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Photodegradation – Direct Photolysis

Direct photodegradation occurs through the absorbance of photons (typically in the wavelength range 290-700 nm) by a substance. If the absorbed energy is sufficiently high, the substance may undergo transformation. The most relevant kind of substance in Oxooil LS9 accessible to absorb light are olefins with one double bond (typical 27%), though they do not absorb light energy above 290 nm (Harris, 1982). Thus, direct photolysis will not significantly contribute to the degradation of LS9.


Photodegradation – Indirect Photolysis (Atmospheric Oxidation)

Indirect photodegradation was estimated using EpiSuite v4.11; AOP v1.92 (US EPA, 2012). This estimation method includes the calculation of atmospheric oxidation potential. Atmospheric oxidation is a result of hydroxyl radical or ozone attack instead of direct photochemical degradation.

Oxooil LS9 readily volatilizes to air and evaporate from water to air, where the substance undergoes reaction with photosensitized oxygen in the form of ozone and hydroxyl radicals.

The half-life for hydroxyl radical reaction (25 °C, OH radical concentration 1.5E06/cm³) ranges from 1.14 h to 15.49 h for the constituents of Oxooil LS9. With the constituents 3-Methylheptane, 3,4-Dimethylhexane, Octane (sum of typical concentrations 75%) having half-lifes of 14.5 – 15.5 hours.

For olefins, in addition, reaction with ozone occurs; half-lives range from 13.75 min to 22.92 h (25 °C, Ozone concentration 7E-11/cm³).

Overall, these results suggest that, once volatilized to the air, Oxooil LS9 will degrade rapidly with a worst case half-live of 15.5 h.


Stability in Water

The constituents of Oxooil LS9 are branched and linear alkanes and olefins, molecular structure which are not subject to hydrolysis. Thus, this degradative process will not contribute to their removal in the environment.



Oxooil LS9 was not readily biodegradable in an OECD TG 310 study; the substance reached a biodegradation rate of 6% in 28 days.

For Oxooil LS9, other than biotic degradation pathways are more relevant, e.g. photodegradation in the air, since the substance is highly volatile from water and soil. In the environment, the atmosphere is therefore the main target compartment. In the atmosphere, Oxooil LS9 undergoes rapid degradation by oxidation with OH-radicals (see Iuclid section 5.1.1. Phototransformation in air):half-lives for hydroxyl radical reaction range from 1.14 h to 15.49 h; for olefins, additionally reaction with ozone is possible; half-lives range from 13.75 min to 22.92 h.

For the relevance of atmospheric degradation for the entire environment (and the P-criterion), not only the rate of degradation in the atmosphere has to be considered: Also transport between compartments plays a major role. Volatilisation half-lives of all relevant constituents of Oxooil LS9 from a model river and lake were estimated to be 1.1 hours for river and 101.5 hours (4.2 days) for lake.

The half-life of the volatilization out of a lake of 4.2 days results, after 10 and 28 days, respectively, in a residual content of the substance of 19.2%, and 1% (elimination 80.8% and 99%, respectively). For comparison: a test for ready biodegradability is passed, if 60% degradation is achieved within 10 days (28 days for UVCB substances such as Oxooil LS9).A steady state, non-equilibrium fugacity model (Mackay level III model, included in EpiSuite v. 4.11) demonstrated that all relevant components will predominantly partition to water or volatilise into air to significant amounts (>90% partition to air and water; only <10% partition to sediment and soil) when using actual release rates Persistence times ranging from 80.9 to 273 hours (3.4 – 11.3 days) were calculated, which is significantly lower than the 960 hours of the persistence criterion in freshwater (40 days).



The estimation of the bioaccumulation of all relevant constituents of Oxoil LS9 by QSAR (EpiSuite v4.11, US EPA, 2012; BCFBAF v3.01) resulted in values ranging from 27.8 to 1220 L/kg for the constituents and a weighted mean of 326.5 L/kg. The highest BCF value of 1220 L/kg was obtained for one constituent present at low quantity in Oxooil LS9 - all other constituents have BCF values lower than 300 L/kg, which is below the cut-off of </=2000 L/kg. Therefore, the overall bioaccumulation potential of Oxooil LS9 is low.



The Koc of Oxooil LS9 was determined in a study according to OECD TG 121 resulting in a Koc of 1750 L/kg.


Henry’s Law Constant

Henry’s Law Constants of Oxooil LS9 were determined by QSAR (EpiSuite v4.11, US EPA, 2012; HENRYWIN v3.20) and range from 3.14 Pa-m³/mole (for the alcohol) and 8.92E+004 to 3.77E+005 Pa-m³/mole (for the hydrocarbons). These high values suggest that there is a high pressure for the Oxooil LS9 constituents to evaporate from water into air.

According to the Water Volatilization Model, volatilisation half-lifes are approx. 1 h (hydrocarbons) and 22.72 h (alcohol) in rivers and 101.5 h (hydrocarbons) and 343.6 h (alcohol) in lakes.


Distribution modelling

A Level III fugacity model calculates the distribution of a chemical under steady state, non-equilibrium conditions, can show the percent distribution, and estimates of chemical concentrations in each of the environmental compartments (air, water, soil, sediment, suspended sediment, biota) during constant emission into each compartment, advection and reaction.

Based on modelling, Oxooil LS9 has a high advection of the emissions from soil and water to air. Air is the compartment were reaction (OH-radicals) and degradation mainly takes place. Soil and Sediment are minor compartments for distribution.



Although the substance was not readily biodegradable in an OECD TG 310 study and hydrolysis is not considered to be a relevant pathway of degradation, the substance is not persistent according to fast reaction with OH-radicals in air (predominantely) and water in combination with a high fugacity in non-air compartments (water, soil, sediment) resulting in evaporation to air.

A fugacity model (Mackay level III model) demonstrated that the components will be degraded predominantly in air, with high advection from soil, water, sediment into air.

Volatilization from water is predicted to occur rapidly (hours to days), with Henry’s Law Constants (bond method) ranging from 3.14 Pa-m³/mole to 3.77E+005 Pa-m³/mole. Due to its volatility, photodegradation is the major pathway of degradation with half-lives for hydroxyl radical reaction ranging from 1.14 h to 15.49 h; for olefins, additionally reaction with ozone is possible; half-lives ranged from 13.75 min to 22.92 h. Overall, these results indicate fast photodegradation of the substance. Consideration of these degradation processes supports the assessment that the substance will degrade relatively rapidly in the environment and does not persist.




Harris JC (1982). Rate of Aqueous Photolysis.In:Handbook of Chemical Property Estimation Methods. Chapter 8 Edited by Lyman WJ, Reehl WF, and Rosenblatt DH. McGraw-Hill Book Company.