Registration Dossier

Diss Factsheets

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
2.4 µg/L
Assessment factor:
10
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
2.4 µg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
2.4 µg/L
Assessment factor:
10
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
1.4 mg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
159 µg/kg sediment dw
Assessment factor:
100
Extrapolation method:
assessment factor

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
159 µg/kg sediment dw
Assessment factor:
100
Extrapolation method:
assessment factor

Hazard for air

Hazard for terrestrial organisms

Hazard for predators

Additional information

As explained in several sections of this dossier, Na2S and NaHS will not occur as such in the environment. Upon release to the aquatic environment, these substances are hydrolyzed immediately, establishing a pH-dependent equilibrium between H2S, HS- and S2-. H2S is by far the most toxic species and therefore ecotoxicity tests using Na2S, NaHS or their respective hydrates focus on H2S formation and toxicity in most cases. When effect concentrations resulting from these tests would be expressed on a test material basis, an extremely large range of effect concentrations would be obtained, because the toxicity of these substances depends on the relative abundance of H2S which in its turn depends on the physicochemical characteristics of the aquatic environment under consideration (e.g, pH, temperature, salinity, redox conditions). In other words, H2S concentrations seem to be much better predictors of toxicity than concentrations of Na2S, NaHS or their respective hydrates. Therefore the PNECs calculated for the reaction mass are based on H2S concentrations, using the worst-case assumption in which the total amount of sulfide contained by Na2S and NaHS is converted to H2S.

Since oxidation of sulfides to sulfate will counter the formation of the extremely toxic H2S in most environments, toxicity data are presented also for other components of the reaction mass. Of these, sodium hydroxide NaOH (1 -5 %) has, after H2S, ecotoxicological effects in the aquatic environment at the lowest levels of concentration. While due to limited experimental ecotoxicity data, it is not possible to calculate PNECs for NaOH, the few reported EC50s for the aquatic invertebrate Ceriodaphnia sp. (Warne, 1999) and the microorganism Photobacterium phosphoreum (Bulich et al., 1990) range from 20 to 40 mg/L, while "significant changes" in the biology of a fish were observed at 25 -100 mg/L (Rustamova, 1977). For Na2CO3, the aquatic toxicity data indicate toxicity to various organisms at 200 -1000 mg/L, and for NaSO4, a PNECaquatic of 1.285 mg/L for freshwater organisms can be calculated from the available data (sulfide dossier).

It should be noted that due to the high alkalinity (pH 13) of the reaction mass, to which both NaOH and Na2CO3 contribute, releases into the aquatic environment may locally have acute ecotoxicological effects by raising the pH of water. The alkalinity may similarly have local acute ecotoxicological effects in sediment and soil, although reactions with water and organic material should quickly neutralize the bases.

Conclusion on classification

The classification of Na2S is harmonized. According to Annex I of the Dangerous Substances Directive, the substance is classified as N (dangerous to the environment) and R50 (very toxic to aquatic organisms). This harmonized classification was translated to a similar classification as GHS09 and Acute Aquatic 1 with hazard statement H400 under the CLP regulation. This classification is supported by the available toxicity data for aquatic organisms. The lowest acute effect concentration was a 96-h LC50 of 0.0027 mg H2S/L for fish, obtained from a test using Na2S.9H2O as a test substance. When expressed on a test material basis, this effect concentration is still below 1 mg/L, justifying classification as very toxic to aquatic life. No classification for chronic toxicity (long-term effects) would apply because increasing exposure durations do not result in increased toxicity and because the substance has no potential for bioaccumulation. Although the classification of NaHS has not been harmonized yet at this point in time, the same classification applies as for Na2S.

Due to the lowest acute effect concentration for H2S being between 0.001 and 0.01 mg/L, the multiplying factor (M) used for H2S concentrations when determining the environmental classification of mixtures containing it is 100. Therefore a H2S concentration of only 0.25 % (w/w) is required to classify a mixture containing H2S as Acute Aquatic 1. While only specific environmental conditions (reductive, low pH) favour the formation of H2S, 0.25 % is only 2 % of the total amount of H2S that the reaction mass has potential to form, and the reaction mass itself should therefore be classified as Acute Aquatic 1.

NaOH, Na2CO3 and NaSO4 have no environmental classification.