Application of SEM/EDS to environmental geochemistry of heavy metals

Abstract

Heavy metals represent a ubiquitous constituent of the near-surface environment, present in widely varying concentrations that typically have little impact on human behaviour and health. However, the mining of metals and use of these metals in industrial processes has produced significant anthropogenic inputs of metals to both local and global environments. As such, a rigorous overview of the current accumulation of heavy metals and knowledge of mineralogy of heavy metal-bearing phases is important for understanding their stability, solubility, mobility, bioavailability and toxicity. These data are of fundamental importance for environmental risk assessment and evaluation of future scenarios. Since conventional geochemical analyses provide limited information, other analytical methods have to be utilized for the characterisation of heavy metal-bearing phases. Significant analytical method for identification and characterisation of heavy metals in environmental media is a scanning electron microscope coupled with energy dispersive X-ray spectrometer (SEM/EDS), an apparatus for qualitative and semi-quantitative chemical analysis at microne level, newly introduced to Geological Survey of Slovenia. Use of SEM/EDS was already introduced to environmental studies world-wide. In Slovenia, SEM/EDS analyses of environmental media were firstly carried out on the Meža River stream sediments and snow deposits from Ljubljana urban area. Heavy metal-bearing phases in the Meža River stream sediments were apportioned to three source areas: Mežica mining/smelting area (geogenic-technogenic origin), Ravne ironworks area (technogenic origin) and the Meža River catchment area (geogenic origin), which corresponds to data obtained by conventional geochemical and multivariate statistical methods. Airborne particles, identified in urban snow deposits, were interpreted as geogenic particles, represented by fragments of heavy metal-bearing minerals, and technogenic particles that originate from combustion of solid and liquid fuels, iron and steel melting processes and road traffic emissions. SEM/EDS proved to be a very useful analytical method for the study of heavy metal-bearing phases and characterisation according to their sources and genesis.