Mehri et al. 2024 — Potentially toxic elements in edible vegetable oils, Hamadan, Iran
This study measured five potentially toxic elements (tAs, Cd, Pb, Fe, Zn) in 40 samples of traditional and industrial edible vegetable oils (peanut, sunflower, olive, sesame) from Hamadan, western Iran, collected in 2022 using ICP-OES after microwave-assisted acid digestion. Industrial oils had significantly higher concentrations of tAs, Fe, and Zn than traditional oils (p < 0.001), though all samples fell below Codex and Iranian national limits for Pb (0.1 mg/kg), Cd (0.05 mg/kg), and tAs (0.1 mg/kg). While non-carcinogenic risk (TTHQ) was within safe ranges for both adults and children, carcinogenic risk from inorganic arsenic in industrial oils exceeded the safe threshold (CR > 1×10⁻⁶), driven by the high tAs concentrations in industrial olive and peanut oils.
Key numbers
Method: ICP-OES with microwave acid digestion (HNO3 65% + H2O2 30%). LOD: As 0.16 µg/L, Cd 0.02 µg/L, Pb 0.12 µg/L. LOQ: As 0.50 µg/L, Cd 0.09 µg/L, Pb 0.41 µg/L. Recovery: 95–100%.
Traditional oils (n=20, mean ± SD, mg/kg wet weight):
- Olive: tAs 0.060 ± 0.022; Cd 0.005 ± 0.002; Pb 0.014 ± 0.004; Fe 8.928 ± 0.913; Zn 3.756 ± 0.538
- Sunflower: tAs 0.052 ± 0.032; Cd 0.011 ± 0.006; Pb 0.011 ± 0.003; Fe 2.195 ± 1.226; Zn 2.102 ± 0.654
- Sesame: tAs 0.064 ± 0.037; Cd 0.009 ± 0.004; Pb 0.009 ± 0.004; Fe 15.091 ± 1.182; Zn 3.192 ± 2.143
- Peanut: tAs 0.005 ± 0.003; Cd 0.006 ± 0.002; Pb 0.025 ± 0.035; Fe 5.655 ± 1.477; Zn 2.863 ± 1.977
Industrial oils (n=20, mean ± SD, mg/kg wet weight):
- Olive: tAs 0.113 ± 0.028; Cd 0.007 ± 0.002; Pb 0.016 ± 0.002; Fe 11.739 ± 2.147; Zn 3.644 ± 0.458
- Sunflower: tAs 0.053 ± 0.021; Cd 0.010 ± 0.004; Pb 0.016 ± 0.003; Fe 0.097 ± 0.028; Zn 3.551 ± 0.542
- Sesame: tAs 0.091 ± 0.033; Cd 0.009 ± 0.003; Pb 0.013 ± 0.002; Fe 23.664 ± 2.698; Zn 6.299 ± 0.974
- Peanut: tAs 0.089 ± 0.038; Cd 0.009 ± 0.002; Pb 0.027 ± 0.045; Fe 11.323 ± 1.726; Zn 8.835 ± 1.346
Health risk (probabilistic Monte Carlo, 50,000 iterations):
- TTHQ adults/children traditional: 0.201 / 0.133 (both < 1, safe)
- TTHQ adults/children industrial: 0.408 / 0.285 (both < 1, safe)
- Carcinogenic risk (CR) for inorganic As, traditional: adults 7.54×10⁻⁵, children 5.28×10⁻⁵ (both > 1×10⁻⁶, unacceptable)
- CR industrial: adults 1.61×10⁻⁴, children 1.15×10⁻⁴ (both > 1×10⁻⁶, unacceptable)
Codex/ISIRI limits: Pb 0.1 mg/kg, Cd 0.05 mg/kg, tAs 0.1 mg/kg. Fe limit (ISIRI) 1.5 mg/kg — all Fe values from traditional oils (except industrial sunflower) exceeded this quality threshold.
Methods
ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry). Microwave-assisted acid digestion: 1 mL sample + 6 mL HNO3 (65%) + 2 mL H2O2 (30%); stage 1 at 80°C (1 h), stage 2 at 150°C (3 h). Arsenic reported as total arsenic (tAs) — ICP-OES does not speciate; iAs fraction not determined. Non-carcinogenic risk assessed via THQ/TTHQ; carcinogenic risk via cancer slope factor for inorganic As (CSF = 1.5 [mg/kg-d]⁻¹). Monte Carlo simulation (log-normal distributions, 50,000 iterations). Ingestion rates: adults 100 g/day oil, children 20 g/day. Study period: 2022. n=5 per oil type per category.
Note: the cancer risk calculation applies the inorganic arsenic CSF to total arsenic concentrations; if tAs includes significant organic fractions (less toxic), the carcinogenic risk may be overstated. This is a methodological limitation acknowledged implicitly by the study.
Implications
Certification: Pb and Cd values in all samples were below Codex/ISIRI limits. The elevated Fe in sesame oils (15–24 mg/kg) and arsenic carcinogenic risk signal areas for supplier specification attention, particularly for industrial-sourced oils.
Courses: Illustrates that industrial processing (bleaching, refining, deodorization) can concentrate certain metals (tAs, Fe) relative to traditionally pressed oils, contrary to consumer expectation.
App: Supports flagging industrial vegetable oils — especially olive and peanut — for elevated tAs relative to traditionally pressed equivalents. Pb and Cd remain low across all oil types in this Iranian study.