Wetlands are well known to be efficient at sequestering pollutants from contaminated water. We investigated metal accumulation in the peats of the Klip River, a natural wetland that has received contaminated water from gold mining operations in Johannesburg for over 130 years. Previous work conducted in the downstream portion identified the wetland as an important system for sequestering metals. We focused on the upstream section of the wetland, more proximal to the source of acid mine drainage, to provide a better understanding of the pollutant sources and the role of the wetland in pollutant attenuation. Geochemical and mineralogical analyses of peat cores revealed considerable metal enrichments in the peat ash, particularly in Co, Ni, Zn, Pb, Cu and U. Metal concentrations are typically between 4 to 8 times higher than those previously reported for the downstream, more distal portion of the wetland. The distribution of metal accumulation within the peat profiles suggests that contamination arises from a combination of sources and processes. Elevated concentrations in the shallow peat are attributed to the input of contaminated surface water via tributaries that drain the Central Rand Goldfield, whereas enrichments in the deeper peat suggest significant sub-surface inflow of contaminated water through the underlying dolomitic rocks. Metal immobilisation occurs through a combination of mechanisms, which include the precipitation of gypsum, metal sulfides, Fe-Mn oxyhydroxides and phosphates. Our study highlights the environmental and economic importance of natural wetland systems which have the ability to accumulate large quantities of metals and thus remediate polluted waters.
Inductively coupled plasma optical
emission spectroscopy (ICP-OES)
is one of the most commonly used analytical techniques for the measurement
of metals in environmental matrices. However, one of the drawbacks
of ICP-OES is interference, viz., spectral and nonspectral (due to
transport effects) interference. In this simple laboratory experiment,
spectral interference during ICP-OES analysis of soil samples was
investigated. The role of Fe as an interferent was highlighted upon
consideration of the analysis of Co. Students digested serpentine
soil samples with acid and quantified the Co using several different
emission lines. Since Fe is present at levels several orders of magnitude
higher than that of Co, spectral interference occurs at 236.380 nm
and at 238.892 nm for the analysis of Co. Using the data and spectral
emission plots, students selected the appropriate wavelength for quantification
and identified specific interference sources. The learning goals include
preparing samples successfully , understanding the criteria to select
wavelengths for ICP-OES analysis, and the calculating the metal concentration.
The experiment is suitable for senior undergraduate and early postgraduate
students in analytical and environmental chemistry courses.
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