Type of food, conditions in which the food was grown, meteorological conditions and anthropogenic contamination of the environment are all very important factors affecting the concentration of Cd in food. As reports of regulatory bodies have shown, most foods have relatively low Cd content, lower than 20 ng/g (5; 41). Cadmium levels are typically low in meat, eggs, milk and fish. On the other hand, high Cd levels are frequently present in leafy vegetables, potatoes, cereals, shellfish, and cephalopods. EFSA made a survey on Cd dietary exposure in the European population in 22 EU member countries with data collected from 2003 to 2011 (42). The results revealed that the highest Cd content in food items sold in the EU market was found in algae, cocoa and cocoa products as well as in the edible offal, horse kidney as much as 61 µg/g. A Swedish study has shown that the highest average Cd content was found in spinach (104 ng/g), seafood (170 ng/g) and herring liver (660 ng/g) (43). Similar results of Cd concentrations in foods were obtained in our study. The median Cd concentrations in the tested foods were the highest in mollusks and cephalopods (89 ng/g). The median Cd content was also high in oilseeds, potato products, stalky vegetables and mammal offal, over 30 ng/g. Cadmium concentrations below 10 ng/g were measured in foods highly present in the diet such as fruits, milk and dairy products, eggs and egg products and meat and meat products. Cadmium concentrations in all tested samples were below the maximal permissible concentration given by the national rule book (40).
Despite the fact that the average content of Cd in mollusks and cephalopods is the highest, a very small intake of these foods in the Serbian adult population (on average 1.6 g/day) leads to a very low intake of Cd through this food group. On the other hand, a high intake of some staple foods like cereals and flour, milk or potatoes that have relatively low Cd concentration may possibly affect Cd exposure estimates. Potatoes have a relatively low Cd content compared to some other food groups, however, the daily average intake of 193.4 g caused their highest contribution to total dietary intake of Cd in the Serbian adult population. In addition to potatoes, mammal offal also had a noteworthy share in total Cd intake for the adult Serbian population, thanks to high values of the median concentration (56 ng/g).
The group of fruit and vegetable juices were the major source of dietary Cd in Serbian preschool children (43.7% of the total Cd intake) since the consumption of this foodstuff was fairly high (66.1 g) and the measured Cd concentration was noteworthy (19 ng/g). Mammal offal (14.8%) and potato products (9.9%) also had a significant share in the Cd intake in preschool children. Due to relatively low Cd concentration in cereal products, these foods were not the significant source of dietary Cd in preschool children even though cereal products were a significant dietary source with 20.7% of the total Cd intake.
A similar conclusion about Cd intake in adults derived in our study was provided by Sand and Becker (43), who found the share of potatoes and wheat flour in the total intake of Cd in the Swedish population of 40-50%. Further, the main sources of Cd exposure in Catalonia were legumes, potatoes and cereals (44). The US population consumes the most Cd through leafy vegetables, potatoes and cereals, while Cd intake was higher in people who had used larger amounts of shellfish and offal in their diet (3). In contrast to data relating to Europe, a Japanese study showed that in Japan Cd is mostly ingested through the rice (up to 40%) (6). Similarly, in China, vegetables, rice and flour were the food groups that contributed the most to Cd ingestion in the general population with 74.9% of the total Cd intake (45).
Tolerable weekly intake (TWI) of 2.5 µg/kg bw that was used as a reference dose for calculation of HI in this study was set by EFSA (39) based on an inquiry of numeral human studies regarding the relationship between urinary Cd levels and beta-2-microglobulin, a protein excreted in the urine, used as a biomarker for renal function. Taking these two markers and linking them to dietary Cd exposure, TWI was not established on the outcome of an actual renal injury, but on an initial indicator of alterations in kidney function implying likely damage of the renal function later in life. This way, even when the Cd intake exceeds the TWI, the risk of the immediate adverse health effect is relatively low.
In our study total weekly Cd intake in the adult population ranged from 1.41 mg/kg bw to 4.74 mg/kg bw, while in preschool children it ranged from 2.07 mg/kg bw to 4.93 mg/kg bw. These differences in total dietary Cd intake between the subpopulation of preschool children and the adult population were expected, given the differences in the diet and the differences in their body weights. These results are in line with the conclusion given by EFSA (39) that vegetarians, children, smokers and people living in extremely polluted regions, are likely to exceed weekly intake.
Acquired HI values in our study were lower than 1 in 45.5% of adults, and only in 15.6% of preschool children. Children population has a higher risk of Cd adverse influence, compared to the adult population.
Many studies have shown that dietary Cd intake is significant in other countries as well. Leblanc et al. (46) showed that the intake of Cd was 17 µg/day in France, which on a weekly basis and calculated on the average body weight of 60 kg is 2 µg/kg bw. Slightly lower values were registered in Spain (1.7 µg/kg bw Cd per week) (47). In Europe, the average Cd intake in children was 3.96 µg/kg bw per week, which is higher than TWI (42).
In comparison to Cd exposure calculated in our study, slightly lower values were acquired in Sweden where median dietary Cd exposure of 1 µg/kg bw was obtained for the average adult population, and 1.8 µg/kg bw for the 95th percentile of the adult population (43). Marti-Cid et al. (44) have estimated an average of 0.98 µg/kg bw for the population of Catalonia, calculated on a body weight of 70 kg.
The Dutch study found that the median daily intake of dietary Cd in the adult population was 0.14 µg/kg bw, and 0.32 µg/kg bw for the children aged 1-6 years (48). Translating daily Cd intake to weekly intake, 0.98 μg/kg bw was obtained for adults and 2.24 μg/kg bw for children, which is a 2.8 times lower intake in adults and 1.5 times lower intake in children compared to our assessment results, for the same calculation method.
Liu et al. in a 2010 paper (49) presented data on Cd intake in the population of the Jinhu area of China. The average weekly intake in adults was 1.49 µg/kg bw, while in children aged 1.9 to 7 years the intake was slightly higher (2.07 µg/kg bw). In both population groups, the intake was lower than the currently valid TWI.
In the United States, the estimated weekly intake of Cd in the adult non-smoking population was 2.45 µg/kg bw for men, and 2.1 µg/kg bw for women (3). These values correspond to the values obtained in our study for the adult population in the Republic of Serbia.