Journal of Agricultural Science; Vol. 11, No. 6; 2019 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 260 Arsenic in Soils: Natural Concentration and Adsorption by Oxisols Developed From Different Lithologies Maurício P. F. Fontes 1 , Cecília C. Almeida 1 , Adriana C. Dias 1 , Sandro M. Caires 2 & Guilherme F. Rosa (in memoriam) 3 1 Soil Science Department, Universidade Federal de Viçosa, Viçosa, MG, Brazil 2 Instituto Federal do Mato Grosso, Juína, MT, Brazil 3 Chemistry Department, Universidade Federal de Viçosa, Viçosa, MG, Brazil Correspondence: Adriana C. Dias, Soil Science Department, Universidade Federal de Viçosa, Viçosa, MG, 36570-900, Brazil. E-mail: dias.adrianacristina@yahoo.com.br Received: February 9, 2019 Accepted: March 12, 2019 Online Published: May 15, 2019 doi:10.5539/jas.v11n6p260 URL: https://doi.org/10.5539/jas.v11n6p260 Abstract Arsenic (As) is a toxic and a carcinogenic element naturally occurring in the environment. Therefore, studies on As natural concentration in soils and its adsorption process are important tools for the evaluation of potential risks of soil contamination in order to adoption of control actions or monitoring of potential As-contamination sources. The objective of this study was to evaluate the natural levels of As and determine the maximum adsorption capacity of As (MACAs) of six Oxisols (Latossolos) of Minas Gerais State, Brazil, developed from different lithologies. The soil sample’s total As content was determined using the USEPA 3051A method. The adsorption experiments were performed using different As concentrations, and the MACAs was measured by the Langmuir isotherm. On average, the natural As content in Oxisols was 13.13 mg kg -1 , which is above the reference value of soil quality (RVQ) for As, in Brazil (8 mg kg -1 ). The levels of As in Oxisols originated from metamorphic/igneous rocks were significantly higher than those of Oxisols from sedimentary rocks. Globally, the evaluated soils showed a mean MACAs equal to 2,548 mg kg -1 . Soil horizon Bw showed a higher MACAs than that of A horizon. In general, the levels of clay, iron oxides, iron forms (especially poorly-crystallized) and organic carbon had a positive influence on MACAs. Although the RVQ for As is well below the MACAs in all soils, the soil adsorbed As naturally present, rendering it unavailable in the soil aqueous phase. Therefore, there was no risk of contamination for human health. Keywords: toxic element, maximum adsorption capacity, soil horizon, reference value of soil quality, environmental pollution 1. Introduction Arsenic (As) is a toxic and carcinogenic element. After the analytical detection of elements in solution has been improved in the last decades, relationships were established between very low As concentrations and (i) some cancer forms (skin, lung, liver, bladder, kidney, and colon), (ii) other common diseases (cardiovascular diseases, diabetes, and anemia), (iii) neurological changes, and (iv) reproductive and immunological dysfunctions in humans (Aviñó et al., 2008). This metalloid is widely distributed in the environment and occurs in the Earth’s crust at concentrations between 0.5 and 2.5 mg kg -1 . However, contents above 13 mg kg -1 can be found in clayey sediments (Kabata-Pendias & Mukherjee, 2007). According to the World Health Organization (WHO, 2001), the levels of As naturally occurring in soils vary from 1 to 40 mg kg -1 , with an average of 5 mg kg -1 . Arsenic mobility depends largely on geochemical environmental characteristics, mainly pH, redox potential, and adsorption and desorption equilibrium, which are controlled by soil mineral and organic matrices. Oxide surfaces, especially iron (Fe), aluminum (Al), and manganese (Mn) oxides, have a high affinity for As (Cui & Weng, 2013), influencing the mobility of this element in the environment. Brazilian climatic conditions increase the weathering degree of Oxisols (Latossolos), wherein the clay fraction is predominantly composed of kaolinites, and Fe and Al oxides (Fontes & Weed, 1991).