Trace Element Content of Monovarietal and Commercial Portuguese Olive Oils

Overview

This study measured 11 elements in 23 Portuguese olive oils, comparing 11 small-scale cold-extracted monovarietal oils (produced for the study from certified orchard cultivars using the Abencor system) with 12 commercial mechanically extracted oils bought at local markets. Elements were classified as quality parameters (Na, K, Ca, Cu, Mg, Fe, Zn, Mn) and safety parameters (Al, cadmium (Cd), Pb). Multivariate analysis (PCA, cluster analysis) was applied.

Commercial olive oils presented higher values for aluminium and lead, and lower quantities of cadmium, compared with the monovarietal oils. Lead in monovarietal samples ranged from 0.030 to 0.116 μg/g, while commercial samples ranged from 0.141 to 0.327 μg/g, with no overlap between the two groups.

Key numbers

Safety metals (Table 3, p. 7; μg/g, mean ± SD, n=3 replicates per sample):

Aluminium aluminum (Al):

• Monovarietal: ranged from not detected (CS, GAL) to 22.775 ± 1.733 (COB). Other values: VER 0.178 ± 0.001; REDA 19.150 ± 1.344; MAD 21.655 ± 1.502; CCB 4.715 ± 0.401; AZ 9.327 ± 0.812; CAR not detected; BL 14.844 ± 0.978; REDI 8.667 ± 0.501.
• Commercial: ranged from 7.660 ± 0.546 (Com 8) to 27.091 ± 1.064 (Com 12). Other values include Com 1: 27.021 ± 1.589; Com 5: 20.915 ± 0.996; Com 6: 24.986 ± 1.003.
• EFSA recommendation: 1.0 mg/kg body weight per week TWI (p. 7).

Cadmium (Cd):

• Monovarietal: ranged from 0.178 ± 0.001 (VER) to 1.019 ± 0.007 (GAL). Higher Cd in monovarietal samples overall.
• Commercial: ranged from 0.212 ± 0.021 (Com 4) to 0.591 ± 0.043 (Com 12).
• Literature comparison: 0.0028 (Pehlivan et al.), 0.05 (Cindric et al.), 0.00008-0.000366 (Benincasa et al.), 2.64 (Zhu et al.) μg/g (p. 7).

Lead (Pb):

• Monovarietal: ranged from 0.030 ± 0.003 (CS) to 0.116 ± 0.004 (BL).
• Commercial: ranged from 0.141 ± 0.003 (Com 12) to 0.327 ± 0.007 (Com 8).
• “The Pb content varied among the monovarietal and commercial samples, with the highest monovarietal sample values (0.116 ± 0.004 μg/g) being lower than the lowest commercial sample values (0.141 ± 0.003 μg/g)” (p. 7).
• EFSA former provisional tolerable monthly intake (PTMI) for Pb: 25.0 μg/kg body weight, set aside due to lack of comprehension of dose-response (p. 7).

Quality metals (Table 2, p. 5; concentrations in mg/g or μg/g as printed):

Fe: ranged from 3.3E-4 ± 0.00 (BL) to 18E-3 ± 8.1E-3 (Com 11) mg/g; commercial samples generally higher. Cu: ranged from not detected (BL, REDI) to 1.72 (Com 11) mg/g. Zn: monovarietal ranged from 0.31E-3 ± 1.1E-3 (CS) to 7.1E-3 ± 6.0E-3 (REDI) mg/g; some commercial samples had Zn not detected. K: ranged from not detected (several) to 7.2E-3 ± 0.04 (Com 4) mg/g.

PCA findings (Table 4, pp. 8-9; Fig. 2, p. 8):

PCA on all trace elements: PC1 explained 29.62% of variance, separating monovarietal from commercial. Cu (loading 0.4895) and Pb (loading 0.4882) had the greatest loadings on PC1.

PCA on safety parameters only: PC1 explained 53.39% of variance. Al loading 0.5330, Pb loading 0.7577 (highest), Cd loading -0.5859 (inverse, reflecting lower Cd in commercial samples).

Evidence Fitness

EF-2 (reconstructable dataset). Table 3 provides individual sample-level data for Al, Cd, and Pb with means and standard deviations for all 23 oils. The comparison of production types (small-scale monovarietal vs. commercial blends) is informative for understanding how production route and blending are associated with different metal levels, though the study cannot attribute the difference to a single processing step because cultivar, origin, and blending also differ between the two groups. No exposure or intake calculation was performed.

Methods

Sample preparation: 0.5 g oil digested with HNO3 (1.0 mL) and H2O2 (5.0 mL), heated stepwise from 50 to 155 ℃ with overnight hold, cooled, dissolved in 10.0 mL HNO3 matrix (1.5 mL acid per 1000 mL water).

Instruments:

• FAES (flame atomic emission spectrometry): Na, Cu, K.
• FAAS (flame atomic absorption spectrometry): Ca, Mg, Fe, Zn (Thermo Scientific ICE 3000).
• GFAAS (graphite furnace AAS): Mn, Al, Cd, Pb (Unicam 939 AA spectrometer, GF90 furnace).

Calibration with aqueous mixed standards in HNO3 (1.0 M), five dilutions plus blank per run.

LOD/LOQ: Not reported as a separate table. Some elements reported as “not detected” (ND) for specific samples.

CRM/Recovery: Not reported. No standard reference material was used for olive oil validation.

Limitations: No CRM was used; accuracy assessment is absent. The two groups (monovarietal and commercial) differ in cultivar, origin, production scale, and blending, so the metal differences cannot be attributed to any single factor. The licence for the paper is not stated (free access on J-STAGE). Commercial oils are retail purchases, not supplier-provided data.

Implications

Certification: Provides evidence that commercial blended olive oils had higher Al and Pb and lower Cd than small-scale monovarietal oils in Portugal. The complete separation of Pb ranges between the two groups (highest monovarietal 0.116 lower than lowest commercial 0.141 μg/g) is notable. However, the confounding of cultivar, origin, and production scale prevents attributing the difference to processing alone.

Courses: The clear cluster separation between monovarietal and commercial oils using PCA on safety parameters (Al, Cd, Pb) provides a teaching example for how trace element profiling can distinguish production types.

Provenance notes

Free-to-read on J-STAGE; no licence stated in Unpaywall or Crossref. Deposit: HMI-MIT-olive-oil. Units throughout are μg/g.

Related evidence

• Olive Oil (Section 1: processing)

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