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Environmental fate & pathways

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Phototransformation in air

Hydrocarbons, C14 -C20, aliphatics, ≤2% aromatics are UVCBs. Therefore, the phototransformation in air was estimated from the AOPWIN v1.92 calculations of phototransformation of selected hydrocarbons likely to be constituents of Hydrocarbons, C14 -C20, aliphatics, ≤2% aromatics. The single representative hydrocarbons were selected among all the classes and the whole carbon range of the category.

 

The phototransformation rate is in the range 12.59 - 42.13 x 10-12cm3/molecule/sec. The calculated half-lives are in the range 0.254 - 0.850 d (3.047 -10.195 hrs). These values are largely below the trigger limit (2 days). Therefore, Hydrocarbons, C14-C20, aliphatics, ≤2% aromatics are not persistent.

 

The phototransformation rate for icosane is 25.24 x 10-12cm3/molecule/sec. The calculated half-life is 0.424 d (5.085 hrs). This value is largely below the trigger limit (2 days). Therefore, icosane is not persistent.      

 

Hydrolysis

 

Hydrolysis is a reaction in which a water molecule of hydroxide ion substitutes for another atom of group of atoms present in a chemical resulting in a structural change of that chemical. Potentially hydrolysable groups include alkyl halides, amides, carbamates, carboxylic acid esters and lactone epoxides, phosphate esters, and sulfonic acid esters. The lack of a suitable leaving group renders compounds resistant to hydrolysis.

 

The chemical constituents that comprise hydrocarbons, C14-20 Aliphatics (≤2% aromatics) consist entirely of carbon and hydrogen and do not contain hydrolysable groups. As such, they have a very low potential to hydrolyze. Therefore, this degradative process will not contribute to their removal from the environment.

 

Phototransformation in water

 

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. Hydrocarbons, C14-C20, aliphatics, ≤2% aromatics contain hydrocarbon molecules that absorb UV light below 290 nm, a range of UV light that does not reach the earth's surface. Therefore, Hydrocarbons, C14-C20, aliphatics, ≤2% aromatics 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 these substances from the environment.

 

Phototransformation in 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. Hydrocarbons, C14-C20, aliphatics (≤2% aromatics) contain hydrocarbon molecules that absorb UV light below 290 nm, a range of UV light that does not reach the earth's surface. Therefore, Hydrocarbons, C14-C20, aliphatics (≤2% aromatics) do not have the potential to undergo photolysis in soil, and this fate process will not contribute to a measurable degradative loss of these substances from the environment.

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