Zinc speciation in a contaminated aquatic environment: Characterization ofenvironmental particles by analytical electron microscopy

Analytical electron microscopy (AEM) was used to characterize individual aq uatic particles in a lake that has been contaminated by zinc smelting opera tions. Samples were collected from the sediments and the water column of th e lake along a gradient of metal contamination. The samples were prepared t o preserve their aqueous nature, and thin sections were observed by transmi ssion electron microscopy (TEM). Zinc bearing particles were characterized by different morphologies ranging from near spherical large colloids (i.e., a few 100 nm) to small grains either intimately associated with biological templates or present as separate amorphous entities. Elemental association s were determined for each individual particle by X-ray energy dispersive s pectrometry (EDS). These analyses revealed the pervasive presence of Zn thr ough the aquatic environment and its intimate combination with Fe and P in biotic structures. The association of Zn and P was most prevalent close to the source of contamination, whereas afar Zn was primarily found in sulfur moieties. Cluster analyses, performed on four different sets of EDS measure ments, exemplify the fate of Zn in the lake by quantifying changes in eleme ntal associations.