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Toxicity to microorganisms

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Description of key information

Inhibition of WWTP microorganisms (linear and essentially-linear alcohols in the chain length range C12-15): no significant inhibitory effects on respiration of activated sludges or specific microbial strains relevant to WWTP, at or above the limit of solubility (based on inhibition tests and lack of toxicity in ready biodegradability tests). 

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
10 000 mg/L

Additional information

In accordance with Column 2 of REACH Annex VIII, the activated sludge respiration inhibition study (required in Section 9.1.4 of REACH) does not need to be conducted as the substance is readily biodegradable and the applied test concentrations are in the range that can be expected in the influent to a sewage treatment plant. Reliable studies are available, for the species Pseudomonas putida. The C12 constituent dodecan-1-ol has EC0 of 10000 mg/l and the longer-chain alcohol octadecan-1-ol has EC0 of 10000 mg/l in the same types of study; i.e. the EC50is greater than the limit of solubility.

The alcohol constituents of Alcohols, C12 -15 -branched and linear are all expected to have consistent lack of inhibition to WWTP microorganisms.

This is supported by results of non-assignable reliability studies with shorter and longer chain-length alcohols indicating EC50 in the hundreds of mg/l for respiration of a mixed microbial culture. Additionally, consistent results (ECx >= 10000 mg/l) are reported in the public domain for tetradecanol and C12 -14 mixed alcohols, although original studies were not available from the data owner.

 

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

 

A number of studies of the toxicity of LCAAs to single species of micro-organisms have been identified. A range of results are shown in Table 7.21 of the Category CSR, for test species relevant to WWTP (studies on various other organisms are also available).

 

The ready biodegradation studies (Federle, 2009 and Flach, 2012, discussed in Section 5.2.1) gives evidence that rapid biodegradation by aquatic activated sludge microorganisms is seen, even in the presence of an excess of test substance (for the longer chain length category members tested). It is notable that the biodegradation in the ready test was very high compared to ThCO2, indicating that over the course of the test the exposure of organisms to test substance must have been complete.

 

At or above the limit of solubility, the data set shows that the alcohols in the chain length range C6-24 category have no significant inhibitory effects on respiration of activated sludges or specific microbial strains relevant to WWTP. There is limited evidence of inhibition of growth in some specific microbial strains but ready biodegradation evidence suggests this is not significant for mixed populations.

The reliability of some of these data individually is not high, but it presents a consistent weight of evidence.

 

In general it can be said that the micro-organisms examined in these tests were less susceptible to the LCAAs than fish, invertebrates and algae and that in general, IC50values for respiration effects are at or significantly above the limit of water solubility.

 

WWTP microorganisms have been demonstrated to be capable of synthesising significant concentrations of aliphatic alcohols (e.g. Mudge et al., 2008).