Slags, nickel smelting

Endpoint summary

Description of key information

Complex metal containing substance
Water solubility of the substance is poor (for metal constituents)
Several high quality studies on nickel slag and analogue substance (copper slag) demonstrate no negative effects .An LDs 50 of > 2000 mg/kg bw were assessed. Nickel slag is considered non toxic via oral, dermal and inhalation route.
Classification based on rules for mixtures 
In vitro bio-accessability in artificial biological fluids ( gastric and sweat)

Key value for chemical safety assessment

Acute toxicity: via dermal route

Endpoint conclusion

Dose descriptor:

discriminating dose

Additional information

The nickel slag is a complex metal containing substance (UVCB). It mainly contains iron silicate and silicates of aluminum and calcium. Traces of metals exist in metal, mineral form or included in silicate phases.

Substance is used in massive or granular form with varying particle size distribution (IUCLID section 4.5). Routes for exposure to consider are therefore oral and inhalation.

Nickel slag is inorganic solid poorly soluble in water. It is not likely to penetrate though organic media. Absorption of nickel slag through the skin is therefore considered to be of less significance than absorption through the respiratory and gastrointestinal routes.

 The following test data were obtained for the analogue substance (copper slag)

- The acute oral effects - LD₅₀> 2000 mg/kg (3 studies)

- The acute dermal effects - LD₅₀> 2000 mg/kg (2 studies)

These data are used to predict the absence of acute oral and dermal effects (LD₅₀> 2000 mg/kg ) for the nickel slag based on read accross from the analogue substance.

Additionally classification of the nickel slag was derived based on rules for mixtures:

-         The calculated Oral Acute toxicity estimate of the mixture is > 2000 mg/kg

-         The calculated Inhalation Acute toxicity estimate of the mixture is > 5mg/l

Results from calculated classification are further supported (WoE) by consideration of physical chemical properties of the UVCB substance.

Chemistry and mineralogy of the slag (see IUCLID section 4.23 chemical and mineralogical characterization) were taken into account.

Water solubility (IUCLID section 4.8) and Sequential dissolutions (IUCLID 4.23 Chemical assays) furthermore confirmed species present and their solubility behavior.

In vitro measurements of bio-accessibility in solvent that resembles gastric fluid performed according to ASTM D5517.07. (pH 1.5) The fraction of metals that solubilize under these conditions can be considered as worst case determinant of bio-associability of metals contained in the slag. Results demonstrated reduced bio-accessibility of metals (Cu 0.04, Ni 0.05, Co 0.06, dissolved concnetrations of Pb and As below detection limit) thus further confirm that there is no need for classification.

Justification for classification or non-classification

Acute oral classification

Based on the available acute oral toxicity data for the analogue substance (i. e LD50> 2000 mg/kg) and calculated Oral Acute toxicity estimate (ATE >2000 mg/kg) nickel slag is not classified as hazardous for acute toxicity by the oral route.

 Acute inhalation classification

No test data on acute inhalation toxicity are available. The calculated Inhalation Acute toxicity estimate of the mixture is > 5mg/l thus nickel slag is not classified as hazardous for acute toxicity by the inhalation route. Result is further confirmed by extrapolation from oral to inhalation route based on worst case 100% absorption rate. Using ATE oral: 2000 mg/kg bw and the extrapolation formula 1mg/kgbw = 0.0052 mg/l/4h, theinhalation ATE will be 10.4 mg/l/4h.

 Acute dermal classification

Consideration of available acute dermal toxicity data on the analogue substance (i. e. LD₅₀>2000 mg/kg) leads to the conclusion that the target substance nickel slag does not require classification for acute lethal effects.

Nickel slag is an inorganic solid poorly soluble in water. It is not likely to penetrate through skin in any significant quantity and so would therefore not cause any toxic effects following dermal exposure. Furthermore, negligible metal release in in-vitro bio-accessibility test in artificial sweat fluid was observed (0.018 µg Ni/cm2/week).

The classification derived is applicable to all nickel slags.See end-point record and discussion above for detailed justifications. 

The assessed samples and derived classifications are representative for typical nickel slags, across the industry, and defined within the concentration ranges outlined under IUCLID section 1.2.

Self-classification of the UVCB substance (IUCLID Section 2.1 & 2.2) was performed based on the following outline:

1. Characterization

The substance is accurately described with elemental composition (typical concentrations and concentration ranges–IUCLID Section 1.2), and specific speciation data (mineralogical composition) obtained from the respective representative samples (IUCLID Section 4, in particular 4.23). This detailed information on the substance identity is used as a basis for the classification.

2. Classification by the rules for mixtures

The UVCB is considered as complex metal containing substance with number of discrete constituents (metals, metal compounds, non-metal inorganic compounds).

The classification is based on summation (additivity) referring to the classified constituents present in the UVCB substance. Specific concentration limits are taken into account.

This concept and classification rules are incorporated in easy to use IT tool which is used to classify the UVCB substance.

3. Bridging or Read-Across

Toxicological data (oral and dermal toxicity) are available for the analogue/surrogate substance copper slag.

Read accross from the analogue substance (copper slag) to the target substance (nickel slag) is applied (structural analogues with similar chemical and mineralogical composition and physical/chemical properties).

Considering variability in composition, read-across and bridging is applied by using representative mineralogical/speciation composition combined with the metal concentration ranges (see composition in section 1.2) as a basis for the classification of the UVCB substance see IUCLID 1.4 for information on Sampling procedure).

4. Bioavailability consideration

Data from bio-accessibility test in solutions that resemble gastric fluid and sweat are used to further confirm the classification.

SeeArche Complex Metal Mixture classification calculator (copper version June 2010); MeCLAS webpage: www. meclas. eu