Sodium dichromate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

2.5 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

2.5 µg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.5 µg/L

Assessment factor:

50

Extrapolation method:

assessment factor

PNEC marine water (intermittent releases):

8.6 µg/L

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

705.4 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1.76 mg/kg sediment dw

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.18 mg/kg sediment dw

Assessment factor:

1 000

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.09 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.353 mg/kg food

Assessment factor:

30

Additional information

Read-across

For the assessment of the environmental toxicity of sodium dichromate, a read-across approach is applied based on information available for the hexavalent chromium substances: sodium (di)chromate, potassium (di)chromate and chromium (VI) oxide in accordance with the EU risk assessment of hexavalent chromium substances (EU RAR, 2005). This grouping of chromium (VI) substances for estimating the toxicity is based on the assumption that it is a result of the presence of the common hexavalent chromium ion. After emission of hexavalent chromium compounds into the environment, it is the potentially bioavailable hexavalent chromium ion that is liberated in solution and that is the moiety of ecotoxicological concern. This assumption can be considered valid since differences in solubility do not affect the environmental toxicity, i.e. all of these substances are very soluble in water (> 100 g/L).

“The processes that are important in determining the fate and distribution of chromium in the environment include: redox transformations, precipitation and dissolution, and adsorption/desorption…Chromium exists in the environment in a number of valence states. Chromium (VI) and chromium (III) are the most stable. However, in the environment, kinetic and other non-equilibrium factors mean that chromium (III) species dominate in nature, with high levels of chromium (VI) species generally only found as a result of man-made pollution. Although chromium (VI) is thermodynamically stable only under oxidising conditions, the kinetics of reduction to chromium (III) under certain conditions can be slow” (EU RAR for hexavalent chromium substances, 2005). At environmentally relevant pH, the species found in solution are a mixture of Cr₂O₇^2-, HCrO₄^-and CrO₄^2-, irrespective of the form in which the chromium (VI) enters the environmental solution. Thus, we may assume that the environmental conditions affect the speciation of hexavalent chromium and not the particular hexavalent chromium source. Therefore, read-across is justified. 

For a documentation and justification of the read-across approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for sodium dichromate.

Conclusion on classification

Conclusion on classification

The harmonised classification (Annex VI of Regulation (EC) No 1272/2008) of sodium dichromate is Aquatic Acute 1 (H400) and Aquatic Chronic 1 (H410) with acute and chronic M-factors of 1, respectively.

Acute (short-term) toxicity: Short-term LC/EC50 values are available for three trophic levels: fish, aquatic invertebrates and algae. The lowest reliable LC/EC50 value is the 48-h EC50 of 0.03 mg Cr/L observed for the toxicity to Ceriodaphnia sp. (Dorn et al., 1987) and based on a chromium content of 39.7 % corresponds to 0.08 mg/L Na2Cr2O7. Accordingly, sodium dichromate meets classification criteria of Acute (short-term) aquatic hazard category 1 (Table 4.1.0 (a)). In accordance with Table 4.1.3 an acute M-factor of 10 can be derived.

Chronic (long-term) toxicity: Long-term EC10/NOEC values are available for three trophic levels: fish, aquatic invertebrates and algae. The lowest EC10 for the inhibition of growth rate of algae amounts to 0.01 mg Cr/L as observed for Pseudokirchneriella subcapitata, corresponding to an EC10 of 0.03 mg Na2Cr2O7/L. Thus, sodium dichromate as not-rapidly degradable substance meets classification criteria of Long-term aquatic hazard category 1 (Table 4.1.0 (b)). In accordance with Table 4.1.3, a chronic M-factor of 1 is derived (similar to the harmonised classification).