Ashraf 2012 — Heavy metals in seven vegetable oil varieties consumed in Saudi Arabia
This study determined concentrations of seven heavy metals (Cu, Zn, Fe, Mn, Cd, Pb, As) in 161 commercially available edible vegetable oil samples from Saudi hypermarkets using graphite furnace atomic absorption spectrometry (GF-AAS) after microwave digestion, verified against NIST SRM 1577b. The authors conclude that estimated daily and weekly dietary intakes from 25 g of oil per day (WHO recommended maximum) remain well below the JECFA provisional tolerable weekly intakes (PTWIs) for all metals, posing no significant health risk to the Saudi population.
Key numbers
All concentrations are wet weight, µg/g, except cadmium (ng/g).
Arsenic (total tAs): range 0.011–0.018 µg/g across all oil types; sesame oil and rapeseed oil highest (0.018 µg/g each), corn oil lowest (0.011 µg/g). LOD = 0.121 µg/g — note: all reported As values fall below the GF-AAS LOD listed in Table 6, indicating these values may represent estimated upper-bound concentrations or were derived from the certified reference material calibration; interpret with caution.
Cadmium: range 2.36–6.34 ng/g (i.e. 0.00236–0.00634 µg/g or 2.36–6.34 ppb); corn oil highest (6.34 ± 0.51 ng/g), olive oil lowest (2.36 ± 0.11 ng/g); sesame oil (5.78 ± 0.21 ng/g) and rapeseed oil (5.71 ± 0.11 ng/g) also elevated.
Lead (Pb): range 0.011–0.017 µg/g for oils with detectable Pb; corn oil, olive oil, and rapeseed oil were below detection limit (BDL); sesame oil highest (0.017 ± 0.002 µg/g). LOD for Pb by GF-AAS = 0.098 µg/g — all reported Pb values also fall below the stated LOD, rendering them as < LOD or near-LOD estimates rather than reliable quantification; flag this limitation.
Estimated weekly dietary intake (EWDI) vs JECFA PTWI (for 70 kg adult, 175 g oil/week):
- Cd: 0.006–0.016 µg/kg bw/week vs PTWI of 7 µg/kg bw — less than 0.3% of PTWI
- Pb: 0.028–0.043 µg/kg bw/week vs PTWI of 25 µg/kg bw — less than 0.2% of PTWI
- As: 0.028–0.045 µg/kg bw/week vs PTWI of 15 µg/kg bw — less than 0.3% of PTWI
Methods
GF-AAS (Shimadzu AA-6200 with HGA graphite furnace, ASC 6100 autosampler). Microwave digestion with HNO3 and H2O2. Argon inert gas. Recovery >95% for all elements (Table 5). Certified reference material NIST SRM 1577b (bovine liver); agreement within 1–3% of certified values (Table 6). Measurements on wet weight basis. Samples run in triplicate.
Analytical limitation: The detection limits reported in Table 6 are notably high relative to reported concentrations — Pb LOD 0.098 µg/g and As LOD 0.121 µg/g exceed or approach most reported values in Table 1, calling the quantitative reliability of Pb and As results into question. These values may represent upper-bound estimates rather than confirmed detections. Cd LOD (0.092 ng/g reported as µg/g — likely a typographical unit inconsistency in the source) is more plausible given the ng/g-scale Cd values reported.
Implications
Certification: Vegetable oils from the Saudi market show very low Cd (< 6.4 ng/g = < 6.4 ppb) and near-detection-limit Pb values. This provides useful international comparison data for HMT&C ingredient profiles for culinary oils, though the LOD issues limit confidence in the As and Pb numbers specifically.
Courses: Illustrates the role of GF-AAS methodology and the importance of matching analytical LODs to expected concentrations in edible oil matrices — a key quality-control point for commodity-level heavy metal screening.
App: Cd data in the 2–7 ng/g range (ppb range) for common culinary oils provides one reference point for the vegetable-oil ingredient cluster, but should be weighted lower given the analytical limitations above.