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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Hazard for aquatic organisms

Freshwater

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

Marine water

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

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
16 µg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

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

Sediment (marine water)

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

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
no exposure of soil expected

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

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 hydrolysed 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, no PNECs were derived for the substances themselves, but the PNECs are expressed as H2S concentrations.

However, because H2S formation will only occur under reducing conditions, such as in hypoxic/anoxic and/or organic-rich environments, it would be a worst case approach only to consider H2S toxicity. In oxic environments, sulphides are quickly oxidised to - eventually - the much less harmful sulphate. Because oxidation will counter the formation of the extremely toxic H2S in most environments, it was decided also to present some toxicity data for sulphate. Therefore, Na2SO4 was selected as the most interesting substance for read across purposes. The most critical aquatic toxicity data presented in the OECD SIDS for this substance are therefore also included in this dossier. Below the derivation of aquatic PNEC values for sulphate is presented. Because the aquatic compartment (water column) is considered to be the most critical, only PNECaquatic values (for freshwater) and a PNECstp were presented. No PNEC values were derived for sediment and soil.

For sulphate toxicity to aquatic organisms, only acute data were available. The most critical effect concentrations were a 96-h LC50 value of 5383 mg/L for fathead minnow (Pimephales promelas) (Mount et al., 1997), a 48-h EC50 of 2083 mg/L for Ceriodaphnia dubia (Mount et al., 1997), and a 120-h EC50 of 1285 mg/L for the freshwater diatom Nitzschia linearis (Patrick et al., 1968). No chronic toxicity data are available. Using an assessment factor of 1000 to the lowest acute effect concentration results in a PNEC for sulfate of 1.285 mg/L for freshwater organisms. It must be kept in mind that the abovementioned effect concentrations were taken from toxicity tests using Na2SO4 by recalculating the overall effect concentrations to sulfate concentrations. However, since the toxicity of Na2SO4 is a combination of possible adverse effects of both sodium and sulfate, this represents a worst case approach. Indeed, comparing the PNEC for sulphate with typical background concentrations for sulphate, it is obvious that the PNEC is unrealistically low. An overview of aquatic background concentrations for sulphate in several EU countries can be found on the EIONET website (http://www.eionet.europa.eu). The EIONET database includes data that were directly retrieved from environmental agencies and institutes involved in monitoring. The average of the 90th percentiles of sulfate concentrations for individual countries was taken forward as PNEC for freshwater organisms. This average value is 105 mg/L.

Further, based on the lowest NOEC of ca. 5.4 g/L for occurrence of stalked ciliates in activated sludge (Tokuz and Eckenfelder, 1979) and an assessment factor of 1, a PNECstp of 5.4 g/L for sulfate was obtained. Here too, it must be kept in mind that the effect concentration was taken from an experiment using Na2SO4 by recalculating the overall effect concentration to the sulphate concentration. This action assumes that sodium does not contribute to toxicity of the substance. Therefore, the PNECstp for sulphate may be largely underestimated. Here too, the PNEC is unrealistically low compared to typical background concentrations for surface water. Moreover, typical sulphate concentrations in sewage can be expected to be much higher than for surface water. However, no typical values are available. The PNEC for freshwater organisms suggested above (based on sulphate background concentrations) may therefore be used as a worst case PNECstp for indicative risk characterization if needed.

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 tranlated 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.