Hexadecan-1-ol

Endpoint summary

Additional information

Short term toxicity

Fish

A 96 h LC₅₀ value of >0.4 mg/L has been determined for the effects of hexadecan-1-ol on mortality of Oncorhynchus mykiss (Safepharm, 1996). The substance is therefore non-toxic at the limit of solubility, LC₅₀ >0.024 mg/L.

 

Invertebrates

No measured data are available for short-term toxicity to aquatic invertebrates. This endpoint has been calculated based on a validated reliable QSAR method. Hexadecan-1-ol has been predicted to be non toxic at the limit of solubility, therefore the EC₅₀ is >0.024 mg/L.

 

Algae

A 96 h EL₅₀ value of 100 mg/L and an EL₅₀ value of >1000 mg/L have been determined for the effects of hexadecan-1-ol on growth rate of Scenedesmus subspicatus. These results are much higher than the limit of solubility of the test substance and should be treated with caution; the test substance did not appear to be toxic at the limit of solubility. Therefore the EL₅₀ is >0.024 mg/L (>Limit of Solubility).

 

Micro-organisms

At or above the limit of water solubility, the registered substance has no significant inhibitory effects on respiration of activated sludges or specific microbial strains relevant to WWTP, based on consistent category evidence for C6-24 aliphatic alcohols. There is no hazard for WWTP microorganisms.

 

Long term toxicity

Fish

In accordance with Column 2 of REACH Annex IX, the long-term aquatic toxicity to fish study (required in Section 9.1.6) does not need to be conducted as the chemical safety assessment according to Annex I indicates that this is not necessary.

 

Invertebrates

According to REACH Annex XI, section 1, the studies required in Annex 9.1.5, are not needed for linear alcohols with carbon chains >C15 because sufficient information is available to predict no toxicity at their limit of solubility. Moreover, from experience gained in tests that have been conducted with substances in this category, considerable technical difficulties would be expected in the conduct of such a test, due to the very rapid biotic removal of the substance from the test system.

 

 

Sediment

In accordance with Column 2 of REACH Annex X, long-term toxicity testing with sediment organisms (required in Section 9.5.1) is not needed as the chemical safety assessment according to Annex I indicates that this is not necessary.

 

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

Many short-term aquatic toxicity tests have been carried out on this family of long chain aliphatic (LCAAs), addressing toxicity to organisms from three trophic levels; fish, invertebrates and algae. For studies in which the test substance had a single carbon chain length, a key study has been identified for each taxonomic level. Where there were two or more reliable studies of the same quality but on different species within the same taxonomic group, the lower toxicity value (highest level of toxicity) was chosen. For studies in which the test substance was a multi-constituent LCAAs (commercial products) and where there was more than one type of the substance a key study was identified for each type. 

 

The results of short-term tests performed on single carbon chain length LCAAs are generally reported in terms of the nominal or measured dissolved concentration of the alcohol in the test medium and are identified as EC₅₀ or LC₅₀ values. However, there are also instances where the reported effect concentration exceeded the solubility of the LCAA. These instances are distinguished in the results tables either by the result being reported as an LL₅₀ or EL₅₀, implying that the test medium was a water accommodated fraction (WAF), or by a note indicating that the test substance loading exceeded the solubility of the LCAA. In the latter case it has had to be assumed (because it is not apparent from the test report) that undissolved LCAA may have been present in the test medium and that there was the potential for physical (rather than toxicity) effects to occur.

 

For studies using multi-constituent substances it is possible to interpret the results on the basis of measured dissolved concentrations of the LCAA constituents but they cannot be directly related to the concentration of the multi-constituent substance itself. This is because the test medium does not contain dissolved concentrations of the constituents in the same ratio as present in the substance itself. The toxicity data for mixed carbon chain length LCAAs are therefore also expressed using different conventions. Where the effect concentrations occurred at concentrations below the solubility limit of a multi-constituent substance they are reported as nominal or measured concentrations and are again identified as EC₅₀ or LC₅₀ values. In cases where the test media were WAFs, or where the loading of a multi-constituent substance exceeded the solubility of one or more of its constituents, the result is reported either as an LL₅₀ or EL₅₀, denoting that the test medium was a Water Accommodated Fraction (WAF), or by a note indicating that the test substance loading exceeded the solubility limit of the multi-constituent substance. Once again in the latter case it has had to be assumed (because it is not apparent from the test report) that undissolved LCAA may have been present in the test medium and that there was the potential for physical (rather than toxicity) effects to occur.

In the environmental fate and pathways section it was highlighted that biodegradation is likely to be a significant loss mechanism from aquatic media for the LCAAs under review. If loss of test substance from aquatic test media is significant it will undermine the results of tests where analysis of exposure was not performed. For example, exposure concentrations of 1-octanol (No. 111-87-5) in a 7-day test with the fathead minnow (Pimephales promelas) declined by >90% in the unspecified period between media renewals (Pickering et al., 1996). However, the NOEC has been expressed relative to nominal concentrations and must represent a significant overestimate of the true value and therefore an underestimate of the true toxicity. Similarly, the exposure concentration of the same substance that corresponded to the NOEC determined in a 21-day semi-static long-term test with Daphnia magna, declined by >35% over the 3-4 day period between media renewals (Kuhn et al., 1989). This suggests that exposure concentrations, expressed as nominal values, would have significantly overestimated the actual concentrations. The above examples highlight that test results expressed only in terms of nominal concentrations must be treated with considerable caution and may underestimate the toxicity of the substance.

 

Trends in results, described in this section, are supported by reliable measured data for branched LCAAs which are members of the Oxo Alcohols Category. For full details please refer to the Oxo alcohols SIAR and SIDS dossiers.

 

Where there were no available data for a linear LCAA the data has been read-across (see CSR section 1.4) from reliable data for the closest linear alcohols with a smaller carbon chain length.

 

For multi-constituent substances lacking measured short-term toxicity data, the data has been read-across from the major constituent linear LCAAs in cases where these formed >90% of the multi-constituent substance. This approach is deemed valid because it is considered very unlikely that the minor constituents present at <10% will contribute significantly to short-term effects. This approach has not been adopted for long-term toxicity data because here the potential for the minor constituents to contribute to effects is much greater.

 

In the absence of suitable read-across data for linear and multi-constituent LCAAs, validated QSAR methods have also been developed to fill data gaps for short-term toxicity to fish and invertebrates. QSARs for linear alcohols have also been developed to fill data gaps for long-term toxicity to invertebrates.

 

References:

Kuhn, R., Pattard, M., Pernak, K., and Winter, A. (1989). Results of the harmful effects of water pollutants to Daphnia magna in the 21 day reproduction test. Wat. Res. 23(4): 501-510.

Pickering, Q.H., Lazorchak, J.M., and Winks, K.L. (1996). Subchronic sensitivity of one-, four-, and seven-day-old fathead minnow (Pimephales promelas) larvae to five toxicants. Environ. Toxicol. Chem. 15(3): 353-359.