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Chuni L. Chakrabarti
Distinguished Research Professor
Carlton University, Department of Chemistry,  1125 Colonel By Drive, Steacie Building, Ottawa, ON  K1S 5B6, CANADA

died January 1, 2010
Chuni L. Chakrabarti
Environmental Chemistry
  • Biogeochemistry of trace metals in the natural environment
    Trace metals exist in a variety of chemical forms: free metal ions, metal ions incorporated into colloids or adsorbed onto suspended particles, small inorganic complexes and complexes with Natural Organic Matter (NOM)—each with its own unique properties. Knowledge of the metal distribution among the different physical and chemical forms (i.e. chemical speciation) is therefore essential for predicting their environmental impacts. Traditional approaches to metal speciation in the natural environment are operationally-defined (e.g. "chelex-labile" and "ASV-labile"). This simplistic approach completely neglects the complexity of freshwater systems. We propose to replace the operationally-defined categories with quantitative speciation parameters of metal complexes: dissociation rate coefficients (chemical reactivity), conditional stability constants (thermodynamic stability), and diffusion coefficients (mobility). These speciation parameters are based on the dissociation of the metal complex—a fundamental process in natural systems.
  • Bioavailability of trace metals in the freshwater environment
    Because of their versatility in a wide variety of chemical reactions, many trace metals are essential micronutrients in biological systems. However, their reactivity can also lead to toxicity even at relatively low levels. This delicate limit between trace metals as micronutrients and toxicants plays a crucial role in the balance of life. Mechanistic biogeochemical models such as the Free Ion Activity Model (FIAM) and the Biotic Ligand Model (BLM) are beginning to be applied for setting site-specific acute water quality criteria. Expanding the BLM approach to chronic toxicity and to complex effluents is highly desirable from an effluent discharge point of view, but presents significant challenges in chemistry, toxicology and modelling. The current BLM does not account for the impacts of multiple metal exposure systems where the mode of action differs, nor does it account for the effects of anthropogenic ligands. We are developing the necessary chemical speciation and chronic toxicological inputs to broaden the BLM approach to metal contaminated effluents. 

Analytical Chemistry

  • Development of novel techniques for chemical speciation of trace metals in the natural environment with special emphasis on aqueous environmental samples (e.g., freshwaters, rain water, snow-melt) and solid samples (e.g., fluvial sediments, soils).
  • Cascade Ultrafiltration for Size fractionation studies
  • Anodic Stripping Voltammetry with a Rotating Disk Electrode for physicochemical characterization
  • Adsorptive Cathodic Stripping Voltammetry
  • Competing Ligand Exchange Methods using cation exchange resins
  • Inductively-Coupled Plasma - Mass Spectrometry and Graphite Furnace Atomic Absorption Spectrometry to investigate the dissociation kinetics of the metal-complexes.

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