**3. Cadmium content**

Vast areas of agricultural soils are contaminated with Cadmium (Cd) through the use of super phosphate fertilizers, sewage sludge, and inputs from the mining and smelting industries [18]. Cadmium (Cd) is a highly toxic element for human beings because of its extremely long biological half-life. Soybeans grown in cadmium-contaminated soil take up cadmium by roots and translocate into aerial organs, where it affects photosynthesis and consequently root and shoot growth. Many soybean cultivars can accumulate high Cd concentration in seed when grown on Cd-polluted soil [19, 20]. Consumption of food containing excessive Cd leads to a risk of chronic toxicity. In humans, it can damage kidneys, causing a loss of calcium and associated osteoporosis [21]. To reduce the health risk, it is desirable to limit the concentration of Cd in crops used for human consumption. Due to growing concern about safety of foods and human health, the Codex Alimentarius Commission of Food and Agriculture Organization/World Health Organization (FAO/WHO) has proposed an upper limit of 0.2 mg kg<sup>−</sup><sup>1</sup> for Cd concentration in soybean grain [22]. However, a large-scale survey of agricultural products revealed that the Cd concentration of 16.7% of soybean seeds exceeded the international allowable limit of 0.2 mg kg<sup>−</sup><sup>1</sup> , which is much higher than that of other upland crops [23]. Cultivars with reduced uptake of Cd are needed for

human consumption. Cd uptake depends both on the Cd concentration in the soil and on the characteristics of the specific cultivars. Breeding cultivar with reduced Cd is an attractive method for changing the element profile of crops as the benefit will persist in the seed that can reduce the requirement for other management practices [24].
