Heavy metals burden in vegetable oils consumed by Saudi population

Selected heavy metals, namely Cu, Zn, Fe, Mn, Cd, Pb and As, in seven popular varieties of edible vegetable oils collected from Saudi Arabia, were determined by graphite furnace atomic absorption spectrometry (GF-AAS) using microwave digestion. The concentrations for copper, zinc, iron, manganese, lead and arsenic were observed in the range of 0.035 – 0.286, 0.955 – 3.10, 17.3 – 57.8, 0.178 – 0.586, 0.011 – 0.017 and 0.011 – 0.018 µg/g, respectively. Cadmium was found to be in the range of 2.36 – 6.34 ng/g. The results are compared internationally and with standards laid down by world health agencies. A risk assessment study has been carried out to assess exposure to these metals via consumption of vegetable oils. A comparison has been made with safety intake levels for these heavy metals recommended by Institute of Medicine of the National Academies (IOM), US Environmental Protection Agency (US EPA) and Joint FAO/WHO Expert Committee on Food Additives (JECFA). The results indicated that the dietary intakes of the selected heavy metals from daily consumption of 25 g of edible vegetable oils for a 70 kg individual should pose no significant health risk to local population.

Vegetable oils are widely used in cooking, cosmetic, pharmaceutical and chemical industries. The presence of essential fatty acids, fitosterols and a tocopherol, enhances the nutritional value of vegetable oils. Vegetable oils are beneficial  and  popular  due  to  their cholesterol-lowering effect. This is largely a result of  the high levels of antioxidative substances and monosaturated fatty acids found in most pure vegetable oils. In contrast, animal fats are predominantly saturated and do not react readily with oxygen.

The quality of edible oils regarding their freshness, storability and toxicity can also be evaluated by the determination of several trace metals. Levels of trace metals like Copper, Zinc, Iron and Manganese are known to increase the rate of oil oxidation while other elements such as Arsenic, Cadmium and Lead are very important on account of their toxicity and metabolic role. The presence of metals in vegetable oils depends on many factors: they might originate from the soil, fertilizers, and presence of industry or highways near the plantations, and be incorporated in the oil. The metals may also be introduced during the production process or by contamination from the metal processing equipment and thus, be suspended in the oil.

Toxic metals
The harmful effects induced by toxic metals only occur when they are overdosed. In general, a hazardous metal is defined as a metal which could induce adverse symptoms in the human body when consumed even in trace amounts. There is currently considerable interest in the determination of heavy metals in foods. It is necessary to study the migration of trace elements and to monitor the highly toxic microcomponent content at all stages of the ecological chain (soils, waters, biological systems) because there are immediate sources of heavy metals that reach the human organism.

Toxic elements can be very harmful even at low concentration when ingested over a long time period. The essential metals can also produce toxic effects when the metal intake is excessively elevated. The trace metals enhance the rate of oxidation of edible oils by increasing the generation of free radicals from fatty acids or hydroperoxides. It is necessary to assess the levels of heavy metals in edible vegetable oils and to report possible contamination that would represent a health hazard.  Researchers from different parts of the world have determined heavy metals in vegetable oils. Food consumption had been identified as the major pathway of human exposure to toxic metals, compared with other ways of exposure such as inhalation and dermal contact. Taking into account the metabolic role of some metals and the large use of vegetable oils, it is of great significance to evaluate the presence of heavy metals in commercially available vegetable oils.

Saudi consumers increasingly sought to adopt a healthier diet with widening awareness of the health problems caused by excessive weight. There is a big turn over from animal fat based cooking oils to vegetable oils. However, there has been no or little information on the heavy metal levels in edible vegetable oils in Saudi Arabia.

Copper is an essential element for the human body but very high intake can cause adverse health problems. Its deficiency leads to anemia and osteoporosis in children. Minimum and maximum values of copper were shown by corn oil and olive oil, respectively. The lowest manganese content was in rapeseed oil while the highest was found in the peanut oil. The U.S National Academy of Sciences recommended 2.5-5 mg per day manganese intake. Manganese deficiency can produce skeletal and reproductive abnormalities. Cadmium, arsenic and lead levels were found to be within the legal limits set by Joint FAO/WHO Expert Committee on Food Additives. The minimum and maximum lead levels were found in rapeseed oil and sesame oil, respectively. Lead and cadmium levels in all investigated edible oils were found to be lower than legal limits.

Intake of elements from food consumption is dependent on the element concentrations in food and the quantity of food consumed by individuals. World renowned agencies like US Environmental Protection Agency (US EPA), Joint FAO/WHO Expert Committee on Food Additives (JECFA) and Institute of Medicine of the National Academies (IOM) have provided guidelines on the intake of trace elements by humans. The IOM of the National Academies recommended the adequate intake (AI) and the tolerable upper intake level (UL) values for some essential elements; the JECFA recommended permissible tolerable weekly intakes (PTWIs) and acceptable daily intakes as guidelines for food additives and certain contaminants in foods. Also, the US EPA provided reference dose (RfDo) values in ug/kg body weight/day for some elements.

The study
In a recent study, an attempt was made to evaluate the possible health threats from the consumption of edible vegetable oils by local population. According to a maximum dietary intake of 25g of a single type of fat or oil for an adult per day recommended by World Health Organization, the estimated daily dietary intakes (EDDIs) of heavy metals from edible oils analysed were calculated with mean concentration values. Also, the estimated weekly dietary intakes (EWDI) were also generated from average concentration values, 175 g of edible vegetable oil consumption per week, and average body weight of 70 kg. The UL, AI, guideline and PTWI values were used to compare the estimated dietary intakes of trace elements. Moreover, the values of contribution of EDDI to UL or AL, EWDI to guideline or PTWI were also calculated in this study.

The results suggest that the EDDI of Cu, Zn, Fe and Mn by a 70kg adult consuming 25g of edible vegetable oils per day were all far below the respective AI and UL recommended by IOM. The EWDI of Copper, Zinc, Iron, Manganese, Cadmium, Lead and Arsenic by a 70 kg adult consuming 175 g of edible vegetable oils per week were all less than the derived guideline values and PTWI served by JECFA, therefore, weekly consumption of 175 g of edible vegetable oils in KSA generally did not pose any serious health risks to local population. This may be attributed to the fact that these edible oil processing industries had good raw materials, advanced processing technology and strict quality control standards, they, thus guaranteed the qualified products.

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