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Long-term toxicity to aquatic invertebrates

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Description of key information

NOEC (21 d) = 1.8 mg/L (measured concentration) for Daphnia magna (RA CAS No. 111-11-5)

Key value for chemical safety assessment

Additional information

No data evaluating the chronic toxicity of methyl hexanoate (CAS No. 106-70-7) to aquatic invertebrates are available. Therefore, data from a structurally related analogue substance, methyl octanoate (CAS No. 111-11-5) are used as read-across in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. Both substances are fatty esters esterified with methanol, differing only in the C-chain length of the fatty acid component: C6 (CAS No. 106-70-7) and C8 (CAS No. 111-11-5) respectively. They are both water soluble (water solubility of 1330 mg/L and 64 mg/L for methyl hexanoate and methyl octanoate, respectively). Therefore, a comparable behavior in the water phase can be expected

Within the SCAE Me category, a trend in the acute toxicity of monoconstituent substances to aquatic invertebrates can be observed, related to the mode of action (narcosis). Thus, a linear dependence on log Kow is expected (see table below). The highest toxicity has been determined for methyl laurate (CAS No. 111-82-0, fatty acid chain length C12), with an EC50 (48 h) of 0.255 mg/L (Daphnia magna). Toxicity decreases at shorter fatty acid C-chain lengths (C10, C8 and C6) and longer chain lengths (C14, no toxicity within the limit of water solubility).

 

 

CAS-No.

106-70-7

(C6)

111-11-5 (C8)

110-42-9

(C10)

111-82-0

(C12)

124-10-7

(C14)

Acute toxicity to aquatic invertebrates

Experimental result, D. Magna       EC50 (48h) = 40 mg/L (nom.)

QSAR, EC50 (48h) = 5.6 mg/L

Experimental result, D. Magna       EC50 (48h) = 1.1 mg/L (meas.)

Experimental result, D. Magna       EC50 (48h) = 0.255 mg/L (meas.)

Experimental result, D. Magna, EC50 (72h) > 0.02 mg/L (meas. TWA), EL50 (72h) > 100 mg/L (nominal)

 

The same trend is observed for chronic values:

CAS-No.

111-11-5 (C8)

111-82-0

(C12)

Acute toxicity to aquatic invertebrates

Experimental result, D. Magna       NOEC (21 d) = 1.8 mg/L (meas.)

Experimental result, D. Magna       NOEC (21 d) = 0.0814 mg/L (meas.)

 

In the absence of studies evaluating the chronic toxicity of methyl hexanoate (CAS No. 106-70-7) to aquatic invertebrates and considering the observed toxicity trend in the SCAE Me category, read-across from methyl octanoate (CAS No. 111-11-5, in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5) is applied. This read-across option is a worst-case scenario for methyl hexanoate, for which lower toxicity than that of methyl octanoate is expected. Nevertheless, due to the lack of reliable data for methyl hexanoate and being aware of a possible overestimation of the toxicity, read across from methyl octanoate is performed.

One study is available on the long-term toxicity of methyl octanoate (CAS No. 111-11-5) to aquatic invertebrates. Due to the low water solubility of the test substance, a 100 mg/L dispersion was first prepared, stirred for 3 hours and filtered. The test organism Daphnia magna was then exposed to dilutions of 1:200, 1:63, 1:20, 1:6.3 and 1:2 of the filtrate, for 21 days. At the two highest concentrations, no offspring were produced due to the mortality of the parent animals. At the three remaining concentrations, no significant mortality and no effect on reproduction were observed. The dilution of 1:20 therefore corresponds to the NOEC, which was shown to be 1.8 mg/L by analytical measurement.

Based on the above information, similar results as those of the test conducted on the structurally related analogue substance (in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5), can be expected for methyl hexanoate (CAS No. 106-70-7).