Triangulating health risks of PM2.5 and trace elements in Pretoria: evidence from health risk assessment, case-crossover, and concentration-response function analyses.

Fine particulate matter (PM2.5) is a major contributor to the global burden of disease. Previous studies have assessed health risks using toxicological screening or epidemiological association separately, with limited attention to chemical composition. This study integrates health risk assessment (HRA), case-crossover (CCO) analysis, and concentration-response functions (CRFs) to quantify the respiratory burden of PM2.5 mass and PM2.5-bound trace elements in Pretoria, South Africa. Secondary datasets of sampled PM2.5 concentrations, elemental composition, and respiratory hospital admissions (ICD-10 J00-J99) from April 2017-February 2020 were analysed. HRA estimated hazard quotients (HQs) for adults, children, and infants. CCO models quantified short-term associations per 10 µg/m3 increase in PM2.5, per interquartile range (IQR) increase in elements. CRFs translated coefficients into attributable fractions and cases under South African and World Health Organization counterfactual scenarios. PM2.5 HQs exceeded unity across all age groups. The CCO estimated an OR of 1.027 (95% CI: 1.006-1.049) per 10 µg/m3 increase. Aligning concentrations with the South African standard would avert 158 admissions annually, increasing to 342 and 748 under WHO daily and annual guidelines. Element-specific CRFs estimated 110-608 attributable admissions annually.