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Short-term toxicity to aquatic invertebrates

Additional information

Read-across Hypothesis The reaction mass is composed of the following substances: sodium sulphite, sodium thiosulphate, sodium polysulphide and disodium sulphide, with residual amounts of sodium sulphate. The reaction mass can be considered as a mixture of different salts which fully dissociate in aqueous systems. Because they are chemically related their effects are considered to be additive. Therefore, the aquatic toxicity of the mixture can be determined based on respective data/classification of the single compounds and the quantitative composition of the reaction mass.

Applicability domain Reaction mass of sodium sulphite, sodium thiosulphate, sodium polysulphide and disodium sulphide

Target substances, molecular formulas:	Source substances, molecular formulas:
sodium sulphite (NA2SO3)	disodium disulphite (Na2S2O5)
sodium thiosulphate (NA2S2O3)	ammonium thiosulphate (NH4)2S2O3
sodium polysulphide (NA2Sn)	sodium sulphate (Na2SO)4
disodium sulphide (NA2S)	hydrogen sulphide (H2S), sodium sulphate (Na2SO4)

Purity / Impurities sodium sulphate, Na2SO4 The impurity sodium sulphate is a naturally occurring inorganic compound and not environmentally classified or labelled. Since sodium sulphate is also used as read-across substance for sodium polysulphide and disodium sulphide, it is taken into account for the classification of the reaction mass.

Category justification The constituents of the reaction mass consist of sodium as cation and sulfur compounds as anion. They all have a high water solubility and fully dissociate in water. All compounds are registered under REACH and detailed ecotoxicological information can be found in the respective dossiers. Because the reaction mass can be considered as a mixture of its compounds, this data is used to determine the aquatic toxicity of the reaction mass.

Conclusions per endpoint for C&L Toxicity studies investigating the toxicity of Na2S or NaHS to aquatic organisms have focused in most cases on the toxicity of H2S, which is the most toxic sulfur species that can be formed upon dissolution of Na2S and NaHS. For H2S toxicity, two key studies were identified. The key study for freshwater aquatic invertebrates is the study of Oseid and Smith (1974a) and that for marine aquatic invertebrates is the study of Gopakumar and Kuttyamma (1996). Oseid and Smith (1974a) obtained a 96-h LC50 of 0.02 mg H2S/L for mayfly larvae of the species Baetis vagans. Gopakumar and Kuttyamma (1996) reported a 96-h LC50 of 0.032 mg H2S/L for the penaeid prawn Penaeus indicus. In oxic environments, released sulphides will be oxidized to - eventually - sulphate. In these cases, the risks entailed by the released sulfur should be evaluated using toxicity data for sulphate. Na2SO4was identified as the most relevant substance for this purpose. For sulphate toxicity, the study of Mount et al. (1997) was identified as a key study. This study reports a 48-h LC50 of 3080 mg Na2SO4/L for Ceriodaphnia dubia. This value can be recalculated to an LC50 of 2083 mg SO4^2-/L. A standard acute invertebrate toxicity test was conducted with cladoceran Daphnia magna, using ammonium thiosulphate as test compound. A 48-h LC50 of 230 mg test item/L was derived, which corresponds to 174 mg S2O3^2-. This data point can be used for hazard/effects assessment purposes for ammonium thiosulphate and other thiosulphate compounds (read-across principles). For the assessment of sodium sulphite toxicity, a standard acute invertebrate toxicity test was conducted with disodium disulphite as test compound. A 48-h EC50 of 89 mg test item/L was derived, which corresponds to 74.9 mg SO3^2-/L. This data can be used for the environmental assessment of sodium disulphite and other sulphite compounds (read-across principles).   Conclusion The environmental classification of the reaction mass is determined as described in Regulation (EC) No 1272/2008 (Part 4: Environmental hazards, 4.1.3.5). The classification is derived with the summation method (4.1.3.5.5)., In principle, the summation method is based on the summation of the respective concentration of its classified components. Existing M-factors are included in the calculation. Sodium polysulphide and disodium sulphide are both classified as Acute Aquatic 1, without M-factors, according to Annex VI of Regulation (EC) No 1272/2008. Summed up, their concentration in the reaction mass is >25%. If the sum of the concentrations of all components of a mixture classified as Acute Aquatic 1, multiplied by their corresponding M-factors is >25%, the classification of the mixture results in Acute Aquatic 1 (Regulation (EC) No 1272/2008, 4.1.3.5.5.3.1). Therefore, the summation method leads to a classification of the reaction mass as Acute Aquatic 1, H400.