Abstract

Hexavalent chromium (Cr6+) is formed in chrome-tanned leather due to oxidation of trivalent chromium (Cr3+) under certain conditions and may induce dermatitis and cancer. Specifically, significant amounts of Cr6+ are generated during the heat-ageing process by pre-heating at 80°C for 24 hours in accordance with ISO method 17075, promoting the formation of Cr6+ from Cr3+ in chrome-tanned leather. Thus, inhibiting or minimizing the production of Cr6+ is needed badly. A previous report demonstrated that 0.1mol/L potassium phosphate buffer (P-buffer; pH5.5) was highly efficient as an extractant for the measurement of Cr6+ from chrome-tanned leather as compared with P-buffer (pH8.0).

The present report describes efforts to control the redox behaviour of Cr3+ with the goal of inhibiting the formation of Cr6+ in chrome-tanned leather using a low-molecular weight (Mw 9,400) collagen peptide (CP-9), 2, 6-di-t-butyl-4-methylphenol (BHT), 3(2)-t-butyl-4-hydroxyanisole (BHA), and ascorbic acid (AsA) as inhibitors, even with heat-aged leather. Chrome-tanned leather was treated with the inhibitors, and the resulting leather samples were extracted with P-buffer (pH5.5) to determine the amount of Cr6+ in the extracts. The results showed that CP-treatment significantly reduced the amount of Cr6+ formed, probably due to a combination of chelation of CP on the Cr3+ complex, quenching of reactive oxygen, and radical scavenging. The BHT, and BHA, and AsA treatments also reduced the amount of Cr6+ formed, probably due to scavenging radicals from the oxidative products of the fatliquoring agent and alterations in the reducing conditions. However, treatment with any of the inhibitors individually did not cause complete inhibition of Cr3+ oxidation. Therefore, the action of the combined inhibitors was investigated. The results demonstrated that treatment with BHA + CP and with BHA + AsA produced a synergistic reduction in Cr6+ production. Use of BHA + AsA + CP completely inhibited the formation of Cr6+ from heat-aged leather samples.