The Study of the Uptake of Chromium, Zinc, Cadmium and Lead from Spiked Nutrient Solution in Tomato Plants ^†

The reuse of treated wastewater for irrigation can preserve freshwater resources. However, treated wastewater carries health risks due to residual contaminants. For safe food production, it is essential to understand the uptake of potential contaminants and their distribution in edible parts. Chromium (Cr), zinc (Zn), cadmium (Cd) and lead (Pb) are commonly found in municipal wastewaters. In the present study, the uptake of Cr, Zn, Cd and Pb was studied. Tomatoes were cultivated in Hoagland nutrient solution (pH 7) prepared using potable water and nutrients [1]. Treated tomatoes were grown in the Hoagland solution spiked with naturally abundant elements ⁵²Cr (100 ng/mL), ⁶⁶Zn (100 ng/mL), ¹¹¹Cd (50 ng/mL) and ²⁰⁸Pb (100 ng/mL) and their enriched stable isotopes ⁵³Cr, ⁷⁰Zn, ¹⁰⁶Cd and ²⁰⁴Pb at the same concentration levels. The use of enriched isotopes enabled distinguishing between the concentration of an individual element, which is naturally present in Hoagland’s solution and is uptaken by plant during growth, and the concentration of an individual element uptaken by plant as a result of its addition in the nutrient solution. Tomatoes were raised 5 weeks in 40 L pots. Nutrient solution or spiked nutrient solution were weekly replenished to volume. Plants were harvested 5 weeks after exposure and divided into roots, stems, leaves and fruits. Samples were decomposed using microwave digestion, and element concentrations were determined by ICP-MS. The results showed that the roots exhibited the highest accumulation of Cr, Zn, Cd and Pb, while low concentrations of Cr and Pb were determined in fruits. In the fruits, the highest accumulation was observed for the essential element Zn. In compliance with Commission Regulation, the concentration of Cd in fruits exceeded four times the permissible levels set for fruiting-like vegetables. This study contributes to the understanding of pathways of accumulation of essential and toxic elements in plants and to food safety.