The Uptake and Translocation of Lead, Chromium, Cadmium, and Zinc by Tomato Plants Grown in Nutrient and Contaminated Nutrient Solutions: Implications for Food Safety

The uptake and translocation of Pb, Cr, Cd, and Zn in tomato plants (Solanum lycopersicum L. Rally) were investigated. Tomato seedlings were grown for five weeks in pots containing 40 L of Hoagland nutrient solution (pH 7) or contaminated nutrient solutions at two concentration levels for each element: Cr (100 and 1000 ng/mL), Zn (100 and 1000 ng/mL), Pb (100 and 500 ng/mL), and Cd (50 and 500 ng/mL). The solutions were replenished weekly to maintain a volume of 40 L (pH 7), and 10 mL samples were collected for elemental analysis. After five weeks, the plants were harvested and separated into roots, stems, leaves, and fruits. These samples underwent microwave-assisted digestion, and the element concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). The results revealed that the elements were mainly accumulated in the roots, with much lower concentrations determined in the fruits. Pb and Cr accumulated only minimally in fruits, with Pb levels of 0.0009 mg/kg wet weight at LI and 0.003 mg/kg wet weight at LII, and Cr levels of 0.028 mg/kg wet weight at LI and 0.031 mg/kg wet weight at LII. The Pb levels did not exceed the permissible limits set by EC regulations (0.05 mg/kg wet weight). Zn exhibited the highest accumulation in fruits, with 2.17 mg/kg wet weight at LI and 4.8 mg/kg wet weight at LII. By contrast, the Cd concentrations in fruits (0.25 mg/kg wet weight at LI and 1.1 mg/kg wet weight at LII) exceeded the EC regulatory limit of 0.02 mg/kg wet weight. The uptake of other essential elements into the tomato plant remained largely unaffected by the presence of contaminants. These results provide valuable insights into food safety. Laser ablation (LA)-ICP-MS imaging revealed an even distribution of Cd and Zn in the leaves of plants grown in contaminated nutrient solutions. By contrast, Cr and Pb were predominantly localized in the leaf veins and at the leaf apex, suggesting different transport mechanisms for these elements from the roots to the aerial parts of the plant.