Sequential leaching of trace elements in fine-particle aerosol samples on Teflon filters

The mobility of different elements in the environment is an important factor to consider when assessing the risk of pollution. Airborne particles of micrometre or smaller sizes are known to be transported over vast distances, and may therefore affect regions far away from their sources. As a complement to the more traditional element analysis of fine-particle aerosols, the possibility of obtaining information on the element contents in particle fractions of different environmental mobilities and/or character was explored. A four-stage sequential leaching procedure was tested and applied to establish the distribution of metals in four different fine-particle fractions, namely (1) the fraction considered to be mobile in the environment, (2) the fraction bound to carbonates and oxides, (3) the fraction bound to organic matter, and (4) the fraction bound to silicates. Subtraction of energy-dispersive x-ray fluorescence (XRF) spectra was used to evaluate the element concentrations in the filters. For validation, total-reflection XRF was used in a few cases for analysis of leachates. The methods were applied to airborne particles collected in two locations in Botswana. In both locations the K, Ca, Mn, Zn, Br and Pb compounds were found to occur extensively in the environmentally mobile fraction, whereas Ti and Fe were found to dominate in the silicate fraction.