Interactive e ects of arsenic and selenium on some food crops: Possible implications for arsenicosis in human

Abstract

In this study, a comprehensive investigation was carried out to decipher the relationship between arsenic (As) and selenium (Se) in soil and plants and to assess whether there is any association between the outcome of the interaction of As and Se and the prevalence of arsenicosis in humans. In the initial assessment, soil and plant samples were collected from arsenic-affected regions covering both arsenicosis-prevalent and non-arsenicosis-prevalent areas. No significant differences were observed between arsenicosis-prevalent and non arsenicosis-prevalent areas in terms of As concentrations. On the other hand, Se levels were statistically significantly (p<0.05) lower in soil (0.107 ± 0.021 mg/kg), plants (0.055 ± 0.007 mg/kg), and water (0.592 ± 0.047 µg/L) in arsenicosis-prevalent areas compared to non-arsenicosis-prevalent areas (soil, 0.154 ± 0.023 mg/kg; plants, 0.078 ± 0.008 mg/kg; and water 0.645 ± 0.049 µg/L). These findings are suggestive of an inverse relationship between Se levels and arsenicosis prevalence, highlighting Se's potential protective role. A pot experiment in sand culture using water spinach (Ipomoea aquatica) as a model plant demonstrated negative effects of As on plant growth; fresh weight was found to be significantly (p<0.05) reduced in plants exposed to As at 2.5 mg/kg As (11.60 ± 0.90 g/pot) and at 5.0 mg/kg As (6.56 ± 0.61 g/pot) compared to the control (15.58 ± 1.16 g/pot). Selenium supplementation was found to ameliorate the deleterious effects of As; biomass production was increased when Se was introduced to the growth medium laced with 5.0 mg/kg As. Selenium also significantly reduced arsenic concentrations in roots and shoots (p<0.05), with the greatest reduction observed at 2.0 mg/kg Se. These findings highlight the efficacy of selenium in alleviating arsenic toxicity, improving plant growth, and reducing arsenic accumulation in edible plant parts. Another pot experiment with the soil medium and spinach (Spinacia oleracea) as a model plant confirmed selenium's role in improving biomass production, reducing arsenic accumulation, and enhancing biochemical defense mechanisms. Selenium application was found to enhance (p<0.001) fresh weight in spinach dosed with As in irrigation water. Arsenic concentration in plant tissues was reduced significantly (p<0.001) with Se in the medium demonstrating the fact that Se has antagonistic effects on arsenic. Selenium application also enhanced levels of cysteine, glutamic acid, and i glycine (p<0.05), which are critical components of glutathione (GSH), a key antioxidant protecting plants from arsenic-induced oxidative stress. In a separate experiment with rice (Oryza sativa), selenium was applied at different doses along with As in irrigation water. A similar trend was observed in biomass and grain yield as was seen in water spinach and spinach. Higher doses of Se significantly increased biomass and grain yield (p<0.05) in rice plants fed with As in irrigation water. Selenium supplementation also reduced arsenic accumulation in rice tissues significantly (p<0.001). On the other hand, selenium accumulation in plant tissues was found to increase with a higher dosage of selenium (p<0.001). Importantly, selenium supplementation did not negatively affect the concentrations of N, P, K, and S in rice grains, maintaining nutritional integrity. In another piece of experiment, nutrient dynamics were studied in water spinach (Ipomoea aquatica) grown in pot soil and treated with selenium and arsenic. Selenium application significantly increased nitrogen content (p<0.05) from 1.95±0.18% (control plants) to 2.20 ± 0.09% (treated with 0.50 mg/kg Se). Phosphorus content was found to be increased slightly with the application of Se; however, a non-significant declining trend at higher selenium concentrations was observed. Potassium levels rose from 0.44 ± 0.07% (control) to 0.65 ± 0.10% (treated with 0.50 mg/kg Se). Overall, while selenium influenced nutrient levels slightly in water spinach, changes were generally not statistically significant except for nitrogen concentration. Overall, this study underscores selenium's antagonistic role against arsenic in plants, its role in reducing arsenic accumulation, enhancing the biochemical defenses of plants, and improving growth and yield without compromising the nutritional quality. The findings also highlight the potential of selenium as a sustainable solution to arsenic toxicity in agriculture, maintaining crop productivity and food safety in arsenic contaminated regions.