Effect of Emerging Contaminants Gallium and Indium on the Growth of Rice Seedlings.

Gallium (Ga) and indium (In) compounds are commonly used in semiconductor manufacturing industry and electro-optical industry. Recent studies have discovered that effluents which contain Ga and In are discharged from these information technology industries and resulting in increase of Ga and In concentrations in the environments. To our best knowledge, there are few studies to investigate the effect of Ga and In on the growth of crops. Because rice is the staple food in Asia, it is important to evaluate the effect of Ga and In on the growth and uptake of these two elements of rice seedlings. The rice (Oryza sativa L.) seedlings were exposed to full-strength Kimura B nutrient solutions containing different Ga and In concentrations, which were 0, 0.1, 1, 3, 5, 10 mg Ga and In L^-1 respectively for 25 days in the hydroponic experiments. The SPAD values, length of roots and shoots were measured. The Ga and In concentrations in roots and shoots of rice seedlings were determined. The results showed that there were no significant differences on shoot height, root length, biomass and SPAD value of rice seedlings in Ga treatments. However, Ga concentrations in roots and shoots were raised with increasing Ga concentrations in the hydroponic solutions. It suggested that the growth of rice seedlings was not inhibited when the concentration of Ga was below 10 mg L^-1. The results of In treatments showed that shoot height, root length and biomass of rice seedlings were significantly decreased when In concentration reaching 0.1 mg L^-1. The SPAD values were significantly decreased when In concentration of In was 1 mg L^-1. It suggested that rice might suffer from toxicity and In could be accumulated when In concentrations in culture solutions were above 0.1 mg L^-1. Compared to Ga, In has higher toxicity to rice seedlings.