ belong to a class of chemicals that is comprised almost entirely of aliphatic constituents. The only functional groups are alkyl side chains, which are found on most if not all constituents other than the n-alkanes. Both substances contain of the same types of hydrocarbon constituents, which are variable in carbon chain length. ‘Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear’ is a complex UVCB containing normal and iso-paraffins of chain length C4-C10, while ‘Naphtha (petroleum), hydrotreated light’ (CAS 64742-49-0; EC 265-151-9) consists of hydrocarbons having carbon numbers predominantly in the range of C4 through C11.
Due to the similarities in structure, composition and functional groups, similar physico-chemical properties of the substances are to be expected, which would result in similar toxicokinetic behaviour and most likely also in very similar toxicodynamic and toxicological behaviour. Due to their overlapping hydrocarbon constituent profile, using data from this related substance is reasonable.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)

Source and target chemicals are mixed liquids of which the primary constituents are straight chain (n-), branched chain (iso-), and cyclic aliphatic hydrocarbons or combinations thereof. Cyclic hydrocarbons, if present, represent less than 5% of the total volume of the target substance ‘Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear’ (CAS 848301-65-5; EC 481-730-0). The source chemical ‘Naphtha (petroleum), hydrotreated light’ (CAS 64742-49-0; EC 265-151-9) contains a higher level of cycloparaffins (C6 cycloalkane 28%; C7 cycloalkane 10%) and 53% C7 iso-paraffins (compare table 1).
Both chemicals are UVCB substances for which it is not possible to provide a molecular formula, molecular weight, SMILES codes or an extent of impurities. The main general molecular formula is CnH(2n+2).

Table 1: Composition of ‘Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear’

Compound Target:
Naphtha (Fischer-Tropsch)

Butane (C4) 0-2%
Pentane (C5) 5-15%
n-Hexane (C6) 10-30%
Heptane (C7) 10-30%
Octane (C8) 10-30%
Nonane (C9) 2-10%
Decane (C10) 0-2%
Undecane (C11) n.a.
Branched paraffins 20-40%
> C10 branched and linear paraffins 0-10%
Cyclic hydrocarbons 0-5%
Aromatic hydrocarbons 0-2%
Olefins 0-1%


3. ANALOGUE APPROACH JUSTIFICATION

Due to the above-mentioned similarities of source and target chemical, with regard to their structure, functional groups, composition, toxicokinetic and toxicological behaviour, it can be reasonably concluded that a similar behaviour can be expected.
Based on their analogue chemical profiles, the toxicity will not be significantly different among them.

4. DATA MATRIX

Both, target and source substance, are readily biodegradable. They are also concluded to not qualify as persistent, bioaccumulative and toxic (PBT), or very persistent, very bioaccumulative (vPvB) substances. Hydrocarbon molecules in this range are not well absorbed from the intestinal tract and very poorly absorbed through the skin. However, once absorbed, these molecules are relatively rapidly metabolized and excreted.

Table 2: Physical and chemical properties

Physical/chemical properties Target: Source:
Naphtha (Fischer-Tropsch), light, Naphtha (petroleum), hydrotreated light
C4-10 - branched and linear

Physical state at 25°C Liquid Liquid
Carbon number range C4-C10 C4-C11
Colour Colourless Colourless
Boiling temperature range 62°C to 181°C 20°C to 190°C
Solubility in organic solvents Substance is an organic solvent Substance is an organic solvent
Explosivity Not explosive Not explosive
Oxidising potential No No
Stability in organic solvents Stable Stable
Water solubility Insoluble Insoluble

Reason / purpose for cross-reference:

read-across source

Test performance:

None

Key result

Parameter:

% degradation (O2 consumption)

Value:

98

St. dev.:

12

Sampling time:

28 d

Parameter:

% degradation (O2 consumption)

Value:

83

St. dev.:

16

Sampling time:

10 d

Remarks on result:

other: Biodegradation at the end of the "10 day window"

Description of key information

- 98% ThOD (28 days); < 60 % ThOD (10 days) [OECD 301; read-across substance: "Naphtha (petroleum), hydrated light"

- readily biodegradable [QSAR, "Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear"]

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear is considered to be readily biodegradable based on a read-across study with the structurally related substance "Naphtha (petroleum), hydrated light" and QSAR calculation

Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear is considered to be readily biodegradable based on a read-across study with the structurally related substance “Naphtha (petroleum), hydrated light” and QSAR calculation.

 

Estimated data

Biodegradation of the constituents of GTL Naphtha was predicted initially using the Syracuse Research Corporation BIOWIN program, and validated using published data (PFA, 2009).

 

Although the concept of the 10-day window is not applicable to UVCB substances, the term is retained when individual constituents are discussed (OECD, 2006).

 

Predicted degradation ratings range from ‘readily biodegradable, meeting 10-day window’ for shorter chain, linear constituents to ‘inherently biodegradable, not meeting specific criteria’ for longer chain, highly branched constituents, as shown in the table. No constituents of Fischer-Tropsch process-derived substances are considered likely to be non-biodegradable.

 

On the basis of measured data, the judgement was made to use the BIOWIN Ultimate Model outputs as follows:

Constituents with output >3.2 were ascribedReadily Biodegradable, meeting the 10-day window(termed herein RB10)

>2.8 were ascribed Readily biodegradable, not meeting the 10-day window (RBN)

>2.4 were ascribed Inherently biodegradable, fulfilling the criteria (INHY)

<2.4 were ascribed Inherently biodegradable, not fulfilling the criteria (INHN).

 

These ratings are used as inputs for the SimpleTreat model within the EUSES program, used to determine fate in a waste water treatment plant.

 

Biodegradation rating for the constituents of GTL Naphtha

Carbon Number	Type	BIOWIN (Ultimate)	Ready biodegradation rating[1]
4	Linear	3.3691	RB10
4	Branched	3.0707	RBN
4	Cyclic	n/a	n/a
5	Linear	3.3381	RB10
5	Branched	3.0397	RBN
6	Linear	3.3071	RB10
5	Cyclic	3.0442	RBN
6	Branched	3.0087	RBN
6	Cyclic	3.0132	RBN
7	Linear	3.2761	RB10
7	Branched	2.9777	RBN
7	Cyclic	2.9822	RBN
8	Linear	3.5434	RB10
8	Branched	3.2451	RB10
8	Cyclic	2.9512	RBN
9	Linear	3.5124	RB10
9	Branched	3.2141	RB10
9	Cyclic	2.9202	RBN
10	Linear	3.4814	RB10
10	Branched	3.1831	RBN
10	Cyclic	3.1875	RBN
11	Linear	3.4504	RB10
11	Branched	3.1521	RBN
11	Cyclic	3.1565	RBN

 

 

Since that assessment, a further development of the assessment has been to use the program BIOHCWIN; this model is more tailored to structural descriptions of the constituents. Additional information is given in the attached QM(P)RF documents.

[1]RB10 = Readily biodegradable meeting 10-day window; RBN = Readily biodegradable not meeting 10-day window; INHY = Inherently biodegradable meeting specific criteria; INHN = Inherently biodegradable not meeting specific criteria.