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Hydrolysis is a reaction in which a water molecule or hydroxide ion substitutes for another atom or group of atoms present in a chemical resulting in a structural change of that chemical. Potentially hydrolyzable groups include alkyl halides, amides, carbamates, carboxylic acid esters and lactones, epoxides, phosphate esters, and sulfonic acid esters (Neely, 1985). The lack of a suitable leaving group renders compounds resistant to hydrolysis.

This chemical substance consists entirely of carbon and hydrogen and does not contain hydrolyzable groups. As such, it has a very low potential to hydrolyze. Therefore, this degradative process will not contribute to its removal from the environment.

Phototransformation in air:

The rate constant of the reaction between n-pentane and OH-radicals has been measured by several researchers. The result of the experiments have been reported and reviewed by Atkinson (1985). The reported values are between 3.5 and 5.3 E-12 cm3/(molecule.sec) at 300K (27C). On the basis of the review of available data Atkinson recommends a rate of 4.06.10-12 cm3/ (molecule.sec). The latter value has been used in the risk assessment. Taking into account the OH-radical concentration as given in the TGD of 5 E5 molecules/cm3, atmospheric half-life of n-pentane is estimated to 3.95 days.

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. This substance contains hydrocarbon molecules that absorb UV light below 290 nm, a range of UV light that does not reach the earth's surface. Therefore, this substance does 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.


n-Pentane biodegraded to an extent of 87% after 28 days. The data support characterizing the test substance as readily biodegradable, not expected to persist in the environment under aerobic conditions.

Adsorption / desorption:

The Koc of n-pentane was calculated from Log Kow 3.45 using the TGD calculation of Koc = 0.81 . Log Kow + 0.1. The Koc was cited as the key reference in the EU Risk Assessment Report for n-pentane and so is considered suitable as a key study for this endpoint. This value indicates that although the adsorptivity of n-pentane is moderate it sill has good mobility in the environment.

Distribution modelling:

The distribution of the substance in the environmental compartments, air, water, soil, and sediment, has been calculated using the PETRORISK Model, version 5.3. Computer modeling is an accepted method for estimating the environmental distribution of chemicals. Distribution modeling results are included in the 'Multimedia distribution modeling results' tab in the PETRORISK spreadsheet attached to IUCLID section 13.