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Regarding the toxicity of soluble chromium (VI) substances to terrestrial organisms, data are available based on effects observed for potassium dichromate, sodium chromate and chromium (VI) oxide. According to the EU risk assessment of hexavalent chromium substances and references therein (EU RAR, 2005), chromium (VI) once released into soil is likely to be reduced to chromium (III). Toxicity data available for chromium (VI) in soil are presented below, however it is possible that some of the chromium present was converted to chromium (III) during the tests as observed in some of the studies (e.g. Ueda, 1988b). Data are available for several terrestrial species including invertebrates, plants and microorganisms:

Soil invertebrates

Based on a reliable study with Folsomia candida according to ISO TG 11267, a 28 d NOEC of 10 mg Cr/kg is derived for the toxicity to terrestrial arthropods, i.e. effects on reproduction. In additional supporting studies on the toxicity to soil annelids (OECD TG 220), a 21 d EC10 of 27.18 mg Cr(VI)/kg soil d.w. is reported for the effects on reproduction of Enchytraeus coronatus.

Terrestrial Plants

Regarding the toxicity of Cr(VI) to plants, three reliable studies covering altogether 19 plant species are available. The lowest 14 d EC50 and 14 d NOEC values amount to 1.8 mg Cr(VI) /kg soil d.w. and 0.35 mg Cr(VI) /kg soil d.w., respectively, as determined in a study with Lactuca sativa (OECD TG 208).

Soil microorganisms

Three non-reliable studies on the toxic effects of soluble chromium (VI) substances to soil microorganisms are applied in a weight-of-evidence approach. The lowest effect concentration for the toxicity of chromium (VI) to soil microorganisms is the 28 d NOEC of 3.2 mg Cr(VI)/kg soil derived for the inhibition of nitrification.

Altogether, NOEC/EC10 values for the long-term toxicity of chromium (VI) in soil range from 0.35 mg Cr(VI)/kg soil d.w. as observed for plants to 27.18 mg Cr(VI)/kg soil d.w. as observed for invertebrates, and plants appear to be most sensitive.

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