Fatty acids, tall-oil, manganese salts

Phototransformation in air

Description of key information

The assessment entity “tall oil” is a mixture of different saturated and unsaturated C16 -C18 fatty acids. Therefore, the endpoint is addressed with publicly available data on fatty acids with the same or a similar structure, including conservatively fatty acids with a shorter chain(i.e. C14) if relevant and appropriate in accordance with previously applied read-across approaches (U.S. EPA Fact Sheet, 2008).

A registration dossier shall contain information on the environmental hazard assessment (Regulation 1907/2006, Article 10). For the environmental hazard assessment of tall oil, the standard testing regime set out in Annexes VII to IX is adapted in accordance with Section 1.2 and 1.3 of Annex XI so that “testing does not appear to be scientifically necessary” as follows:

(I) The ecotoxic potential of the fatty acid (tall oil) is assumed to be negligible. Fatty acids are generally not considered to represent a risk to the environment, which is reflected in their exemption from the obligation to register (Annex V, Section 9 and Regulation (EC) No 987/2008).

(II) Fatty acids can enter air (particulate and vapour phases) but would breakdown very quickly by hydroxyl radical reaction and/or removed by wet and dry deposition (e.g. particulate-phase fatty acids) (Health Canada, 2017). Half-lives in air for tall oil were estimated taking into account the major components, oleic and linoleic acid (C18 fatty acids) as well as palmitric acid (C16 fatty acid). Based on the hydroxyl radical reaction at 25°C (AopWin v1.92; EPI Suite v4.1; 12-hr day; 1.5E6 OH/cm3), cis- and trans-isomers of oleic and linoleic acid are estimated to have half-live times of 1.699 and 1.544 hours and 0.998 and 0.892 hours, respectively and the half-live for palmitric acid was estimated with 6.530 hours. Based on the ozon reaction at 25°C (AopWin v1.92; EPI Suite v4.1; at 7E11 mol/cm3), cis- and trans-isomers of oleic and linoleic acid are estimated to have half-live times of 2.116 and 1.375 hours and 1.058 and 0.688 hours, respectively. Estimates could not be retrieved for palmitric acid since the QSAR database apparently does not contain a structure match (“Structure incompatible with current estimation method”). However, based on a similar generic “fatty acid” structure, half-life of the shorter-chain acid is expected to be comparable. Nevertheless, previous QSAR-based estimations with C8 to C18 fatty acids generally pointed to an increase with decreasing chain length with values ranging from 0.6 to 17.5 hours for e.g. C18 and C8 fatty acids, respectively (OECD SIDS, 2014).

(III) Level III fugacity modelling (EPI Suite v4.10) indicates that “aliphatic acids will distribute primarily to soil and water, with lesser amounts to air and sediment. With increasing chain length, the percent distributions to soil and sediment generally increase and the percent distributions to water and air generally decrease” (OECD SIDS, 2014).

In summary, these data point to a fast photodegradation of C16-18 fatty acids as contained in tall oil with half-live times in air of < 1 day. Taking into account that tall oil is expected to be readily biodegradable under aerobic conditions, further tests on the photodegradation of C16-18 fatty acids are not considered to be required.

 

References:

OECD SIDS initial assessment profile- aliphatic acids (2014), CoCAM 6 September 30-October 3, Italy/ICCA, p. 41

Health Canada’s PMRA, Pest Management Regulatory Agency (2017). Ammonium Salt of Fatty Acid Proposed Registration Decision PRD2017-04, p. 36