Human health risk assessment of PM 2.5 -bound heavy metals during a haze season in a semi‑urban agricultural area of Northern Thailand

Abstract

This study assessed PM2.5-bound heavy metals (Cd, Pb, Cr, Cu, and Fe) and associated human health risks at a semi-urban-agricultural site in Phitsanulok, lower northern Thailand, during the 2024–2025 haze season. Enrichment factors (EF), geoaccumulation index (Igeo), and US EPA health risk models were applied to characterize metal sources and to estimate noncarcinogenic and carcinogenic risks for adults and children. The mean 24-h PM2.5 concentration (55.96 µg m−3) exceeded both WHO guidelines (15 µg m−3) and the Thai national standard (37.5 µg m−3). Fe was the dominant metal, followed by Cr, Pb, Cu, and Cd; EF > 10 for Cr, Pb, Cu, and Cd indicated significant anthropogenic enrichment, while Igeo classified Cd as moderately polluted. Hazard indices (HI < 1) indicated negligible noncarcinogenic risk for all exposure routes and age groups. However, total inhalation carcinogenic risk exceeded 1 × 10−4 for children (2.13 × 10−4; moderate risk), primarily driven by Cr, while adults presented a lower but non-negligible risk (6.56 × 10−5). These findings identify Cr containing PM2.5 inhalation during haze episodes as a priority health concern, particularly for children, underscoring the need for targeted emission controls in semi-urban-agricultural areas.