Cadmium in Drinking Water

Heavy metals, metals with specific density of more than 5 gm/cm3, have been used in everyday applications. Human exposure to heavy metals has immediate health concerns. Lead, Cadmium, Mercury, and Arsenic were identified as major threats to human health (Jarup, 2003). Cadmium has been commercially used in PVC products, colour pigment, alloys, rechargeable nickel-cadmium batteries and anti-corrosion agent (IFC, 1998; Jarup, 2003). Drinking water can be contaminated with Cadmium, caused by impure galvanized pipes and cadmium-containing solders in fittings, water heaters, water coolers and taps (WHO, 2011).

Cadmium is highly toxic, non-degradable and persistent element (Rao et al., 2010). Toxic form of Cadmium is free Cadmium divalent ion however other forms such as organic and inorganic ligands may produce adverse health effects (Environment Canada, 2014). Hydrated ion, inorganic and organic complex forms of Cadmium can be found in surface and ground water.  Behaviour of Cadmium in water is affected by pH, hardness, alkalinity, oxidation reduction potential and type and abundance of organic ligands and hydroxides (Environment Canada, 2014). Toxicity of Cadmium is highly influenced by water hardness, the lower the water hardness the lower the toxicity of Cadmium (Environment Canada, 2014).

Causative factors for Cadmium pollution in water include mine water from mine tailings, process water from smelters, phosphate mining and electroplating wastes (IFC, 1998). Diffuse cadmium pollution is mainly caused by fertilizers produced from phosphate ores (WHO, 2011). Soil cadmium contamination is produced from industrial emissions and the application of fertilizer and sewage sludge to farm land (Jarup, 2003). Various pollutants removal technologies can be applied to remove cadmium from drinking water. Chemical precipitation, ion exchange, cementation, solvent extraction, membrane separation and adsorption are available technologies for the removal of cadmium from water (Rao et al., 2010).

References

Environment Canada (2014) Canadian Water Quality Guidelines for the Protection of Aquatic Life [Online] Available at www.ceqg-rcqu.ccme.ca [Accessed on 23 December 2014].

International Finance Corporation (IFC)(1998) Cadmium [Online] Available at www.ifc.org [Accessed on 23 December 2014].

Jarup, L. (2003) Hazards of Heavy Metal Contamination. British Medical Bulletin, Vol 68 (1), pp 167-182.

Rao, K.S., Mohapatra, M., Anand, S and Venkateswarl, P. (2010) Review of Cadmium Removal from Aqueous Solutions. International Journal of Engineering, Science and Technology, Vol 2 (7), pp 81-103.

World Health Organization (WHO)(2011) Cadmium in Drinking Water: Background Document for Development of WHO Guidelines for Drinking Water Quality. [Online] Available at http://www.who.int [Accessed on 23 December 2014].

Super Resolution Fluorescence Microscopy

Eric Betzig, Stefan W. Hell and William E. Moerner were jointly awarded 2014 Nobel Prize in Chemistry for the development of super- resolved fluorescence microscopy. Microscope has been used as a powerful scientific instrument in the study of cell, cell biology and cellular functions. Cellular structure and objects occurs in the size range of tens to few hundreds nano meters however conventional light microscopy is only capable to handle cellular structure that are 200 to 350 nm apart (Schermelleh et al., 2010). Super resolution microscopy resolves more cellular structure at the macromolecular level.  Electron microscopy can resolve molecular and atomic structures with smaller wavelengths of electronic beam however energies of electrons have been found to be destructive for biological samples (Aguet, 3009)

Point spread function (PSF) can be defined as “the fixed size of the spread of a single point of light that is diffracted through a microscope” (Galbraith and Galbraith, 2011). Higher resolution microscopy helps to study smaller cellular structures than the PSF size of conventional microscopes. Cellular objects which are closer than PSF width of microscope appears as a single objects. Galbraith and Galbraith (2011) defined super-resolution microscopy as a technique which has at least double PSF width value than conventional microscopy.

Fluorophores are the molecules with an ability to fluoresce and fluorescence is the phenomenon where fluorophore emits light (Aguet, 2009). Fluoroscence microscopy has been used to distinguish cellular structure and specific protein by marking them (Aguet, 2009). Super resolution fluorescence microscopy has been used to study structures and functions of sub-cellular components and dynamic processes within the cell.

References

Aguet, F. (2009) Super-Resolution Fluoroscence Microscopy Based on Physical Models [Online] Available at www.bigwww.epfl.ch [Accessed on 21 November 2014].

Galbraith, C.G. and Galbraith, J.A. (2011) Super-Resolution Microscopy at a Glance. Journal of Cell Science, Vol 124, pp 1607-1611.

Schermelleh, L., Heintzmann, R. and Leonhardt, H.  (2010) A Guide to Super-Resolution Fluoroscence Microscopy. JCB Review, Vol 190(2), pp 165-175.