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

Endpoint summary

Additional information

Hydrolysis:

"Naphtha (Fischer Tropsch), light, C4-C10 - branched and linear", consists entirely of carbon and hydrogen and do not contain hydrolysable groups. As such, it has a very low potential to hydrolyse. Therefore, this degradative process will not contribute to its removal from the environment.  

Biodegradation:

The biodegradation of the read-across substance "Naphtha (petroleum), hydrotreated light" was investigated by OECD Test Guideline 301 F: Manometric Respirometry Test. Test item was biodegradable [mean of 83% ThOD at the end of the "10 day window"; 98% ThOD at the end of the test (28 days)]. This result could be veriefied by QSA calculation. Therefore, no further biodegradation studies are deemed necessary and "Naphtha (Fischer Tropsch), light, C4 -C10 - branched and linear" is considered as readily biodegradable.  

Phototransformation in air:

The predicted half life in air of respective hydrocarbons (C4 -C10, branched and linear) representing "Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear" ranges from 0.939 to 4.38 days. Therefore, test item can be considered as not persistent in the atmospheric compartment.  

Phototransformation in water and soil:

The direct photolysis of an organic molecule occurs when it absorbs sufficient light energy to result in a structural transformation. The absorption of light in the ultra violet (UV)-visible range, 110-750 nm, can result in the electronic excitation of an organic molecule. The stratospheric ozone layer prevents UV light of less than 290 nm from reaching the earth's surface. Therefore, only light at wavelengths between 290 and 750 nm can result in photochemical transformations in the environment. A conservative approach to estimating a photochemical degradation rate is to assume that degradation will occur in proportion to the amount of light wavelengths >290 nm absorbed by the molecule. Constituents of "Naphtha (Fischer Tropsch), light, C4 -C10 - branched and linear” contain hydrocarbon molecules that absorb UV light below 290 nm, a range of UV light that does not reach the earth's surface. Therefore, these substances do not have the potential to undergo photolysis in water and soil, and this fate process will not contribute to a measurable degradative loss of this substance from the environment.  

Adsorption / Desorption:

The determination of the adsorption coefficient was carried out using the HPLC screening method, EU Method C.19. To allow detection of the test material, which had a high affinity for the HPLC column stationary phase, fractions of eluent were collected from the HPLC instrument for analysis by gas chromatography (GC). The adsorption coefficient (Koc) of the "Naphtha (Fischer Tropsch), light, C4 -C10 - branched and linear" has been determined to be greater than 111 to 4.27 x 105(log Koc2.05 to >5.63). By fraction collection and subsequent GC analysis, 91.4% of the test material had a log10Koc value greater than 5.63, calculated from GC normalisation data.  

Distribution modelling:

The distribution of respective hydrocarbons (branched and linear, C4 -C10) in the environmental compartments, air, water, soil, and sediment, has been calculated using the level III fugacity model, included in EPI Suite model. Distribution ranges of linear hydrocarbons (C4, C7 and C10) is between 29.6 - 48.8 % to air, 50.6 - 69.1 % to water, while partitioning into soil or sediment does not exceed 1.73 % or 2.27 %, respectively. An overall range of the distribution of the respective, branched hydrocarbons (C4, C7 and C10) is between 1.8 - 38.5 % to air, 60.1 - 66.1 % to water, while partitioning into soil or sediment does not exceed 1.27 % or 0.867 %, respectively.

General information on biodegradation of alkanes by microorganisms:

Linear and branched alkanes (spanning the carbon number range of 'Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear') are aerobically and anaerobically biodegradable. Branched-chain alkanes are more difficult to degrade, however, several bacterial strains can degrade branched-chain alkanes such as isooctane. Many microorganisms (bacteria, filamentous fungi and yeasts) can degrade alkanes, using them as the carbon source. A typical soil, sand or ocean sediment contains significant amounts of hydrocarbon-degrading microorganisms, and their numbers increase considerably in oil-polluted sites. Alkanes are also produced by many living organisms such as plants, green algae, bacteria or animals. This probably explains why alkanes are present at low concentrations in most soil and water environments. Various alkane degraders are bacteria that have a very versatile metabolism, so that they can use as carbon source many other compounds in addition to alkanes. Most frequently, alkanes are not preferred growth substrates for these bacteria, which will rather utilize other compounds before turning to alkanes. On the other hand, some bacterial species are highly specialized in degrading hydrocarbons. They are called hydrocarbonoclastic bacteria and play a key role in the removal of hydrocarbons from polluted environments. Under strictly anaerobic conditions alkanes have to be activated through a mechanism that does not rely on O2. There are several bacterial strains able to use alkanes as carbon source in the absence of O2; these microorganisms use nitrate or sulfate as electron acceptor. Growth is significantly slower than that of aerobic alkane degraders. However, anaerobic degradation of alkanes plays an important role in the recycling of hydrocarbons in the environment. The strains analysed normally use a narrow range of alkanes as substrate. For example, strain BuS5, a sulfate-reducing bacteria that belongs to the Desulfosarcina/Desulfococcus cluster, assimilates only propane and butane or Azoarcus sp. HxN1, a denitrifying bacteria, uses C6–C8 alkanes.  

Conclusion:

If the UVCB substance 'Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear' is released to the environment, individual components will disperse and partition according to their individual physical-chemical properties. Their final dispositions are shaped by both abiotic and biotic processes. Based on modelling, individual structures encompassing the different types and molecular weights of hydrocarbons, volatilization to the atmosphere as well as distribution to water are important fate processes. As shown by QSAR calculation distribution to soil and sediment will likely be low and air and water will be the ultimate receiving environment for the main components of the UVCB substance. However, on release to water, 'Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear' will float on the surface and since it is poorly soluble in water, the only significant loss process is that of volatilisation. In air, these hydrocarbons are photodegraded by reaction with hydroxyl radicals, the quoted half lives varying from 0.963 up to 4.38 days (respective branched and linear hydrocarbons, C4-C10). Additionally, hydrolysis in water is not likely to occur, as the chemical linkages of respective hydrocarbons do not allow for these reactions. Biodegradation data show that the read-across substance Naphtha (petroleum), hydrotreated light, which consists of C6 and C7 and is thus very similar to ‘Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear' can exhibit a rapid rate of biodegradation and is considered readily biodegradable. Finally, since constituents are volatile and biodegradable, these substances would not persist due to partitioning and transformation processes.