Biodegradability of Chromium-Free Finished Leather Through ISO 14855-1:2012 and ISO 20136:2020: A Multi-Faceted Analytical Approach

While various methodologies have been used to evaluate leather biodegradability, limited data exist regarding their respective strengths, limitations and complementarity, especially for finished leathers produced using chrome-free tanning systems. Consequently, this work assesses the biodegradation of eight commercial eco-friendly tanned finished leathers (phenolic-, zeolite-, aluminium- and titanium-based treatments) using two standardised laboratory approaches, ISO 14855-1:2012 (controlled composting) and ISO 20136:2020 (liquid-phase biodegradation), together with physicochemical characterisation and phytotoxicity/ecotoxicity endpoints. The results showed that biodegradation generally occurred faster under ISO 20136:2020 conditions, mainly because this assay uses ground leather shavings and an aqueous, well-mixed medium, whereas ISO 14855-1:2012 evaluates mineralisation of larger leather pieces in a compost matrix. Phenolic- and titanium-tanned leathers showed consistently high biodegradation in both assays, whereas the aluminium-tanned leather biodegraded efficiently under ISO 14855-1:2012 but showed limited biodegradation under ISO 20136:2020, highlighting that assay conditions can reveal constraints related to the complete material architecture, collagen stabilisation, effective accessibility and method-specific exposure conditions rather than to a single leaching mechanism. Phytotoxicity and ecotoxicity assessments indicated low environmental impact of the degradation products under the tested conditions. Overall, the combined use of both standards provides a more comprehensive and industrially useful framework for assessing the end-of-life behaviour of finished leathers than either method alone.