Soil Properties and Distance from Arsenic Source on Arsenic Fractionation in Soils from Ronphibun District, Nakhon Si Thammarat Province

Abstract

Ronphibun District, Nakhon Si Thammarat Province, was tin mining area and resulted in arsenic contamination in soils. Soil properties are an important factor affecting the arsenic fractionation. Therefore, soil properties and distance from arsenic source on arsenic fractionation were studied. Topsoil and subsoil samples from 12 areas within a depth of 100 cm at 0.5 to 6.0 km from arsenic source were collected. Soil properties were analysed and arsenic fractionations were determined by the sequential extraction procedure. The results showed that topsoil and subsoil had high total arsenic concentration (365.8−672.8 and 192.8−687.7 mg kg^-1 respectively) when compared with the critical level (3.90 mg kg^-1) of total arsenic in agricultural soil in Thailand. Arsenic fractionations in topsoil were mostly partitioned in the amorphous and poorly–crystalline hydrous oxides of Fe and Al fraction, followed by well–crystallized hydrous oxides of Fe and Al fraction and non–specifically adsorbed fraction was the lowest. Moreover, significantly high correlation between sum of the non–specifically adsorbed and specifically adsorbed fractions with specifically adsorbed fraction (r = 0.997**) was found and correlation between of non–specifically adsorbed and specifically adsorbed fractions with some soil properties such as organic matter (r = 0.681* and r = 0.606*), total N (r = 0.687* and r = 0.683*) and available P (r = 0.770** and r = 0.611*) were found. Whereas, total arsenic, non–specifically adsorbed and specifically adsorbed fractions decreased with increasing distance from arsenic source. The results indicated that arsenic fractions of potential release to the environment had high (23.2–49.8 mg kg^-1). Therefore, it is necessary to investigate strategies for reducing arsenic in soil.