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Sediment toxicity

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Description of key information

Toxic effects on sediment dwelling invertebrates are not expected.	

Key value for chemical safety assessment

Additional information

Octanoic acid (CAS 124-07-2) has a log Kow of 3.05 (HSDB by Hansch et al. 1995) and a log Koc of 2.05 (ChemProp v6.4, Franco, Fu & Trapp model for ionizable substances, estimated from log Kow of 3.05, pKa of 5.3 and pH 7). Thus, the potential to adsorb or bind onto sediment is expected to be low. According to the Guidance on information requirements and chemical safety assessment, R.7b (ECHA, 2017) the equilibrium partitioning method (EPM) can be applied as a first screen to derive the PNEC sediment, in order to conduct a screening risk assessment for the sediment compartment (PEC/PNECsed). As the environmental exposure assessment indicates no risk for the sediment compartment (all Risk Characterisation Ratios (RCR) < 1; please refer to Chapter 9 and 10 of the Chemical Safety Report for detailed information), no risk for the sediment compartment is indicated and further tests are not needed.

In addition, the substance is determined to be readily biodegradable and according to the Guidance on information requirements and chemical safety assessment, Chapter R.7b (ECHA, 2017), readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs). Therefore, this substance has a low potential for persistence and chronic exposure of sediment organisms is unlikely.

Furthermore, as the substance has a high water solubility (680 mg/L at 20 °C) and low potential to adsorb to sediment particles (log Koc of 2.05), the compartment of environmental distribution is water and not sediment. Based on the aquatic toxicity data, Octanoic acid (CAS 124-07-2) is classified as Aquatic Chronic 3 according to CLP. Sediment testing is not relevant for classification purposes and thus no change in classification is triggered by sediment data. Since no high adsorption or binding behavior to sediment particles is expected and the all RCR’s are < 1, no risk for the sediment compartment is indicated and no further testing is considered necessary.

Moreover, fatty acids occur in sediment and soils naturally and are part of physiological pathways. The bioaccumulation potential of Octanoic acid (CAS 124-07-2) is expected to be low i.e. based on log D of 1.34 (pH 7), metabolisation and excretion processes and low BCF values of 225 L/kg after 28 days (OECD 305 E, 1999) from a read-across substance and 83.64 L/kg (EPISuite, BCFBAF, Arnot-Gobas model) based on QSAR. For sediment-dwelling organisms the main uptake route will be ingestion of contaminated sediment. In the case of ingestion, fatty acids are used by sediment organisms as an energy source and for anabolic processes as well. In anabolic processes fatty acid carbon is incorporated into the biological matrix of the organism. The suitability as an energy source was demonstrated by the ready biodegradability of the substance, which is used from microorganisms as energy source by degrading the substance to carbon dioxide. Therefore, fatty acids are generally not considered to be harmful either to sediment organisms. Hence, in case of exposure to sediment, the substance is expected to rapidly dissipate either by degradation or by integration into the organism matrix. Therefore sediment is not expected to be a compartment of concern and the risk to sediment organisms is negligible.

Based on the low adsorption potential, a RCR < 1, water as compartment of environmental distribution, the use of fatty acids as energy source, low bioaccumulation potential and low potential for persistence, it can be concluded that Octanoic acid (CAS 124-07-2) is not expected to be harmful to sediment organisms.