Abstract:
This investigation of geochemistry and mineralogy of heavy metals in fine grained
(<63^m) sediment of the Welland River was imdertaken to: 1) describe metal dispersion
patterns relative to a source, identify minerals forming and existing at the outfall region and
relate sediment particle size to chemistry; 2) to delineate sample handling, preparation and
evaluate, modify and develop analytical methods for heavy metal analysis of complex
environmental samples.
Ajoint project between Brock University and Geoscience Laboratories was initiated
to test a contaminated site of the Welland River at the base of Atlas Speciality Steels Co.
Methods were developed and utilized for particle size separation and two acid extraction
techniques: 1) Partial extraction; 2) Total extraction.
The mineralogical assessment identified calcite, dolomite, quartz and clays. These
minerals are typical of the carbonate-shale rock basement of the Niagara Peninsula. Minerals
such as, mullite and ferrocolumbite were found at the outfall region. These are not typical of
the local geology and are generally associated with industrial pollutants.
Partial and total extraction techniques were used to characterize the sediments based
on chemical distribution, elemental behaviour and analytical differences. The majority of
elements were lower in concentration in the partial extraction technique; suggesting these
elements are bound in an acid extractable phase (exchangeable, organic and carbonate phases).
The total extraction technique yielded higher elemental concentrations taking difficult oxides
and silicates into solution.
Geochemical analyses of grain size separates revealed that heavy metal (Co, Ni, V,
Mn, Fe, Ba) concentrations did not increase with decreasing grain size. This is a function of
the anthropogenic mill scale input into the river. The background elements (Sc, Y, Sr, Mg,
Al and Ti) showed an increase in concentration to the finest grain size suggesting that it is
directly related to the local mineralogy and geology.
Dispersion patterns ofmetals fall into two distinct categories: 1) the heavy metals (Co,
Cu, Ni, Zn, V and Cr), and 2) the background elements (Be, Sc, Y, Sr, Al and Ti). The
heavy metals show a marked increase in the outfall region, while the background elements
show a significant decrease at the outfall. This pattern is attributed to a "dilution effect" ofthe
natural sediments by the anthropogenic mill scale sediments. Multivariant statistical analysis
and correlation coefficient matrix results clearly support these results and conclusions.
These results indicate the outfall region ofthe Welland River is highly contaminated
with to heavy metals from the industrialized area of Welland. A short distance downstream,
the metal concentrations return to baseline geochemical levels. It appears, contaminants
rapidly come out of suspension and are deposited in close proximity to the source. Therefore,
it is likely that dredging the sediment from the river may cause resuspension of contaminated
sediments, but may not distribute the sediment as far as initially anticipated.
