The home-processed food analyzed in this study could be considered an interesting and alternative source of essential trace elements, such as Fe, Zn, Cu, Mn, and Se. Unconventional animals, unlike farm animals, are free-ranging organisms and the chemical composition of their meat can be affected by several factors, including diet, environment, and animal lifestyle [
12]. In addition, game animals present variable Pb contamination of their meat, due to the presence of Pb gunshot.
3.1. Essential Trace Elements
Of the samples analyzed, the highest Fe, Zn, Cu, Mn, and Mo concentrations were detected in snails. The concentrations in raw snail samples were in the range of those determined by other authors in
Helix pomatia [
13] and in
Cantareus aspersus [
14], but higher than those reported in the giant African snail
Achatina achatina [
15]. It is well known that land snails are able to accumulate high concentrations of trace elements, particularly Cu, due to the presence of a specific Cu-metallothionein isoform, which can act as a metal donor for the synthesis of hemocyanin [
16]. This copper-containing protein is the oxygen carrier in the hemolymph of many mollusks [
17]. Interestingly, a biochemical explanation is still lacking regarding the high concentrations of Fe and Mn. In particular, in snails, Fe is not required for hemoglobin, due to the presence of the respiratory protein hemocyanin, and the use of myoglobin seems to be limited to the radular muscles [
18]. Regarding Mn, its high concentrations could be related to shell formation. In fact, it has been reported in freshwater bivalves that this trace element can substitute Ca in aragonite crystals [
19].
In terms of processed vertebrate meat, higher concentrations of Fe, Mn, and Se were found in woodcock preparations, while the hare samples contained higher concentrations of Cu. The data obtained are in the range of those reported by other authors. Muscular Cu and Fe levels are related to the functional and biochemical characteristics of different fiber types. In woodcock and hare, the red color of the oxidative muscle fibers is due to the high levels of Fe and Cu, which are contained in hemoproteins (myoglobin, cytochromes) and cytochrome-c-oxidase, respectively [
20]. Moreover, the pectoralis myosin of woodcock is unique due to a specific myosin heavy chain [
21]. Pheasant preparations contained lower concentrations of Fe and Cu due to the high percentage of white pectoral muscle in the meat used for the preparation. Red muscles are rich in mitochondria, and these organelles are the main source of reactive oxygen species (ROS; particularly superoxide radical) in the cell. Antioxidant systems handling these harmful oxygen species are needed to prevent oxidative stress; superoxide dismutase, catalase, and glutathione peroxidase are the most active detoxifying enzymes metabolizing superoxide radicals and hydrogen peroxide. In particular, the high Mn concentrations detected in processed vertebrate meat are linked to the presence of mitochondrial manganese superoxide dismutase (MnSOD) acting as the chief ROS scavenging enzyme in the cell [
22].
The homogeneity of Zn concentrations in the samples analyzed is due to the essential role of Zn in a wide range of biochemical systems shared by the majority of living organisms [
23,
24]. Consequently, Zn levels in tissues are maintained constant by means of homeostatic mechanisms, including specific membrane transporters and metallothioneins [
25], and this is mirrored in the narrow range of Zn concentrations reported in the livers and kidneys of different organisms from invertebrates to mammals [
2].
Nickel, Mo, and Co presented one-to-two orders of magnitude lower concentrations due to their limited involvement in the biochemical processes.
3.2. Non-Essential Trace Elements
The Pb and Cd concentrations determined in the raw foot of snails are low and of the same order of magnitude as those reported in raw meat samples of
H. pomatia from Poland [
26]. Ziomek et al. [
26] reported that the cooking process likely increased the Cd content in snail meat. In the present study, it was not possible to compare metal concentrations in raw and cooked samples; conversely, it was reported that the metal concentrations were affected by the sampling site. Of interest are the concentrations of Al and Cr detected in snails, which are higher than those measured in all the other samples.
It is known that the wide variability of Pb concentrations in samples from game animals is due to the impossibility of removing all Pb gunshots or, alternatively, removing the contaminated meat [
27,
28]. Accordingly, a wide range of Pb concentrations has been reported in the muscles of game animals containing Pb gunshots, depending on the distance from the wound channel [
29]. The Pb concentrations determined in this study, even though widely variable between 0.01 and 17.3 µg/g, were similar to or higher than the values reported in meat from game animals in Italy [
30,
31]. The lower Pb concentrations determined in the pheasant samples were probably due to the easier removal of Pb pellets in the white meat with respect to those present in the red meat of woodcock and hare. Different results were previously reported by Ertl et al. [
32]. The authors analyzed the concentrations of Pb in the muscles of game animals in Austria, and pheasants were the most affected by Pb contamination, containing a mean metal concentration as high as 125 µg/g wet weight. All the samples of snails and the majority of the samples of the game animals included in this study, with the exception of five pheasant and three hare samples, had Pb concentrations higher than the maximum admissible level (ML) of 0.1 mg/kg established by the Commission Regulation (EC) No 1881/2006 [
33]. Accordingly, it has been reported by Pain et al. [
31] that an elevated proportion of tissues from both cooked and raw gamebirds had Pb concentrations exceeding the ML, even 10 fold, with a few samples exceeding the ML 100 fold [
34]. On the contrary, in four pheasant samples (P1, P5, P6, and P7) and in one hare sample (H1), very low Pb concentrations were observed. These values, in the range of 0.01–0.03 µg/g, were similar to those reported by Gonzales-Weller et al. [
32] in the meat of farmed animals and raised less concern [
35].
The richness of the non-essential trace elements Cd, Al, As, and Hg in the woodcock pâtè could be considered a paradigm of how the different ingredients used for dish preparations, including seasonings, could influence the total metal intake. Therefore, in addition to raw material, it is also essential to determine the metal concentrations in processed food. In this case, Cd and Al derived from the woodcock viscera included in the food preparation while As and Hg came from the anchovies. It is well known that in vertebrates the liver and the kidney are the target organs of Cd accumulation due to the induction of metallothioneins [
36,
37,
38]. In adult woodcock, a mean Cd concentration as high as 15.7 µg/g had previously been reported in the kidney, deriving from the woodcock diet based mainly on earthworms [
39]. On the other hand, the presence of low, but not negligible, concentrations of Hg were due to the inclusion of anchovies during the preparation of the woodcock pâtè. This non-essential trace element is commonly found in fish, for the most part in the highly bioaccessible form methylmercury (MeHg) [
40].
3.3. Benefit-Risk Balance
Assessment of the benefit–risk balance is an essential issue when evaluating the nutritional quality of food. Meat has been consumed for thousands of years and is considered an important source of proteins, vitamins, and essential trace elements. In the following paragraphs, the most relevant issues related to the samples analyzed in the present study will be discussed.
It has been estimated that more than two billion individuals from both developing and industrialized countries suffer from Fe deficiency, with the emphasis on young women [
41]. At the same time, it has been well recognized that the distribution between heme and non-heme Fe is more important in determining the body metal status than the total dietary Fe intake [
42]. Moreover, meat consumption is positively associated with a higher serum ferritin concentration [
43] due to the high content of heme Fe, especially in red meat [
44]. Snail and woodcock processed meat contains the highest Fe concentrations; considering the mean Fe values of 99.6 µg/g for snail and 63.5 µg/g for woodcock and assuming a consumption of 100 g of food, a total Fe intake of 9.96 mg and 6.35 mg, respectively, is obtained. These values represent 90.5% and 57.7%, respectively, of the population reference intake (PRI) of 11 mg/day reported by EFSAfor Fe [
45]; therefore, snails could be considered a tasty and nutritious food, which could help reduce the anemia caused by a lack of Fe in the diet, in particular in developing countries. On the other hand, the high concentration and bioavailability of Fe in red meat could represent a risk for people suffering from cardiovascular diseases (CVDs). Several studies have examined the association between processed red meat consumption and the risk of CVDs, in particular, myocardial infarction. Different hypotheses, including the presence of heme Fe as a possible source of oxidative stress, have been reported to explain this association [
46]. However, recent findings from the EPIC-Heidelberg (European Prospective Investigation into Cancer and Nutrition-Heidelberg) Study do not support the hypothesis that an increased Fe intake represents a mechanistic link between meat consumption and CVD risk because a high Fe status can also be associated with other physiological or pathological risk factors, including older age, male gender, obesity and inflammation [
47]. More studies are needed on this challenging topic.
Snail processed meat contains high Cu concentrations. Considering the mean Cu level of 75.1 µg/g and assuming a consumption of 100 g of food, a total metal intake of 7.51 mg is obtained. This value represents 468% of the AIof 1.6 mg/day reported by EFSA for Cu in adult men. An even worse situation occurs for women, as the value represents 550% of the AI of 1.3 mg/d [
48]. In both cases, the tolerable upper intake level (UL) of 5 mg/d set by EFSA for Cu is exceeded [
49]. Although Cu is an essential trace element, its excess induces oxidative stress through the production of reactive oxygen species. Moreover, recent results of a meta-analysis indicate that exposure to high levels of Cu is associated with an increased risk of CVD and coronary heart disease [
50]; therefore, a limited consumption of snails by people at risk of or suffering from these diseases is advisable.
As discussed above, Zn concentrations are homogeneous, though not particularly high, satisfying at least 19% of AI in case of snails. Other sources, such as beef meat [
11] and oysters, could be considered more interesting to satisfy the nutritional requirements of this essential trace element. In particular, Zn concentration higher than 1000 µg/g wet weight were previously reported in oysters [
2].
The percentages of AI for Fe, Zn, and Cu were also calculated for cooked beef sirloin and pork loin, based on the data reported by Lombardi-Boccia et al. [
11]. All samples from unconventional animals analyzed in the present study ensure higher percentages of AI with respect to the meat obtained from farm animals, with the exception of Zn.
Due to its toxicity, Pb was included on the list of 10 chemicals of major public health concern by the World Health Organization (WHO) [
51]. The most known adverse effects of Pb uptake are developmental neurotoxicity in children and cardiovascular effects and nephrotoxicity in adults [
27,
52]. In 2010, the EFSA Panel on Contaminants in the Food Chain (CONTAM) claimed that the current provisional tolerable weekly intake (PTWI) of 25 μg/kg of body weight (bw) was no longer appropriate to ensure adequate protection for consumers and concluded that no safe uptake level could be derived; as a consequence, Pb uptake should be as low as possible [
53]. Although the majority of the Italian population rarely consumes processed game meat, a restricted population of hunters and their relatives eat wild game meat frequently and could be exposed to elevated Pb intake. In fact, Pb in the H3 sample analyzed in the present study exceeded 17 µg/g. The consumption of 100 g of processed hare meat might determine a Pb intake of 1.73 mg (corresponding to 24 µg/kg bw). On the other hand, using the mean value of 3.39 µg/g or the median value of 0.59 µg/g, a Pb intake of 0.339 mg (corresponding to 4.8 µg/kg bw) or of 0.059 mg (corresponding to 0.84 µg/kg bw) can be obtained, respectively. Only in the latter case, the PTWI of 25 μg/kg bw is not exceeded and, therefore, the negative health effects cannot be excluded in the other two cases.
A considerable amount of information exists regarding the detrimental effects of Cd on human health, and chronic Cd exposure has been associated with kidney disease, osteoporosis, cardiovascular diseases, and cancer [
54]. In particular, Cd was ranked seventh on the Priority List of Hazardous Substances by the Agency for Toxic Substances and Disease Registry (ATSDR). A weekly intake of 0.50 μg/kg bw was recently estimated for a representative sample of the Italian population [
55]. This value is far below the tolerable weekly intake (TWI) of 2.5 µg/kg bw (175 µg for a reference male of 70 kg, corresponding to a daily intake of 25 µg) established by the EFSA Panel on Contaminants in the Food Chain [
55,
56]. However, based on the data reported in the present paper, eating 100 g of cooked snails results in a mean daily intake of 33 µg Cd which represents 132% of the aforementioned daily intake, and 100 g of processed woodcock (mean intake of 14 µg Cd) represents 56%. While the consumption of snails can be considered occasional, a monthly consumption of 126 g of woodcock meat has been reported for Italian hunters [
9]. On this basis, it can be estimated that Cd intake from the woodcock analyzed in this study can reach a mean value of 211 µg Cd/year in hunters. This represents a small, but not negligible, percentage (3.5%) of the total metal intake as it is higher, for instance, than the intake derived from equine meat which, in Italy, was estimated to be approximately 1% of the total Cd intake [
57]. Although Cd from woodcock does not likely constitute a real threat for humans, as it represents only a partial source of food consumed occasionally during the year, environmental Cd contamination, by means of metal accumulation along the food chain, might be envisioned as a risk to human health. To eliminate this source of Cd present in the viscera, it is suggested that woodcock be eviscerated before cooking.