Cadmium Absorption by Tomatoes at Different Growth Stages in Polluted Soil

Environmental pollution by heavy metals is a growing global concern. Most heavy metals accumulate in the top soil and in the long term, increased concentrations in the soil results in increased absorption and accumulation in plants. The usual concentration of cadmium in the soil is 0.001-2.4 mg/kg of dry soil. The level of absorption and accumulation in plants depends on the type of plant, tissue make-up of the plant and physical and chemical characteristics of the soil. There is a deficit of information on the amounts of absorption and accumulation of heavy metals at different tomato growth stages. This study was conducted to analyze the impact of the level of cadmium concentration in soil on its absorption and accumulation at different stages of tomato growth using factorial experimentation in a completely randomized design with three repetitions. The variables were three Cd concentrations (control treatment with no Cd; soil with 50 mg kg-1 Cd; soil with 50 mg kg-1 Cd; soil with 50 mg kg-1 Cd). The soil samples were collected from 400 ha of farmland at the Seed and Plant Improvement Institute in Karaj, Iran. They were sifted twice using 2 mm mesh and the treatments were prepared by adding cadmium nitrate to the soil to make homogeneous mixtures. The experiments were carried out in plastic cylinders 120 cm in length and 85 cm in diameter. The depth of the solution soil was sampled hourly and tomato organs were sampled at different growth stages to record the cadmium absorption rate. SPSS software was used to perform an analysis of variance of the data and the Duncan multiple range test was used to perform a comparison of means (P ≤ 0.05 and P≤ 0.01). Results showed that cumulative cadmium concentration differs in the tissues of the leaf, root, leg, fruit and peel in decreasing order. A negligible amount of the total cadmium added to the soil was absorbed by the plant. Total cadmium absorbed in the cellular colonies of the tomato plant in the control treatment, soil with 50 ppm added Cd, and soil with 100 ppm added Cd were 0.0384, 0.564 and 0.678 g, respectively. The results indicate a direct relationship between Cd accumulation and Cd concentration in the root region. A comparison of the outcomes indicated that increasing the cadmium concentration resulted in a reduction of tomato growth and, especially, the production rate. A 20-35% decrease in production rate was seen in 50-00 ppm cadmium exposure compared to the control. These results show that strong decreases in cadmium concentrations in the solution soil did not decrease the absorption rate of cadmium at various growth stages of the tomato.