Effect of cadmium accumulation on mineral nutrient levels in vegetable crops: potential implications for human health

Consumption of vegetables is often the predominant route whereby humans are exposed to the toxic metal Cd. Health impacts arising from Cd consumption may be influenced by changes in the mineral nutrient content of vegetables, which may occur when plants are exposed to Cd. Here, we subjected model root (carrot) and leaf (lettuce) vegetables to soil Cd concentrations of 0.3, 1.5, 3.3, and 9.6 μg g−1 for 10 weeks to investigate the effect of Cd exposure on Cd accumulation, growth performance, and mineral nutrient homeostasis. The findings demonstrated that Cd accumulation in lettuce (20.1–71.5 μg g−1) was higher than that in carrot (3.2–27.5 μg g−1), and accumulation exceeded the maximum permissible Cd concentration in vegetables when soil contained more than 3.3 μg g−1 of Cd. There was a marked hormetic effect on carrot growth at a soil Cd concentration of 3.3 μg g−1, but increasing the Cd concentration to 9.6 μg g−1 caused decreased growth in both crops. Additionally, in most cases, there was a positive correlation between Cd and the mineral nutrient content of vegetables, which was due to physiological changes in the plants causing increased uptake and/or translocation. This may suggest a general mechanism whereby the plant compensated for disrupted mineral nutrient metabolism by increasing nutrient supply to its tissues. Increased nutrient levels could potentially offset some risks posed to humans by increased Cd levels in crops, and we therefore suggest that changes in mineral nutrient levels should be included more widely in the risk assessment of potentially toxic metal contamination.