Geochemical characterization and health risk assessment of soil-derived dust in the sistan hotspot: an integrated climate–statistical framework

The Sistan region of southeastern Iran represents among the most persistently dust-affected regions documented globally, where interacting climatic and environmental drivers have produced a sustained air-quality burden of documented public-health significance. We propose an integrated climate-statistical framework coupling robust time-series analysis with geochemical characterization and probabilistic health-risk assessment, applied to a 31-year record (1990–2020, Zabol Station). Trend analysis reveals a highly significant intensification of dust-storm days (Z = 6.83, p < 0.001; Sen’s slope = 4.95 days yr-1), culminating in a structural break in 2004 (bootstrap 95% CI 1998–2010) identified consistently by the Pettitt, SNHT and CUSUM tests, with the Sequential Mann–Kendall crossing at 2007 within that interval and coinciding with the near-complete desiccation of the Hamoun wetland, which shifted the mean from ~ 40 to ~ 145 days yr-1. Rescaled-range exponents computed on the raw series exceed unity and are therefore not admissible Hurst estimates; within the post-2004 regime, where the series is approximately stationary, exponents fall to 0.67–0.79, indicating ordinary persistence. Spectral peaks near 9.8 and 5.8 years are not separable from a red-noise background over a 31-year record. A bounded generalized extreme value model, fitted in the logit domain of the annual dusty-day proportion, projects a post-2004 10-year return level of 158 dust days yr⁻¹ (95% profile-likelihood CI 153–166); the corresponding 100-year level of 162 days yr⁻¹ is exploratory, being conditional on the post-2004 GEV model and extrapolated beyond the record length; a likelihood-ratio test decisively favours a non-stationary formulation, so return levels beyond the 10-year horizon are reported as exploratory. Transfer entropy provides no statistically significant evidence of directional coupling in any direction once estimator bias is corrected (smallest surrogate p = 0.29); these results are reported as a null finding. Geochemical profiling indicates enrichment of Pb (EF = 11.5), Cu, Zn and Ni relative to crustal background; the inhalation hazard index is 24.9 and the total incremental lifetime cancer risk is 7.4 × 10⁻⁴ as an upper bound. Annual-mean PM10 (435 ug m-3) and PM2.5 (308 ug m-3) exceed WHO guidelines 29- and 62-fold, with modelled exceedance probabilities approaching unity up to 20× and 50× respectively. On the balance of physical reasoning and the changepoint chronology, hydrological restoration of the Hamoun basin is advanced as the most plausible structural mitigation priority, a hypothesis these data support but do not establish causally.