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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Based on the available data, simulation tests in surface water/sediment and soil are regarded as unnecessary due to a) the established persistence and b) the absence of toxic/adverse effects to the environment of this substance, as well as of the expected metabolites. 

Key value for chemical safety assessment

Additional information

Summary

No experimental simulation tests evaluating the potential of DiPE triisononanoate triethylhexanoate (CAS No. 68443-84-5) to degrade in surface waters/sediments are available. However, a simulation test would provide little additional data as the worst case for persistence (vP) was already established in an enhanced OECD 301 test (Muckle, 2012; see chapter 5.2.1 of the technical dossier). Taking all available information into account, the substance is assessed as not toxic or harmful to aquatic organisms, including microorganisms, and terrestrial organisms. In addition, the substance is not bioaccumulative. Enzymatic hydrolysis by carboxylesterases is yielding into 2-Ethylhexanoic acid, Isononanoic acid and Dipentaerythritol. However, due to the molecular weight range of 1053 g/mol and the high octanol/water partition coefficient of > 10 in combination the low water solubility (<0.05) enzymatic hydrolysis is expected to be slow. All metabolites are not bioaccumulative, nor toxic or harmful to the environment either (see public data on registered REACh substances on ECHA webpage; http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances). Therefore, DiPE triisononanoate triethylhexanoate (CAS No. 68443-84-5) and its metabolites, are unlikely to pose a risk for the environment in general and testing is thus omitted.

Intrinsic properties and fate

DiPE triisononanoate triethylhexanoate (CAS No. 68443-84-5) is not readily biodegradable. In fact, due the low degradation as observed in an enhanced test on ready biodegradation, the substance is regarded as very persistent (vP) according to the criteria laid out in Regulation (EC) No. 1907/2006. The constituents of DiPE triisononanoate triethylhexanoate (CAS No. 68443-84-5) exhibit very high log Kow´s (log Kow > 10) and a water solubility < 0.05 mg/L. The Guidance on information requirements and chemical safety assessment, Chapter R.7b (ECHA, 2012b) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Nevertheless, once this contact takes place, these substances are expected to be removed from the water column to a significant degree by adsorption to sewage sludge (Guidance on information requirements and chemical safety assessment, Chapter R.7a, ECHA, 2012a). Thus, discharged concentrations of these substances into the aqueous compartment are likely to be very low. Should the substances be released into the water phase, due to their hydrophobicity and expected high adsorption potential, they will tend to bind to sediment and other particulate organic matter, and therefore, the actual dissolved fraction available to fish via water will be reduced.

Bioaccumulation and metabolism

Estimated bioconcentration (BCF) and bioaccumulation (BAF) values were calculated for this substance using the BCFBAF v3.01 program (Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US EPA), including biotransformation rates (Arnot-Gobas method). Even though the substance is outside the applicability domain of the used model (model training set is constituted of substances with log Kow values in the range of 0.31 to 8.70), the calculations (especially the low BCF values calculated using the Arnot-Gobas method) reflect the biotransformation assumed for this substance. The calculated BCF and BAF values are < 1 L/kg (Arnot-Gobas method). BCF calculations reflect the bioaccumulation potential after uptake via water, whereas the BAF gives an indication of the bioaccumulation when all exposure routes (water, food, etc.) are taken into account.

This interaction between hydrophobicity, bioavailability and membrane permeability is considered to be the main reason why the relationship between the bioaccumulation potential of a substance and its hydrophobicity is commonly found to be described by a relatively steep Gaussian curve with the bioaccumulation peak approximately at log Kow of 6-7 (e.g., see Dimitrov et al., 2002; Nendza & Müller, 2007; Arnot and Gobas 2003). Substances with log Kow values above 10, which have been calculated for all main components are, however, again considered to have a low bioaccumulation potential (e.g., Nendza & Müller, 2007; 2010). Furthermore, for those substances with a log Kow value > 10 it is recognized by the relevant authorities that it is unlikely that they accomplish the pass level of being bioaccumulative according to OECD criteria for the PBT assessment (log BCF = 2000; ECHA, 2012a).

After uptake by organisms, biotransformation of the substance by carboxylesterases into 2-Ethylhexanoic acid, Isononanoic acid and the corresponding alcohols is expected. However, the molecular weight range of 1053 g/mol and the high octanol/water partition coefficient of > 10 in combination with the low water solubility, indicates a low absorption and correspondently slower hydrolysis rate for this substance. All three metabolites are not of concern for the environment. REACh registration dossiers of 2-Ethylhexanoic acid, Isononanoic acid and Dipentaerythritol are available and can be publicly viewed on the ECHA webpage (http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances).

Aquatic and terrestrial toxicity data

All available data show that DiPE triisononanoate triethylhexanoate (CAS No. 68443-84-5) is not toxic to aquatic organisms, including fish, algae and invertebrates in short and long term tests. In addition, the substance was found not to inhibit microorganisms, based on the high degradation as observed in the toxicity control of an OECD 301B test (Muckle, 2012). Furthermore, a chronic reproduction test to earthworm also resulted in no adverse effects up to the highest concentration tested (NOEC >= 1000 mg/kg soil dw, Eisner, 2013). Therefore, adverse effects of DiPE triisononanoate triethylhexanoate (CAS No. 68443-84-5) to the environment are not anticipated.

Conclusion

Based on the available data, simulation tests in surface water/sediment and soil are regarded as unnecessary due to a) the established persistence and b) the absence of toxic/adverse effects to the environment of this substance, as well of the expected metabolites.

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within the CSR.