Assessing bioavailability and toxicity of technology critical elements Ga and In in the contaminated paddy soils via the soil-water-fish system

Gallium (Ga) and indium (In) are metals extensively used in the semiconductor and optoelectronic industries; however, these elements are emerging as environmental contaminants due to improper disposal and industrial effluents, leading to soil and water pollution. Research indicates that Ga and In can influence the mobility of other metals, notably aluminum (Al), in soil environments. Currently, no established methods or standards exist for addressing Ga and In contamination in soils, and their risks and toxic effects on human health and the environment remain unclear. To investigate the bioavailability and ecotoxicity of Ga and In in paddy soils, we established a soil-water-fish exposure system using juvenile medaka fish (Oryzias latipes) as a model organism. Our findings show that the mobility of Ga and In was low in acidic soil with high aluminum content (e.g., Pc soil). However, a significant increase in available Al was observed in Pc soil under high Ga or In contamination levels. In contrast, neutral soil with low Al content (e.g., Su soil) released higher concentrations of soluble Ga into the pore water and overlying water, whereas Pc soil released higher concentrations of soluble In. Juvenile medaka fish exposed to Pc soil contaminated with high levels of Ga or In exhibited increased mortality rates, and their growth and swimming behaviors were altered. Conversely, fish exposed to contaminated Su soil showed lower toxic effects. These findings suggest that Ga and In contamination in paddy soils with differing properties can cause varying toxic effects on aquatic organisms, potentially disrupting the ecological balance of paddy ecosystems under long-term exposure.