In situ transformations of fine lead oxide particles in different soils.

We present a field application of a new in situ technique to analyze phase transformations of fine lead oxide particles (50-100mum) in different soils directly in the field over 18 months. After the first month of exposure to a calcareous sand we found newly precipitated secondary mineral phases on the lead oxide. The samples exposed to two loamy soils (Dystric Cambisol and Luvisol) showed only very few traces of new phases. We identified the new phases as mainly lead-hydroxy carbonates (hydrocerussite). Whereas the results confirm the transformation of lead phases to lead carbonates in calcareous soil, they also show that an easily soluble phase such as PbO may persist in soils virtually unweathered for more than one year. The formation of a weathering crust is therefore not necessarily needed for preservation of easily soluble phases. The use of experimental in situ methods is thus giving new information on contaminant mineral behavior under field conditions.