Heavy metal pollution in cement tile production: impact evaluation through grey water footprint, ecological risk and life cycle assessment

Cement tile manufacturing is a traditional industry in Iran, yet wastewater-related heavy metal pollution raises sustainability concerns. This study evaluates the environmental pollution using three distinct approaches. (1) The grey water footprint (GWF) quantifies the volume of freshwater required to assimilate pollution, based on net discharged loads and the receiving environment's limitations. (2) The ecological risk index (ERI) assesses contamination factors using pollutant concentrations and their ecological toxicity. (3) Life cycle impact assessment (LCIA) aggregates environmental damages across domains. Fifteen heavy metals were analysed at a facility in Isfahan, central Iran, during a six-month fall‒winter monitoring period (October 2024 to March 2025). The findings presented here reflect this seasonal window and should be interpreted accordingly. On the basis of this fall‒winter dataset, aluminium proved to be the critical pollutant for GWF (10.6 L/m2 of tile; uncertainty range: 4.1–17.1 L/m2 based on ±1 SE propagation), which requires a lot of freshwater to assimilate it per m2 of tile. The most toxic of the elements, cadmium, more than tripled the ERI score at 6845, well above the ‘very high risk’ cutoff. However, the ecological risk assessment, which relies on total metal concentrations and overlooks element speciation, may misrepresent toxicity, evident for chromium, whose risk score ranges from 6845 for trivalent to 7268 for the more toxic hexavalent form. LCIA results showed that global warming accounted for 90% of total damage, overshadowing the impacts of heavy metals on human health (6%) and ecosystems (4%). This LCIA adopted a gate-to-gate scope covering only the tile-forming operation (pressing and curing at ambient temperature); upstream cement production was excluded, meaning the relative contribution of global warming would be substantially higher under a cradle-to-gate boundary. The divergence between significant regional ecological risks posed by heavy metals and the globally dominant impact of carbon emissions highlights the need for comprehensive sustainability assessments that use multiple indicators. These findings reveal that while metal pollution poses significant regional risks, its global impact is dominated by carbon emissions. The contrasting results across methods underscore the necessity of multi-indicator approaches for a comprehensive sustainability assessment.