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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
Please refer to the Read-across Statement attached in Section 13.2.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The underlying hypothesis for the read-across is that the target substance is very prone to hydrolysis resulting in the formation of epsilon-caprolactam and sodium hydroxide. As hydrolysis of the target substance will inevitably occur both under physiological and under environmental conditions, the evaluation of the data of epsilon-caprolactam and sodium hydroxide is considered to be sufficient for hazard assessment. Thus, the toxicological behavior of BRUGGOLEN® C10 can be considered to be determined by the hydrolysis products caprolactam and caustic soda.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Target substance: sodium caprolactamate, CAS-No. 2123-24-2 (for detailed composition please refer to the Read-across Statement attached in Section 13.2)
Source substances: epsilon-caprolactam, CAS-No. 105-60-2 and sodium hydroxide, CAS-No. 1310-73-2

3. ANALOGUE APPROACH JUSTIFICATION
The justification of the read-across hypothesis is mainly based on the hydrolysis of the target substance into the source substances.
BRUGGOLEN® C10 is a combination of sodium caprolactamate (17 – 20 %) and epsilon-caprolactam (80 – 83 %). If diluted in water, sodium caprolactamate easily degrades to caprolactam and sodium hydroxide (caustic soda). Reason is the instability of the ionic N-Na-bond of the sodium caprolactamate.
Thus, the toxicological behavior of BRUGGOLEN® C10 can be considered to be determined by the hydrolysis products caprolactam and caustic soda.

4. DATA MATRIX
Please refer to the Read-across Statement attached in Section 13.2.
Duration:
48 h
Dose descriptor:
EC0
Effect conc.:
500 mg/L
Duration:
48 h
Dose descriptor:
EC100
Effect conc.:
> 500 mg/L
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 500 mg/L

Description of key information

Invertebrates toxicity, freshwater, acute > 500 mg/L

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
500 mg/L

Additional information

Data obtained by Read-Across from ε-caprolactam:

A study with epsilon-Caprolactam (GLP) according OECD 202 performed at the Mitsubishi Chemical Safety Institute

on behalf of the Ministry of Environment, Government of Japan with Medaka as test species resulted in a

EC50 (48h) >1,000 mg/l. A supporting study by BASF (1987) according to EPA guideline EG-1 also indicates a low hazard potential of epsilon-Caprolactam to aquatic invertebrates: EC50 (48h) >500 mg/l.

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Data obtained by Read-Across from sodium hydroxide:

For sodium hydroxide, EC50 values from 40 to 240 mg/l have been reported (see respective study endpoint record). The lowest value, 40 mg/l, is actually one order of magnitude lower than the EC50 that was determined for epsilon-Caprolactam (500 mg/l).

However, it can reasonably be assumed that the toxic effect of sodium hydroxide to aquatic invertebrates can entirely be assigned to the increase of the pH-value. In the OECD-SIDS documentation (see section 13), an estimation of the maximum acceptable concentration of sodium hydroxide in surface water has been made:

Result:

If it is assumed that only bicarbonate is responsible for the buffer capacity of the

ecosystem and if it is assumed that an increase of the pH to a value of 9.0 would be the maximum

accepted value then the maximum anthropogenic addition of sodium hydroxide would be 1.0 and

6.1 mg/l for bicarbonate concentrations of 20 and 195 mg/l, respectively. These examples give an

indication of the maximum amount of NaOH which could be discharged to an aquatic ecosystem if

there was an emission of a pure NaOH solution.

Actually, the freshwater PNEC that was determined from the long-term toxicity to aquatic invertebrates of epsilon-caprolactam is 2 mg/l. This value can assessed to be reasonable with respect to the abovementioned estimation for sodium hydroxide (1.0 to 6.1 mg/l).