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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

Bioaccumulation tests are waived based on the fact that the available information is deemed sufficient for classification purposes, the PBT assessment and the chemical safety assessment.

Key value for chemical safety assessment

BCF (aquatic species):
94 L/kg ww

Additional information

According to REACH Annex IX, information on bioaccumulation in aquatic species, preferably fish, is required for substances manufactured or imported in quantities of 100 t/y or more unless the substance has a low potential for bioaccumulation (for instance a log Kow ≤ 3). However, REACH aims to reduce animal testing where possible and according to the Integrated Testing Strategy (ITS, Figure R.7.10-2) in ECHA Guidance R.7c (Endpoint specific guidance), all available information should be assessed before further testing for bioaccumulation is performed.

For classification purposes an experimentally derived high quality Log Kow value is suitable when a measured BCF on an aquatic organism is not available. Nonanal has a measured log Kow of 3.4. This is below the CLP Regulation EC 1272/2008 cut-off value of 4. Thus Nonanal is not considered to have the potential to bioconcentrate for EU CLP classification purposes.

For the PBT and vPvB assessment a screening criterion has been established, which is log Kow greater than 4.5. According to ECHA Guidance Chapter R.11, the assumption behind this is that the uptake of an organic substance is driven by its hydrophobicity. For organic substances with a log Kow value below 4.5 it is assumed that the affinity for the lipids of an organism is insufficient to exceed the B criterion, i.e. a BCF value of 2000 L/kg (based on wet weight of the organism, which refers to fish in most cases). Nonanal has a measured log Kow of 3.4, which is below the B screening criterion.

For the chemical safety assessment, a reliable estimated BCF value may be used. A consensus modelling approach was employed to predict bioconcentration factors in fish.The experimentally determined high quality Log Kow value of 3.4 was used as an input term in three commonly used and scientifically valid QSARs. The estimated BCF values ranged from 65 to 155.

The BCF estimates of 125 L/kg and 155 L/kg obtained respectively from the Arnot-Gobas BCF QSAR (assuming a biotransformation rate of zero) and the linear model developed by Veith et al (1979) are considered conservative and worst-case.The Arnot-Gobas BCF QSAR (assuming a biotransformation rate of zero) was developed to fit upper bound BCF observations while the linear model developed by Veith et al (1979) is based on a limited data set of 56 chemicals, which are not expected to be metabolised.

Nonanal is readily biodegradable and it is generally accepted that readily biodegradable chemicals have a higher probability of being metabolised to a significant extent in exposed organisms than less biodegradable chemicals. In addition, an in vitro study for an analogue substance, dodecanal, shows that linear aldehydes are rapidly metabolised by trout liver S9 fractions. As such the Arnot-Gobas BCF QSAR(including biotransformation rate estimates) model predictions of 65 L/kg (upper trophic), 88 L/kg (mid trophic) and 94 L/kg (lower trophic) are considered to be more relevant and reliable. The BCFBAF regression-based model predicts a similar BCF value of 81 L/kg. Although this regression model does not include biotransformation estimates (no correction factor was applied for nonanal) it was developed from a large data set of 396 diverse chemical and as such has a tendency to arrive at an average BCF value. The highest value of 94 L/kg from the Arnot-Gobas BCF QSAR(including biotransformation rate estimates) has been chosen as a relevant and reliable conservative estimate for risk assessment purposes. Using this predicted BCF value, the chemical safety assessment does not show a need for further refinement.