Chemistry of Arsenic in Semi-Arid Alkaline Soils of the Southern High Plains, USA: Sorption Characteristics and Interactions with Soil Constituents

Abstract

Limited information is available on the chemistry of arsenic (As) in the semi-arid alkaline soils of the Southern High Plains (SHP), USA. This study examined As sorption characteristics and its interactions with soil constituents in important agricultural soils (Amarillo, Arvana, Patricia, and Pullman) of the SHP using sorption isotherm models and sequential fractionation techniques. Results from fractionation of As into five distinct pools showed that about 52.4 % of the added As was found in the exchangeable and non-adsorbed pool in the Amarillo soil, suggesting this soil could have the highest tendency to release sorbed As to the environment, whereas the Pullman soil exhibited the greatest capacity to fix As as over 45 % of the added As was found in the residual fraction. The distribution of As among the soil constituents was a reflection of the characteristics of these soils. Arsenic sorption behaviors were well described by both the Freundlich and Langmuir models. Arsenic sorption maxima (q max) was highest in the Amarillo soil (~2124 mg kg−1), followed by the Pullman, Arvana, and Patricia soils with q max values of 1692, 1370, and 1317 mg kg−1, respectively. The Freundlich distribution coefficient (K d) was highest in the Pullman soil (21.6 L kg−1) and lowest in the Amarillo (1.38 L kg−1). Sorption parameters such as K d, N (sorption intensity constant) and qmax, varied among the soils, and the variability associated with K d and N in these semi-arid soils was explained by soil properties such as pH, organic matter, calcium carbonate, total free iron (Fe), sand, clay, total aluminum, total Fe, and total manganese contents. Findings from this study are important in understanding the environmental fate of As in semi-arid/arid climates and could be extended to other regions with similar soil characteristics.