Abstract
Various mineral elements were incorporated into lettuce grown in hydroponics to find suitable mineral elements for developing a marking system to certify the provenance of vegetables. Seven mineral elements (Ba, Sr, Mo, Co, Cu, Ni and V) were selected as candidate markers, since the natural abundance of these elements in lettuce were low and they seem to have comparatively low toxicity to human and vegetables. Two varieties of lettuce (Lactuca sativa L., cv: Red-fire and Rakuten) were cultivated in nutrient solution containing each of these elements at various concentrations. Lettuce grown under all treatments with Ba, Sr and Mo and under treatment with Cu at 0.25 and 0.50 mg l-1 and with Ni at a concentration range of 0.05-0.50 mg l-1 showed favorable growth similar to the control, whereas under treatment with Co, Cu and Ni at 5.00 mg l-1 and with Cu at 10.00 mg l-1 , plants showed unfavorable growth. Vanadium was hardly absorbed by lettuce. Concentrations of Ba, Sr, Co, Mo, Cu and Ni in tops of lettuce were increased in proportion to increase in the actual concentration of each element in nutrient solution.
In addition, amounts of elements contained in 470 g of treated lettuce (amount recommended by the Ministry of Health and Welfare of Japan for daily consumption by adult) in several treatments were lower than the Acceptable Daily Intake (ADI) or Tolerated Daily Intake (TDI) and were obviously higher than their natural abundances. These results suggest that Ba, Sr, Mo, Co, Cu, and Ni could be used as marker elements to certify the provenance of lettuce grown in hydroponics when lettuce is cultivated using a nutrient solution within a suitable concentration range.
