Reaction mass of sodium hydrogensulfide and sodium carbonate

Long-term toxicity to fish

Description of key information

For H2S toxicity, several studies yielded reliable NOEC values for freshwater fish. For marine fish, no reliable studies were identified. The study of Smith et al. (1976a) was considered as the key study. This study yielded a 826-d NOEC of 0.0046 mg H2S/L based on mortality data for juvenile bluegill (Lepomis macrochirus). No long-term data were identified for sulfate toxicity.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.005 mg/L

Additional information

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. Among the available studies using either Na₂S, NaHS (or its respective hydrates) or H₂S as test substance, the study of Smith et al. (1976a) yielded the lowest unbound NOEC, i.e. a 826-d NOEC of 0.0046 mg H2S/L based on mortality data for juvenile bluegill (Lepomis macrochirus). Next to a series of long-term studies, several studies have been identified reporting reliable LC50, EC50 or NOEC values obtained in short-term toxicity tests on embryo and sac-fry stages. Most of the effect concentrations reported were higher than the key NOEC reported by Smith et al. (1976a), except for a slightly lower 96-h EC50 value of 0.0028 mg H₂S/L reported by Yusoff et al. (1998) for hatching rate of Javanese carp eggs (Puntius gonionotus). However, because such short-term studies should not be given as much weight as the long-term studies, and the lowest effect concentration is only slightly lower than the NOEC of Smith et al. (1976a), the latter will be used for the aquatic hazard assessment. No reliable information was identified for marine fish. No reliable long-term data were identified for sulfate toxicity.

No reliable long-term data were found for the toxicity of NaOH or Na₂CO₃, although one NaOH study, Rustamova (1977), with guppy (Lebistes reticulatus) reporting "significant changes in the biology of the fish" at 25 -100 mg/L is included in the dossier.