Physicochemical Properties, Trace Elements, and Health Risk Assessment of Edible Vegetable Oils Consumed in Romania

Abstract

The concentrations of trace elements (Cd, Pb, Cu, Cr, Ni, Co, and Mn) and physicochemical parameters of eight types of edible vegetable oils (obtained from a local market in Romania) were determined using graphite furnace atomic absorption spectrometry (GF-AAS) and Association of Official Analytical Chemists (AOAC) standard methods. The values of the physicochemical parameters show that most of the oils analyzed were within the limits established by the Codex Standards for Edible Oils, with a few exceptions (walnut oil acidity 2.080 mg/g; iodine value 72.7 g/100 g). The concentration of metals such as Cr, Ni, Co, Mn, and Cd were found to be within acceptable limits set by FAO/OMS (2002) in the edible vegetable oils, except for Cu (blend oil 0.627 mg/kg; organic extra virgin oil 0.312 mg/kg) and Pb (rice oil 0.217 mg/kg). The results obtained after health risk assessments and incremental lifetime cancer risk calculations showed that their values do not pose a health hazard, but continuous monitoring can provide data on the quality of edible vegetable oils for local consumers. A statistical test at the 0.1 probability level (p < 0.1) was used to determine the degree of association between pairs of the variables. The data corresponding to the correlation coefficients for physicochemical parameters and different metals show significant and insignificant positive/negative correlations.

1. Introduction

Edible vegetable oil is a vital component of our daily diet, and is a product derived from the seeds or germ of a plant’s seeds, pulp, or fruit kernel, obtained by pressing, extraction with organic solvents, or a combined method. Edible vegetable oils provide energy, fat-soluble vitamins (A, C, E, and K), essential fatty acids, and minerals. They are also food products composed mainly of glycerides of fatty acids, obtained only from vegetable sources. They may contain small amounts of other lipids such as phosphatides, unsaponifiable constituents, and free fatty acids naturally present in fat or oil [1].

In addition, edible vegetable oils may contain biologically active substances such as phenolic compounds [2]. Phenolic compounds serve as natural antioxidants, helping to prevent oxidation and rancidity in the oil [3]. This, in turn, can help extend the shelf life of the oil and preserve its nutritional and sensory quality over time. The number of phenolic compounds can be used as a criterion for assessing the overall oil quality and as an indicator for predicting stability [4].

Edible vegetable oils exhibit several physicochemical properties that can be used to evaluate their nutritional qualities. These include their moisture content, refractive index, color, acidity index, saponification, peroxide value, iodine value, and color appearance [5].

However, these properties of edible vegetable oils can be compromised by exposure to oxygen, heat, light, and inappropriate storage conditions [6]. This results in lower-quality products that are rich in trans fats due to oxidation and therefore pose more health risks due to high concentrations of free radicals [7].

Another criterion for assessing the quality of edible vegetable oils is their metal content. The presence and concentration of these elements in the environment and the human body can lead to various health problems [8]. Although some of these elements are essential for human health, their excessive accumulation can pose significant health risks.

In edible vegetable oils, toxic metals can have endogenous and exogenous sources [9]. The endogenous presence of metals is due to their migration from arable soil into oily plants. Heavy metal concentrations in oilseed plants depend on many factors, namely, plant species, soil type, anthropogenic conditions (fertilization and hydrological pressure, fertilization, and irrigation).

Exogenous sources of metal contamination can arise from the use of metal equipment during the production process, seed harvesting time, oilseed extraction techniques, packaging material, and storage area [10]. The presence of metals in the final refined product is undesirable because metals can facilitate oxidative degradation of the oil and decrease shelf life [11]. Trace metal ions are known to have adverse effects on flavor, color and odor. Copper and iron in particular highly reduce the oxidative stability of oil. On the other hand, some metals such as chromium, zinc, and cobalt catalyze the decomposition of hydroperoxides, aldehydes, ketones, and acids. These compounds can have pathological effects on the digestive system [12]. They also increase the carcinogenic effect by reacting with other food components such as proteins and pigments. Therefore, knowing the exact value of the trace metal content is important in the evaluation of the deteriorative effects of the product.

Many studies have indicated the presence of heavy metals in edible vegetable oils and their health risk [13,14]. Another study showed a correlation between the accumulation of metals in soil and their presence in palm oil, indicating the potential health risks of high levels of Cd and Cr [15].

Other researchers have analyzed the quality of indigenous edible vegetable oil varieties (soybean, rapeseed, and sunflower oil) from local markets in Timisoara (Romania) [16]. They mentioned that the values of physicochemical parameters indicate that the edible vegetable oils are suitable for food use. In addition, Popovici et al. (2009) carried out a study on a bicomponent blend of edible vegetable oils (sunflower and grapeseed oil), following the changes in quality indices during storage [17]. The results indicated the stability of the edible vegetable oil blend over time, following the determination of the intensity of the products formed by primary and secondary oxidation.

From the information available so far, no comprehensive studies have been carried out on edible vegetable oils marketed in Romania, regarding their quality and toxic element content as well as their health risks.

Therefore, the objectives of the present study are to evaluate the quality of eight types of edible vegetable oils, available in Romanian markets; to determine the content of toxic metals (Cd, Cr, Pb, Ni, Mn, Co, and Cu) and to estimate the potential health risks exerted by heavy metals; and to correlate physicochemical parameters with toxic metals.

2. Materials and Methods

2.1. Sample Collection

Eight types of edible vegetable oils (sunflower, extra virgin olive, organic extra virgin olive, grapeseed, walnut, rice, rapeseed, and blend (flax, rapeseed, and pumpkin)) used for the study were purchased from local markets located in the city of Constanta, in 2024. Three samples of each edible vegetable oil were analyzed. These oils (24 samples) were selected as they are easily available, recommended in terms of nutritional value, and the products most consumed by the local population.

2.2. Methods

2.2.1. Acidity Index (AI)

A mass of 5 g of edible vegetable oil was dissolved in a 1:2 alcohol–ether mixture, then titrated with 0.1 N NaOH until neutralized in 1% phenolphthalein. The acidity index was calculated as mg of oleic acid [18].

2.2.2. Moisture Content (MC)

A 5 g sample was accurately weighed into a weighing vial previously brought to constant mass. The sample was placed in an oven at a temperature of 105 °C until constant weight, and the weight loss was recorded as moisture content (%, w/w) [19].

2.2.3. Peroxide Value (PV)

A 1 g sample was weighed into a 250 mL conical flask, into which 10 mL of acetic acid/chloroform solution (3:2) was added to dissolve. Then, 1 mL of cold saturated potassium iodide solution was added, and the mixture was stirred for one minute. After that, 2 mL of 1% starch solution was added, and the contents of the flask were gradually titrated with 0.1 N sodium thiosulfate until the blue color disappeared. A blank sample was made under the same conditions [19].

2.2.4. Refractive Index (RI)

Refractive indices of all samples were determined at 20–25 °C with an Abbe NAR-1T solid Refractometer (Atago, Kobe, Japan) according to AOAC (1984) [19].

2.2.5. Iodine Value (IV)

A mass of 1 g of sample was weighed into an iodometric flask and solubilized in 10 mL CHCl₃ solvent, after which 25 mL Hanus reagent was added. The mixture was homogenized by shaking, allowed to rest for 60 min in the dark at room temperature. Then, 20 mL 15% KI solution was added and titrated immediately with 0.1 N Na₂S₂O₃ solution in the presence of starch as indicator [19].

2.2.6. Saponification Value (SV)

A 2 g sample of edible vegetable oil was accurately weighed into a 200 mL conical flask. After the addition of 25 mL of 0.5 N alcoholic KOH solution, the contents of the flask were refluxed for one hour. Excess KOH was titrated with 0.5 N HCI solution in the presence of phenolphthalein as an indicator from red to colorless. A simultaneous blank was run in which all reagents except the oil sample were added [19].

2.2.7. Total Phenolic Compounds (TPCs)

Approximately 10 g edible vegetable oil sample was left to macerate in the dark for one week in 100 mL 98% ethanol. After filtration through Whatman filter paper, the sample was stored at 4 °C until determination [20].

Total polyphenol content (TPC) was determined according to the spectrometric method with Folin–Ciocâlteu reagent [21]. Therefore, 1 mL of sample was mixed with 1 mL of Folin Ciocâlteu reagent (Merck, Darmstadt, Germany) and 1 mL of 20% sodium carbonate (Redox, Otopeni, Romania). After stirring, the absorbance at a wavelength of 675 nm was measured against the blank sample. The spectrometer used was a Jasco 550 UV-VIS molecular absorption spectrometer (Jasco International, Tokyo, Japan). The TPC concentration was calculated from a calibration curve (y = 0.0699x) with an R² of 0.9996 and expressed in mg gallic acid equivalent (GAE, Fluka, Buchs, Switzerland) per kg.

2.2.8. Determination of Mn, Cr, Cu, Cd, Pb, Co, and Ni by Graphite Atomic Absorption Spectrometry

The edible vegetable oil samples were made into solutions according to the protocol of the Berghof Instruments GmbH Speedwave^® ENTRY DAP-60K digestion system, Thuringia, Germany.

A mass of 0.2 g of edible vegetable oil was added to the PTFE vessel of the digestion apparatus together with 10 mL ultrapure nitric acid 65% (Merck, KGaA, Darmstadt, Germany) and 2 mL hydrogen peroxide 30% (Merck, KGaA, Germany). After shaking, it was left to rest for 10 min before closing the vessel. The vessel was closed and placed in the microwave digestion system for 33 min at 200 °C (5 min ramp at 160 °C, 3 min at 200 °C and held at 160 °C for 5 min, at 200 °C for 10 min and 10 min at 75 °C). At the end of digestion, the samples were removed from the digestion oven, cooled to room temperature and diluted to 50 mL final volume with deionized water. Finally, the solutions were filtered using a 0.45 µm pore filter. The samples were kept refrigerated until analysis. A GTAAS atomic absorption spectrometer GTAAS model ContraA 800D, from Analytik Jena Instruments (Jena, Thuringia, Germany), was used to determine the metal concentrations. The performance parameters of the analytical method have been presented in previous studies [22]. A multi-element standard solution (ICP-multi element standard solution IV, Merck, KGaA, Germany) was used for the preparation of the intermediate solutions necessary to draw the calibration curve, while deionized water (Direct Q UV, Millipore, Burlington, MA, USA, about 18.0 MΩ, Analytik Jena Instruments) was used for dilutions.

2.3. Health Risk Assessment

The potential health risk (according to Risk Assessment Information System https://rais.ornl.gov/) of consuming the studied oils was evaluated as the target hazard quotient (THQ). The THQ was calculated using Formula (1) [23,24]:

$$\mathrm{T}\mathrm{H}\mathrm{Q}={\displaystyle \frac{\mathrm{E}\mathrm{D}\mathrm{I}}{\mathrm{R}\mathrm{f}\mathrm{D}}}={\displaystyle \frac{\mathrm{C}·\mathrm{I}\mathrm{R}·\mathrm{E}\mathrm{D}·\mathrm{E}\mathrm{F}}{\mathrm{B}\mathrm{W}·\mathrm{A}\mathrm{T}·\mathrm{R}\mathrm{f}\mathrm{D}}}({\displaystyle \frac{\mathrm{m}\mathrm{g}}{\mathrm{k}\mathrm{g}·\mathrm{d}\mathrm{a}\mathrm{y}}}),$$

(1)

where EDI represents estimated daily intake; C is the concentration of metal in oil samples (mg/kg); IR is ingestion rate (25 g/day); EF, exposure frequency (365 day/year); ED, exposure duration (adults 70 years); BW, body weight (70 kg for adults); AT, average time exposure (25,550 days). In this model, the RfD values were 5 × 10⁻⁴, 4 × 10⁻², 1 × 10⁻³, 3 × 10⁻³, 2 × 10⁻², 2.4 × 10⁻¹, and 2 × 10⁻² mg kg⁻¹ day⁻¹ for Pb, Cu, Cd, Cr, Co, Mn, and Ni, respectively [25,26].

THQ ≥ 1 indicates that the target heavy metals have a potential non-carcinogenic risk; THQ < 1 indicates that the target heavy metal’s non-carcinogenic risk is negligible.

The hazard index (HI) was determined to estimate the total potential health effects of non-cancer risks. These interactive effects were taken into account given the exposure to a mixture of heavy metals found in the analyzed oils. HI represents the sum of the THQ values for all heavy metals and was calculated using Formula (2) [27]:

$$\mathrm{H}\mathrm{I}=\sum \mathrm{T}\mathrm{H}\mathrm{Q}$$

(2)

If the HI value is <1, consumers are considered to be safe, and if the HI value ≥ 1, the oils are a health hazard to the exposed local population (consumers).

After calculating THQ and HI it is necessary to calculate the cancer risk (CR or ILCR—incremental lifetime cancer risk). This is performed using Formula (3):

$$\mathrm{I}\mathrm{L}\mathrm{C}\mathrm{R}=\mathrm{E}\mathrm{D}\mathrm{I}\times \mathrm{C}\mathrm{S}\mathrm{F}\times \mathrm{A}\mathrm{D}\mathrm{A}\mathrm{F},$$

(3)

where CSF is the cancer slope factor (kg.day/mg) used to assess the lifetime probability of a person exposed to chemical agents in terms of carcinogenic risks, and ADAF is the potency adjustment factor for adults and children (1 for adults and 3 for children—dimensionless) [27].

CSFs for Pb, Cd, Cr, and Ni are 0.085, 0.38, 0.5, and 0.84 kg.day/mg, respectively. In addition, CSFs for Co, Cu, and Mn do not exist, and the ILCR for Co, Cu, and Mn cannot be computed.

According to U.S. EPA recommendations, the carcinogenic risk for lifetime cancer risk (CR or ILCR) should be in the range of 1 × 10⁻⁶–1 × 10⁻⁴ (1 in 1,000,000 to 1 in 10,000) [28].

In order to calculate the total (cumulative) cancer risk as a result of multiple heavy metal exposure, the ILCR sum was calculated using Formula (4) [23]:

$$\sum \mathrm{I}\mathrm{L}\mathrm{C}\mathrm{R}={\mathrm{I}\mathrm{L}\mathrm{C}\mathrm{R}}_{\mathrm{P}\mathrm{b}}+{\mathrm{I}\mathrm{L}\mathrm{C}\mathrm{R}}_{\mathrm{C}\mathrm{d}}+{\mathrm{I}\mathrm{L}\mathrm{C}\mathrm{R}}_{\mathrm{C}\mathrm{r}}+{\mathrm{I}\mathrm{L}\mathrm{C}\mathrm{R}}_{\mathrm{N}\mathrm{i}},$$

(4)

2.4. Statistical Analysis

The R package “cooplot” (R Version 4.2.1) was used to compute the pair-wise Pearson correlation between the analyzed samples [29].

3. Results

3.1. Physicochemical Quality Indices

Edible vegetable oils are natural products derived from various plants, containing triacylglycerols [30]. The unsaturated fatty acids in triacylglycerols are vulnerable to oxidation when exposed to oxygen, heat, light, or catalysts. This oxidative process can lead to the development of unpleasant flavors and odors, and can be measured through the degradations of the nutritional quality of the oils [31].

The quality of edible vegetable oils can be assessed by testing certain parameters such as the acidity index (AI), peroxide value (PV), saponification value (SV), and moisture content (MC), which are influenced by the degree of rancidity and hydrolysis of free fatty acids (

Table 1. Assessment of the physicochemical quality indices of the tested oils.

Oil Samples 1	AI (%Oleic Acid) ± sd	MC (%) ± sd	PV (meqO2/kg) ± sd	RI ± sd	IV (g/100 g) ± sd	SV (mgKOH/g) ± sd	TPC (mgGAE/100 g) ± sd
Sunflower	0.110 ± 0.098	0.141 ± 0.121	2.99 ± 0.821	1.469 ± 0.011	181.4 ± 9.512	145.6 ± 10.974	19.74 ± 1.544
Grapeseed	0.188 ± 0.111	0.020 ± 0.066	5.49 ± 0.786	1.470 ± 0.001	142.5 ± 8.011	142.8 ± 9.123	15.87 ± 1.498
Extra virgin olive	0.571 ± 0.235	0.148 ± 0.074	10.1 ± 2.276	1.468 ± 0.020	115.3 ± 7.338	144.48 ± 9.320	27.45 ± 1.692
Organic extra virgin olive	0.614 ± 0.591	0.057 ± 0.032	5.45 ± 0.692	1.467 ± 0.076	79.1 ± 6.098	92.46 ± 6.229	29.28 ± 1.762
Rapeseed	0.209 ± 0.165	0.022 ± 0.011	14.64 ± 2.879	1.470 ± 0.033	104.0 ± 7.598	113.69 ± 7.987	43.01 ± 1.911
Blend	0.088 ± 0.077	0.116 ± 0.076	5.67 ± 0.986	1.469 ± 0.087	116.3 ± 7.981	174.97 ± 10.428	38.46 ± 1.720
Walnut	2.080 ± 1.649	0.013 ± 0.029	9.28 ± 1.098	1.471 ± 0.098	72.7 ± 5.744	166.59 ± 10.208	45.39 ± 1.742
Rice	0.328 ± 0.277	0.045 ± 0.087	5.35 ± 1.562	1.471 ± 0.044	122.7 ± 9.598	170.07 ± 10.728	50.62 ± 2.211

¹ Average of three determinations. sd—standard deviation.

) [32]. A number of factors can affect the quality of edible vegetable oils, which include the growing season of the vegetables, soil fertility, post-harvest storage conditions of the raw materials, and post-process storage conditions of the oils. The highest AI value was found in walnut oil (2.080% ± 1.649 oleic acid), the highest PV was found in rapeseed oil (14.64 ± 2.879 meqO₂/kg), the RI showed little variation across the oils, and the IV showed the largest variations between the oil types (ranged between 72.7 ± 5.744 and 181.4 ± 9.512 g/100 g). The data for the total polyphenol content (TPC) are presented as mg GAE/100 g, with the lowest value recorded for grapeseed oil (15.87 mg GAE/100 g) and the highest for rice oil (50.62 mg GAE/100 g); Table 1.

3.2. Potentially Toxic Metals

Table 2. Potential toxic element concentrations in studied oil samples.

Oil Samples	Concentrations 1 (mg/Kg) ± sd
	Mn	Cr	Cu	Cd	Pb	Co	Ni
Sunflower	0.023 ± 0.005	0.010 ± 0.001	0.098 ± 0.010	0.010 ± 0.001	0.075 ± 0.014	0.010 ± 0.000	0.006 ± 0.001
Grapeseed	0.035 ± 0.008	<LD	0.062 ± 0.006	0.004 ± 0.000	0.011 ± 0.003	0.018 ± 0.005	0.013 ± 0.002
Extra virgin olive	0.010 ± 0.002	0.033 ± 0.007	0.010 ± 0.001	0.001 ± 0.000	0.026 ± 0.004	0.005 ± 0.001	0.012 ± 0.001
Organic extra virgin olive	0.027 ± 0.006	0.011 ± 0.001	0.312 ± 0.023	0.007 ± 0.001	0.101 ± 0.034	0.015 ± 0.002	0.015 ± 0.002
Rapeseed	0.083 ± 0.009	0.018 ± 0.002	0.099 ± 0.026	0.005 ± 0.001	0.061 ± 0.009	0.031 ± 0.005	0.007 ± 0.001
Blend	0.023 ± 0.004	0.062 ± 0.006	0.672 ± 0.045	0.004 ± 0.000	0.099 ± 0.011	0.013 ± 0.001	0.006 ± 0.001
Walnut	0.017 ± 0.004	0.006 ± 0.000	0.085 ± 0.008	0.005 ± 0.001	0.059 ± 0.006	0.009 ± 0.002	0.003 ± 0.000
Rice	0.007 ± 0.002	0.020 ± 0.002	0.029 ± 0.004	0.005 ± 0.001	0.217 ± 0.051	0.003 ± 0.000	0.006 ± 0.001

¹ Average of three samples. sd—standard deviation.

shows the metal concentrations in the analyzed oil samples. Ni (0.003–0.015 mg/kg) and Cd (0.001–0.010 mg/kg) were the least abundant metals in the studied oils, while Cu was found in the highest concentration (blend oil 0.672 mg/kg). The lowest amount of Cu was found in the extra virgin olive oil (0.010 mg/kg). The concentration range of Mn was between 0.007 and 0.083 mg/kg, while for Cr, the range was 0.006–0.062 mg/kg. Co ranged between 0.003 and 0.031 mg/kg, and the lowest metal concentration was found in extra virgin olive oil for Cr. It had a concentration lower than the detection limit of the method. The highest metal concentration was found in the blend oil (Cu 0.672 mg/kg).

3.3. Health Risk

The health risk related to oil consumption was assessed by THQ calculation.

Table 3. The target hazard quotients (THQs) calculated for heavy metals.

Oil Samples	THQ (mg/kg/day)							$\sum \mathbf{T}\mathbf{H}\mathbf{Q}$
	Mn	Cr	Cu	Cd	Pb	Co	Ni
Sunflower	3.42 × 10−5	1.19 × 10−3	8.75 × 10−4	3.57 × 10−3	7.65 × 10−3	1.78 × 10−4	1.07 × 10−4	0.01360
Grapeseed	5.18 × 10−5	-	5.53 × 10−4	1.42 × 10−3	1.12 × 10−3	3.21 × 10−4	2.32 × 10−4	0.00369
Extra virgin olive	1.48 × 10−5	3.92 × 10−3	0.89 × 10−4	0.35 × 10−3	2.65 × 10−3	0.89 × 10−4	2.14 × 10−4	0.01047
Organic extra virgin olive	3.99 × 10−5	1.30 × 10−3	27.85 × 10−4	2.50 × 10−3	10.30 × 10−3	2.67 × 10−4	2.67 × 10−4	0.01745
Rapeseed	12.28 × 10−5	2.14 × 10−3	8.83 × 10−4	1.78 × 10−3	6.22 × 10−3	5.53 × 10−4	1.25 × 10−4	0.01182
Blend	3.40 × 10−5	7.38 × 10−3	60.00 × 10−4	1.42 × 10−3	10.10 × 10−3	2.32 × 10−4	1.07 × 10−4	0.02527
Walnut	2.51 × 10−5	0.71 × 10−3	7.58 × 10−4	1.78 × 10−3	6.02 × 10−3	1.60 × 10−4	0.53 × 10−4	0.009506
Rice	1.03 × 10−5	2.38 × 10−3	2.58 × 10−4	1.78 × 10−3	22.14 × 10−3	0.53 × 10−4	1.07 × 10−4	0.02672

shows the estimated THQ results for adults, and

Table 4. The incremental lifetime cancer risks (ILCRs) calculated for heavy metals.

Oil Samples	ILCR (×10−6)				∑ILCR
	Cr	Cd	Pb	Ni	×10−6
Sunflower	1.78	1.35	2.27	1.79	7.19
Grapeseed	0.00	0.53	0.33	3.89	4.75
Extra virgin olive	5.88	0.13	0.78	3.59	10.38
Organic extra virgin olive	1.69	0.95	3.06	4.48	10.18
Rapeseed	3.21	0.67	1.85	2.10	7.83
Blend	11.07	0.53	3.00	1.79	16.39
Walnut	1.06	0.67	1.79	0.89	4.41
Rice	3.57	0.67	6.58	1.79	12.61

shows the ILCRs calculated for heavy metals.

The highest value of ∑THQ was that for the rice oil sample (0.02672 mg/kg/day), and the lowest value was that for the grapeseed oil sample (0.00369 mg/kg/day); Table 3.

The sums of the ILCRs for the heavy metals (the sum of Cr, Cd, Pb, and Ni) for adults were 7.19 × 10⁻⁶ for sunflower oil, 4.75 × 10⁻⁶ for grapeseed oil, 10.38 × 10⁻⁶ for extra virgin olive oil, 10.18 × 10⁻⁶ for organic extra virgin oil, 7.83 × 10⁻⁶ for rapeseed oil, 16.39 × 10⁻⁶ for blend oil, 4.41 × 10⁻⁶ for walnut oil, and 12.61 × 10⁻⁶ for rice oil, respectively.

4. Discussion

4.1. Physicochemical Quality Indices

4.1.1. Acidity Index

The amount of free fatty acids (acidity index) in an oil indicates its quality. The higher the levels, the less likely the oils are to be used for cooking. Higher levels suggest that triglycerides are converted into fatty acids and glycerol, which induce rancidity [33]. In this study, the acidity index ranged from 0.088 to 2.080 mg/g (Table 1), with values above the permitted limit of 0.3 mg/g being obtained for olive and nut oils [18]. It is possible that a number of factors such as raw material, extraction conditions, and incorrect or prolonged storage of the products may influence the fatty acid content of these samples. A higher acidity value may also influence the peroxide value, due to peroxides that are produced by the oxidation of free fatty acids [34].

4.1.2. Moisture Content

Moisture is an important influence on the quality of oils during storage. A high water content can generate free fatty acids and unfavorable flavors [35]. In this study, the moisture content of the oils analyzed ranged from 0.013% to 0.148%, which is lower than the WHO recommended value of 0.2% for edible vegetable oil [36]. These results would indicate a longer shelf life of the products by inhibiting the action of microorganisms and reducing oxidative degradation.

4.1.3. Peroxide Value

The peroxide value (PV) is an indicator used for measuring the rancidity of fats and oils and also a criterion for predicting the quality and stability of oils [37]. The PVs for the oils analyzed were below 10 meqO₂/kg oil, set by the Codex Standards for edible oils, except for walnut oil [18]. A low PV could indicate the presence of reduced amounts of hydroxy peroxides, and hence, less oxidation reactions during storage. Considering that most of the oils fell within the standard values, it is likely that the oxidation process in walnut oil may have a cause other than storage.

4.1.4. Refractive Index

The refractive index (RI) is used to determine the purity of edible vegetable oils and to indicate the degree of unsaturation and the chain length of fatty acids. An increase in the acid chain length results in an increase in the refractive index value [38]. The refractive index values of the analyzed oils were within the limits set by Codex (1.463–1.471), indicating high-quality products [39].

4.1.5. Iodine Value

The iodine value is used to indicate the degree of unsaturation (double bonds) in fats and oils. Therefore, higher iodine values correspond to oils rich in polyunsaturated fatty acids, while oils with low iodine values have a lower degree of unsaturation [40]. The iodine values for the analyzed oil types are shown in Table 1.

The results show different values of iodine indices, with the samples being from different sources. High iodine values were found in most of the samples, indicating a high content of unsaturated fatty acids. The degree of unsaturation is a measure of the oil stability and oxidation resistance. For most of the oils, the iodine values were in the range recommended by the standards (132–162 gI₂/100 g), except for walnut oil [18].

4.1.6. Saponification Value

The saponification value (SV) provides information on the fatty acid characteristics of fats, namely, the longer the carbon chain, the less acid is released per gram of hydrolyzed fat [41]. It is also considered a measure of the average molecular weight (or chain length) of all fatty acids present. Long-chain fatty acids in fat have a low saponification value because they have a relatively small number of carboxylic functional groups per unit mass of fat, and, therefore, a high molecular weight. Thus, the shorter the average chain length (C₄–C₁₂), the higher the saponification value [41].

In the present study, for the analyzed oil samples, low SVs were obtained compared to the values allowed for cooking oils [42]; 188–196 mg/KOH/g for linseed oil; 184–196 mg/KOH/g olive oil; 168–181 mg/KOH/g rapeseed oil; and 189–195 mg/KOH/g sunflower oil. This indicates the presence of higher amounts of long-chain fatty acids in the studied oils.

4.1.7. Total Phenolic Compounds

Besides triacylglycerols, edible vegetable oils also contain biologically active substances such as phenolic compounds [2]. Phenolic compounds serve as natural antioxidants, helping to prevent fat oxidation and rancidity. This, in turn, can help to extend the shelf life of the product and maintain the nutritional and sensory quality over time.

The data in Table 1 show a variation in the TPCs in the analyzed oils, with rice oil having the highest value, followed by walnut oil, rapeseed oil, and the linseed, rapeseed, and pumpkin oil blend. Studies in the literature have mentioned that the extraction methods of bioactive compounds can influence their amount in the analyzed samples [43].

In the present study, methanol was used as a solvent for the extraction of phenolic compounds, and the differences observed between the oil samples were also due to the nature of these compounds in the plant material. Thus, a lower content of TPC can be conditioned by the hydrophilic nature of some phenolic compounds (trans-resveratrol and ferulic and coumaric acids) in the plant material, which may limit their solubility in oil [44].

The results obtained were compared with those of other studies performed on edible vegetable oils (

Table 5. Literature reports on the physicochemical contents of oils.

Oil Samples	Country	AI (%Oleic Acid)	MC (%)	PV (meqO2/kg)	RI	IV (g/100 g)	SV (mgKOH/g)	TPC (mgGAE/100 g)	References
Sunflower	Turkey	0.81		4.19		102.02			[45]
	Russia	1.40		3.50					[46]
	Romania	0.10–0.62	0.04	3.63–10.50		122.00–123.00	185.00–204.80		[1,47,48]
	India			10.63	1.461				[56]
Grapeseed	Romania					129.50	184.00		[47]
Olive	Turkey	0.82		6.39		80.03			[45]
	Bangladesh	4.20	0.47	12.43		78.38	185.80		[49]
	Romania	0.80		0.50		89.00	191.00		[1]
	Spain	0.48	0.15	5.31				20.90	[54,55]
	Marocco	1.46–2.40		3.50–7.00		89.50		21.67	[50,51]
	Libya	2.19		7.81	1.4686	81.14			[52]
Rapeseed	Turkey	0.65		9.46		107.51			[45]
	Russia	0.80		4.50					[46]
	Romania	0.65		11.50		102.00–113.20	182.00–186.20		[1,47]
Walnut	Romania					149.70	188.20		[47]
	Republic of Moldova	3.44	0.10	7.70	1.473	147.70	185.77		[53]
Rice	Bangladesh	0.09–1.11	0.82–3.05	1.43–4.33	1.465	88.07–110.59	191.38–203.31		[41,49]

). The studied edible vegetable oils’ properties determined the quality of these samples. Comparing the results obtained in this study with the data in Table 5, it can be observed that the AI values were lower than those reported in Turkey, Russia, Bangladesh, Morocco, Libya, and the Republic of Moldova for all types of edible vegetable oils [45,46,47,48,49,50,51,52]. The PV and IV vary within larger limits; the PV of sunflower oil was lower in this study than values reported in the literature [1,45,46,47,48], and the PVs of walnut, rapeseed, and rice oils were higher [41,45,46,47,49,53]. Also, a lower IV was reported for walnut oil [47,53], and higher values were reported for the other studied types of edible vegetable oils [1,41,45,46,47,48,49,50,51]. The TPC values of the olive oils were slightly larger than those found in Spain or Morocco [50,51,54,55].

4.2. Potentially Toxic Metals

Table 2 shows the content of potentially toxic metals, namely, Pb, Cd, Cu, Cu, Ni, Cr, Mn, and Co, in the eight types of edible vegetable oils.

According to international requirements, the maximum level of heavy metal content in oils is 0.1 mg/kg for Cu and Pb. There is currently no legislation for Cd [57,58].

The Food and Agriculture Organization (FAO) and the World Health Organization (WHO) have established a limit for heavy metal intake based on body weight [59]. For a 60 kg adult, the tolerable daily intakes for Cu and Pb are 3 mg and 214 μg/g [59].

Based on the results of this study, it was found that in sunflower oil, the content of metals varied in the following order: Cu > Pb > Mn > Cr = Cd = Co > Ni; in grapeseed oil, this was Cu > Mn > Co > Ni > Pb > Cd > Cr; in extra virgin olive oil, this was Cr > Pb > Ni > Cu = Mn > Co > Cd; and in organic extra virgin olive oil, this was Cu > Pb > Mn > Co = Ni > Cr > Cd. In walnut and rapeseed oil, the concentration of metals varied as follows: Cu > Pb > Mn > Co > Cr > Cd > Ni, and Cu > Mn > Pb > Co > Cr > Ni > Cd, respectively. In the case of rice oils and blends (linseed, rapeseed, and pumpkin), the variation was as follows: Pb > Cu > Cr > Mn > Ni > Cd > Co, and Cu > Pb > Cr > Mn > Co > Ni > Cd, respectively.

From these observations, it can be concluded that in six of the eight types of studied oils, the most abundant metal was Cu, except for rice oil, in which Pb predominated, and extra virgin olive oil, in which the most abundant metal was Cr. Cd was the least abundant element in the studied samples.

Generally, the concentrations of the determined metals are at an acceptable level in the oil samples, exceeding the permissible value in a few cases, such as Cu in the blend oil and organic extra virgin olive oil, and Pb in rice oil, with organic extra virgin olive oil having Pb concentration at a permissible value of 0.1 g/kg [59]. Some of these metals can cause adverse effects on the oxidative stability of oils if they are present [60].

The most possible explanation for the increased concentration of Pb is that, in urban and industrial areas, the air carries toxic substances to the surface of plants. The use of chemical pesticides and fertilizers during crop cultivation is also an explanation for such contamination [60,61,62]. Plant leaves can absorb heavy metals during development, transport them to the seeds, and hence, result in heavy metal contamination of oils (bioaccumulation) [12,63,64]. Another explanation for the presence of toxic metals in oils may be contamination during the refining process or contact with storage materials [60].

Some metals are considered to be essential if they occur in low concentrations because they are involved in metabolic functions (Co, Cr, Cu, and Mn), while others (Cd, Ni, and Pb) are considered carcinogenic. They can cause cancers of the bladder, liver, and kidneys, and peripheral and central nervous system damage [65].

Based on research on chronic exposure to Pb, it has been observed that it can cause anemia, hypertension, nervous system disorders, infertility, and brain damage [66]

Chronic diseases driven by excess Cr include nasal, pulmonary, and gastrointestinal irritations; gastric ulcers; and dermatitis. Cr, Pb, and Cd are toxic metals that catalyze the decomposition of aldehydes, acids, ketones, and epoxides in the body; affect the digestive, endocrine, and immune systems; and increase the carcinogenic effect due to their reaction with proteins or pigments [60,67].

The Cd concentration found in this study (0.001–0.010 mg/kg) is lower than the metal values reported by other researchers in all of the studied oils. For example, Mohajer et al. [61] found a range of 0.005–0.01 mg/kg Cd in rice oil, and Zhu et al. [12] reported a Cd range in extra virgin olive oil of 2.39–2.76 mg/kg, a range of 6.11–6.45 mg/kg in rapeseed oil, and a range of 3.34–3.75 mg/kg in sunflower oil.

The Pb concentration in the rice oil in the current study (0.217 mg/kg) was within the limits reported by Mohajer, 2019 (0.066–0.30 mg/kg) [61]. Bakota et al. [68] reported a value of Pb in rice oil from Iran of 0.15 mg/kg.

A higher amount of Pb was also found in the studied rapeseed oil, at 0.061 mg/kg, compared to the range reported by Zhu et al. (0.007–0.016 mg/kg) [12]. A similar behavior was observed for sunflower oil. Thus, in the present study, the Pb concentration was 0.075 mg/kg, while such values reported in other studies are in the range 0.006–0.039 mg/kg [12,24,63].

For extra virgin olive oil, the Pb concentration in the current study (0.026 mg/kg) was slightly higher than that reported by Zhu et al. [12] (0.013 mg/kg), and those reported by Niu et al. [24] (0.009–0.016 mg/kg).

The concentrations of Cu, Mn, Co, and Ni in the studied oils vary within wide limits depending on the oil analyzed. The concentrations of these metals are lower in the oils used in the current study (0.010 mg/kg in extra virgin olive oil for Cu) than in the oils analyzed by other researchers (range 0.248–0.276 mg/kg Cu for the same type of oil) [12,24,63,65].

4.3. Non-Carcinogenic Risk

The THQ values for Mn, Cr, Cu, Cd, Pb, Co, and Ni in sunflower oil were 3.42 × 10⁻⁵, 1.19 × 10⁻³, 8.75 × 10⁻⁴, 3.57 × 10⁻³, 7.65 × 10⁻³, 1.78 × 10⁻⁴, and 1.07 × 10⁻⁴; Table 3. Finally, the HI for the heavy metals studied was 0.01360 (1.36 × 10⁻²). For grapeseed oil and extra virgin olive oil, the THQ values were in the ranges of 0 and 1.42 × 10⁻³ and 1.48 × 10⁻⁵ and 3.92 × 10⁻³, respectively, while the HI values ranged between 0.00369 and 0.01047. For the organic extra virgin olive oil, rapeseed oil, and blend oil, the THQ values were in the following ranges: 3.99 × 10⁻⁵ and 1.03 × 10⁻²; 12.28 × 10⁻⁵ and 1.78 × 10⁻³; and 3.4 × 10⁻⁵ and 10.1 × 10⁻³, respectively. The HI values for these oils were 0.01745, 0.01182, and 0.02527, respectively. For the walnut oil, the THQ was in the range between 2.51 × 10⁻⁵ and 6.02 × 10⁻³, with an HI of 0.009506, and for the rice oil, the HI was 0.02672, while the THQ was in the range between 1.03 × 10⁻⁵ and 22.14 × 10⁻³.

For comparison, the average THQ values for 6387 edible vegetable oils in Chinese supermarkets studied in 2017–2019 were 0.01574 for Cd and 0.9446 for Cr [24], much higher than those obtained in this study (the average THQ was 0.00182 for Cd in all oils). In the case of Pb, a mean THQ of 0.00635 was found in China, whereas in the present study, the THQ values for Pb ranged from 0.00112 to 0.02214, with higher values observed for the organic extra virgin olive oil, blend oil, and rice oils.

These HI values are <1 and are considered to be at an acceptable level, and not a health risk. The HI values are in the range of 0.00369 and 0.02672. They are <1, indicating that the oils are not cause for concern and can be considered safe for consumption [24,61].

4.4. Cancer Risk

The ILCR amount for heavy metals (amount of Cr, Pb, Cd, and Ni) for adults ranged between 1.63 × 10⁻⁵ and 4.41 × 10⁻⁶. The results obtained from the cancer risk calculations show that the ILCR values for adults are at an acceptable level based on the U.S. EPA recommendation of 1 × 10⁻⁴ and 1 × 10⁻⁶ [61]. However, the surveillance and monitoring of heavy metals in edible vegetable oils should not be discontinued in order not to exceed the maximum residue standards for heavy metals in edible vegetable oils.

4.5. Correlations

In order to show the relationships between metal concentrations and physicochemical parameters, a correlation matrix was performed on the obtained data set. Thus, high correlations (r = 1, or r > 1) indicate a perfect relationship or a very strong relationship between the variables, while p values assess the significance of the relationships between the values; a low p value indicates a statistically significant relationship between the variables, whereas a high p value suggests that the observed correlation could indicate an insignificant relationship [69].

In this study, the 0.1 probability level statistical test (p < 0.1) was used to determine the degree of association between pairs of variables. The results between the assessed physicochemical parameters and heavy metals showed positive and negative and significant (p < 0.1) and insignificant correlations (p > 0.1) (

Table 6. The pairwise Pearson correlation coefficients.

	AI	MC	PV	RI	IV	SV	TPC	Mn	Cr	Cu	Cd	Pb	Co	Ni
AI	1.00	−0.34	0.25	0.26	−0.65	0.16	0.36	−0.27	−0.32	−0.22	−0.11	−0.13	−0.26	−0.32
MC		1.00	−0.28	−0.34	0.43	0.16	−0.29	−0.40	0.57	0.25	0.04	−0.02	−0.44	0.02
PV			1.00	−0.15	−0.50	−0.25	0.41	0.63	0.04	−0.25	−0.48	−0.31	0.53	−0.12
RI				1.00	0.36	0.52	−0.05	0.04	−0.38	−0.22	0.30	−0.18	0.03	−0.61
IV					1.00	0.22	−0.56	−0.07	−0.05	−0.17	0.36	−0.05	−0.11	−0.05
SV						1.00	0.32	−0.54	0.39	0.11	−0.24	0.25	−0.58	−0.66
TPC							1.00	0.03	0.27	0.08	−0.18	−0.64	−0.07	−0.51
Mn								1.00	−0.15	0.00	0.10	−0.31	0.97	0.02
Cr									1.00	0.72	−0.40	0.19	−0.14	−0.18
Cu										1.00	0.04	0.13	0.12	−0.04
Cd											1.00	0.25	0.10	−0.20
Pb												1.00	−0.38	−0.32
Co													1.00	0.13

The values in bold are significant (the p-value is below 0.1); r: perfect = 1, very strong = 0.75, strong = 0.5, moderate = 0.3, weak = 0.1. +: positive correlation, −: negative correlation. p-value < 0.1 significant, p-value > 0.1 insignificant.

).

For the physicochemical parameters, a strong, negative, and significant (p < 0.1) correlation was observed between the acidity and iodine value r = 0.65, showing that, in most samples, acidity was observed to vary inversely regarding the iodine value. The significant correlation is given by the nature of free acids in the oil samples.

Similarly, a strong but non-significant (p > 0.1) negative correlation was observed between IV and PV (r = 0.50) and IV and TPC (r = 0.56), respectively, indicating that an increase in the value of one member of the pair (e.g., high unsaturated fatty acid content), will result in a decrease in the value of the other.

On the other hand, a strong but insignificant positive correlation was observed between the RI and SV (r = 0.52), the strong relationship being a measure of the fatty acid chain length.

Regarding the relationship between the metals, a positive, significant correlation was observed between Co and Mn at a value of r = 0.97, showing the existence a similar origin in the soil matrix. The next significant correlation involves the Cu–Cr pair with r = 0.72; similarly, moderate correlations were observed between the Co–Pb and Cr–Cd pairs.

The corresponding correlation coefficient data for the physicochemical parameters and different metals also show significant positive/negative correlations.

Thus, the correlation between the TPC and some metals suggests their competitiveness towards the hydroxyl groups of the phenolic compounds [70]; the negative correlations shown for Pb (r = −0.64) and Ni (r = −0.51) may indicate a lack of interaction between these metal ions with the hydroxyl groups of the phenolic compounds.

The peroxide value (PV) was strongly correlated with some metal ions, the relationship being strong and significant with Mn (r = 0.63) and insignificant with Co (r = 0.53, p > 0.1). These data show that the quality of cooking oils may be related to the low presence of potentially toxic metals and the degree of oxidation.

The saponification value (SV) was negatively correlated with Ni, the binding being strong and significant, while in the case of other metal ions (Co and Mn), the binding was insignificant. It can be said that these metals show weak interactions with the long-chain acids in the oil samples.

At the same time, moderate or weak correlations were observed between the metals and the MC, PV, IV, and SV, suggesting weak associations between the trace metals and physicochemical parameters of the edible vegetable oil samples.

In conclusion, the statistical analysis showed that variables with positive associations suggest that they may have similar sources of oxidation and photo exposure, exhibit similar behavior during storage, and are dependent on each other. Variables with a negative association could be from different sources or are independent of each other.

5. Conclusions

Edible vegetable oils are an important source of energy for the human body, so research into their quality is very important.

The results obtained from the analysis of the various edible oils show that the quality parameters were within the maximum limits assumed for most of the samples, indicating the oxidative stability of the edible vegetable oils. Also, the results for the toxic metal content in the oils consumed and commercially available in the city of Constanta were below the acceptable limit for human consumption.

After performing the statistical test at the 0.1 probability level (p < 0.1), it was observed that the results of the link between the evaluated physicochemical parameters and heavy metals showed positive and negative and significant (p < 0.1) and insignificant (p > 0.1) correlations.

Although this study showed that the heavy metal content in oils is not high and does not pose a risk for consumption, it may represent a threat if their monitoring is not frequent. The evaluation of oils and removal of heavy metals from oils should be considered to prevent the excessive accumulation of these metals in the human body. The results of this study could contribute to consumer awareness by assessing the quality and safety of edible vegetable oils on the Romanian market. Protecting humans from non-carcinogenic and carcinogenic effects should be performed by raising awareness on this important topic.