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Ecotoxicological information

Short-term toxicity to fish

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Administrative data

Link to relevant study record(s)

Reference
Endpoint:
short-term toxicity to fish
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Justification for type of information:
REPORTING FORMAT FOR THE CATEGORY APPROACH

1. HYPOTHESIS FOR THE CATEGORY APPROACH
This scenario covers the category approach for which the hypothesis is based on transformation to a common compound. For the REACH information requirement under consideration, the effects obtained in studies conducted with different source substances are used to predict the effects that would be observed in a study with the target substance if it were to be conducted. The same type of effect is observed for the different source substances; this may include absence of effects for every member of the category. No relevant differences in strengths of effect are observed for several source substances.
There are no relevant variations in properties among source substances and the same potency is predicted for all target substances. This corresponds to Scenario 5 of the RAAF (ECHA, 2017). The substances ATG, MEATG, KTG, CaTG, and NaTG are different inorganic salts of a common acid, thioglycolic acid (TGA; synonym: 2-mercaptoacetic acid). They dissociate rapidly in aqueous media to the common thioglycolate anion and to their different counter ions. The water solubility of all category members is high.
This approach serves to use existing data on aquatic toxicity endpoints for substances in this category.
It can be predicted with high confidence that the target substances will display the same mode of action and lead to the same type and strength of effects as observed with the source substances.


2. CATEGORY APPROACH JUSTIFICATION
For details, refer to Justification for read-across attached to Iuclid section 13
Reason / purpose for cross-reference:
read-across: supporting information
Key result
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: read-across
Basis for effect:
mortality (fish)

Description of key information

96 h LC 50 >100 mg/L (OECD TG 203, Oncorhynchus mykiss, RL1, GLP; read across from TGA, ATG, and MeaTG)

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Dose descriptor:
LC50
Effect concentration:
> 100 mg/L

Additional information

Experimental data on short-term toxicity to aquatic invertebrates are available for TGA, ATG and MeaTG.


 


TGA


The objective of this 96 hour study was to evaluate the acute toxicity of the test item to fish in accordance with OECD Guideline 203. For this purpose, juvenile Rainbow Trout were exposed in a flow-through test to aqueous test media containing the test item at the limit concentration of 100 mg/L (nominal). The recorded effects were mortality and symptoms of intoxication of the test fish. 7 fish were exposed for 96 hours to thioglycolic acid.


Based on the test results the 96 hour LC50 of Thioglycolic Acid for Oncorhynchus mykiss was determined to be higher than 100 mg test item/L based on nominal concentration.


 


The acute toxicity to Oryzias latipes (Japanese Medaka) has been investigated in a study according to OECD Guideline 203 (1992) under semi-static conditions with daily renewal of the test solutions. 10 fish/concentration were exposed to the test item for 96 hours at concentrations of 9.5 mg/L, 17.1 mg/L, 30.9 mg/L, 55.6 mg/L, and 100.0 mg/L and one pH-adjusted (neutralized) concentration of 100.0 mg/L.


Concentrations were based on a pre-test, in which preliminary results showed a 96 h LC50 of 55.9 mg/L, a 0% lethal maximum concentration of 25 mg/L, and a 100% lethal minimum concentration of 125 mg/L. 


Because the measured concentration deviated from the set concentration by ± 20%, the geometric mean of the measured concentration was used to calculate the test results.


Mortality rate of fish exposed to mercaptoacetic acid for 96 hours was 0% in the lowest concentration of 5.9 mg/L and 100% in the highest concentration of 102.5 mg/L. The mortality rate in the control was 0%. The mortality rate in the pH-adjusted (neutralized) test solution was 10%.


Abnormal swimming was observed in the concentration of 56.3 mg/L as a toxic symptom. No abnormal symptoms were observed during the test in the control and other concentrations. Based on the test results the 96 hour LC50 of the test item was 39.8 mg/L, and its 95% confidence interval was 28.1 mg/L to 56.3 mg/L and in the pH adjusted (neutralized) test solution was > 74.8 mg/L (geom. Mean; corresponding to > 100 mg/L nominal).


Since the pH was in the range of 3.4-4.0 at the two highest concentration levels, the result with the neutralised pH is considered to be more relevant, which is also in line with the test conducted in rainbow trout.


 


ATG


This study was performed to assess the acute toxicity of the test material to rainbow trout (Oncorhynchus mykiss) in accordance with OECD TG 203 (1992).


Following a preliminary range-finding test fish were exposed, in two groups of seven, to an aqueous solution of the test material, at a single concentration of 100 mg active ingredient (ai)/l for a period of 96 hours at a temperature of approximately 14°C under semi-static test conditions. The number of mortalities and any sub-lethal effects of exposure in each test and control vessel were determined 3 and 6 hours after the start of exposure and then daily throughout the test until termination after 96 hours.


The 96-Hour LC50 based on nominal test concentrations was greater than 100 mg ai/l.
Data supplied by the Sponsor indicated that the test material, ammonium thioglycolate (ATG) was prone to oxidation to give diammonium dithiodiglycolate (DADTDG). Therefore analysis was performed to determine the concentration of both ATG and DADTDG.
The recovery analysis performed using test medium at room temperature showed the recovery rates for ATG and DADTDG to be 96% and 98% of fortification respectively. The stability analysis performed showed values for ATG to be 94% to 99% of the initial concentration after 24 hours. Analysis of the stability samples for DADTDG using test medium at room temperature showed concentrations between 7.7 and 9.5 mg/l after 24 hours. Given that the concentration of ATG was between 94% and 99% of initial concentration after 24 hours it was considered justifiable to perform the test using semi-static test conditions as opposed to dynamic, continuous flow test conditions.


Preliminary test samples were analysed for ATG at 0 and 24 hours. The results showed measured concentrations at 0 hours to be 96% and 99% of nominal and 99% and 102% of nominal after 24 hours.
Analysis of the test preparations for ATG at 0, 24 and 96 hours showed the measured concentrations to range between 96% to 102% of nominal. Analysis for DADTDG at 0 hours showed the concentrations to be 1.4 and 2.2 mg/l. However, after 24 hours concentrations of 2.9 and 3.0 mg/l of DADTDG were determined which were in-line with the stability analysis performed. The concentration of DADTDG in the 96-Hour test samples was not determined at the time point due to instrument malfunction but were analysed later when elevated levels of DADTDG were observed. Analysis of duplicate frozen samples showed elevated levels of DADTDG. However this was due to further degradation of the parent test material during the thawing process. It was however considered that the results would have been similar to the 24-Hour old test media result had the sample been analysed immediately.
Given that the measured concentrations of ATG were near nominal it was considered justifiable to estimate the results on nominal concentrations only.


 


MeaTG


A study was performed to assess the acute toxicity of the test material to rainbow trout (Oncorhynchus mykiss). The method followed that described in the OECD Guidelines for Testing of Chemicals (1992) No 203, "Fish, Acute Toxicity Test" referenced as Method C.1 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC).
Following a preliminary range-finding test, fish were exposed, in two groups of seven, to an aqueous solution of the test material, at a single concentration of 100 mg active ingredient (ai)/l for a period of 96 hours at a temperature of approximately 14°C under dynamic, continuous flow test conditions. The number of mortalities and any sub-lethal effects of exposure in each test and control vessel were determined 3 and 6 hours after the start of exposure and then daily throughout the test until termination after 96 hours.
The 96-Hour LCs9 based on nominal test concentrations was greater than 100 mg ai/l and correspondingly the No Observed Effect Concentration was 100 mg ai/I.
The test material was known to oxidise, when diluted to very low concentrations in oxygenated water, to give dimonoethanolamine dithiodiglycolate (DiMEADTDG). As the analysis was carried out under acid conditions, the DIMEADTDG was converted to dithiodiglycolic acid (DTDGA) and MEATG was converted to thioglycolic acid (TGA). Therefore, all test preparations were analysed for TGA (calculated as MEATG) and DTDGA (used as a marker for DiMEADTDG).
Analysis of the test preparations at 0, 24, 48, 72 and 96 hours showed measured test concentrations of MEATG to range from 96% to 114% of nominal and measured concentrations of DTDGA of 2.41 to 3.76 mg/l. Given that the measured concentrations of the parent test material MEATG were within the 80% to 120% acceptance limits, it was considered justifiable to base the results on nominal test concentrations only.


 


Conclusion


In the available short-term toxicity studies, the examined substances were not toxic to fish up to and including the limit concentration of 100 mg/L. The 96 h LC50 for all substances within this category is >100 mg/L.