Effects of Inorganic and Organic Arsenical Pesticides on Rice Growth and Development: A Comparative Greenhouse Study

For decades repeated and widespread use of arsenical pesticides has significantly contributed to elevated concentration of arsenic (As) in soils. Residues of these arsenicals may result in phytotoxicity of crops where rotation is practiced. Humans can be affected if these crops accumulate As to a significant degree, which would depend on the soil as well as the plant species. A greenhouse study was conducted to evaluate the effect of two pesticides on the vegetative response of rice (Oryza sativa) as a function of soil properties involving dynamic interaction between soil-pesticide-water and plants. Four soils (Immokalee, Millhopper, Pahokee Muck, and Orelia) with varying As retention capabilities were used that were amended by two arsenical pesticides (Sodium arsenate and Dimethylarsinic acid) at two rates (675 and 1500 mg kg-1). Arsenic availability to rice was influenced by its soil fractionation. Soil As fractionation was influenced by soil properties. Low As retention capacity lead to higher As uptake by rice grown in Immokalee soil compared to the other soil types. For Millhopper soil with moderate As retention capacity, equal distribution of As in the surface soil and leachate affected plant growth in Sodium arsenate spiked soils. For Pahokee Muck and Orelia, soil proved to be the major As pool. Orelia witnessed no plant growth, while high organic matter in Pahokee Muck favored germination and subsequent plant growth. The source of soil As did not affect plant As uptake, shoot length, or its labile form. A significant negative correlation (P< 0.05) was observed between the labile form of As and the vegetative response. Rice biomass, shoot height, and root length decreased with increased As concentrations in all soil types.