Pehlivan et al. 2008 — Inorganic metals in Turkish edible vegetable oils by ICP-AES
This study determined nine metals (Cu, Fe, Mn, Co, Cr, Pb, Cd, Ni, Zn) in 17 edible vegetable oil samples from Turkish markets using ICP-AES after direct acid extraction with dilute nitric acid. The study demonstrates a simple sample preparation approach — 2–3 g oil + 1 mL 10% HNO3, shaken and incubated 2 h at 50°C, then centrifuged — that avoided the losses associated with wet digestion or dry ashing. All measured metal concentrations were low and generally within regulatory limits. Virgin olive oil had the highest lead among oil types (0.0074 mg/kg), and almond oil showed the highest values for Cu, Cr, Ni, and Zn.
Note on evidence tier: downgraded from A to B. The paper predates current open-access norms; license status is unknown. The study is older (2008), uses ICP-AES without speciation, and the variety of oil subtypes within a single category (e.g., 5 sunflower oil brands) means per-variety n=1. Total chromium is reported; this cannot be treated as Cr-VI.
Key numbers
All values in mg/kg wet weight. n=17 total; analysis in triplicate.
Selected maximum concentrations by oil type:
- Cu: almond oil 0.0850 mg/kg (highest); corn oil-c 0.0082 mg/kg (lowest)
- Fe: corn oil-c 0.0352 mg/kg (highest); corn oil-a 0.0039 mg/kg (lowest)
- Mn: soybean oil 0.0220 mg/kg (highest); riviera olive-a 0.0007 mg/kg (lowest)
- Co: sunflower oil-b and almond oil 0.0040 mg/kg (highest)
- Cr (total): almond oil 0.0010 mg/kg (highest); sunflower oil-d 0.0005 mg/kg (lowest) — note: total Cr, not Cr-VI
- Pb: virgin olive oil 0.0074 mg/kg (highest); many oils at or near 0 mg/kg
- Cd: sunflower oil-e 0.0045 mg/kg (highest); almond oil 0.0003 mg/kg (lowest)
- Ni: almond oil 0.0254 mg/kg (highest); natural olive oil 0.0013 mg/kg (lowest)
- Zn: almond oil 0.2870 mg/kg (highest); sunflower oil-e 0.0184 mg/kg (lowest)
Key per-oil-type summary (mg/kg, mean ± SD from Tables 2–4): Olive oils (natural, riviera a/b/c, virgin, frying):
- Pb: 0.0000–0.0074 (virgin highest); Cd: 0.0009–0.0033; Ni: 0.0013–0.0041; Cu: 0.0097–0.0194; Fe: 0.0125–0.0295 Sunflower oils (a–e):
- Pb: 0.0000–0.0026; Cd: 0.0007–0.0045; Ni: 0.0015–0.0060 Corn oils (a–c):
- Pb: 0.0000; Cd: 0.0002–0.0013; Fe: 0.0039–0.0352 Soybean oil:
- Pb: 0.0000; Cd: 0.0013; Mn: 0.0220; Cu: 0.0273
EU regulatory limit (Regulation EC 466/2001, as noted by authors): Pb 0.10 mg/kg for vegetable oils. All values well below this limit. No regulatory limit for Cd, Cu, Ni, Zn in vegetable oils at time of publication.
Recovery: all metals > 95% at low concentrations. Precision: RSD below 10–20% depending on metal.
Methods
ICP-AES (Varian Vista). Acid extraction: 2–3 g oil + 1 mL 10% HNO3; shaken at 50 Hz for 60 s; incubated in shaking water bath at 50°C for 2 h; centrifuged at 2800 rpm for 10 min; aqueous layer diluted to 25 mL. No microwave digestion — direct extraction method. Wavelengths: Al 396.152, Cd 228.802, Cu 324.754, Fe 259.940, Mn 257.610, Co 238.892, Cr 257.716, Pb 220.353, Ni 231.604, Zn 213.857 nm. Working range 0.001–0.1 ppm for all metals. No speciation performed: total Pb, total Cd, total Cr. Data collected from Turkish food markets, specific city/date not stated. Study published in Grasas y Aceites (Spain), received 2/2/06, accepted 7/2/08.
Limitation: This is a 2008 study with no speciation. The extraction method (dilute acid, room-temperature shaking rather than microwave digestion) may underestimate metals that are tightly matrix-bound. Per-oil n=1–3 samples per brand across 17 total.
Implications
Certification: Provides historical Turkish market baseline for Pb and Cd in vegetable oils. Values are low (Pb maximum 7.4 µg/kg in virgin olive oil, Cd maximum 4.5 µg/kg in sunflower oil-e), consistent with later EU regulatory experience that vegetable oils generally present low Pb and Cd compared to solid food matrices.
Courses: Useful as an older reference illustrating the acid-extraction methodology for ICP-AES and the range of metals determinable in a single run. Also illustrates that total Cr data (not Cr-VI) does not enable toxicological assessment for the hexavalent form.
App: Values are low and relatively dated (2008, Turkish market). Use only for broad order-of-magnitude framing; prefer more recent and larger-n studies for ingredient profiling.