Health risk assessment of combined exposure to heavy metals diazinon and mycotoxins in Iranian rice

Rice ecosystems in northern Iran face co‑exposure to heavy metals; lead (Pb), cadmium (Cd), chromium (Cr), and nickel (Ni); the organophosphate pesticide diazinon, and major mycotoxins. We conducted an integrated Human Health Risk Assessment (HRA) to translate concentration data into actionable non‑carcinogenic risk indices; the Target Hazard Quotient (THQ) and Hazard Index (HI); for adults and children. Composite samples from five counties (Sari, Fereydunkenar, Rasht, Astaneh‑Ashrafieh, Kalat) were collected across two cropping seasons (no second‑season rice in Kalat). Metals were quantified by Atomic Absorption Spectrometry (AAS), Graphite Furnace AAS (GFAAS) for Pb and Cd, Flame AAS (FAAS) for Cr and Ni; diazinon by Gas Chromatography-Mass Spectrometry (GC-MS); and mycotoxins by High‑Performance Liquid Chromatography with Fluorescence Detection (HPLC‑FLD) following national standards. Non‑carcinogenic risk was estimated using THQ and HI. In rice, mean concentrations spanned Cd 0.04-0.44, Cr 0.08-4.80, Pb 0.33-0.74, and Ni 0.38-1.25 ppm; diazinon was 3.3-6.7 ppb. Ochratoxin A (OTA) exceeded 5 ppb in all regions except Kalat; Totat aflatoxin and aflatoxin B1 remained below 10 and 5 ppb, respectively; Zearalenone and deoxynivalenol were below 200 and 1000 ppb. For non‑carcinogenic risk, HI_Total > 1 in all Region × Season combinations for adults (9/9) and children (9/9). The maxima occurred in Sari‑second crop (adults ≈ 5.86; children ≈ 11.94). In humid Guilan (Rasht, Astaneh‑Ashrafieh), OTA dominated HI, whereas in Mazandaran (Sari, Fereydunkenar), Cr was the principal driver; diazinon contributed negligibly (THQ ≪ 1). The integrated HRA identifies Cr and OTA as the key risk drivers, with consistently higher HIs in children due to a larger IR/BW ratio. Priority actions include source control for Cr (e.g., fertilizer management, water quality safeguards) and post‑harvest moisture control to suppress OTA; diazinon residues, while detectable, are unlikely to materially impact non‑carcinogenic risk at current levels.