Heavy metals are elements with an atomic weigh over 63.5 and a specific gravity higher than 5.0 that are generally dangerous to human health and the environment. The major elements included in this class are as follows: lead—Pb; cadmium—Cd; cobalt—Co; chromium—Cr; copper—Cu; iron—Fe; arsenic—As; nickel—Ni; zinc—Zn; and mercury—Hg [1]. The development of industry, the excessive use of chemical substances in agriculture, as well as the intensification of car traffic, in addition to the multiple benefits brought to humanity, continuously produce great ecological imbalances, sometimes reversible, sometimes irreversible, with a particular impact on the quality and safety of food, food resources, and the health of consumers. Heavy metals can originate from both natural (rocks) and anthropological sources (metal mining, smelting, trash dumping, incineration, pesticides, etc.) [2]. So, with the industrial revolution and economic globalization, the numerous environmental contaminants have significantly increased. These contaminants do not dissolve, and they accumulate in the environment [2]. The diverse and emerging food security issues have become a global concern ^[3][4][3,4]. Traces of different heavy metals were found in food (vegetables, meat, fish, milk, etc.) due to their mobility and bioaccumulation in water sources. By whatever means heavy metals enter food and beverages, once they enter the body, they are oxidized and form stable bonds to enzymes or protein molecules. This results in dysfunction, abnormalities, or even damage [5]. Nowadays, there is a growing preoccupation regarding the heavy metal contents in food and beverages and their subsequent consequences for the daily diet and human life chain safety.

2. Sources and Health Concerning

Heavy metals are potentially toxic in high amounts or after long-term exposure ^[6][12]. These elements manifest the ability to move and concentrate in different organs, leading to various health issues ^[7][13]. For example, lead affects the normal activity of enzymes and is linked with carcinogenesis, mutagenesis, and teratogenesis in experimental animals ^[8][14]. Lead poisoning is still a major public health risk, especially in developing countries ^[9][15]. The toxic action of lead is influenced by the chemical form in which the element is found, being absorbed in the body in a proportion of about 90%. Initially, the manifestations are non-specific, with Burton’s line present (a blue-gray area on gums) ^[10][16]. Organic lead accumulates mainly in the bones, producing various transformations of the hematoforming marrow, and less in the nervous system, organs (liver, kidneys), or muscle tissue. Inorganic lead is absorbed from the intestinal tract, more so in children (around 40–50%). Of the total absorbed lead, most of it is eliminated through urine (about 75%) and about 16% through feces. The most dangerous entry route is considered the respiratory one, as lead reaches the blood directly, without the possibility of elimination through urine or feces. Lead poisoning begins with anemia, caused by a reduction in the life span of erythrocytes and a decrease in hemoglobin synthesis. Disorders of the central nervous system appear later, such as hyper reactivity, impulsive behavior, changes in perception, and decreased learning capacity. In the peripheral nervous system, claw-hand disease can develop. In acute forms, irritability, restlessness, muscle tremors, headaches, ataxia, unclear consciousness, and memory loss may occur. In the last stage, renal failure, convulsions, coma, and finally death are observed. However, lead poisoning following the consumption of food is rare; the cases reported so far have had the source of alcoholic beverages (liqueurs, cider wine) kept for a long time in ceramic vessels varnished with varnishes containing lead or fraudulently distilled beverages by using car radiators ^[8][11][14,17]. The widespread use of cadmium in industries has caused an important ecotoxicological problem. It is freely found in living organisms such as clams, crustaceans, mushrooms, etc. Following the consumption of foods with a high level of cadmium, associated with an irrational diet and insufficient intake of vitamin D, osteomalacia (soft bones) can occur ^[12][18]. Cadmium is a cumulative toxicant; its action is exerted on both the urinary and respiratory systems ^[13][19]. Cadmium is easily absorbed by plants, with the highest concentration found in fungi. In the case of animals, it is absorbed in the liver and kidneys. The main foods contaminated with this element are pork, fish, potatoes, milk, and beer. It does not accumulate in eggs, while seafood can present significant amounts of cadmium. The concentration of cadmium absorbed by the human body following food ingestion is between 5% and 16%, the value doubling under the influence of Ca²⁺, protein, or Zn²⁺ deficiencies. Cadmium is absorbed in the liver, spleen, adrenal glands, and duodenum (in the first 48 h after ingestion). Accumulation in the kidneys occurs much more slowly, with the maximum level being reached after approximately 6 days. Cadmium is involved in high blood pressure ^[8][14]. This element is characterized by high stability in the body, the excretion is very slow, and the life span is estimated at 20–40 years. Lung and kidney functions are affected by increasing the excretion of glucose, amino acids, uric acid, and proteins; the liver is also affected by increasing gluconeogenesis, thus resulting in hyperglycemia. There is an increase in the circulating levels of epinephrine, norepinephrine, and dopamine in the brain. It has also been established that it has hypertensive and teratogenic effects and is considered to be one of the most powerful metallic carcinogens known to date.  Copper presents a high degree of toxicity ^[14][21], being found in combined forms (coveline, chalcosine, chalcopyrite, etc.). This element is used in the metallurgical and paint industries, glass, ceramics, and the manufacture of phytosanitary products. An important source of contamination is the equipment used in processing, handling, and storing food. Intoxications can also be caused by medication, by using copper sulfate as an emetic or tenifuge, but such situations are very rare. Copper is considered an essential element for the body, and deficiencies in this element cause different disorders, such as Menkes disease (manifested by stunting and the appearance of severe neurological difficulties) or Wilson’s disease (copper is stored in the liver and in the central nervous system) ^[14][21]. The toxicity of copper is higher through skin penetration, the respiratory tract, or directly into the blood because it can be eliminated through vomiting from the digestive tract. Food poisoning is rare in the case of copper, occurring in situations where the food product is highly acidic and, following prolonged contact with the metal, a significant amount of metal is dissolved. Thus, foods kept for a long period of time in copper packaging will turn green and present a metallic taste.  Zinc is an essential element that the human body can tolerate up to 2 mg/kg when administered for a long-term period ^[15][22]. This metal can be found in numerous food substrates, such as fish, red meat, grains, dairy products, cereals, etc. The elimination of zinc from the body is ensured by the excretion of feces and urine. The consumption of small amounts of zinc supplements by children would favor a significant increase in height and weight ^[16][23]. Arsenic can be found as arsenite or arsenate, both of which are lethal to humans and animals. This element originates from natural sources (volcanic ash and geothermal springs) ^[17][24], agro-industrial treatments (herbicides, pesticides, and fungicides) [5], and electronics ^[17][24]. The toxicity of arsenic is usually determined by its ability to interact with the sulfhydryl groups of proteins and enzymes and to substitute the element phosphorus in biochemical reactions ^[18][25].  Mercury is usually used in different industries, such as paint batteries, chloro-alkali production, in thermometers, fluorescent lights, and dental amalgams [5]. Mercury exists in many chemical forms (inorganic and organic mercury). The degree of toxicity varies according to the form and concentration in which mercury is found in the analyzed substrate. Thus, methylmercury is quickly absorbed through the intestine and is deposited in numerous tissues. This form does not cross the blood–brain barrier as efficiently as elemental mercury. In the brain, methylmercury is transformed into elemental mercury by demethylation. Mercury and mercury salts affect internal organs (especially the intestinal mucosa and kidneys), while methylmercury is distributed throughout the body ^[19][28]. The contamination by mercury was reported in fish, sediments, hair, blood, and urine ^[20][29]. This metal induces tremors and sleep disturbances, irritability, excitability, excessive shyness, muscular spasms, loss of memory, depression, etc. ^[17][24]. Chromium can be found in different fertilizers, industrial equipment, textiles, and paper industries [5]. Its toxicity refers to allergic reactions, anemia, pathophysiological defects, burns, and respiratory and gastrointestinal cancers ^[21][30]. Chromium can be found in different forms (with chemical valences from 0 to 6), but the Cr(III) and Cr(VI) forms are usually stable. Large amounts of Cr(III) negatively influence the absorption of trace elements in animals and humans and affect neuronal functions and kidney and liver activity. Cobalt is used in coloring glasses, pigment production, or the alloys industry [5]. This element accumulates in the human body and causes allergic contact dermatitis, asthma, hepatotoxicity, memory loss, optic atrophy, cardiovascular diseases, a reduction in fertility, etc. ^[22][33].  Nickel cans originate from electroplating activities, storage batteries, casting industries, nickel-plated jewelry, smoking cigarettes, and electrical pieces [5]. Acute toxicity symptoms may manifest as headaches, vertigo, tachycardia, sweating, and visual disturbances. In cases of chronic inhalation exposure, severe respiratory disorders were reported. Nickel exposure determines the formation of free radicals in the human body, the modification of DNA bases, and has carcinogenic effects ^[23][35]. 

3. Methods of Analysis

Identification and quantification of heavy metals in food can be made using different methods, such as Inductively Coupled Plasma Atomic Absorption Spectrometry—ICP-AES ^[24][25][26][37,38,39]; Flame Atomic Absorption Spectrometry—FAAS ^[26][39]; Mass Spectrometry with Inductive Coupling—ICP-MS ^[27][28][40,41]; Graphite Furnace Atomic Absorption Spectrometry—GF-AAS ^[29][42]; High-resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry—HR-CS-GFAAS ^[30][31][43,44]; Anion Exchange Chromatography Coupled to Inductively Coupled Plasma Mass Spectrometry—AEC-ICP MS ^[32][45]; Microwave Induced Plasma Optical Emission Spectrometry—MIP OES ^[33][46]; Electrochemistry ^[34][47]; Liquid Chromatography coupled with Mass Spectrometry (LC-MS/MS) ^[35][48]; Gas-Chromatography—tandem Mass Spectrometry (GC-MS) ^[36][49]. Among those mentioned, FAAS and GF-AAS are often used in most analytical laboratories. FAAS allows for identifying and quantifying a lot of metals (Co, Cd, Cd, Cu, Fe, Fe, Mn, Ni, Pb, and Zn) that are found even at trace levels. This method is characterized by low operation costs and good analytical performance, but the main disadvantage is the limitation of mono-elemental detection and the range of linear responses ^[37][50]. The ICP-MS technique enables a multi-element analysis with a large analytical range of linear responses, a low detection limit, easy and simple sample preparation, high-resolution tandem mass-spectrometry, etc. However, the equipment and laboratory setup costs are high, involve a high level of expertise of the operators, and multiple high purity gases are needed ^[27][40]. Compared to ICP-MS, FAAS and GF-AAS techniques enable a single-element analysis, require a higher sample volume, have a limited analytical range, and involve the utilization of flammable gases ^[27][40].

4. The Presence of Heavy Metals in Food

4.1. The Presence of Heavy Metals in Fruits and Vegetables

Fruits and vegetables present high nutritional values, and their consumption in fresh form helps in the maintenance of health and the prevention and treatment of various diseases. Fruits and vegetables contain both essential and toxic heavy metals in different amounts ^[38][53]. Numerous studies were conducted to analyze the content of heavy metals in fruits and vegetables from various countries and regions, especially those with large industrial activity or a high level of pollution ^{[39][40][41][42]}[54,55,56,57].

4.2. Milk and Dairy Products

Milk is a basic component of the daily diet and contains essential nutrients for the normal functioning of the human body. Several studies regarding the concentrations of heavy metals in milk and dairy products were conducted over time ^{[43][43][44][45][46]}[61,61,68,69,70]. High levels of these compounds may be due to the exposure of animals to environmental pollution or the consumption of contaminated water and feed ^[47][71]. Pilarczyk et al. ^[48][72] demonstrated that heavy metal content in milk is influenced by a cow’s breed. The authors obtained significantly higher concentrations of Pb²⁺, Cd²⁺, Cu²⁺, and lower levels of essential minerals in milk from Holstein Friesian cows compared to samples from Simmental cows.

4.3. Meat and Meat Derivatives

Heavy metals in meat and meat products come from contaminated animal feeds, especially in regions with intense industrialization ^[49][76]. Some authors reported various amounts of heavy metals in meat and meat derivatives produced in different countries ^{[49][50][51][52][53][54]}[52,76,77,78,79,80]. Hoha et al. ^[51][77] obtained higher values of heavy metals in pork salami and sausages obtained in Romania, compared to less processed samples like ham and bacon. The authors postulated that higher quantities of contaminated spices could be the main explanation. The concentrations of the analyzed metals were below the Codex Alimentarius limits ^[55][9], but their cumulative effect should be taken into consideration.

4.4. Edible Oils

Vegetable oils contain trace metals such as Fe²⁺, Cu²⁺, Ca²⁺, Mg²⁺, Co²⁺, Cd²⁺, and Mn²⁺, which can accelerate the rate of oil oxidation ^[56][81]. Heavy metals in oils may originate from the soil, primarily due to the intensive use of fertilizers and pesticides or from contamination during the manufacturing process ^[57][58][82,83]. Their occurrence in vegetable edible oils is a result of environmental contamination, refining processes, transfer during transport, or the packaging process. Even if the used seeds contain high amounts of metals, most of them are not extracted from the resulting oils ^[28][41].

4.5. Alcoholic Beverages (Wine and Beer)

Most of the heavy metals present in alcoholic beverages can originate from agricultural pesticides or contamination from processing equipment (pipelines, containers, tanks, filtration systems, aluminum cans, etc.) ^[59][60][58,99]. In the beer industry, trace components, including heavy metals, represent approximately 0.02% of malt extract. This includes hazardous metals, which can be transferred from source ingredients to the final beer product and brewing residues. The concentrations of these metals depend on the chemical composition of the raw materials and their capacity to dissolve into the solution over the brewing process. Considering that beer is one of the most widely consumed beverages globally, regular consumption can have adverse effects on people’s health. In winemaking, heavy metal sources are similar to those in beer production. According to Han ^[61][66], heavy metals such as Cu²⁺ and Pb²⁺ can be absorbed by the waste yeast. Winemaking byproducts have shown efficiency in absorbing heavy metals from aqueous solutions. This can be attributed to their concentrations of proteins, carbohydrates, and phenolic compounds, which contain carboxyl, hydroxyl, sulphate, phosphate, and amino groups capable of binding metal ions ^[62][102]. Existing research papers generally report low amounts of heavy metals in wine ^[59][63][64][58,103,104]. 

4.6. Reduction of Metal Content

Extensive anthropogenic activities, combined with a lack of recycling or proper disposal practices, pose a significant threat to both human life and the environment. Given that most procedures are expensive and logistically challenging, current research efforts are focused on developing cost-effective methods for the removal of contaminants. An overview of the procedures for the reduction of heavy metals in food products is presented below. Chemical precipitation refers to the administration of some coagulants (lime, alum, and organic polymers) [5]. Pohl ^[65][111] highlighted the effectiveness of sulfur-containing precipitation agents in significantly removing several heavy metals (Cd²⁺, Cr²⁺, Co²⁺, Cu²⁺, Hg²⁺, etc.) from water. Chemical reagents like Ca(OH)₂–calcium hydroxide or NaOH–sodium hydroxide have been used to remove Cu²⁺ ions from aqueous solutions ^[66][67][68][112,113,114]. This procedure is easy to operate and practicable for most metals, with low costs, but is limited by the high consumption of precipitants and lower removal efficiency, with extra operational costs for sludge disposal ^[69][115]. Different electrochemical methods (ion exchange, electrooxidation, electrochemical reduction, and electroflotation) were developed for removing food contaminants ^[70][116]. Of these, the ion exchange procedure manifests excellent selectivity for metals but implies high costs with raw materials and a small range of action on metal ions ^[69][115]. Electrodialysis is based on the effect of electric potential when a semi-permeable membrane is used to remove metal ions [5]. On this line, Ottosen et al. ^[71][117] achieved an 80% reduction of Cu²⁺, Cr²⁺, and As³⁺ from wood wastes after 7 days of treatments with oxalic acid.  Coagulation and flocculation processes are effective methods for removing certain metals, and compounds like aluminum, ferrous sulfate, or ferric chloride can be employed for this purpose [5]. The main drawback of this method is its high operational costs. Moreover, large quantities of coagulants and flocculants are necessary to achieve the required level of flocculation ^[69][115]. Flotation methods include dissolved air, ions, and precipitation flotation. In the ion flotation process, a surfactant is used to increase the hydrophobicity of the metal ions, which are then removed by air bubbles [5]. The technique is characterized by high efficiency and separation selectivity, but the operation process is complex, with high costs, and the elimination efficiency is reduced ^[69][115]. Photocatalytic removal methods refer to the use of light and semiconductors, particularly when applied to wastewater treatment [5]. This technique permits the simultaneous removal of metals, and the resultant by-products present low toxicity.