Physical and chemical characterisation of ophthalmic lens-grinding wastewater: uncovering environmental implications

The ophthalmic industry's eyewear lens production generates substantial waste during the lens grinding processes, contributing to significant environmental challenges. This process consumes approximately 20 L of water per eyeglass lens pair, which is subsequently discharged directly into wastewater systems, releasing a complex mixture of pollutants, including micro- and nanoplastics, into the environment. This study investigates the wastewater generated by lens grinding machines within the optical retail sector and provides a detailed physical and chemical characterisation of this waste stream. The results revealed a significant material loss during grinding, with approximately 50% of each initial lens mass being discharged during cutting. Based on conservative estimates, 5,770 tonnes of plastic waste are released into the environment each year, the equivalent of filling and discarding a marine container every 42 h. RAMAN analysis identified TiO2 in both anatase and rutile crystalline forms in the lens coatings, both of which are recognised as emerging environmental pollutants. The characteristic N-H stretching vibrations of polyurethanes were detected in the FTIR analysis. Other hazardous contaminants, including particles below 2 µm, heavy metals, bisphenol A, phthalates, and fluorine-containing compounds, were also identified through SEM, NMR, and GC-MS. The presence of these substances raises significant concerns, as they are known endocrine-disrupting chemicals and persistent organic pollutants, which pose a significant risk to aquatic ecosystems and human health. Our findings revealed that while global lens consumption is driven by diverse regional preferences and multiple factors, waste generation is inherently systemic and independent of consumer choice, representing a structural technological constraint of current optical manufacturing processes. This study provides new, valuable information to alert the practitioners, competent authorities, policy makers, and society, supporting the development of future policies, alternative materials, and improved waste management strategies within the downstream ophthalmic value chain.