Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
2.67 µg/L
Assessment factor:
3
Extrapolation method:
sensitivity distribution
PNEC freshwater (intermittent releases):
5.5 µg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
2 µg/L
Assessment factor:
3
Extrapolation method:
sensitivity distribution

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
1 500 µg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
8.2 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
6.2 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
0.1 mg/kg soil dw
Assessment factor:
10
Extrapolation method:
assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
PNEC oral
PNEC value:
1 mg/kg food
Assessment factor:
1

Additional information

Read-across approach

The chemical safety assessment of zinc selenite is based on the elemental Zn and Se concentrations and read-across to Zn and Se substances. Zinc selenite releases almost equal amounts of Zn and Se upon dissolution (100 mg ZnSeO3 releases 34 mg Zn and 41 mg Se), and a comparison of PNEC values for Zn and Se learns that Se is the most critical element in all compartments, except for toxicity to micro-organisms in STP. The PNEC for Zn in STP is still a factor 20 above the PNEC for Se in freshwater, which is larger than the standard dilution factor 10 for release of STP in surface water, and therefore it is assumed that toxicity to STP is not critical for the risk assessment of zinc selenite. The large difference (>factor 10) in PNEC values for Zn and Se in sediment will cancel out the larger adsorption of Zn compared to Se to solids in sediment and suspended matter. For these reasons, it was concluded that the chemical safety assessment of ZnSeO3 will be based on read-across to Se only and hence, only information on the ecotoxicity of selenite is discussed here.

Comparison of PNEC values for Zn and Se in the various environmental compartments:

 Compartment Unit  PNEC Zn  PNEC Se  Factor differencea
Freshwater  µg/L  20.6*   2.67*  9.3
Marine water  µg/L  6.1*   2.0*  3.7
STP  µg/L  52   1500  0.04
Freshwater sediment  mg/kg dw  235.6*   8.2*  34.7
Marine sediment  mg/kg dw  56.5*   6.2*  11.0
Soil  mg kg/dw  106.8*   0.1*  >1000
Oral  mg/kg food  No potential for bioaccumulation   1  /

*: added value

a: ratio of PNEC Zn and PNEC Se, corrected for the difference in Zn and Se exposure at complete dissolution.

In the assessment of the ecotoxicity of selenite, a read-across approach is followed based on all relevant and reliable information available for inorganic Se compounds. This grouping of selenium compounds for estimating their properties is based on the assumption that properties are likely to be similar or follow a similar pattern as a result of the presence of the common selenium ion.

This assumption can be considered valid when

i) differences in solubility among Se compounds do not affect the results for ecotoxicity (i.e. toxicity occurs below the solubility limit),

ii) ecotoxicity is only affected by the selenium-ion and not by the counter ions, and

iii) after emission to the environment, the various Se compounds do not show differences in speciation of selenium in the environment or differences in speciation do not affect toxicity.

In order to correct for differences in solubility among Se compounds, all reliable data on ecotoxicity selenium to aquatic organisms were selected based on measured dissolved selenium concentrations. It is indeed assumed that toxicity is not controlled by the total concentration of an element, but by the bioavailable form. No evidence is available on the bioavailable form of selenium, but as a conservative approximation, it can be assumed that the total soluble selenium pool is bioavailable. For soils, data were only available for the soluble sodium selenite and sodium selenate salts (solubility > 1g/L) and therefore no effect of solubility on the toxicity was expected.

The reliable ecotoxicity results were all mainly derived for sodium selenite (Na2SeO3) and sodium selenate (Na2SeO4), but some reliable data are also available for H2SeO3, SeO2, seleno-methionine and seleno-cysteine. There is no concern on the effect of the counter-ions (Na+) in the concentration ranges tested.

The data for organic Se compounds (Se-methionine and Se-cysteine) were not taken into account for the assessment of direct effects of selenite to aquatic or terrestrial organisms because there is some concern on different biochemical behaviour of this selenium containing amino acid compared to inorganic Se compounds. However, because inorganic Se can be transformed into this organic form in the environment, data for seleno-methionine and seleno-cysteine are included for the assessment of secondary poisoning (through PNECoral and bioconcentration factors).

For aquatic organisms, the comparison in toxicity among the various inorganic Se substances (H2SeO3, Na2SeO3, SeO2 or Na2SeO4) did not yield consistent or significant differences. Therefore, results for all these substances were used in a read-across approach. In contrast, for soils a clear difference in toxicity was observed between selenite and selenate, with selenate showing significantly higher toxicity to terrestrial invertebrates (Somogyi et al. 2007) and plants (Cartes et al., 2005; Carlson et al., 1991). This is consistent with the lower adsorption and resulting higher bioavailability of selenate in soil compared to selenite. Therefore, only the available reliable results for toxicity of selenite to terrestrial organisms (plants, invertebrates and micro-organisms) are taken into account for the hazard assessment of zinc selenite in soils.

Selenium is chemically related to sulphur and can exist in a multitude of different oxidation states from -2 to +6 and in both organic and inorganic forms. Under conditions commonly found in oxic fresh waters (i.e., pH between 5 and 9; redox potential [Eh] between 0.5 and 1 V), the hexavalent oxidation state is predicted to be the most prevalent (Takeno, 2005). However, tetravalent selenium also exists under some conditions (low pH, low redox potential).

No information is available on the speciation of the selenium compounds of interest upon dissolution in water and on the redox speciation of the selenium compounds during the various tests available. Some measured data were found on speciation of selenium in the environment. These results confirm that hexavalent Se dominates in most surface waters, while elemental Se and organic Se species dominate in sediments (Zhang and Moore, 1996; Van Derveer and Canton, 1997). Based on limited information available, the environmental conditions are expected to largely control the (redox) speciation of selenium upon dissolution in water, regardless of the Se compound added. However, as mentioned above, a significant difference in adsorption of selenite (SeO32-) and selenate (SeO42-) to soil was observed, with lower adsorption for selenate (median log Kp of 0.87 L/kg dry weight) compared to selenite (median log Kp of 1.73 L/kg dry weight).

In conclusion, all available reliable data for inorganic selenium compounds were used in a read-across approach for aquatic toxicity. Only data for selenite were selected for toxicity to terrestrial organisms (plants, invertebrates and micro-organisms). For toxicity to above-ground organisms (birds, mammals and reptiles) and fish via diet all Se compounds were taken into account, including Se containing amino acids seleno-methionine and seleno-cysteine. All results for ecotoxicity of Se are expressed based on elemental selenium concentrations.

Zhang Y.Q., Moore J.N. (1996) Selenium Fractionation and Speciation in a Wetland System. Environmental Science & Technology 30:2613-2619.

Van Derveer W.D., Canton S.P. (1997) Selenium Sediment Toxicity Thresholds and Derivation of Water Quality Criteria for Freshwater Biota of Western Streams. Environmental Toxicology and Chemistry 16:1260-1268.

Takeno N. 2005. Atlas of Eh–pH diagrams. Intercomparison of thermodynamic databases. Geological Survey of Japan Open File Report No. 419. Tokyo (JP): National Institute of Advanced Industrial Science and Technology, Research Center for Deep Geological Environments. 285 p. Available from:

http://www.gsj.jp/GDB/openfile/files/no0419/openfile419e.pdf

Added risk approach

Selenium is a natural element and therefore naturally present in all environmental compartments. Median background concentrations in pristine waters, agricultural soil and grazing land in Europe are 0.32 µg Se/L, 0.35 and 0.40 mg Se/kg, respectively (Vercaigne et al., 2010). Background Se concentrations are significant compared to the PNEC values for both freshwater and soil and therefore, the added risk approach is preferred. All NOEC and EC10 values are based on added selenium concentrations, without taking into account the natural background. In essence this added risk assessment approach assumes that species are fully adapted to the natural background concentration and therefore that only the anthropogenic added fraction should be regulated or controlled (Appendix R.7.13-2 of the REACH guidance on “Environmental risk assessment for metals and metal compounds”). For essential elements, like Se, this assumption is most plausible. Although the added risk approach acknowledge that negative effects from the bioavailable fraction of the background concentration on some organisms in the ecosystem may occur, or that organisms may even have become acclimated/adapted to it, from an environmental policy point of view, such effects may be ignored and may even be regarded as desirable, since these effects may in theory lead to an increase in ecosystem differentiation or biodiversity (Crommentuijn et al, 1997). Another argument for the added risk approach is the extremely narrow range between dietary essentiality and toxicity for selenium. Application of assessment factors on total concentrations (including background concentration) may result in total PNEC values that cause deficiency for some species.

Crommentuijn T, Polder M. and Van de Plassche, E 1997. Maximum permissible concentrations and negligible concentrations for metals, taking background concentrations into account. RIVM, Report 601501001

Vercaigne, Claeys and Oorts (2010) Exposure assessment of selenium: Measured Se-levels in EU surface water and soil. Report for the Selenium & Tellurium Consortium.

Comparison of background concentrations of Se in the environment with derived PNEC values.

 Compartment Unit  Median background concentration  90th percentile of background concentrations PNECadded 
Fresh surface water (unimpacted areas) µg Se/L 0.32 0.85 2.67 (direct toxicity)0.21 (secondary poisoning)
Marine water µg Se/L 0.085 no data 2.00
Freshwater sediment mg Se/kg dw 0.1a 0.27a 8.2
Agricultural soil (0 -20 cm) mg Se/kg dw  0.35 0.59 0.1
Grazing land (0 -10 cm) mg Se/kg dw  0.40  0.71 0.1

a: based on the data for surface water and the equilibrium partitioning approach

Conclusion on classification

Acute and chronic reference values for environmental classification are based on standard test as laid down in Council Regulation (EC) No 440/2008 on “test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)”

Acute and chronic toxicity data are available for the three trophic levels for both selenium and zinc.

For zinc, the acute and chronic reference values are 0.136 and 0.019 mg Zn/L, respectively for pH ≥7 – 8.5 and 0.413 and 0.082 mg Zn/L, respectively for pH 6 – <7.

For selenium, the lowest L(E)C50 for fish, crustacean or algae growth rate are 2.06, 0.55 and 44.24 mg Se/L, respectively. The 48-h LC50 of 0.55 mg Se/L (based on dissolved Se concentration) was observed for the effect of Na2SeO3 on mortality of Daphnia magna (Maier et al., 1993). This value is selected as the acute reference value for classification of inorganic selenium compounds.

The lowest chronic NOEC or EC10 for the toxicity of Se to freshwater fish, invertebrates or algae are 0.01, 0.07 and 4.57 mg Se/L, respectively. The lowest value of 0.010 mg Se/L was oserved in a 258-d study on the effect of Na2SeO3 on pre-spawning mortality of Lepomis macrochirus (Hermanutz et al., 1992). This is however neither a standard fish species, nor a standard test and therefore not selected for classification. The lowest standard test resulted in a 90-d NOEC of 0.021 mg Se/L for the effect of Na2SeO3 on mortality of Oncorhynchus mykiss (Hunn et al., 1992) and this value was selected as chronic reference value for classification of selenium.

All acute and chronic reference values for Zn and Se are based on dissolved elemental concentrations.

Taking into account the acute and chronic reference values for Zn and Se, the proportion of both Zn and Se in ZnSeO3 and its solubility, the classification for zinc selenite is “Aquatic Chronic Category 1” (acute reference value ≤1 mg/L and chronic reference value ≤1 mg/L).