SPECIATION OF ARSENIC IN A CONTAMINATED SOIL BY SOLVENT-EXTRACTION

Soil collected from a disused cattle dip in northern New South Wales w as studied with the aim of developing an inexpensive, yet effective me thod for quantitative determination of arsenic(III), arsenic(V) and to tal organic arsenic in a contaminated soil. Hydrochloric acid extracti ons were used as a method for removal of the arsenic from the soil in a form suitable for speciation. It was found that the extraction effic iency varied with the ratio of soil to acid, and the concentration of the acid. Arsenic(III), as arsenic trichloride, was selectively extrac ted into chloroform from a solution highly concentrated in hydrochlori c acid. This was followed by back-extraction of the arsenic into water . Total inorganic arsenic was determined in a similar manner after the reduction of arsenic(V) to the trivalent state with potassium iodide. Arsenic(V) was determined by the difference between the results for a rsenic(III) and total inorganic arsenic. All analyses for the various arsenic species were performed by hydride generation-atomic absorption spectroscopy; concentrations of total arsenic in the soil were confir med using X-ray fluorescence spectrometry. It was found that all the a rsenic in the soil was present as inorganic arsenic in the pentavalent state. This reflects the ability of arsenic to interchange between sp ecies, since the original species in cattle dipping solution is arseni c(III).