Physiological Responses, Cadmium Partitioning, and Mineral Nutrient Disruption in Brassicaceae Crops Exposed to Cadmium Stress

Cadmium (Cd) contamination of agricultural soils poses a serious threat to crop productivity and food safety due to its high mobility, bioaccumulation potential, and toxicity. This study investigated the effects of increasing Cd levels on growth performance, physiological responses, Cd partitioning, mineral nutrient disruption, and Cd accumulation in four Brassicaceae crops (cress, watercress, broccoli, and white cabbage). Plants were grown in plastic pots filled with 4 kg of soil under controlled greenhouse conditions and exposed to five different Cd concentrations (0, 5, 10, 20, and 50 mg kg−1). Cd exposure significantly affected growth and physiological responses in a species-dependent manner. Compared to the control, shoot dry weight decreased by up to 66.4% in broccoli and 51.7% in cress at the highest Cd level, while white cabbage exhibited comparatively greater tolerance. Oxidative stress indicators showed contrasting patterns, with hydrogen peroxide (H2O2) increasing by up to 8.8-fold, whereas proline and membrane permeability (MP) responses varied among species. Photosynthetic pigments declined in cress but increased in broccoli under high Cd conditions, suggesting differential adaptive strategies. Cd accumulated predominantly in roots; however, root retention capacity declined at elevated Cd concentrations (20–50 mg kg−1 soil), leading to greater Cd translocation to shoots. Elevated translocation factors and shoot Cd distribution demonstrated that physiological tolerance did not necessarily limit Cd accumulation in edible tissues. Cd stress also induced notable imbalances in essential mineral nutrients, particularly potassium (K), calcium (Ca), and zinc (Zn), reflecting strong Cd–nutrient interactions at uptake and transport levels. These nutrient disruptions not only exacerbated physiological stress responses but also reduced the nutritional quality of plant tissues. Notably, species maintaining relatively stable growth under moderate Cd exposure still accumulated substantial Cd concentrations in shoots, highlighting a critical disconnect between agronomic performance and food safety. In conclusion, the findings demonstrate that Brassicaceae crops exhibit contrasting strategies in response to Cd stress, with significant implications for Cd entry into the food chain. The study emphasizes the importance of integrating physiological assessment with metal partitioning and nutrient balance analyses when evaluating crop suitability for cultivation in Cd-contaminated soils and for mitigating potential risks to human health.