The Growth of Rice Seedlings in Different Soils As Affected By Addition of Gallium and Indium.

Emerging contaminants gallium (Ga) and indium (In) are trace elements extensively used in semiconductor manufacturing and electro-optical industry. Assessing the behavior of Ga and In in soils and the potential effect of Ga and In on the plant growth are indispensable, whereas related research is still in its infancy. To better understand the impact of Ga and In on the environment, pot experiments with rice seedlings (Oryza sativa L.) were carried out. Rice seedlings were grown in three different soils (Pinchen, Chengchung, and Changhua) spiked with 50 mg/kg, 100 mg/kg, 200 mg/kg, and 400 mg/kg of Ga or In, respectively. The results suggested that both Ga and In addition caused the growth inhibition of rice seedlings. For Ga treatments, low CEC and lack of O.M in Pinchen soil made Ga more easily to be released into soil solutions. In addition, the increase of Al concentration in soil solutions with the increase of Ga application rates was observed, due to that Al rich in Pinchen soils would be replaced by Ga into soil solutions. Since the Al concentration in soil solutions was higher than the toxicity levels of Al to rice plants, the Al replaced by Ga may be the dominant factor causing growth inhibition on rice seedlings. For In treatments, the availability of In is relative low in neutral and alkaline soils (Chengchung and Changhua) due to precipitation, which mitigated the toxic effect of In on rice seedlings even though the soil concentration of In was up to 400 mg/kg. Although the substitution of Al for In was also observed in Pinchen soils, the concentrations of Al in soil solutions was still below the toxicity levels to rice seedlings, which indicated that Al may not be the major factor affecting the growth of rice seedlings.