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Toxicity to terrestrial plants

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Description of key information

In general, it can be said that Slags, ferronickel manufg. do not contain substances that are toxic to the terrestrial environment. Iron, Calcium, Aluminium and Magnesium are common elements that have no toxicity towards terrestrial organisms.Chromiumexistsin its less toxic formofCr(III). A study on the speciation of Chromium in Ferronickel slags using alkaline digestion and colorimetric analysis (EPA 3060A and EPA 7196A respectively) showed that no hexavalent Chromium species were present up to the limit of detection of the analytical method (20mg/kg) so all Cr in the substance is considered to be in trivalent form(NTUA 2011c). 
The read-across approach for the available studies has shown that Nickel is the constituent of highest concern, but its toxicity for terrestrial organisms is much lower than its aquatic toxicity.
Additionally, the substance has very low solubility in water (ref.), therefore it poses no risk for plant life and soil microorganisms. Its most soluble components, Calcium and Magnesium, are common nutrients. Other terrestrial organisms that feed directly from the ground are more exposed, but the lack of solubility of the slags in water does not allow them to pass to tissues and cause toxicity. The coarse form of the material’s particles (see granulometry studies) decrease the bioavailability (and the solubility) of the substance to other soil macroorganisms (such as earthworms).
The various constituents of the slags are chemically bound in the mineral matrix of the substance and they do not dissociate readily into ionic form. Ionic forms of elements are more water soluble and, in general, more toxic (locally or systemically) to living organisms. Very low concentrations of nickel and chromium in ionic form indicate that toxicity is highly unlikely.

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for terrestrial plants:
2 200 mg/kg soil dw

Additional information

Data on the toxicity to terrestrial plants for slags, ferronickel-manufg. is not available for the whole substance. Until a relevant study is performed on slags, ferronickel-manufg., it was attempted to identify possible adverse effects based on data for its recognised constituents, even though the results cannot be applied directly, due to the way the constituents are bound in the matrix of the substance and are not as bioavailable as the free substances that are examined. So, the results must be taken into consideration with care.

Studies on Cr(III), which is the chromium species in ferronickel slags showed some effects only at the highest load of 1000mg/kg dw, leading to a NOEC of 750mg/kg soil dw which would lead to a significantly higher slag concentration in the range of 23 g slags/kg soil dw. A short-term exposure of wheat saplings to metalic ions (Al, Ni, Fe, Cr, Mg, Mn) resulted in growth inhibition of the roots and shoots of the tested species for Al(3+), Ni(2+) and Cr(2+), while no significant effects were observed for Fe(2+), Mg(2+) and Mn(2+). The effects for aluminium were observed at a pH of around 4, while for the other elements in neutral pH. Cr(2+) showed the more severe effects, followed by Nickel. However, it is in a form different than the one observed in Ferronickel slags, so these results must be carefully considered. Additionally, Nickel in ferronickel slags is in a very insoluble form and thus not much bioavailable, so it is unlikely that it will produce such inhibitory effects on terrestrial plants.

Studies on the effects of Nickel species to various plants has resulted in a broad range of long-term NOEC values, namely from 13mg Ni/kg dw to 467mg Ni/kg dw. Taking the worst case scenario for Nickel content of the Ferronickel slags (0.6%), a NOEC of 2200mg Ferronickel Slag/kg dw can be derived, after projecting to the whole substance. This number is only indicative and might be higher, however, because the bioavailability of Nickel in Ferronickel slags is expected to be very low.

In general, it can be said that Slags, ferronickel manufg. do not contain substances that are toxic to the terrestrial environment. Iron, Calcium, Aluminium and Magnesium are common elements that have no toxicity towards terrestrial organisms.Chromiumexistsin its less toxic formofCr(III). A study on the speciation of Chromium in Ferronickel slags using alkaline digestion and colorimetric analysis (EPA 3060A and EPA 7196A respectively) showed that no hexavalent Chromium species were present up to the limit of detection of the analytical method (20mg/kg) so all Cr in the substance is considered to be in trivalent form(NTUA 2011c).

The read-across approach for the available studies has shown that Nickel is the constituent of highest concern, but its toxicity for terrestrial organisms is much lower than its aquatic toxicity.

Additionally, the substance has very low solubility in water (ref.), therefore it poses no risk for plant life and soil microorganisms. Its most soluble components, Calcium and Magnesium, are common nutrients. Other terrestrial organisms that feed directly from the ground are more exposed, but the lack of solubility of the slags in water does not allow them to pass to tissues and cause toxicity. The coarse form of the material’s particles (see granulometry studies) decrease the bioavailability (and the solubility) of the substance to other soil macroorganisms (such as earthworms).

The various constituents of the slags are chemically bound in the mineral matrix of the substance and they do not dissociate readily into ionic form. Ionic forms of elements are more water soluble and, in general, more toxic (locally or systemically) to living organisms. Very low concentrations of nickel and chromium in ionic form indicate that toxicity is highly unlikely.

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