Octanoic acid, 6,8-dimercapto-

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

10.10.2000 - 12.10.2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

The test samples were diluted in methanol prior to analysis.
Standard solutions of test material and Lipoic Acid were prepared in methanol:water (50:50 v/v) at a nominal concentration of 25 mg/L.

Vehicle:

no

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Species. Daphnia magna
- Source: in-house laboratory culture
- Age at study initiation: adult
- Feeding during test: fed daily
- Food type: suspension of algae (Chlorella sp.)

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Remarks on exposure duration:

Immobility (including mortality) was measured at 24 hours and at 48 hours.

Post exposure observation period:

not applicable

Hardness:

250 mg/l expressed as CaCO3 and the pH: 7.8 ± 0.2.

Test temperature:

temperature controlled room at 21 °C

pH:

6.4 - 7.8

Dissolved oxygen:

8.1 - 8. 4 mg O2/L

Salinity:

not applicable

Nominal and measured concentrations:

Range-Finding study: 0.10, 1.0, 10 and 100 mg/L
Definitfive study: 1.0, 1.8, 3.2, 5.6, 10, 18, 32, 56 and 100 mg/L

Details on test conditions:

see under "any other information on materials and methods incl. tables"

Reference substance (positive control):

no

Key result

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

16 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: 14 -19

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: 4.3 - 5.8

Duration:

24 h

Dose descriptor:

NOEC

Effect conc.:

5.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: based upon zero immobilisation at this concentration

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

1.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: based upon zero immobilisation at this endpoint

Results with reference substance (positive control):

no data

1 Range-finding Study

Cumulative immobilisation data from the exposure of Daphnia magna to the test material during the range-finding study are given in Table 1.

Table 1: Cumulative Immobilisation Data in the Range-finding Study

Nominal Concentration (mg/L)	Cumulative Immobilised Daphnia (Initial Population: 10 Per Replicate)
	24 Hours	48 Hours
Control	0	0
0.10	0	0
1.0	0	0
10	0	6
100	10	10

2 Definitive Study

Cumulative immobilisation data from the exposure of Daphnia magna to the test material durign the definitive study are given in Table 2.

Table 2: Cumulative Immobilisation Data in the Definitive Study

Nominal Concentration (mg/L)	Cumulative Immobilised Daphnia (Initial Population: 10 Per Replicate)
	24 Hours				48 Hours
	R1	R2	Total	%	R1	R2	Total	%
Control	0	0	0	0	0	0	0	0
1.0	0	0	0	0	0	0	0	0
1.8	0	0	0	0	0	0	0	0
3.2	0	0	0	0	2	0	2	10
5.6	0	0	0	0	7	5	12	60
10	0	2	2	10	10	10	20	100
18	6	7	12	65	10	10	20	100
32	10	9	19	95	10	10	20	100
56	10	10	20	100	10	10	20	100
100	10	10	20	100	10	10	20	100

3 Verification of test concentrations

During perliminary recovery and stability analyses Dihydrolipoic Acid was shown to rapidly oxidise to Lipoic Acid. Therefore, it was considered apporpriate to determine levels of both Dihydrolipoic Acid and Lipoic Acid in the test samples during the definitive study. Pre-study chemical analyses also showed that it was possible to stabilise both Dihydrolipoic Acid and Lipoic Acid by the addition of methanol to the test samples. Therefore, during the definitive study all samples were immediately stabilised with metahnol directly after preparation.

The results from analysis of the freshly prepared test media at 0 hours showed measured values of Dihydrolipoic and Lipoic Acid combined to range from 87 % to 101 % of the nominal test concentrations. The measured concentrations of Dihydrolipoic Acid ranged from less than the limit of quantitation at the lower nominal concentrations to 95.7 mg/L in the 100 mg/L nominal test concentration. Measured concentrations of Lipoic Acid ranged from less than the limit of quantitation to 12.7 mg/L.

The results from the analysis of the freshly prepared test media showed that the test system had been correctly dosed but that rapid oxidation had occured converting Dihydrolipoic Acid to Lipoic Acid. This process was shown to be more rapid at the lower test concentrations employed in the study, with no Dihydrolipoic Acid beeing detected with nominal concentrations of 1.0, 1.8 and 3.2 mg/L. The percentage conversion of Dihydrolipoic Acid to Lipoic Acid was shown to decrease with increasing nominal concentrations and at the highest nominal concentration of 100 mg/L no Lipoic Acid was detected.

Analysis of the old or expired test media sampled at 48 hours showed that further oxidation had occured over the study duration with measured values of Lipoic Acid ranging from 1.01 mg/L to 71.0 mg/L. Dihydrolipoic Acid was detected in the highest test concentration only (5.40 mg/L). The measured values of Dihydrolipoic Acid and Lipoic Acid combined ranged from 55 % to 101 % of nominal test concentrations, with losses occurring at the higher test concentrations of 18, 32, 56 and 100 mg/L. The decline in the overall measured concentrations was consiedered to be due to eighter an undetermined secondary chemical degradation route or possible biologocal degradation of the Dihydrolipoic Acid within the complex biological test system. Pre-study stability work showed that the Lipoic Acid was stable once formed.

During the study a mixture of Dihydrolipoic Acid and Lipoic Acid were present in variable amounts in the test system. Therefore, given that toxicity cannot be attributed to one or both of thecomponents but to the mixture as a whole the results are based on nominal test concentrations only.

Validity criteria fulfilled:

yes

Conclusions:

The acute toxicity of Dihydrolipoic Acid to the freshwater invertebrate Daphnia magna has been investigated and gave a 48-Hour EC50 value of 5.0 mg/L with 95 % confidence limits od 4.3 - 5.8 mg/L. The No Observed Effect Concentration at 48 hours was 1.8 mg/L.

Executive summary:

A study was performed to assess the acute toxicity of Dihydrolipoic Acid to Daphnia magna. The method followed that described in OECD 202 and EU-Method C.2.

Folowing a preliminary range-finding study, twenty daphnids (2 replicates of 10 animals) were exposed to an aqueous solution of the test material at concentrations of 1.0, 1.8,3.2, 5.6, 10, 18, 32, 56 and 100 mg/L for 48 hours under static test conditions. The numbers of immobilised Daphnia were recorded after 24 and 48 hours.

The 48-Hour EC50 for Dihydrolipoic Acid to Daphnia magna based on nominal test concentrations was 5.0 mg/L with 95 % confidence limits of 4.3 - 5.8 mg/L. The No Observed Effect Concentration was 1.8 mg/L

Description of key information

The acute toxicity of Dihydrolipoic Acid to the freshwater invertebrate Daphnia magna has been investigated and gave a 48 -Hour EC50 value of 5.0 mg/L with 95 % confidence limits od 4.3 - 5.8 mg/L. The No Observed Effect Concentration at 48 hours was 1.8 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

5 mg/L

Additional information

A study was performed to assess the acute toxicity of Dihydrolipoic Acid to Daphnia magna. The method followed that described in OECD 202 and EU-Method C.2.

Folowing a preliminary range-finding study, twenty daphnids (2 replicates of 10 animals) were exposed to an aqueous solution of the test material at concentrations of 1.0, 1.8,3.2, 5.6, 10, 18, 32, 56 and 100 mg/L for 48 hours under static test conditions. The numbers of immobilised Daphnia were recorded after 24 and 48 hours.

The 48-Hour EC50 for Dihydrolipoic Acid to Daphnia magna based on nominal test concentrations was 5.0 mg/L with 95 % confidence limits of 4.3 - 5.8 mg/L. The No Observed Effect Concentration was 1.8 mg/L