Fluorescence characterization of the natural organic matter in deep ground waters from the Canadian Shield, Ontario, Canada Franc ¸ois Caron • Karen Sharp-King • Stefan Siemann • D. Scott Smith Received: 16 July 2010 / Published online: 19 August 2010 Ó Akade ´miai Kiado ´, Budapest, Hungary 2010 Abstract Deep groundwater samples from a deep bore- hole in the Canadian Shield, Ontario, Canada, have been analyzed by fluorometry, to determine the difference in character of the natural organic matter (NOM) with depth. This work was done to obtain a set of geochemical char- acteristics of deep groundwaters at the site. The fluores- cence signal is a complex signature of excitation and emission of light from fluorescent molecules which are part of all natural waters. Fluorescent components have char- acteristic excitation/emission components, defined as a humic-like (C1), fulvic-like (C2), and protein-like (C3); these are found in various proportions in natural samples. Changes in relative fluorescence intensities of these com- ponents have been used in the past to determine the origin and/or processes of the NOM between sampling locations. In this work, six samples were taken at different depths, from *108 to 650 m below the surface in the borehole. The fluorescence signals of the samples showed three main patterns: (1) the shallower samples (*108, 139 and 285 m) had a pattern similar to that of surface groundwaters, dominated by components C1 and C2; (2) the samples in deep groundwaters (*620 and 650 m) had a weak overall signal, dominated by component C3; finally (3) the mid-depth sample (*503 m) had a component pattern intermediate between the shallower and deeper zones. This set of data is consistent with other data for the ground- waters from this borehole, such as chlorinity, suggesting that the three sampling intervals represent three different types of groundwaters. Keywords Fluorescence Á Natural organic matter Á Deep groundwaters Á PARAFAC Introduction Natural organic matter (NOM) is a constituent of all types of natural waters (rain, surface, groundwater, landfills, marine, etc.). Its role has been linked, among others, to a change of speciation and transport of metals and radio- contaminants [1–4], acid–base buffering of natural waters [5, 6], changes in toxicity and contaminant or nutrient uptake to biota [7–9], and concerns on the quality of drinking waters [10–12]. NOM contains molecules of dif- ferent sizes, with various functional groups and acid–base properties [5, 13–15]. It is expected that the NOM in freshwaters and groundwaters contains molecules origi- nating from the breakdown of carbohydrate residues (cel- lulose, lignin, etc.), plant residues (chloroplasts, etc.), plus the breakdown of lipids, fats, and proteins. NOM from these origins are often called terrestrial (terrigenous) or allochtonous [11, 13]. The NOM produced from secondary sources, such as exudates from biological activities, breakdown of dead biomass, and residues from the build- up of biomass is often referred to as autochtonous [11, 13]. Most allochtonous NOM in terrestrial waters is refrac- tory to degradation, as the biodegradable portion contain- ing sugars is readily assimilated. Because of its plant-based F. Caron (&) Á S. Siemann Chemistry and Biochemistry Department, Laurentian University, Sudbury, ON P3E 2C6, Canada e-mail: fcaron@laurentian.ca K. Sharp-King Environmental Technologies Branch, Chalk River Laboratories, Chalk River, ON K0J 1P0, Canada D. S. Smith Department of Chemistry, Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON N2L 3C5, Canada 123 J Radioanal Nucl Chem (2010) 286:699–705 DOI 10.1007/s10967-010-0735-x