Quality and Trace Element Profile of Tunisian Olive Oils Obtained from Plants Irrigated with Treated Wastewater

Overview

This study measured 19 elements in olive oils produced from Chemlali olive trees in Sfax, Tunisia, comparing oils from trees irrigated with treated wastewater (TWW, continuous and alternate regimes), conventional water (CW), and non-irrigated controls. For each irrigation regime, olives were either hand-picked from the tree or collected from the ground after varying contact periods with irrigated soil. Multi-element data were submitted to ANOVA, LDA, and PCA. The primary aim was to evaluate whether TWW irrigation and olive-soil contact time affected the quality and trace element profile of the oil.

Nineteen elements are reported in Table 4 (p. 7): Li, B, Na, Mg, aluminum (Al), K, Ca, Sc, chromium (Cr), Mn, Fe, Co, nickel (Ni), Cu, Zn, Sr, Mo, Ba, La. Cadmium and lead appear in the LOD/recovery table (Table 2) but are not reported in Table 4; no lead (Pb), cadmium (Cd), arsenic (As), or mercury (Hg) values in oil are available from this paper.

Key numbers

Instrument and analytical quality (Table 2, p. 6; mg/kg):

LODs ranged from 0.000 to 5.118 mg/kg (Mg highest at 5.118); LOQs from 0.000 to 17.061 mg/kg (Mg highest at 17.061). Recovery of spiked solutions: Spike 1 ranged 80% (Ca) to 120% (Pb); Spike 2 ranged 69% (Zn) to 115% (Pb).

Cd: Spike 1 recovery 92%, Spike 2 recovery 92%, LOD 0.000, LOQ 0.000. Pb: Spike 1 recovery 120%, Spike 2 recovery 115%, LOD 0.000, LOQ 0.000.

Cd and Pb are not reported in Table 4 (olive oil concentrations); the paper does not claim Pb, Cd, As, or Hg values in oil.

Selected element concentrations in olive oil (Table 4, pp. 7-8; mg/kg; values printed with decimal commas in the original, transcribed here with decimal points):

Mg (mg/kg): ranged from 16,586 (sample K150, from-tree, TWW alternate) to 63,346 (K672, third fall, not irrigated). Non-irrigated control oils and fourth-fall olives showed the highest Mg. Values above 50 mg/kg were common: 56.586, 57.543, 53.690, 50.292, 59.414, 55.682, 55.673, 57.455, 59.915, 61.493, 59.968, 60.040, 61.289 mg/kg (as printed after correcting for the decimal-comma convention).

Zn (mg/kg): ranged from 68.014 (K644, first fall, CW) to 162.894 (K652, third fall, CW). All values exceeded 95 mg/kg except K644 (68.014) and K656 (95.394), printed as 133,349; 134,715; 131,816; 122,980; 134,205; 135,066; 141,022; 68,014; 135,414; 132,173; 134,367; 134,062; 126,257; 142,977; 162,894; 158,817; 124,821; 127,282; 95,394; 129,939 (all mg/kg, decimal commas in original).

Fe (mg/kg): ranged from 3.578 (K640, from-tree, CW) to 17.596 (K677, fourth fall, not irrigated). Most samples between 3.5 and 4.4, with the exception of K677 (17.596, the non-irrigated fourth-fall sample).

Ni (mg/kg): ranged from 0.000 (K153, third fall, TWW alternate) to 0.082 (K668, second fall, not irrigated).

Cr (mg/kg): ranged from 0.107 (K661, from-tree, CW) to 0.167 (K652, third fall, CW).

Cu (mg/kg): ranged from 0.000 (K150) to 0.088 (K677).

Al (mg/kg): ranged from 14.402 (K661) to 98.075 (K187, fourth fall, TWW continuous).

Effect of irrigation regime (p. 5):

“The control plants produced oils with a lower concentration of trace elements and minerals.” Oils from TWW-irrigated trees had richer trace element profiles, and oils from olives that contacted TWW-irrigated soil carried higher Na, K, Ni, La, Sr, B, and Mo than oils from tree-picked olives.

Effect of harvest mode (p. 5):

“The oils produced from olives collected from the ground after a short permanence are characterized by higher values of Na, K, Ni, La, Sr, B, and Mo, while those produced from olives collected from the ground after a longer period are characterized by higher values of Li, Cu, Fe, Mn, and Sc.”

EU regulatory note (p. 9):

“The European Community sets limit only for PB in edible oils, which is 0.1 mg/kg (European Commission 2006) [43].”

Evidence Fitness

EF-3 (modeled or limited evidence). The study provides a controlled field comparison of trace element profiles in olive oil under different irrigation and harvest conditions. The 19-element data in Table 4 are original measurements in olive oil by ICP-MS. Cadmium and lead appear in the method validation (Table 2) but are not reported in the oil samples, so this paper cannot support claims about Pb, Cd, As, or Hg concentrations in olive oil. The study supports the finding that irrigation water source and olive contact with irrigated soil affect the multi-element profile of the oil, but does not quantify reduction from any deliberate mitigation treatment.

Methods

Sample preparation: Olive oil samples (0.5 g) weighed directly into the digestion vessel; nitric acid added; digested three times at increasing temperatures. Solutions diluted in HNO3 matrix solution (1.5 mL of acid to 1000 mL of water) to 10.0 mL.

Instrument: Agilent 7500c ICP-MS (Agilent Technologies, Santa Clara, USA). Milestone MES-1200 open-system microwave digestion.

LOD/LOQ: LODs reported in the range 0.000 to 5.118 mg/kg (Table 2, p. 6). LOQs ranged from 0.000 to 17.061 mg/kg.

CRM/Recovery: Spike recovery of two standard solutions (Table 2). No certified reference material for olive oil was used; the paper used spiked solutions only. Recoveries ranged from 69% (Zn, Spike 2) to 120% (Pb, Spike 1).

Statistical analysis: ANOVA, LDA, and PCA (STATGRAPHICS Plus Version 5.1). LDA on 90 oil samples (30 samples x 3 replicates) classified 78% or 86.67% correctly depending on validation approach.

Limitations acknowledged by the authors:

The determination of metal concentrations in edible oils and fats is a challenge in quality control analysis, owing to the low concentration levels and difficulties arising from matrix characteristics (p. 9). The study is limited to one cultivar (Chemlali) at one location (Sfax, Tunisia).

Implications

Certification: This paper provides evidence that irrigation water quality and olive-soil contact affect the multi-element profile of olive oil, relevant to understanding how growing conditions may influence trace element levels. It does not provide Pb, Cd, As, or Hg data for olive oil and cannot inform HMT&C threshold discussions for those analytes.

Courses: Useful for teaching how pre-harvest factors (irrigation water quality, harvesting practice) can affect the trace element profile of an edible oil.

Provenance notes

Open access (CC BY). Hindawi journal (The Scientific World Journal). No retraction or update notice found in Crossref (checked 2026-11-10). Deposit: HMI-MIT-olive-oil. Table 4 values are printed with decimal commas (European convention); this source page transcribes them with decimal points.

Related evidence

• Olive Oil (Section 2: mitigation and inputs)

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