The total Hg content was determined in the twenty-eight menu samples employed in this study. The results are expressed in µg Hg per kg of dry weight (d.w.) per sample. As Table 4 shows, the baby food samples contained between 0.57 and 41.9 µg kg− 1 d.w. of Hg. The lowest levels corresponded to vegetable purée (0.57–7.38 µg kg− 1 d.w.), followed by foods containing meat (2.51–21.8 µg kg− 1 d.w.). The highest concentration corresponded to fish and those with rice or vegetables (11.5–41.9 µg kg− 1 d.w.).
On considering fast food menus aimed at children, the values found varied between 0.54 and 67.7 µg kg− 1 d.w. It must be noticed that there was no significant difference in the menu composition of these samples (Table 1). Also, variations in the mercury concentration could not be assigned to any of the components, and no relation with the brand was found. Regarding canteen menus, a mercury range from 0.43 to 19.4 µg kg− 1 d.w. was found, except for Daily Meal 8, where there was a high level of 638 µg kg− 1 d.w. of Hg. Once again, the level of Hg seems to be related to the presence of fish on the menu (13.5–19.4 µg kg− 1 d.w.), specifically the presence of tuna (638 µg kg− 1 d.w.), and rice with seafood products (3.14 µg kg− 1 d.w.).
According to Cheng et al. (2013), the results for THg ranged from 0.16 to 171 µg kg− 1, with the levels of Hg in fish significantly higher than in other food groups, such as vegetables, fruits, meat, viscera, eggs, and rice. Moreover, among the foods studied by these authors, rice and fish contributed most to the total daily intake of mercury. Other researchers have also studied the level of mercury in various types of food, including fish and shellfish.
Martorell et al. (2011) studied the dietary intake of Hg for 12 food groups, including meat, fish and seafood, vegetables, tubers, fruits, eggs, milk, and cereals. Among the analyzed foods, the tuna presented the highest concentration of Hg (222–776 µg kg− 1), only behind swordfish (869 µg kg− 1).
De Roma et al. (2017), in turn, evaluated the occurrence of toxic elements (As, Cd, Hg, and Pb) in different meals (baby food, fast food, vegetarian meal, canteen meal, and restaurant meal) in Italy. The Hg concentrations determined were relatively low (< 1.5–3.27 µg kg− 1), except for a restaurant meal sample (14.9 µg kg− 1). These authors related the higher level of Hg to the presence of seafood and cereals on this menu, placing these two foodstuffs among the most significant contributors to THg intake.
González et al. (2019), finally, investigated the presence of As, Cd, Hg, and Pb in foodstuffs (meat and meat products, fish and seafood, vegetables, eggs, milk and derivatives, bread and cereals, oils, industrial bakery, sauces, chocolates, and infant food) widely consumed in Catalonia, Spain. The Hg levels were below the LOD (< 2 µg kg− 1) of the method for most of the analyzed foods, except for fish and seafood, which showed a mean concentration of 152 µg kg− 1. The detailed study of this foodstuff revealed Hg concentrations ranging from 3 µg kg− 1 (panga) to 856 µg kg− 1 (swordfish), which confirms the tendency of this metal to accumulate in fish and seafood.
From the data above, given the percentages of moisture and the average mass of sample consumed in fresh form, the daily intake of Hg per person could be calculated (Table 4). Data found indicated ranges from 0.02 to 1.4 µg in the case of baby food, from 0.09 to 11.2 µg for fast food, and from 0.09 to 4.1 µg for adult canteen menus, except for the Daily Meal 8, which provided 134 µg. Table 4 also shows the percentage of the tolerable daily intake (TDI) provided by each menu analyzed.
The percentage contribution of samples to the TDI for baby food varied from 0.3 to 18.8% or 27.8% depending on the age (Table 4). This is considered not alarming, taking into account that it represents the daily main meal and the percentages were lower than 30%. In the case of children’s fast food, the percentage of TDI varied from 0.5 to 56.2% or 102.2%, depending on the body weight considered, in both cases, higher than 50%, posing a potential problem for children’s health. Regarding the canteen menus, which were the main meal, the percentage of TDI, except for Daily Meal 8, varied from 0.3 to 12.1%, causing no human health problems. For Daily Meal 8, the percentage was 395.7% of TDI for adults and half of the Provisional Tolerable Weekly Intake (134 µg/person in front 240 µg/person/week) in a single meal, which confirms the recommendation from the European Food Safety Authority (EFSA) (Dietetic Products, Nutrition, and Allergies 2014) that the consumption of fish/seafood species with a high content of mercury in the daily diet should be limited to only a few of servings (< 1–2) per week.
A comparison of the concentrations of Hg found in baby food from different countries is shown in Table 5. The Hg concentration was studied in European countries and the levels varied between < 0.10 and 29.9 µg kg− 1. The lowest mean was obtained for the samples of baby food from Portugal (0.40 µg kg− 1) and the shortest range in the samples from the Czech Republic, Republic of Hungary, and Slovak Republic (0.3 to 10.2 µg kg− 1). A comparison of the results obtained in the present study for samples of baby food 11 and 13 with those found in the literature shows that they agree with the observations of Tóth et al. (2014). The latter reported the highest level of Hg in the sample with the addition of the tuna, with a value of 10.2 µg kg− 1. Martins et al. (2013) also reported the highest value of Hg in a baby food containing fish (19.6 µg kg− 1). A possible explanation for this is that mercury concentrations are found mainly in muscle tissues, the liver, and the kidneys of marine fish (Kasper et al. 2009).