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Description of key information

Leuko Sulphur Brown 37 has a polymeric structure and becomes insoluble at pH below 12. It is, therefore, not bio-available beyond the portal of entry. Relevant distribution as well as metabolism and excretion are most unlikely for such a material.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Leuko Sulphur Brown 37 is produced and handled as a strongly alkaline solution of the reaction product of formaldehyde and m-phenylene-diamine with sodium sulfide and sulphur. The pH-value of this solution is about 13. The solution is corrosive and cannot be tested in biological systems. The dye molecules are supposed to have a variable polymeric structure made of a three-dimensional network of sulphur chains connecting the condensates of formaldehyde and the aromatic amine. The molecular weight of this material is mostly between 2000 and 150 000. Less than 1.3 % is below 1000 Dalton.

Absorption: Leuko Sulphur Brown 37 is soluble only at high pH. Therefore, the solution is expected to act corrosive on living tissues and to destroy the natural barriers. The material is soluble in water and, as long as the pH is high, it is expected to be readily bio-available at the portal of entry. However, if the material should diffuse into tissue or be applied in small amounts the pH value will be influenced by the buffering capacity of physiological media, which leads to precipitation of the neutral form of the dye. Thus in the acidic environment of the stomach immediate precipitation will occur. After application to the skin either corrosive action or neutralization with consequent precipitation will occur. The salt form will therefore, not be absorbed systemically. Due to the minimal solubility of the neutral form significant absorption is also not expected.

Distribution: Due to the low solubility of the neutral form of the dye, which is the only form compatible with living tissue, and the high molecular weight no distribution beyond the portal of entry is expected.

Metabolism: Leuko Sulphur Brown 37 has mostly a molecular weight above 1000 Dalton and is very poorly soluble at physiologic pH. Significant metabolism is only expected if the substrate is soluble in water at physiological pH and is transported through biological membranes into cells. Due to the high molecular weight, the poor solubility and the polymeric structure such transport is not expected. Significant metabolism is therefore also considered unlikely.

Excretion: As Leuko Sulphur Brown 37 is not expected to become available to metabolism or transport in a living organism, it is also not expected to be excreted via the main excretory organs (kidney or liver/gall bladder). If applied orally most of the material will be eliminated via the feces. After skin exposure it will be eliminated via the natural turnover of skin cells.