The microbial decomposition of chromium tanned leather

The microbial decomposition of chromium tanned is poorly understood with relatively few reported studies existing. In this study, investigations into the microbial decomposition of leather waste, under a variety of simulated environmental conditions, were performed. Also investigated was the action of collagenase and pepsin enzymes on leather substrates and the effects of chromium oxidation state on proteolytic hydrolysis. Animal derived waste such as leather, containing high levels of nitrogen (ca. 16%) are generally considered high quality resources capable of degrading readily. However, the tanning process, whereby chromium and pesticides are incorporated into the collagen matrix, results in the reduction of substrate quality and reduced microbial decomposition. In this study, significant decomposition (20% as evidenced by nitrogen mineralization), was observed after long term (330 day) incubation. No increase in decomposition was observed with carbon and nitrogen amendments, although hydrolysis (autoclaving) of samples resulted in extensive decomposition (75%) after an initial 20 day delay. The cumulative enzyme action of collagenase and pepsin was required for the complete dissolution of chrome leather (95%), suggesting that collagenolytic activity is required to cleave the collagen structure, prior to proteolysis. Pepsin was not affected by chromium, whereas collagenase was significantly inhibited by concentrations of Cr(III) greater than 1 ppm, when available in solution, but was not inhibited by bound inert chromium in leather. Results from microbial and enzyme studies suggest that the intracellular physiology of decomposer microorganisms may be affected by the assimilation of chromium bound amino acids, although further work is needed in this area