Slags, ferronickel-manufg.

Endpoint summary

Additional information

Ecotoxicity tests on Ferronickel slags show a lack of toxic effects and no need for classification as hazardous to the aquatic environment. The substance has very low solubility and its individual constituents are bound in the mineral matrix and are thus less bioavailable than in their free form. Such low concentrations tend to dissipate very quickly in large water bodies due to the currents, so it is improbable to maintain a sufficiently high concentration in the long-term. Literature read-across review was performed on the effects of the individual constituents of the substance.

Most of its main constituents are highly insoluble and only Calcium and Sulfur seem to have a more significant solubility, according to the results of the water solubility test. Sulfur has no toxic effects for the aquatic environment, while calcium's effect is mainly its contribution to the water's pH after its transformation to Ca(OH)2. However, in large dilutions (e.g. in sea or in rivers where constant current exists) this has insignificant effect and, furthermore, Calcium Oxide is bound in the mineral matrix of the slags which reduces significantly its reactivity (this was proven with the two acute irritation/corrosion tests that were performed in a high-CaO sample of ferronickel slags (Stelter 2010a, Stelter 2010b)).

Of the other components, Iron and Magnesium have no known toxic effects to the aquatic environment whatsoever and their solubility in water is insignificant. Aluminium has been found to produce toxic effects in short-term exposure, but its low solubility (due to its stable form of Aluminium Oxide and its inclusion in the matrix of the slag) and concentration in the slag prevent it from producing any adverse effects.

Nickel and Chromium are considered to be the two most potentially hazardous constituents. Nickel exists in the slag in its metallic form (in the form of ferronickel granules), while Chromium is in its less toxic form Cr(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 maximum solubilities in water of these elements that were identified with the water solubility test (Endpoint 4.8) are insufficient to produce adverse effects in short-term exposure of aquatic flora and fauna. Even though, long-term exposure requires lower concentrations of these elements, available chronic exposure tests in various aquatic organisms show no toxicity of the slags (Weber 2012, Gonsior 2012).

In-house and published studies have shown that there is some (inconclusive) evidence for bioaccumulation of slags. Generally, experimental studies in the local environment, where ferronickel slag is known to be deposited, indicate that the local environment is enriched with a variety of metals and these metals are accumulated by marine organisms. However, different species accumulate different metals to a different extent and assessments of the effects of pollution must be taken into account.

Based on the information above, there is sufficient data to characterise slags, ferronickel-manufg. as not dangerous for the aquatic environment. The information is also insufficient to classify it as dangerous for the aquatic environment for chronic effects, but care should be taken due to the presence of substances like Trivalent Chromium and Nickel and possible chronic aquatic hazards may be expected. The Aquatic toxicity of slags, ferronickel-manufg. is under continuous evaluation.

It is noted that the Chromium from the slags has been experimentally verified to be trivalent and no hexavalent chromium has been identified in measurements at aquatic environments near production plants (in-house stydy, available at request).