Potential Metal Contamination in Foods of Animal Origin—Food Safety Aspects

Abstract

This literature review provides an overview of the food safety and toxicological characteristics of various heavy metals and metalloids and the public health significance of their occurrence in food. Metals also occur as natural components of the environment, but they can enter food of animal origin and the human body primarily due to anthropogenic (industrial, agricultural, transport-related) activities. The persistent heavy metals (e.g., Hg, Pb, Cd) found in the environment are not biodegradable, can accumulate, and can enter the bodies of higher animals and subsequently, humans, where they are metabolized into various compounds with differing toxicity. Thus, due to their environmental contamination, they can accumulate in living organisms and their presence in the food chain is of great concern for human health. Regulations of the European Community in force lay down maximum levels for a limited number of metals, and the types of regulated foodstuffs of animal origin are also narrower than in the past, e.g., wild game animals and eggs are not included. The regulation of game meat (including offal) deserves consideration, given that it is in close interaction with the environmental condition of a given area and serves as indicator of it.

1. Introduction

Various metals and non-metallic metalloids are an integral part of human civilization due to their widespread occurrence and use in nature.

In the past, different metal-based pesticides were used in large quantities on crops to control pests and microorganisms. Due to the rapid development of toxicology, numerous research and studies have demonstrated the high toxicity of certain metals to various organisms living in the environment. Based on these results, the majority of metal-containing pesticides have been restricted or even banned by the competent authorities. However, due to their previous widespread use, the entire biosphere has been contaminated. Furthermore, they have been found in different natural sources.

During various industrial processes (e.g., mining, processing industry, etc.) using metal-containing natural sources (ores, stones, rocks, etc.), environmental areas (water, soil, air) can again be polluted with dust, slag, soot, smoke, particulate matter, and combustion products. Similarly, plants, water, and soil can be contaminated by industrial wastewater emissions. Municipal and industrial emissions from anthropogenic activities are of greater significance than the release of metals of natural environmental origin [1].

The release of toxic heavy metals into the environment began several centuries ago, but it remains highly significant today. The heavy metal contamination of agricultural areas, groundwater, and surface waters can lead to severe environmental pollution, damaging the ecosystem and endangering or destroying the lives of animals and plants. Heavy metals are not biodegradable (rather persistent), they accumulate in living organisms, and they are transformed into more toxic or, in fewer cases, less toxic forms through biochemical processes [2,3].

Persistent heavy metals (e.g., Hg, Pb, Cd) released into the environment can also enter the bodies of higher animals through the food chain. Organisms at higher trophic levels, such as humans, are thus exposed to higher concentrations of pollutants.

Currently, due to their environmental polluting effects and cumulative properties, the enrichment of metals in the food chain is a critical issue from a health protection standpoint. Various metals and heavy metals also occur as natural environmental components, but they primarily enter foods of animal origin and the human body because of anthropogenic activities (e.g., industrial and agricultural activity, household use, transport, waste incineration, etc.).

Some metals (e.g., zinc, calcium, cobalt, chromium, copper, selenium, iron) are essential for life in small concentrations; they activate various proteins and enzymes, maintain ion and pH balance, ensure bone and teeth strength, and regulate metabolic homeostasis. The physiological roles of others (e.g., arsenic, mercury, cadmium, nickel, lead, etc.) are currently unknown, although some (e.g., arsenic) may have beneficial effects. Arsenic in small amounts exhibits anabolic effects in animal studies, by inhibiting oxidation, stimulating appetite, increasing body weight gain, and enhancing red bone marrow, thereby increasing the number of erythrocytes and reticulocytes, but it is not established as essential for humans [4,5,6,7].

However, heavy metal exposure has not ceased due to its historical widespread use in plant protection and other industrial processing. The current focus is on the chronic toxic and harmful effects of long-term, low-dose metal exposure and their cumulative nature, which may lead to micro-toxicological alterations, or even mutagenic and carcinogenic effects, immunotoxicity, and reproductive issues [8].

The number of registered chemicals exceeds 10 million, of which 70.000–80.000 are compounds with which humans may come into direct contact [5]. Most of these substances can potentially enter food and adversely affect consumer health. The vast majority of chemical contaminants enter the bodies of food-producing animals and plants during primary production, on the farm, or externally, while a smaller portion originates during food processing or appears in products as additives causing secondary contamination.

Among the large number of possible environmental contaminants, toxic heavy metals and metalloids such as cadmium, lead, mercury, and arsenic are significant in terms of the chemical contamination of our food.

2. Major Toxic Metals in Food

2.1. Arsenic (As)

The trivalent arsenite (As³⁺) form of arsenic is increasing day by day in soil and water, causing loss to crop productivity. Its presence in the soil and irrigation water in a higher concentration exceeding the permissible limit has become a threat to crop production and human livelihood. In plants, the uptake of As³⁺ is affected by oxidizing or reducing the environment of the soil, and the pH and is mediated by various transporters such as Nodulin-26-like aquaporins (such as Lsi1 and Lsi2). The phytotoxic behavior of As³⁺ severely affects the growth and development of crop plants, which not only reduces productivity but also consecutively affects human lives. Deposition of As³⁺ in staple food crops allows direct As exposure, affecting around 80% of the world population [9].

The concentration of As in plants is usually less than 1.0 mg/kg dry weight (d.w.). Besides the physical–chemical properties and the chemical speciation of As in growth medium, As uptake by plants is also controlled by various physiological/tolerance mechanisms taking place in different tissues of plants under As stress [10].

In aquatic environments, the arsenic content of algae is in the range 1–180 mg/kg, in marine fish and bivalves it is <2–170 mg/kg, and in freshwater fish it is <0.1–3 mg/kg [11]. However, organic arsenic compounds (e.g., arsenic betaine, arsenic sugar) found in these foods are generally non-toxic.

Arsenicals can cause oxidative stress and affect biotransformation methylation processes and the metabolism of other essential metals. Thus, based on these processes, it is classified as a carcinogenic compound [12,13,14,15].

Arsenates can replace phosphate compounds in various biochemical reactions due to their similar structure and properties, thus uncoupling oxidative phosphorylation and reducing the amount of ATP. Trivalent arsenic derivatives (e.g., arsenites) bind to thiol and sulfhydryl groups of enzymes, receptors, and coenzymes, inhibiting their physiological function [12,14].

Arsenite, arsenate, dimethyl arsenate, and monomethyl arsonate can induce developmental abnormalities, perinatal death, and growth retardation in hamsters, mice, and rats [16].

Absorption of inorganic arsenate and arsenite compounds from aqueous solutions is substantial (<90%) in humans. Absorption of inorganic compounds from food is lower (60–75%) [17].

Monomethyl-arsonate has been detected in human urine following the ingestion of large amounts of inorganic arsenic compounds [18]. Francesconi et al. detected nearly 12 arsenic metabolites in human urine following the ingestion of synthetic arsenic sugar [19].

The proportion of arsenic compounds excreted in urine is generally 20% inorganic, 15% monomethyl-arsonate, and 65% dimethylarsenate in humans [20]. The ratio depends on the type of foods ingested and the types of arsenicals found in them. In the urine of Japanese university students who consumed large amounts of marine fish and shellfish and thus ingested organic arsenic compounds (e.g., arsenic betaine), 9.4% inorganic, 3.0% monomethyl-arsonate, and 58.2% trimethyl-arsenate were measured [21].

Less than 90% of orally ingested organic arsenic compounds (e.g., Na-p-N-glycolarsenylate) are excreted in the feces within 3 days, with only about 4–5% appearing in the urine [22].

Aquatic organisms (fish, shellfish, squids) can contain relatively high levels of arsenic, but the majority (about 95%) is found as organic derivatives (arsenocholine, arsenobetain, arsenosugars). Their toxicity is lower, and they are quickly excreted from the human body. Generally, the remaining 5% of arsenicals are inorganic, with potential toxic effects [11,23,24,25].

The total arsenic concentrations detected in marine fish, shellfish, and other edible aquatic animals were variable, such as 0.98 ± 0.47 mg/kg in tuna (Thunnus albacares), 3.26 ± 0.39 mg/kg in sardines (Sardina pilchardus), 1.28 ± 0.52 mg/kg in squids (Loligo vulgaris), 2.88 ± 1.12 mg/kg in oysters (Crassostrea gigas, C. angulata), and 3.01 ± 1.46 mg/kg in shellfish species (Mytilus galloprovincialis, M. edule, Venerupis philippinarum, Glycymeris glycym), respectively [26,27,28]. In freshwater fish, such as rainbow trout (Oncorhynchus mykiss), the measured arsenical content was 1.65 ± 0.49 mg/kg [29].

The bioavailability of organic derivatives in fish is significant in humans. Between 66 and 86% of arsenic in fish cakes and flounder is absorbed, and 80% of arsenic sugar is excreted in the urine within 4 days [19,30].

However, in sheep fed seaweed, arsenic sugar is more highly absorbed and metabolized, and significant arsenic concentrations can be measured in wool, blood, and urine, although arsenic sugar is not detected in the urine [31].

It is well distributed in the animal body; higher concentrations are found in the skin and horny issues. Significant amounts can also be present in the liver and kidneys, which may raise food safety concern. Organic arsenic compounds in marine fish and shellfish are less objectionable because they have lower toxicity and are rapidly eliminated from the human body.

However, arsenical concentrations detected in the muscle of roe deer (Capreolus capreolus) ranged from 0.03 to 0.51 mg/kg wet weight (w.w.) [32].

The highest total arsenic levels have been detected in fish and seafood, alga-containing products, and cereal and cereal products, especially in rice and rice-based products with high concentrations. Exposure of inorganic arsenic from food and water ranges from 0.13 to 0.56 µg/kg body weight (b.w.)/day in average consumers of EU countries; however, it is higher (0.37–1.22 µg/kg b.w./day) in high consumers. Young children (<3 years) are most exposed to inorganic derivatives (0.50–2.66 µg/kg b.w./day) [33].

2.2. Cadmium (Cd)

Cadmium can be measured in the Earth’s crust at levels ranging from 0.1 to 1 mg/kg [34]. It can be found in rocks and ores at concentrations 10- to 20-times higher [35,36], mainly in zinc-containing ores and, to a lesser extent, in lead- and copper-bearing ores [37].

Similarly, cadmium can be detected in water but at lower concentrations (surface and groundwater: <1 µg/L; oceans: 0.001–0.1 µg/mL). However, it may occur in higher amounts in areas rich in phytoplankton [35,36].

Plants can take up and accumulate cadmium, which may increase due to phosphate-containing fertilizers, acidic soils, and industrial wastewater used for irrigation [38]. Feeding and grazing on such forage crops can result in significant exposure for food-producing animals [39].

Calcium phosphate used as a feed additive can also contain cadmium, with concentrations high enough to pose a risk to humans through consumption of the liver and kidneys of food-producing animals [35].

In aquatic environments, cadmium is evenly distributed in the food web and does not undergo biomagnification. Its level in freshwater organisms depends on their capacity for absorption [35].

Based on structural similarity and physicochemical properties, cadmium can replace zinc, calcium, and other metals in various metal-containing proteins (enzymes), altering their structure and function [35].

It can affect the antioxidant system by inducing oxidative stress and lipid peroxidation and by modifying the membrane lipid layer [40,41]. It has genotoxic potential (alteration of DNA synthesis, DNA strand break) due to the generation of reactive oxygen species. The International Agency for Research on Cancer classifies cadmium as a Category 1 carcinogen, a well-known human carcinogen. It also induces the expression of various genes (e.g., metallothionein, heme oxygenase, heat shock proteins) [42].

Cadmium can bind to the thiol groups of membrane proteins, resulting in depolarization of the mitochondrial membrane, leading to ATP deficiency and cytotoxic effects, or it can trigger the release of mitochondrial enzymes through damaged membranes, causing apoptosis [43].

It also has estrogen-like effects, disrupting sexual maturation and accelerating puberty in mammals [43].

Cadmium compounds are generally poorly absorbed from the intestinal tract (0.5–3% in monkeys, 2% in goats, 5% in pigs and sheep, and 16% in cattle). The extent of absorption depends on their solubility in the digestive tract. The absorption of highly soluble cadmium salts (e.g., chloride, nitrate, acetate, sulfate) is significantly higher than that of poorly soluble salts (e.g., sulfide) [35]. Cadmium in foods of animal origin is less readily absorbed than soluble salts, but at low concentrations, the absorption of organic and inorganic compounds is similar [44,45].

In the blood, it is transported primarily bound to albumin and, to a lesser extent, to globulin, metallothionein, cysteine, glutathione, or directly to cells [46].

It is distributed throughout the body, but more than half of the total cadmium load accumulates in the kidneys and liver. Initially, it is found at the highest concentrations in the liver, then, after a few days, it moves to the kidneys, which serve as the final storage site. Cadmium is excreted very slowly from the body, partly in urine and partly in feces. Its biological half-life is very long (7–30 years) in the animal body. Due to its low molecular weight, the Cd-metallothionein complex is filtered through the glomeruli but is reabsorbed by cells of the S1 and S2 segments of the proximal tubules, thus concentrating in the renal cortex [47].

The biological availability of different cadmium compounds varies, depending on the chemical form. In aquatic environments, cadmium is likely present in free ionic form, but in foods, it is usually found in complexes bound to proteins (e.g., metallothionein). The bioavailability of cadmium in animal tissues (e.g., mammalian liver, hepatopancreas of crustaceans) is generally lower than that of highly soluble cadmium chloride [44,45,48,49].

Cadmium levels are highest in shellfish, oysters, salmon, and of course, in liver- and kidney-containing products, while they are lower in dairy products, meat, and poultry. During chronic exposure, cadmium accumulates most in the kidney, followed by the liver, testis, pancreas, and spleen [49,50]. It accumulates to a lesser extent in muscle and bone [51,52]. Cadmium was not detectable in the muscle or fat tissue (<0.3 mg/kg) of pigs fed phosphate supplementation (and thus a cadmium content of 1.2 mg/kg in feed) until they reached a slaughter weight of 90 kg; however, it was present in the liver at 0.35 mg/kg and in the kidney at 1.68 mg/kg [53].

In fish (e.g., rainbow trout), cadmium is primarily concentrated in the gills and kidneys, with lower levels measured in the liver [43].

Cadmium concentration was lower in marine and freshwater fish (sardine: 0.07 ± 0.02 mg/kg, tuna: 0.03 ± 0.01 mg/kg, rainbow trout: 0.03 ± 0.02 mg/kg), but it was 5–10 times higher in shellfish species (0.26 ± 0.12 mg/kg, oysters (0.28 ± 0.08 mg/kg), and squids (0.30 ± 0.16 mg/kg) [26,27,28,29,54].

Cadmium levels in the kidneys of 6–7-week-old broiler chickens raised for human consumption were 0.05 mg/kg, and in muscle, they were <0.005 mg/kg w.w. [55]. Even in cases of very high cadmium intake in laying hens (100 mg/kg in wet liver), cadmium could not be detected in the egg white, and the yolk contained only about 0.1 mg/kg [56,57].

A similar trend was observed in dairy cows. Long-term intake does not significantly increase the cadmium content of milk [52,58,59]. In a study using radioactive cadmium, it was found that cadmium is primarily bound to casein, to a lesser extent to albumin and lactose, and is undetectable in milk fat [60].

Data suggest that cadmium levels in meat, milk, and eggs of food-producing animals are lower than in feed, although cadmium concentrations in the liver and kidney may be higher [61].

However, in wild animals, the Cd content in the muscle, liver, kidney, and fat of roe deer (Capreolus capreolus) ranged from 0.24 to 1.46 mg/kg w.w. [62].

The most important sources of Cd exposure to humans are several types of meat and meat products and different plants (e.g., cereals and cereal products, vegetables, nuts and pulses, starchy roots or potatoes) primarily due to their high consumption. Compared to the world average, the consumption of cocoa products among children in the EU is higher, which also contributes to the higher intake. Vegetarians, due to the consumption of highly contaminated vegetables, may have higher dietary exposure. The average exposure by consumption of different foods ranges from 1.9 to 3.0 μg/kg b.w./week in adult humans of EU Member States and is between 2.5 and 3.9 μg/kg b.w./week in high consumers. Exposure in infants and children may be higher than in adults, primarily due to the consumption of larger amounts of food relative to body weight [63].

2.3. Lead (Pb)

Lead is present in the Earth’s crust at a concentration of about 13 mg/kg, but this varies by region and soil type. It can be detected in different concentrations in different types of soil (volcanic and sedimentary rocks: 10–20 mg/kg; sandstone and coal-bearing shale: 10–70 mg/kg; phosphate-bearing rocks: 100 mg/kg) [64,65]. Lead pollution due to anthropogenic activities (e.g., smelting, foundry, chemical production, battery production) is of greater importance than natural occurrence.

The use of tetraethyl and methyl leads as fuel additives was banned after 1995. Despite this, due to its very persistent nature, this “historical source” remains the most significant pollutant.

Dissolved lead concentrations in surface, ground, and marine waters are low because it is usually present in the form of carbonates, sulphates, and phosphates, which have low water solubility. It is not subject to biomagnification. The highest concentrations are generally found in aquatic and terrestrial organisms living near lead-contaminated areas. Neuman and Dollhopf measured elevated lead levels in the blood of cattle grazing near a lead processing plant [66].

In aquatic environments, lead is found in higher amounts in algae and benthic organisms than in carnivorous predatory fish at higher trophic levels.

Lead concentrations in raw edible plants are usually <0.05 mg/kg. However, silage, for example, can be an important intermediate source if the plant used for ensiling is contaminated from the soil. Coppock et al. measured 25.89 mg/kg of lead in alfalfa at harvest, which “migrated” during three weeks of ensiling and accumulated at the bottom of the silo (118.6 mg/kg) [67].

In the body, lead most likely binds to proteins and alters their function, inhibits or mimics the effects of calcium (e.g., activation of calmodulin and protein kinase C), and can be incorporated into various enzymes instead of zinc causing oxidative stress [68,69,70,71]. It can influence the capacity and activity of different enzymes because it can bind to their functional groups (e.g., sulfhydryl, amine, phosphate, carboxyl). In bones, it is incorporated in the form of tertiary lead phosphate instead of calcium. Lead inhibits the function of several enzymes (δ-aminolevulinic acid dehydratase, ferrochelatase), thus causing disturbances in heme synthesis. As a result, the amount of δ-aminolevulinic acid increases in plasma and urine, and iron incorporation into the protoporphyrin molecule is blocked. Due to reduced hemoglobin production and damage to red blood cells, hypochromic normocytic anemia and reticulocytosis develop [72,73].

Cardiovascular effects can be attributed to the fact that Pb can cause nerve conduction velocity disturbances (contractility disorders, arrhythmogenic effects), degenerative structural and biochemical changes in the heart muscle, and increased tone of the smooth muscles of blood vessels, causing vasoconstriction [74,75].

By blocking voltage-gated calcium channels, lead inhibits the influx of calcium, which, under physiological conditions, regulates neurotransmitter efflux. However, when it enters cells—using calcium channels—it acts as a calcium agonist, increasing the spontaneous efflux of neurotransmitters [76].

It can cross the placenta (depending on the animal species) and be present in significant amounts in fetal brain tissue, disrupting the synaptic organization and functional development of neurons in the early stages of postnatal development, leading to later learning problems [76,77,78,79].

The absorption of lead is influenced by the chemical form of the compound, the composition of the feed (diet), and the age and health status of the animals. Soluble salts are more readily absorbed than insoluble derivatives. In adults, absorption varies between 10 and 80% and is more efficient in young animals. The calcium and phosphate content of the feed reduces [80,81] and iron deficiency and magnesium increase lead resorption from the duodenum. Feeding diets with severe protein deficiency or very high protein and fat content also increases lead absorption. It can also enter the body through the lungs, which is significant if the particle size of lead-containing dust is <0.5 μm.

Lead absorbed from the intestinal tract is transported to the liver via the portal circulation, where some is excreted in bile. The excreted compounds may be reabsorbed depending on their lipophilic properties (showing enterohepatic circulation). The majority (>90%) of the lead entering the bloodstream is bound to hemoglobin in red blood cells [82]. It is also bound to albumin, γ-globulins, and low molecular weight compounds containing sulfhydryl groups. It is found bound to proteins in peripheral tissues [83]. The free fraction is partly excreted by the kidneys and salivary and intestinal glands, but a larger amount is incorporated into the hydroxyapatite crystal structure of bones as tertiary lead phosphate [84,85]. The release of accumulated lead from bones is facilitated by the body’s increased calcium demand (e.g., pregnancy, lactation). Similar consequences occur with heavy exertion (e.g., driving to grazing land), starvation, and pathological conditions (e.g., acidosis, osteoporosis). Lead can also be incorporated into horny materials, fur, and sloughed skin cells [86]. Depending on the type of placenta, lead can significantly pass to the fetus and cause damage or abortion. In rats and humans, the placental barrier does not protect embryos from it, but in pigs, it inhibits transport [87,88]. It crosses the blood–brain barrier, causing neurological symptoms in adults and affecting fetal nervous system development. Excretion is slow and varies by species, occurring in urine (e.g., dogs) and feces (e.g., rats, sheep) [89]. In birds, it can be found in eggshells and yolks and also in mammal milk [90,91]. The elimination half-life of lead from blood and soft tissues is about 1 month; from bones, it is much longer, and complete elimination is not expected.

The Pb content measured in the following marine fish, shellfish, and other edible aquatic animals was variable: 0.95 ± 1.12 mg/kg in shellfish species (Mytilus galloprovincialis, M. edule, Venerupis philippinarum, Glycymeris glycym), 0.66 ± 0.56 mg/kg in oysters (Crassostrea gigas, C. angulata), 0.59 ± 0.33 mg/kg in squids (Loligo vulgaris), 0.50 ± 0.34 mg/kg in sardines (Sardina pilchardus), and 0.39 ± 0.37 mg/kg in tuna (Thunnus albacares), respectively [26,27,28]. In freshwater fish, such as rainbow trout (Oncorhynchus mykiss), the measured lead concentration was 0.16 ± 0.16 mg/kg [29].

The presence of lead in game meat poses a particular health concern. Various lead bullets—especially their explosive fragments—are secondary sources of lead in meat and can significantly increase its level. High lead levels can also be a problem in commercially sold game meat products, increasing human health risks [92].

Today, lead from ammunition represents a significant dietary exposure pathway for consumers who frequently eat game meat. This issue may primarily affect hunters and their families but also others who prefer to consume game meat for ethical, health, or other reasons [93].

The harmful effects of lead from various types of lead-containing ammunition can also affect consumers through multiple exposure routes, including ingestion of contaminated water and contaminated plant and animal organisms in contact with spent ammunition in the environment [94]. Lead can leach from bullets and their fragments [95].

Both humans and animals are sensitive to lead exposure, especially young organisms. However, in addition to age, the solubility of the lead compound is also a key factor [96].

The lead concentrations in game meat ranged from 0.05 to 6.13 mg/kg in wild boar (Sus scrofa), 0.13 to 91.57 mg/kg in European roe deer (Capreolus capreolus), and 0.03 to 19.42 mg/kg in red deer (Cervus elaphus) in various European countries (

Table 1. Lead content in wild animals (wild boar [Sus scrofa], European roe deer [Capreolus capreolus], and red deer [Cervus elaphus]) in European countries (mg/kg w.w.) [32,63,92,97,98,99,100,101,102,103,104].

Animal Species	Sampling Site (Country)	Sample (Tissue)	Average	Reference
European roe deer	Spain	m. diaphragmaticus	0.13 ± 0.13	[97]
(Capreolus capreolus)	Hungary	m. biceps femoris	0.48 ± 0.21	[32]
	Hungary	m. biceps femoris	buck: 0.40 ± 0.29	[63]
			doe: 30.41 ± 91.57 *
Wild boar	Croatia	hind limb	0.07 ± 0.012	[98]
(Sus scrofa)	Poland	m. longissimus dorsi	0.05–0.08	[99]
	Italy	40 cm distance from the tissue damage caused by the bullet	0.12	[100]
	Italy	m. masseter	2.60 ± 3.27	[101]
	Slovakia	m. semimembranosus	0.04–6.13 (range)	[102]
	Hungary	m. biceps femoris	male: 0.22 ± 0.06 female: 0.36 ± 0.16	[103]
Red deer	Poland	not determined	0.18	[92]
(Cervus elaphus)	Italy	masseter	2.04 ± 3.32	[101]
	Germany	thigh, back and firing channel together (with lead bullet)	19.42	[104]
		thigh, back and firing channel together (with lead-free bullet)	0.03

* The high concentration is most probably due to contamination and/or residue from ammunition.

). Generally, lead concentrations in the tissues of wild animals, including muscle, are not objectionable. However, lead-containing bullets can significantly increase the lead concentration in tissues [32,63,92,97,98,99,100,101,102,103,104].

Most plants do not absorb significant amounts of lead from the soil. Plant-based feed ingredients generally contain little lead unless contaminated from the air or post-harvest [105]. However, the lead content of mineral supplements can be significant. Feed-grade copper sulfate and complete mineral mixtures can contain 640 and 460 mg/kg of lead, respectively [106,107].

Following dietary administration, lead is primarily detected in the kidneys and liver (and of course in bones) of food-producing animals (cattle, sheep, pigs, broiler chickens). It reaches low concentrations in muscle [58,106,108,109].

From the point of view of lead exposure, the most important foods are cereal grains and cereal-based products, potatoes, and leafy vegetables in the EU population. The mean dietary exposure of lead ranges from 0.36 to 1.24 µg/kg b.w./day (average consumers), and from 0.73 up to 2.43 µg/kg b.w./day (high consumers) in adults of EU Member States. Lead exposure varies as follows depending on consumed foods: 0.21–0.94 µg/kg b.w./day in infants, 1.10–3.10 µg/kg b.w./day (average consumers) and 1.71–5.51 µg/kg b.w./day (high consumers) in children aged under 3 years, 0.80–2.61 µg/kg b.w./day (average consumers) and 1.30–4.83 µg/kg b.w./day (high consumers) in children aged 4 to 7 years [110].

2.4. Mercury (Hg)

The average mercury content of the Earth’s crust is 80 µg/kg, but its actual concentration can vary significantly from area to area. In shale soil, for example, it can reach 10 mg/kg. Important natural sources of mercury are volcanic activity and ocean evaporation. However, human activities also release significant amounts into the environment through the burning of fossil fuels, steel and cement production, metal processing, and gold and mercury mining. Mercury released into the air spreads widely and can persist for years. The concentration of dissolved mercury in aquatic environments varies as follows: 0.5–3 ng/L in oceans, rivers, and lakes and 2–15 ng/L in coastal waters [111].

Inorganic mercury in natural waters and soils is strongly bound to sediment or organic matter. In this form, living organisms cannot absorb it. However, in aquatic environments, bacteria living in sediment methylate inorganic compounds, and the resulting methylmercury, due to its strong lipophilic properties, enters the food web. The best-known example of this is Minamata disease. Since methylmercury accumulates in animals faster than it is eliminated, even at low levels of environmental contamination, bioaccumulation is a possibility, leading to potentially dangerous concentrations in fish, fish-eating wildlife, and humans. The highest mercury levels are found in long-lived predatory fish living in the oceans (e.g., swordfish [Xiphias gladius] and shark species [Selachimorpha]) and in freshwater pike and perch. In fish, mercury accumulation increases with age and size. It is found in the highest concentrations in the kidney, spleen, and liver and, to a lesser extent, in the gills, reproductive organs, brain, and muscle [112,113]. Mercury biomagnifies and thus causes toxic effects in consumers at the top of the aquatic food chain. The bioconcentration factor is 1000–8000 in algae, <0.1 in plants, >1000 in invertebrates and fish, and 2 in birds [111].

Mercury concentrations in food are generally below the detection limit (20 ng/g), but they can be significant in aquatic organisms (fish, marine mammals). Mercury levels in the edible tissues of various fish species range from 50 to 1400 µg/kg, but in polluted environments, they can reach 10 mg/kg [114]. The liver is the largest source of mercury, followed by the kidney and then the muscle. In skeletal muscle, methylmercury is found primarily (70–90%) bound to cysteine or in chemically related compounds, while in the liver, it forms a complex with selenium [115]. Mercury levels are relatively low in fish at the lower levels of the food chain (e.g., anchovy, herring) and in foods made from them, while mercury levels in products made from the offal of fish at higher levels (e.g., shark, tilefish) are 1–2.4 mg/kg, and in whales, it can be as high as 10 mg/kg [109].

Generally, low total mercury content has been detected in the flesh of aquatic animals (marine and freshwater fish species, shellfish species, oysters, squids) [23,24,25,26,27,28,29].

The mercury concentrations measured in the muscle of roe deer (Capreolus capreolus) were 0.24–1.46 mg/kg w.w. [32].

Basically, mercury has a very limited solubility in soil and has a low uptake capacity for plants. Generally, the main source of mercury in plant leaves is air pollution with Hg⁰, not soil pollution. Different plants, e.g., mushroom, rice, and wild plants, have been identified as organisms that accumulate more mercury than other plants. Certainly, these plants can contribute to the mercury burden of human and animal bodies after their consumption [116,117,118].

Mercury is not an essential compound for the body. However, according to the literature data, at low doses, it has been shown to enhance growth in rodents, pigs, and chickens, but this has not been demonstrated in fish [119].

Its absorption depends largely on its chemical form. Elemental mercury is absorbed from the gastrointestinal tract in humans and animals at a rate of about 0.01%. Absorption of inorganic mercury compounds is higher (1–40%), but this is influenced by species, age, diet, intestinal pH, and solubility of the compound. The absorption rate of organic forms is much higher; for example, methylmercury is almost completely absorbed (>90%) in mammals and chickens [120,121]. However, in ruminants, rumen microorganisms convert methylmercury to the inorganic form by demethylation, significantly reducing its absorption [122]. In fish, the absorption of organic mercury compounds (e.g., methylmercury) is 100 times faster than that of inorganic ones and is more efficient through the food chain [119].

Inorganic mercury is distributed almost equally between plasma and red blood cells [123]. In plasma, it is bound to sulfhydryl groups of proteins (primarily albumin), and in red blood cells, it is bound to hemoglobin and glutathione. Organic compounds (e.g., methylmercury) account for 90% of the total red blood cell concentration. Methylmercury has a high affinity for thiol-containing amino acids, allowing it to cross membranes through mechanisms that regulate amino acid transport. Inorganic mercury is generally unable to penetrate cell membranes, but its ionic form becomes more lipophilic when bound to selenium, improving its membrane transport. Elemental, inorganic, and organic mercury compounds can be interconverted within various organs and tissues of the body [124]. Tissue distribution also depends largely on the chemical form of mercury. Inorganic mercuric chloride (HgCl₂) is found in high concentrations in the liver and kidneys, and only to a small extent in the brain and muscle. Methylmercury is distributed to all tissues, with the highest concentrations in the liver, kidneys, and spleen [125,126]. In poultry and other domesticated species, methylmercury is detected in much higher amounts in muscle tissue than inorganic compounds. The amount of mercury in the feed that is safe for the animal can reach concentrations in the muscle that can be dangerous (toxic) to the consumer. In fish, methylmercury is concentrated mainly in the muscle, while its inorganic compounds are concentrated in the epithelial cells of the gastrointestinal tract. Following oral exposure, it can also accumulate in the fur of mammals and in the feathers of birds, where mercury concentrations approach tissue levels [118,123]. Methylmercury crosses the blood–brain barrier and the placenta, reaching high tissue levels in fetal and maternal brain tissue. The passage of inorganic compounds through specialized membranes is low.

The direction and extent of excretion also depend on the compound. Inorganic and elemental mercury are excreted from the body in the urine and feces. Methylmercury is excreted in the bile, where it binds to the sulfhydryl groups of glutathione [127,128]. The intestinal flora can convert it to an inorganic form, but intact molecules are reabsorbed via the enterohepatic circulation and continue to burden the body. The total body half-lives of methylmercury and mercuric chloride are 70 and 40 days, respectively, in humans [118]. Methylmercury has a half-life of 700 days in fish and persists in the body for about 2–5 times longer than inorganic compounds [114,119]. Organic mercury compounds can also be excreted in milk and through eggs in birds [129,130].

Cellular mechanisms caused by damage of inorganic and organic mercury compounds are basically similar, but due to their different tissue distribution, they can cause damage to different organs and tissues. Mercury ions (Hg²⁺) bind with high affinity primarily to thiol or sulfhydryl groups, but they can also bind to hydroxyl, carboxyl, and phosphoryl groups [120]. Sulfhydryl groups play a significant role in the structure and function of proteins; therefore, after mercury binding, enzyme activity decreases, membrane damage and other structural changes occur, and transport processes also become insufficient [123]. By altering intracellular thiol levels, mercury promotes oxidative stress and lipid peroxidation, alters mitochondrial processes and heme metabolism, and disrupts cellular calcium homeostasis. Its cytotoxic effects are threshold-dependent, presumably due to the buffering effect of endogenous ligands (e.g., metallothionein, glutathione). Up to a certain dose level, there is no cell death, but if the buffer system is saturated, then at higher doses, cell death develops rapidly, often as an all-or-none response. The main target organ of inorganic mercury compounds is the kidney. Damage to the proximal tubules and glomeruli is primarily observed (tubular dilation, degeneration and atrophy of tubular epithelial cells, thickening of the basal membrane). Kidney damage is indicated by proteinuria, oliguria, dilution of urine, and elevated plasma creatinine levels. Neurological symptoms (muscle tremors, inactivity, abnormal posture) may also occur, despite the fact that inorganic compounds only partially cross the blood–brain barrier. Salivation, gastrointestinal symptoms, and anemia may also be observed. The lethal dose of mercuric chloride (HgCl₂) in an adult is 10–42 mg/kg [123].

The target organ of organomercury compounds is primarily the nervous system. The severity of damage and the symptoms that develop are influenced by the duration and amount of exposure, as well as the developmental stage of the nervous system. Young organisms with an immature nervous system are much more sensitive to damaging effects than adults. Due to damage to the central and peripheral nervous systems, ataxia, incoordination, muscle convulsions, paralysis, and visual disturbances can be observed. Behavioral, learning, and memory disorders, as well as reduced activity, may also develop. Methylmercury reduces spermatogenesis and sperm motility, can cause abortion, and increases fetal resorption and developmental abnormalities. It crosses the placenta and is involved in causing fetal Minamata disease, which is characterized by microcephaly, degeneration and atrophy of cortical structures, dilation of the brain ventricles, gliosis, loss of myelin, and lack of cellularity. Convulsions, muscle rigidity, blindness, and severe learning disabilities are observed in such newborns [120].

The concentrations of total mercury are the highest in fish and other seafood, mainly in the flesh of fish (especially tuna, cod and whiting, swordfish, pike, hake, and shark). The average exposure to inorganic mercury via foods was estimated as 0.13–0.25 μg/kg b.w./week in adults and 2.16–4.06 μg/kg b.w./week in children. Due to the consumption of methylmercury-containing fish meat, the estimated methylmercury dietary exposure was 0.06–0.14 μg/kg b.w./week in elderly adults; it was higher in infants (1.57 μg/kg b.w./week), children (7.48 μg/kg b.w./week), and adolescents (5.05 μg/kg b.w./week) [131].

3. Current Regulatory Standards

The Codex Alimentarius is a collection of internationally adopted food standards and related texts presented in a uniform manner. These food standards and related texts aim to protect consumers’ health and ensure fair practices in the food trade. The publication of the Codex Alimentarius is intended to guide and promote the elaboration and establishment of definitions and requirements for foods to assist in their harmonization and, in doing so, to facilitate international trade. The Codex Alimentarius includes provisions in respect to food hygiene, food additives, residues of pesticides and veterinary drugs, contaminants, labeling and presentation, methods of analysis and sampling, and import and export inspection and certification [132].

The legal procedure in the European Union (EU) is based and started on standards of Codex Alimentarius. Related to contaminants, EFSA (European Food Safety Authority) prepares a risk assessment based on European consumer behavior and food consumption data. These assessments sometimes lead to different results, which makes the EU limit system slightly different from the Codex regulatory environment [132].

There are significantly fewer legal requirements regarding heavy metal contamination in foods of animal origin today than in the past. This is probably due to the fact that metal compounds were used more widely in the last century for industrial, agricultural, and other purposes, which meant a greater risk of food contamination than in present days.

However, the potential hazards posed by heavy metals to the consumer have by no means disappeared. At present, the multiple, long-term, and prolonged intake of smaller quantities is more typical, which can primarily lead to the development of chronic diseases due to the cumulative property of heavy metals [8]. Accordingly, the heavy metal contamination of different foods must continue to be regulated with acceptable and tolerable maximum limits. However, it should be noted that, in the case of contaminants of environmental origin—given their irregular and uncontrolled application and generation—the risk probability is significantly higher than in the case of substances with officially controlled use.

European Union regulation is binding for all Member States of the European Union.

The European Union regulates the maximum levels of certain contaminants in food at the regulatory level. However, the previous regulation (Regulation (EC) No 1881/2006) only laid down the maximum levels for lead, cadmium, and mercury, and it did not contain any provisions for arsenic in raw milk and dairy products, meat and offal of bovine animals, sheep, pigs and poultry, horsemeat, and the flesh of different fish species, crustaceans, bivalve mollusks, and cephalopods (

Table 2. Maximum limits of lead, cadmium, and mercury in foods of animal origin (1881/2006/EC Regulation) [133].

Foodstuffs	Maximum Levels (mg/kg Wet Weight)
	Lead	Cadmium	Mercury
Raw milk, heat-treated milk, and milk for the manufacture of milk-based products	0.02	-	-
Meat (excluding offal) of bovine animals, sheep, pig, and poultry	0.10	0.05	-
Offal of bovine animals, sheep, pig, and poultry	0.50		-
Liver of bovine animals, sheep, pig, poultry, and horse	-	0.50	-
Kidney of bovine animals, sheep, pig, poultry, and horse	-	1.0	-
Horsemeat, excluding offal	-	0.20	-
Muscle meat of fish (general), fishery products	0.30	0.05	0.50
Muscle meat of the following fish: anchovy (Engraulis species), common two-banded seabream (Diplodus vulgaris), grey mullet (Mugil labrosus labrosus), horse mackerel or scad (Trachurus sp.), louvar or luvar (Luvarus imperialis), sardine (Sardina pilchardus), sardinops (Sardinops sp.), and wedge sole (Dicologoglossa cuneata)	-	0.10	-
Muscle meat of the following fish: bonito (Sarda sarda), eel (Anguilla sp., A. anguilla), and tuna (Thunnus sp., Euthynnus sp., Katsuwonus pelamis)	-	0.10	1.0
Muscle meat of the following fish: anglerfish (Lophius sp.), Atlantic catfish (Anarhichas lupus), emperor, orange roughy, rosy soldierfish (Hoplostethus sp.), grenadier (Coryphaenoides rupestris), halibut (Hippoglossus hippoglossus), marlin (Makaira sp.), megrim (Lepidorhombus sp.), mullet (Mullus sp.), pike (Esox lucius), plain bonito (Orcynopsis unicolor), poor cod (Trisopterus minutus), Portuguese dogfish (Centroscymnus coelolepis), rays (Raja sp.), redfish (Sebastes marinus, S. mentella, S. viviparus), sail fish (Istiophorus platypterus), scabbard fish (Lepidopus caudatus, Aphanopus carbo), seabream, pandora (Pagellus sp.), shark (all species), snake mackerel or butterfish (Lepidocybium flavobrunneum, Ruvettus pretiosus, Gempylus serpens), and sturgeon (Acipenser sp.)	-	-	1.0
Muscle meat of swordfish (Xiphias gladius)	-	0.30	1.0
Crustaceans, excluding brown meat of crab and excluding head and thorax meat of lobster and similar large crustaceans (Nephropidae and Palinuridae)	0.50	0.50	0.50
Bivalve molluscs	1.5	1.0	-
Cephalopods (without viscera)	1.0	1.0	-

) [133].

However, this regulation was repealed in 2023, and a newer one came into force with modifications to certain maximum limits (ML) [134]. Based on the scientific literature and results, the modification of the ML of environmental contaminants to more rigorous values is necessary and important to ensure food safety for human consumers.

The acceptable maximum concentrations of lead in the offal are differentiated based on animal species. The previous ML of Pb was 0.50 mg/kg in the offal of food-producing animals (bovine, sheep, pig, poultry) [133]. The newer MLs of Pb in offal are lower, which are 0.10 mg/kg for poultry, 0.15 mg/kg for pigs, and 0.20 mg/kg for bovine animals and sheep (

Table 3. Maximum limits of lead, cadmium, and mercury in foods of animal origin (2023/915/EC Regulation) [134].

Foodstuffs	Maximum Levels (mg/kg Wet Weight)
	Lead	Cadmium	Mercury
Raw milk, heat-treated milk, and milk for the manufacture of milk-based products	0.02	-	-
Meat of bovine animals, sheep, pig, and poultry, except offal	0.10	0.05	-
Offal of bovine animals and sheep	0.20	-	-
Offal of pig	0.15	-	-
Offal of poultry	0.10	-	-
Liver of bovine animals, sheep, pig, poultry, and horse	-	0.50	-
Kidney of bovine animals, sheep, pig, poultry, and horse	-	1.00	-
Horsemeat, except offal	-	0.20	-
Muscle meat of fish (general) except the listed species below	0.30	0.05	0.50
Muscle meat of the following fish: mackerel (Scomber sp.), tuna (Thunnus sp., Katsuwonus pelamis, Euthynnus sp.), and bichique (Sicyopterus lagocephalus)	-	0.10	-
Muscle meat of bullet tuna (Auxis sp.)	-	0.15	-
Muscle meat of the following fish: anchovy (Engraulis sp.), swordfish (Xiphias gladius), and sardine (Sardina pilchardus)	-	0.25	-
Muscle meat of the following fish: axillary seabream (Pagellus acarne), black scabbardfish (Aphanopus carbo), blackspot seabream (Pagellus bogaraveo), bonito (Sarda sarda), common pandora (Pagellus erythrinus), escolar (Lepidocybium flavobrunneum), halibut (Hippoglossus sp.), kingklip (Genypterus capensis), marlin (Makaira sp.), megrim (Lepidorhombus sp.), oilfish (Ruvettus pretiosus), orange roughy (Hoplostethus atlanticus), pink cusk-eel (Genypterus blacodes), pike (Esox sp.), plain bonito (Orcynopsis unicolor), poor cod (Trisopterus sp.), red mullet (Mullus barbatus barbatus), roundnose grenadier (Coryphaenoides rupestris), sail fish (Istiophorus sp.), silver scabbardfish (Lepidopus caudatus), snake mackerel (Gempylus serpens), sturgeon (Acipenser sp.), surmullet (Mullus surmuletus), tuna (Thunnus sp., Euthynnus sp., Katsuwonus pelamis), shark (all species), and swordfish (Xiphias gladius)	-	-	1.00
Muscle meat of following fish: anchovy (Engraulis sp.), Alaska pollock (Theragra chalcogramma), Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus), Basa (Pangasius bocourti), carp (species belonging to the Cyprinidae family), common dab (Limanda limanda), mackerel (Scomber sp.), European flounder (Platichthys flesus), European plaice (Pleuronectes platessa), European sprat (Sprattus sprattus), Mekong giant catfish (Pangasianodon gigas), pollock (Pollachius pollachius), saithe (Pollachius virens), salmon and trout (Salmo sp., Oncorhynchus sp., except S. trutta), sardine or pilchard (Dussumieria sp., Sardina sp., Sardinella sp., Sardinops sp.), sole (Solea solea), striped catfish (Pangasianodon hypopthalmus), and whiting (Merlangius merlangus)	-	-	0.30
Crustaceans, excluding brown meat of crab and excluding head and thorax meat of lobster and similar large crustaceans (Nephropidae and Palinuridae)	0.50	0.50	0.50
Bivalve molluscs	1.5	1.0	0.50
Cephalopods (without viscera)	0.3	1.0	0.30
Marine gastropods	-	-	0.30

) [134].

Previously, the ML of Cd was 0.10 and 0.30 mg/kg depending on the fish species [133]. However, it was changed to 0.10–0.15–0.25 mg/kg in several fish species [134].

The previous ML of Hg was modified from 0.50–1.00 mg/kg to 0.30–0.50–1.00 mg/kg in different fish species (Table 2 and Table 3) [133,134].

Basically, under the legal regulation, the regulated foods of animal origin include meat and offal of food-producing animals (bovine, sheep, swine, poultry, horse, fish, crustaceans, bivalve mollusks, cephalopods), as well as milk; however, for example, game meat and eggs are not included (Table 2 and Table 3) [133,134].

There is a problem with this regulation. The uptake levels/concentrations of heavy metals and metalloids from feed and their maximum levels in the tissues/organs of food-producing animals can be regulated by official legal measures. These regulated maximum levels of heavy metals and metalloids are the same for wild animals used for human consumption (e.g., wild boar, deer species) as they are for domesticated animals (ruminants, swine). However, the concentration of heavy metals and metalloids cannot be regulated in the natural nutrition sources of wild animals. Thus, their levels may be significantly higher in the tissues of wild animals than in domesticated species.

Based on these aspects, the muscle and edible offal of wild animals may be unsuitable for consumption due to the higher hazard and risk. However, the consumption of wild animal tissues is considered healthy due to their beneficial physiological content and composition (excluding different contaminants, e.g., heavy metals, industrial contaminants such as dioxins, pesticides, etc.). Thus, the regulation of acceptable levels for environmental contaminants and other chemicals in game meat and edible offal would be very important to ensure consumer safety.

Furthermore, heavy metals and other potentially toxic elements can contaminate birds’ bodies during feeding by uptake of contaminated sources (e.g., water, feed plants, etc.) and, through their kinetic processes, can be excreted via eggs, resulting in residue in them [135,136,137,138,139,140,141,142]. Thus, they can be measured in egg components (egg white, egg yolk) in amounts that can pose potential hazards to human consumers [143,144,145,146,147,148].

Based on available experimental data, the following variable metal concentrations with a wide range were detected in chicken eggs: Cd: 0.324 ng/kg–0.06 mg/kg (egg white), 1.44 ng/kg–0.04 mg/kg (egg yolk), and 0.27 µg/kg–0.18 mg/kg (whole egg); Pb: 0.12–0.13 mg/kg (egg white), 0.06–0.09 mg/kg (egg yolk), and 12.85 µg/kg–1.330 mg/kg (whole egg); As: 5.82 ± 0.723 ng/kg (egg white), 15.4 ± 3.13 ng/g (egg yolk), and 0.29 µg/kg–1.8 mg/kg (whole egg); Hg: 0.04–33.10 µg/kg (whole egg) [135,136,142,145,148].

However, besides the EU legal regulations, Member States are entitled to establish their own supplementary regulations in areas not covered by Community law.

In accordance with this, there is a local national regulation in Hungary. Copper is an essential metal, but it may be hazardous if it enters the body in higher amounts. Nevertheless, its tolerable maximum limit value is not regulated in different types of food in the EU. Regulation No. 49/2014 (IV. 29.) of the Ministry of Agriculture sets the limit values for copper as a technological contaminant in various food groups and types (meat products, canned and preserved meat products, liver pâté, game meat) and regulates the permissible lead content in special formulas for infants and young children as a contaminant of environmental origin (

Table 4. Maximum limit of copper and lead in foods of animal origin (49/2014. (IV.29.) Regulation of Ministry of Rural Development) [149].

Type of Food	Maximum Limit, to Total Weight (mg/kg)
	Copper
Meat products (raw-smoked, fermented, stuffed, cooked, smoked meat products, etc.)	5.0
Preserved meat products in can (excluding liver paté)	10.0
Liver paté in tube or can	20.0
Game meat, meat product produced from them	5.0
	Lead
Special formulas for infants and young children	0.02

) [149].

4. Exposure Calculation for Risk Management

Different health-based guidance values have been introduced and can be determined to ensure the consumers’ health [150,151,152].

4.1. Tolerable Intake

In order to protect the health of consumers, the maximum daily, weekly, or monthly (the latter in the case of cumulative substances) intakes of major pollutants are determined, which do not cause health damage even in the case of continuous, lifelong intake. This amount is called tolerable daily, weekly, or monthly intake (TDI/TWI/TMI) for pollutants.

The international organization (the relevant joint expert committee of Food and Agriculture Organization [FAO] and Word Health Organization [WHO]; Joint FAO/WHO Expert Committee on Food Additives [JECFA]) dealing with risk assessment and the determination of tolerable intake values based on this can often only provide provisional (provisional = P) TDI, TWI, and TMI values (PTDI/PTWI, PTMI) based on the available data, which are reviewed from time to time based on new toxicological and epidemiological data and, if necessary, changed.

The previous PTWI value of arsenical (15 µg/kg b.w.) has been withdrawn by EFSA and a new one has not yet been estimated [33]. Similarly, the EFSA decided that the PTWI of 25 μg/kg b.w. for lead is no longer appropriate [111]. Regarding mercury, the following two PTWI values are set: 4 µg/kg b.w. for inorganic mercury and 1.3 µg/kg b.w. for methylmercury [133]. The CONTAM Panel of EFSA established a tolerable weekly intake (TWI) for cadmium of 2.5 μg/kg b.w. [63].

During the calculation of intake level, the following equation is used:

Tolerable Intake = (Conc × Cons)/BW

(1)

where Conc is the concentration of the metal (mg/kg) in the investigated food; Cons means the daily average consumption of the examined food (g/day/person); and BW is an average human body weight (kg).

Then, this amount must be multiplied by seven for the calculation of weekly intake or by twenty-eight for the establishment of monthly consumption.

The calculated intake must be compared to the existing officially recommended PTWI or PTMI value mentioned above to decide whether the investigated food is safe for human consumers or if it is objectionable.

Due to the withdrawal of some of them, newer terms/parameters, such as EDI (estimated daily intake), THQ (target hazard quotient), and HI (Hazard Index) were introduced to assess the potential exposure of contaminants.

4.2. Estimated Daily Intake

The tolerance of contaminants depends on different factors, such as the concentration of the metal in food consumed, the daily consumption of food, and the body weight of the consumer. EDI was introduced and recommended to assess daily exposure [33,63,111,113].

To estimate the potential exposure level of contaminants, the following formula is used for the calculation of EDI [153]:

EDI = (Conc × Cons)/BW

(2)

where Conc is the concentration of the metals (mg/kg) in the examined food; Cons means the daily average consumption of the investigated food (g/day/person); and BW is an average human body weight (kg).

The estimated EDI value must be compared to the dietary reference doses (RfD) of chemicals. RfD means the estimated daily exposure of a chemical to the human population that is unlikely to induce observable significant risk of adverse, undesirable effects during a lifetime. In the cases of major toxic metals discussed in this review, the dietary RfD is 0.3 µg/kg/day for As [33,154], 1 µg/kg/day for Cd [63,154], 0.3 µg/kg/day for Hg [131,155], and 0.16 (adult) and 0.26 (children) µg/kg/day for Pb [111,154].

4.3. Target Hazard Quotient

THQ value may be estimated using the following formula [156]:

THQ (non-dimensional) = EDI/RfD

(3)

To calculate THQ, the previously estimated EDI value must be divided by the RfD of contaminants (e.g., metal).

If the THQ value is below 1, then the concentration of contaminants induces no harmful effect; however, if the value is above 1, then it indicates risk to the human consumer.

4.4. Hazard Index

The sum of THQ values of the investigated contaminants (e.g., metals, As, Cd, Hg, Pb) is used to establish the HI. The following equation is applied to evaluate the potential risk of adverse health effects of the mixture of contaminants [157]:

HI (non-dimensional) = THQ_{contaminant 1} + THQ_{contaminant 2} + THQ_{contaminant n}

(4)

If the HI is below 1.0, then it is unlikely that there will be adverse effects; while, if the HI is above 10, it indicates a high risk.

4.5. Margin of Exposure (MoE)

For the quantitative comparative assessment of risk for genotoxic carcinogens, EFSA, in collaboration with WHO, recommends the use of a margin of exposure (MOE). The MOE is determined based on the 95% confidence level of the lowest carcinogenic dose that causes tumor formation in 10% of experimental animals (BMDL₁₀—Benchmark Dose Lower Confidence Limit 10%). The MOE is the ratio of the BMDL₁₀ to the human intake (exposure) value. If the MOE value is 10.000 (which is an uncertainty factor resulting from the differences between different experimental animal species, the animal and human organism, and possible differences in the carcinogenic process) or higher, then the risk is not significant from a public health perspective.

Margin of exposure was calculated by the following formula [158]:

MOE (non-dimensional) = Reference Value (BMDL₁₀, mg/kg b.w./day)/Exposure (EDI, mg/kg b.w./day)

(5)

Certainly, besides the health-based guidance values, several multivariate statistical methods, e.g., principal component analysis, hierarchical cluster analysis, positive matrix factorization, geostatistical analysis, Monte Carlo simulation, numerical modeling, machine learning, and artificial intelligence modeling, may be used as chemometric methods for the evaluation of data of different contaminants [152].

5. Conclusions

Based on the above, it can be stated that the current Community and complementary local and national regulations set limit values for fewer heavy metals and metalloids, and the range of regulated foods of animal origin is also narrower; for example, wild animals or eggs are missing.

The most important sources of exposure to inorganic arsenic are cereal and cereal-based products (particularly rice grain and its products), followed by tap and bottled water, beverages (coffee, beer), fish, and vegetables. However, in aquatic organisms (fish and seafood), arsenic is found in the form of organic derivatives that are not toxic to the consumer.

The highest cadmium concentrations can be found in food of animal origin, including seaweed, fish and seafood, and edible offal (liver, kidney), and in food of plant origin, including fungi, oilseeds, and chocolate. However, due to monitoring systems and investigations in the European Union, its detected concentrations do not exceed the ML levels; thus, they are safe and not objectionable.

The most important exposure of lead in humans is mainly foods of plant origin, such as cereals and their products, potatoes, and vegetables. Basically, these foods are safe, but the dietary exposure of lead may pose potential risk to high consumers. However, lead levels may be higher in the muscle and offal of wild animals due to lead-containing bullets still being used.

Mercury can accumulate primarily in the tissues of aquatic organisms, particularly as methylmercury; thus, fish, shellfish, and other edible marine animals may pose potential risk to consumers.

In the case of domesticated food-producing animals, their housing and nutrition are generally properly regulated and controlled; thus, their edible organs and tissues are basically safe to consume despite the aforementioned legal shortcomings.

The regulation of game meat (including offal) in particular would be worth considering, given that it is closely correlated with the environmental status of the given area and serves as an indicator of it. Re-thinking and amending the regulation of lead concentration in foods of animal origin may be justified so that only truly safe food can reach the consumer’s table from the farmland.

Based on the previously mentioned properties, the acceptable maximum levels of metals should/must be regulated in eggs used for human consumption, or even in different egg products.

In the EU, the consumption of meat of domesticated food-producing animals was 66 kg/person in 2024. However, the consumption of game meat is low, ranging from 0.2 to 1.1 kg per person/year in different countries. Based on this, applying the ML for domesticated farm animals based on the legal regulation may be recommended for wild game, which can highly protect consumers.

The egg consumption in the EU was around 13 kg/person/year. It is one-fifth of meat consumption; thus, the same risk management method as game meat may be recommended [159].