# Comparative Study of the Presence of Heavy Metals in Edible Vegetable Oils
## 2 Analysis of Publications and Trend of Heavy Metals in Edible Vegetable Oils  
This section shows a preliminary compilation of relevant data extracted from the different studies analyzed in this research:  
Geographical location of the regions with the most studies on the presence of heavy metals in edible vegetable oils. For this, the sampling point with which the analysis will be carried out is taken as a reference, taking into account that, in most cases, the oils have been acquired in the place of origin or in local markets. Likewise, the countries that carry out the most studies are located in the northern hemisphere, except for Brazil and Argentina. This distribution is not random as there is a direct correlation between said distribution and those countries that consume the most of this type of oil. Figure 1 shows the percentage of studies in each country. Brazil is the country with the highest percentage with 17.19%, followed by Turkey, China, Iran, and India, with 15.63, 10.94, 9.38, and 6.25%, respectively. Among them are the studies of metals in edible oils in Brazil [23], Turkey [24], China [25], Iran [26], and India [27]. Domestic consumption of vegetable oils expressed in millions of metric tons is also represented, Mill. M.T., in which China is leading with 40.79 Mill. M.T., followed by the European Union, India, Indonesia, and the United States, with 25.13, 23.08, 22.22, and 18.10 Mill. M.T., respectively. In this way, it can be verified that those countries with the most consumers carry out a greater number of studies, as China, India, the United States, or Brazil. It is necessary to mention some countries in which the consumption of vegetable oils and the percentage of studies have no direct relationship, as is the case of Turkey where consumption is low, with a value of 2.65 Mill. M.T. and the percentage of studies is high (second place), with a value of 15.63% [28; 29; 30]. In the opposite case, the United States is the fifth most consuming region with 18.10 Mill. M.T. and the percentage of studies is low, with a value of 3.13% [31; 32]. Edible vegetable oils studied. A total of 35 oils were considered, being the most studied olive oil with 14.36%, followed by sunflower oil with 13.81%, and rapeseed oil and corn oil, with 9.94%. In these four oils the majority of the investigations on metals are focused on: iron (Fe), copper (Cu), cadmium (Cu) and lead (Pb). Also, manganese (Mn) in olive oil [33], cadmium (Cd) in sunflower oil [34], nickel (Ni) in rapeseed oil [35], or lead (Pb) in corn oil [36] are importat. There are other oils in a lower percentage such as: avocado oil [37], organ oil [38], linseed oil [30], or peach oil [39]. Heavy metals in edible vegetable oils. The most analysed heavy metal is Cd, with 14.60% of studies. This is followed by Pb, Cu, and Fe with 12.41, 12.04, and 9.49%, respectively. There are other heavy metals in lower percentage such as: cobalt (Co) in camellila oil (walnut variety) [40], mercury (Hg) in olive oil [41], or titanium (Ti) in coconut oil [42]. Analytical techniques used for determination and quantification. The most used analytical technique is Induction Coupled Plasma Atomic Emission Spectroscopy (ICP-OES/ICP-AES) with 25% of the studies, followed by Flame Atomic Absorption Spectrometry (FAAS), Mass Spectrometry with Inductive Coupling (ICP-MS), and Graphite Furnace Atomic Absorption Spectrometry (GF-AAS) with 17.65, 16.18, and 14.71%, respectively. There are other analytical techniques to a lesser extent such as: High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry (HR-CS GFAAS) [43; 44], Ion Exchange Chromatography Coupled to Inductively Coupled Plasma Mass Spectrometry (AEC-ICP MS) [45], or Microwave Induced Plasma Optical Emission Spectrometry (MIP OES) [37]. Chemical reagent used for the analytes extraction. In this regard, the research focuses on studies of heavy metals in olive oils, since they are the most analyzed vegetable oils.