Evaluation of cadmium, lead, copper, iron and zinc in Turkish dietary vegetable oils and olives using electrothermal and flame atomic absorption spectrometry

Overview

This study determined cadmium (Cd), lead (Pb), Cu, Fe, and Zn in 53 edible vegetable oil samples (soybean, sunflower, flower, nut, corn, olive) and 70 table olive samples (olive-1, black, green, and black/green crushed-with-seeds preparations) purchased from supermarkets in Ankara, Turkey. Cd, Pb, and Cu were determined by electrothermal atomic absorption spectrometry (ETAAS) using a novel Sc + Ir + NH4H2PO4 chemical modifier mixture; Fe and Zn were determined by flame atomic absorption spectrometry (FAAS). All samples were prepared by microwave-assisted nitric acid/hydrogen peroxide digestion. Across vegetable oils, Cd ranged 31–58 µg/kg, Pb 0.04–0.11 mg/kg, Cu 0.04–0.13 mg/kg, Fe 0.96–2.14 mg/kg, and Zn 1.01–1.74 mg/kg. Across table olive preparations, Cd ranged 43–108 µg/kg, Pb 0.11–0.32 mg/kg, Cu 2.17–3.80 mg/kg, Fe 10.6–18.1 mg/kg, and Zn 2.33–4.44 mg/kg. The author reports Cd in olive samples as higher than several literature values cited but in agreement with the EC Commission Regulation 1881/2006 maximum contaminant levels and Turkish food codex regulations. The paper measures total Pb and total Cd (no speciation); arsenic and mercury are not measured.

Note on evidence tier: assigned B. Single-author study with reasonable analytical rigor (SRM 1577b bovine liver recovery 96–101%, RSDs 3.4–6.2%, microwave digestion, well-described modifier optimisation), but per-oil-type n is small (n=8–12), the geographic frame is restricted to Ankara market supply, and the panel omits arsenic and mercury (the two HMI-priority analytes most regulated in food safety contexts). Total Cd and total Pb are reported without speciation, which is appropriate for these elements in foods.

Key numbers

All values are wet weight basis. Cadmium is reported in µg/kg throughout (Table 3 footnote b); Pb, Cu, Fe, Zn are in mg/kg. Reported as mean ± standard deviation (95% CI) over min–max, n = five replicate measurements per sample (Table 3).

Vegetable oils (Table 3, page 390):

Table olive preparations (Table 3, page 390):

Across-preparation ranges (Table 4 “This study” column, page 391):

• Cd in oils: 31–58 µg/kg (= 0.031–0.058 mg/kg); Cd in olives: 0.04–0.11 mg/kg.
• Pb in oils: 0.04–0.11 mg/kg; Pb in olives: 0.11–0.32 mg/kg.
• Cu in oils: 0.04–0.13 mg/kg; Cu in olives: 2.17–3.80 mg/kg.
• Fe in oils: 0.96–2.14 mg/kg; Fe in olives: 10.6–18.1 mg/kg.
• Zn in oils: 1.01–1.74 mg/kg; Zn in olives: 2.33–4.44 mg/kg.

Comparison with cited literature ranges for Pb in oils (Table 4): 0.009–0.0074 (Zhu et al. 2011), 0–0.0074 (Pehlivan et al. 2008), 0–0.03 (Mendil et al. 2009), 0.074–0.104 (Bakkali et al. 2009); the maximum 0.11 mg/kg reported here exceeds Bakkali’s upper bound. For Cd in oils the literature ranges cited (Mendil 0.09–4.57, Zhu 2.64–8.43, Pehlivan 0.2–4.5, Bakkali 0.0013–0.0123 — all reported as mg/kg in Table 4) span more than four orders of magnitude; the present study’s 31–58 µg/kg (0.031–0.058 mg/kg) sits within that broad envelope but on the higher side compared with Bakkali and Pehlivan. The author notes Cd in oils is higher than literature values but consistent with the EC 1881/2006 maximum allowed Cd for vegetable oil-containing foods.

Recovery (Table 2, SRM 1577b bovine liver and oil-sample spike, page 388):

• Cd: certified 0.50 ± 0.03 mg/kg, found 0.48 ± 0.02, recovery 96%. Oil-sample 1.0 µg/L spike → 2.40 ± 0.08 (98%); 2.0 µg/L spike → 3.41 ± 0.13 (99%).
• Cu: certified 160 ± 8 mg/kg, found 158 ± 7, 99%.
• Pb: certified 0.129 ± 0.004 mg/kg, found 0.13 ± 0.01, 101%.
• Fe: certified 184 ± 15 mg/kg, found 181 ± 9, 98%.
• Zn: certified 127 ± 16 mg/kg, found 124 ± 6, 98%.

Limits of detection (LOD, 3σb/m on 20 blanks): Cd 0.1 µg/L, Cu 0.6 µg/L, Pb 0.9 µg/L, Fe 15.0 µg/L, Zn 12.0 µg/L. Characteristic masses (m0, ETAAS, integrated absorbance 0.0044): Cd 0.8 pg, Pb 8.3 pg, Cu 19 pg. RSDs of analytes in samples were below 7% (range 3.4–6.2%).

Regulatory benchmarks cited by the author (page 390):

• Maximum permissible values in Turkish standards (TS 2812:1991; TS 3606:1997) and Turkish food codex regulations (TKB 2002) for vegetable oils and refined liquid oils: 1.5 mg/kg Fe, 0.1 mg/kg Cu, 0.1 mg/kg Pb (no Cd value cited for vegetable oils in this set).
• TKB 2002 cap for olive oil and non-refined vegetable oil: Cu 0.1 mg/kg, Fe 3.0 mg/kg; Cu 0.4 mg/kg and Fe 5.0 mg/kg cited as alternative refining-state-dependent caps.
• Kowalewska et al. 2005 / Zhu et al. 2011 “approved contents of some metals in oils from national and international requirements” as cited by the author: 0.05 mg/kg Cd, 1–1.5 mg/kg Fe, 0.1 mg/kg Cu, 0.1 mg/kg Pb.
• IOOC 2003 / Economic European Communities 2006 maximum recommended levels cited by the author: 0.3 mg/kg Fe, 0.1 mg/kg Cu and Pb for oils and olives, 0.2 mg/kg Cd for soybeans, and 0.050 mg/kg Cd for vegetables, pine nuts, etc.
• Turkish local food standards for table olives (TS 774:2003) cited as the safe-limit benchmark for olive samples; no numerical value is reproduced in the paper.
• EVM 2003 safe upper level for Cu intake: 10 mg for a 60 kg adult.
• Birick and Basoglu 2006: maximum allowed Fe concentration 150 mg/kg.
• JECFA 1999 PTDI cited by author: Fe 48 mg, Cu 3 mg, Pb 214 µg, Zn 60 mg per 60 kg adult.

The author concludes that intake of Cd, Pb, Cu, Fe, and Zn from daily consumption of these Turkish oils and olives may not be a risk for human health, and that the various metal levels are below the safe limits specified for table olives by Turkish local food standards (TS 774:2003).

Methods (brief)

ETAAS for Cd, Pb, Cu: Hitachi Model 180/78 graphite furnace with Zeeman background correction; pyrolytically coated graphite tubes (P/N 190-6007) with graphite platforms (P/N 190-6008); peak-area (integrated absorbance) mode. Element lamps: Cd 10 mA / 228.8 nm; Cu 10 mA / 324.8 nm; Pb 10 mA / 283.3 nm. Argon (99.98% v/v) carrier gas. Heating program (Table 1): pyrolysis 900 °C (Cd), 1,300 °C (Cu), 1,250 °C (Pb); atomization 1,500 °C (Cd), 2,700 °C (Cu), 2,000 °C (Pb); ramp/hold and cleaning steps as specified.

Chemical modifier (novel mixture, the paper’s analytical contribution): Sc + Ir + NH4H2PO4 mixture — 2.0 g/L Sc + 0.4 g/L Ir + 5.0 g/L NH4H2PO4. Modifier solutions prepared from Sc2O3 (Merck, 99.99% pure) dissolved in HNO3, IrO2 (Merck) dissolved in HNO3, and NH4H2PO4 (Merck, 99.99% pure). The mixture stabilizes Cd, Pb, and Cu to higher pyrolysis temperatures and was selected after comparison with Sc-only and Sc + Ir variants and with previously reported modifiers including W-Rh, W-Ir, W-Ru, and Sc + Pd + NH4NO3 systems.

FAAS for Fe, Zn: Hitachi Model 180/80 flame AAS, air-acetylene; Fe 248.3 nm, Zn 213.9 nm; element lamps Fe 12.5 mA, Zn 10 mA. Slit width 1.3 nm for all lamps.

Sample digestion: microwave-assisted closed-vessel digestion (Milestone Ethos 1600, MLS Ethos, Italy). Triplicate 1.00–2.00 g oil, 1.00–2.00 g olive, and 0.50–1.00 g SRM 1577b bovine liver portions were weighed into separate Teflon digestion vessels with 2 mL ultra-pure water, 6 mL HNO3 (65% m/m), and 2 mL H2O2 (30% m/m). Vessels stood at ambient temperature for 4 h with gentle swirl, then digested at 160 °C, 800 W maximum power, for 20–25 min. Digest transferred to 25 mL volumetric flasks with 1% v/v HNO3 wash. Blank solutions prepared with the same procedure to check reagent contamination. Standard-addition method used to verify digestion validity: known amounts of analyte added to the second and third vessels of each triplicate.

Auto-sampler solution: 0.1% v/v HNO3 + 0.1% v/v Triton X-100 to disperse sample solutions onto the platform. Calibration: aqueous standard solutions diluted from 1,000 mg/L BDH stock standards in 0.1% v/v nitric acid, freshly prepared before use. Calibration dynamic ranges: Cd 0.3–6 µg/L, Pb 3.0–80 µg/L, Cu 2.0–80 µg/L, Fe 0.05–6.0 mg/L, Zn 0.04–1.0 mg/L. Correlation coefficients (R²) > 0.99 for all analytes. LOQ = lower limit of dynamic range = 10σb/m.

Sample sizes: 53 oil samples (8 soybean, 12 sunflower, 8 flower, 8 nut, 8 corn, 9 olive) and 70 table olive samples (20 olive-1, 15 black, 12 green, 10 black crushed with seeds, 13 green crushed with seeds), all purchased from various supermarkets in Ankara on different dates and originating from various plants and regions of Turkey. For olives crushed with seeds, the seeds were separated by hand or crushed, and the flesh was homogenized with a stainless blender to assess possible contamination from the olive seed.

No speciation: this paper reports total Pb, total Cd, and total Cu (and total Fe, total Zn). Arsenic and mercury are not measured.

Basis: wet weight throughout (page 387, section 3.4: “All metal concentrations found in samples were on a wet weight basis as mg kg−1 except cadmium” — Cd reported in µg/kg). Figure 2’s y-axis label “Concentration (mg/kg)” for the Cd panel is inconsistent with Table 3’s footnote-b µg/kg units and with Table 4’s Cd Olive “This study” 0.04–0.11 range (mg/kg-equivalent of 40–110 µg/kg); the µg/kg reading from Table 3 is the consistent unit basis used throughout this page.

Implications

• Certification (HMTc): contributes Turkish-market occurrence data for Pb and Cd in dietary vegetable oils and table olives, n = 53 oils and 70 olives across 11 distinct product subtypes. Pb values in oils (0.04–0.11 mg/kg) reach but do not clearly exceed the 0.10 mg/kg Pb cap the author cites from Turkish standards and IOOC/EC requirements; one oil-category maximum (sunflower 0.11 mg/kg, soybean 0.10 mg/kg, corn 0.10 mg/kg, olive 0.10 mg/kg) sits at or just above that line. Pb values in table olives (0.11–0.32 mg/kg) materially exceed the 0.10 mg/kg oil cap and are presented in the paper against a Turkish table-olive safety standard (TS 774:2003) that the paper does not numerically reproduce. Cd in oils (31–58 µg/kg = 0.031–0.058 mg/kg) sits below the 0.2 mg/kg TKB 2002 cap for soybean oil and pine nuts cited by the author and at or near the 0.05 mg/kg IOOC/EC Cd value the author also cites for oils.

• Courses: useful as a worked example of (1) the Sc + Ir + NH4H2PO4 modifier system for stabilizing Cd, Pb, and Cu in oil/olive matrices in ETAAS, (2) the standard-addition method’s use as a digestion-validation check, and (3) the basis convention that table olives are reported in mg/kg wet weight while Cd values are routinely reported in µg/kg even in the same table.

• App: oil-side Pb and Cd inputs are in the low end of the range that ingredient-list-driven estimators care about; the table-olive Pb range (0.11–0.32 mg/kg) is the more contaminant-relevant signal from this paper and should be carried into per-serving estimators for olive-as-ingredient and table-olive-as-snack use cases. Table-olive Cd (43–108 µg/kg) is the second most contaminant-relevant signal. Treat as one of several Turkish-market data points; combine with Pehlivan et al. 2008 (n=17 oils), Karatasli 2018 (n=26 table olives, Mediterranean Turkey), and other regional studies before drawing geographic conclusions.

Related evidence

• Olive Oil
• Olives
• Sunflower Oil
• Corn Oil
• Soybean Oil
• Vegetable Oils
• Olive oil
• Other cooking oils (canola, sunflower, coconut, avocado, sesame)
• Non-Root Vegetables
• Lead
• Cadmium
• Copper
• Iron
• Zinc
• Radionuclide and Heavy Metal Content in the Table Olive (Olea europaea L.) from the Mediterranean Region of Turkey
• Determination of some inorganic metals in edible vegetable oils by inductively coupled plasma atomic emission spectroscopy (ICP-AES)

Update history

No substantive edit history is available in this build. The full commit record is available in git.