Competitive Sorption Between Arsenic and Phosphorus On High and Low Phosphorus Ultisols.

Arsenic (As) is an element of great concern because of its potential to harm human health and the environment. Competition between As and P for adsorption sites in soil can be a limiting factor to evaluate As bioavailability and transport within the soil. Ultisols are known for their moderate to high P fixation capacity to amorphous and microcrystalline iron and aluminum oxyhydroxides.  The effect of fixed P on As mobility is largely unknown. This study evaluates adsorption-desorption mechanisms of various As species (arsenite, arsenate) in soils that have low and high levels of P due to consistent long-term P management strategies using batch experiments. Results indicate that As sorption is a function of As species, P level in the soil, and soil pH. Arsenate adsorption was greater than arsenite at all pH and soil P levels.  With increasing soil P concentration, rates of As adsorption decreased indicating competition between As and P for high P soils. Maximum adsorption occurred at pH 4.5. The results indicate that competitive sorption between As and P can be modeled to predict As mobility from soils receiving different P inputs.