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Clean Sampling and Analysis of River and Estuarine Waters for Trace Metal Studies
Published on: July 1, 2016
Comparative floc-bed sediment trace element partitioning across variably contaminated aquatic ecosystems
Amy V C Elliott1, Janina M Plach, Ian G Droppo
1School of Geography and Earth Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
Environmental Science & Technology
|November 19, 2011
Summary
Flocs, not bed sediments, concentrate trace elements (TEs) in aquatic ecosystems. This is due to abundant and reactive iron oxyhydroxides (FeOOH) in floc, influenced by organic matter.
Area of Science:
- Environmental Chemistry
- Aquatic Geochemistry
- Biogeochemistry
Background:
- Trace element (TE) concentrations in aquatic ecosystems are influenced by sediment composition and geochemistry.
- Flocs, distinct from bed sediments, can play a significant role in element cycling.
- Understanding TE partitioning in aquatic solids is crucial for environmental monitoring and risk assessment.
Purpose of the Study:
- To investigate the partitioning and sequestration mechanisms of trace elements (TEs) in aquatic flocs compared to bed sediments.
- To identify the primary mineral phases responsible for TE binding in flocs.
- To elucidate the role of organic matter in the formation of TE-sequestering mineral phases within flocs.
Main Methods:
- Comparative analysis of TE concentrations in floc and bed sediments across six aquatic ecosystems.
- Mineralogical characterization of floc and bed sediments, focusing on amorphous iron oxyhydroxides (FeOOH).
- Assessment of TE reactivity associated with FeOOH in both floc and sediment matrices.
- Investigation of the relationship between floc organic content and FeOOH formation.
Main Results:
- Flocs exhibited significantly higher concentrations of Ag, As, Cu, Ni, and Co than bed sediments.
- Amorphous iron oxyhydroxides (FeOOH) were the dominant phase controlling TE sequestration in flocs (30-79% of total TE concentrations), irrespective of site or element.
- Floc-associated FeOOH were more abundant and reactive than sediment-associated FeOOH, leading to enhanced TE uptake by flocs.
- Floc organic matter (live cells and exopolymeric substances) directly correlated with FeOOH concentrations, suggesting a templating role.
Conclusions:
- Flocs act as significant sinks for trace elements in aquatic environments due to the abundance and reactivity of FeOOH.
- Organic matter in flocs plays a critical role in the formation and structure of FeOOH, thereby controlling TE sequestration.
- Flocs represent a distinct solid phase with unique geochemical controls on TE behavior, differing from proximate bed sediments.
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