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

Analytical electron microscopy (AEM) was used to characterize individual aquatic particles in a lake that has been contaminated by zinc smelting operations. Samples were collected from the sediments and the water column of the lake along a gradient of metal contamination. The samples were prepared to preserve their aqueous nature, and thin sections were observed by transmission 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 associations were determined for each individual particle by X-ray energy dispersive spectrometry (EDS). These analyses revealed the pervasive presence of Zn through 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 measurements, exemplify the fate of Zn in the lake by quantifying changes in elemental associations.