Comparison of Uptake of Cadmium at Low Concentrations Under Hydroponic and Soil‐Based Agriculture Systems for Lettuce, Indian Spinach and Methi

ABSTRACT Using recycled water for agriculture offers a sustainable approach by adding inherent nutrients and moisture to the soil. However, it contains unwanted contaminants such as heavy metals like cadmium at lower concentrations. This study assessed the comparative response of three leafy crops ‐ lettuce, Indian spinach and methi, against cadmium exposure under hydroponic and soil‐based cultivation. Crops were irrigated with cadmium‐spiked water (0, 0.03, 0.06, and 0.09 mg L −1 ), using a nutrient film technique for hydroponics and fertilized soil pots for soil cultivation. All crops exhibited a biphasic hormetic response, with growth stimulation up to 0.06 mg L −1 and decreased response at 0.09 mg L −1 . Cadmium accumulation increased linearly in crops with rising concentrations in irrigation water, and higher accumulation was recorded in roots than shoots. The crops' response varied significantly between the two cultivation systems, with greater cadmium accumulation under the hydroponic (0.092, 0.109 and 0.088 mg Cd kg −1 of dry weight of lettuce, Indian spinach and methi, respectively) than soil based cultivation (0.025, 0.022 and 0.021 mg Cd kg −1 of dry weight of lettuce, Indian spinach and methi, respectively). Under soil‐based cultivation, Indian spinach and methi exhibited more root cadmium, limited translocation and higher growth response to cadmium than lettuce, which recorded higher shoot cadmium and lower response. On the other hand, under hydroponic cultivation, lettuce had lower accumulation and moderate response, while methi and Indian spinach showed higher uptake in respective root and shoot, and better response, indicating a stimulation effect at low cadmium doses. Despite cadmium accumulation, the human health risk index remained below one, indicating that it is safe to consume these leafy crops. However, under higher Cd concentrations, there could be an increased risk. This study indicates that crops grown hydroponically are more susceptible to cadmium accumulation than those grown in soil. These results indicate that, for using recycled water for growing food crops in hydroponics, it should be of desired quality, which can be achieved through appropriate treatment.