Cobalt chromite green spinel

Endpoint summary

Additional information

The chemical and physiological properties of the pigment Cobalt chromite green spinel are characterised by inertness because of the specific synthetic process (calcination at high temperatures, approximately 1000°C), rendering the substance to be of a unique, stable crystalline structure in which all atoms are tightly bound and not prone to dissolution in environmental and physiological media. This manufacturing process leads to a very low bioaccessibility of the elements contained in the pigment. This has been investigated experimentally in vitro by simulating dissolution under physiological conditions considered to mimic the most relevant exposure routes (oral, dermal and inhalation), as follows:

 

1.) Gamble’s solution (GMB, pH 7.4) which mimics the interstitial fluid within the deep lung under normal health conditions,

2.) phosphate-buffered saline (PBS, pH 7.2), which is a standard physiological solution that mimics the ionic strength of human blood serum,

3.) artificial sweat (ASW, pH 6.5) which simulates the hypoosmolar fluid, linked to hyponatraemia (loss of Na+ from blood), which is excreted from the body upon sweating,

4.) artificial lysosomal fluid (ALF, pH 4.5), which simulates intracellular conditions in lung cells occurring in conjunction with phagocytosis and represents relatively harsh conditions and

5.) artificial gastric fluid (GST, pH 1.5), which mimics the very harsh digestion milieu of high acidity in the stomach.

 

Solubility of Co from the pigment Cobalt chromite green spinel in physiological media was in a range of 17.2µg/L (GMB) and 99.1 µg/L (ALF) after 2 hours. After 24 hours a dissolution range from 12.8 µg/L (GMB) - 108 µg/L (ALF) was measured.

 

Solubility of Cr from the pigment Cobalt chromite green spinel in physiological media was in a range of 0.264µg/L (GMB) and 5.95 µg/L (GST) after 2 hours. After 24 hours a dissolution range from 0.452 µg/L (GMB) - 6.80 µg/L (GST) was measured.

 

In conclusion, since the dissolved Co and Cr concentrations from this pigment under simulated physiological conditions were below 93.8 µg/L and 6.8 µg/L (GST) , respectively even at the highest loading of 0.1g/L, corresponding to a solubility of less than 0.106 % after 24 hours, this pigment may reasonably be considered biologically inert.

 

Justification for classification or non-classification

The chemical and physiological properties of the pigment cobalt chromite green spinel are characterised by inertness because of the specific synthetic process (calcination at high temperatures, approximately 1000°C), rendering the substance to be of a unique, stable crystalline structure in which all atoms are tightly bound and not prone to dissolution in environmental and physiological media. Bioavailability which is the basis for the oral, dermal or inhalation exposure route is negligible. In consequence, this substance may reasonably be considered inert in nearly all media relevant for uptake into the body and also the compartment relevant for distribute within body tissues. Hence, no toxicity effects after repeated dosing are expected and no further testing is considered to be required. No classification for repeated dose toxicity according to EC Regulation No. 1272/2008 is anticipated.