Analysis of antimony (Sb) in environmental samples

Metals and metalloids from ammunition residues in shooting ranges and landfills may leach into the soil and surrounding watercourses and may pose a threat to exposed wildlife and humans. To assess the mobility of metals in solid waste, classify hazardous waste and evaluate its leaching potential in a landfill, standard procedures of leaching tests are established. Such tests, both at our institute and elsewhere, have shown that antimony has a high mobility in soil. Therefore, solid waste containing Sb are often classified as hazardous materials. It is important to establish adequate methods for analysis of Sb to make proper evaluations of environmental fate of this compound, both in the field and in the laboratory. This work has evaluated some aspects about antimony analysis and fate in environmental samples compared with lead and copper. The work has focused on three main objectives: a) Evaluate recovery of Sb in soils and biological materials after extraction with different digestion methods; b) Evaluate the leachability of Sb in soil from shooting ranges with standard leaching tests in order to determine the easily exchangeable fraction of Sb; c) Compare analyses of Sb, Cu and Pb in soil between a portable XRF instrument and an ICP-MS instrument. Recoveries of Sb from microwave assisted digestion of mineral soil and peat soil were determined for three different acids: nitric acid, a combination of nitric acid and HCL (Aqua Regia) and a combination of nitric acid and hydrofluoric acid (HF). A sample of cod were, in addition, spiked with Sb and subjected to different extraction procedures. Extraction of mineral soil and peat soil with nitric acid was shown adequate for Pb and Cu, whereas Aqua Regia or HF have to be used for Sb. Approximately 5% of the total Sb-content was recovered from the mineral soil with nitric acid. HF is a highly toxic and corrosive acid and Aqua Regia is the preferable acid for Sb extraction. The recovery was dependent on extraction temperature. Biological material can be digested with nitric acid in combination with some hydrogen peroxide. The portable XRF instrument is convenient for use in the field for analysis of metals in soil. The study shows a very good correlation between actual level in mineral soils of Pb and Cu, measured with ICP-MS after Aqua Regia digestion, and XRF-analysis. The XRF tend to underestimate Pb and Cu concentration in mineral soil and overestimate the concentration in peat soil. This might be due to how the instrument is calibrated. The XRF is less suitable for Sb analysis, especially in peat soil, but may be used on grounded mineral soil if the concentration is higher than 50 mg/kg. The XRF is quite sensitive for Pb, and in shooting range soil Sb and Pb are expected to correlate. Standard leaching test shows that Sb is readily mobilized into the water fraction from contaminated soil. The mobility of Sb is higher than that of Cu and Pb and it appears that the Sb extracted with nitric acid is the mobile fraction. The concentration of Sb in the leachate was correlated with the concentration in soil.