The methodology and results of determination of inorganic arsenic species in mobile fractions of tsunami deposits by a hyphenated technique of HPLC-HG-AAS

A method of extraction has been proposed for the determination of inorganic species of As(III) and As(V) in the exchangeable fraction of sediments left by the 2004 tsunami. The method combines the fractionation of solid samples with speciation analysis by high performance liquid chromatography with hydride generation and atomic absorption spectrometry (HPLC-HG-AAS). The proposed extraction liquid is a phosphate buffer of Na2HPO4 and KH2PO4, with different concentrations of phosphate ranging from 5 to 50 mmol L-1. This method has been tested for different masses of samples as well as for different times of extraction, pH, temperature, and the presence or absence of mixing. The optimum conditions of extraction have been obtained by the use of buffer (50 mmol L-1 under pH from 5.8 to 6.2) at 80°C. The new technique was applied for the analysis of tsunami deposits left on land and sampled shortly after the tsunami (2005) and after the first (2006) and second rainy seasons (2007). The obtained results show that the exchangeable fraction of tsunami deposits was enriched in arsenic in comparison to reference soil samples. The major changes after the rainy seasons were not in the total concentration of inorganic As species, but in the ratio of As(III) to As(V). More toxic As(III) was removed from the deposits or oxidised, and after two years was hardly detectable in the tsunami deposits.