Freshwaters are recognized as dynamic systems that may be far-removed from equilibrium. A kinetic approach using the competing ligand exchange method with Chelex 100 as the competing ligand and inductively coupled plasmamass spectrometry to measure the dissociation kinetics was used to investigate the chemical speciation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) in model solutions of a well-characterized fulvic acid (Laurentian fulvic acid) and a freshwater sample collected from the Grand River (Ontario, Canada). The kinetic distribution of the metal species were quantitatively characterized by their first-order dissociation rate constants. This kinetic speciation approach has the advantage of providing an objective method for estimating the dissociation rate constants without any a priori assumptions about the number of kinetically distinguishable components or the shape of the distribution. Three factors were found to influence the kinetics of trace metal competition in the freshwater environment: (i) metal-to-ligand ratio, (ii) ionic potential (z2/r), and (iii) ligand field stabilization energy. The results illustrate the importance of considering the valence-shell electron configuration in predicting the kinetics of trace metal competition in the freshwater environment. The markedly slow dissociation kinetics of Ni(II) and Cu(II) species suggest that the usual equilibrium assumption for freshwaters may not be valid. This study has demonstrated the ability of the kinetic model to correctly predict the relative rates of trace metal reactions, indicating that the kinetic model provides a chemically significant description of the kinetic processes in natural waters.

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For the routine determination of metals in environmental samples, we require microwave-assisted digestion methods that yield 'total' or 'near-total' recoveries while avoiding the use of HF acid. As inductively coupled plasma mass spectrometry (ICP-MS) is the method of detection, it is desirable to minimize the use of HCl to avoid spectral interferences caused by high Cl -concentrations. Using certified reference materials, we performed a series of modifications to the US EPA method 3051 which included: increasing the temperature and durations of microwave digestion, varying the ratio of sample mass to acid volume, and alterations to the compositions of the acid digestion mixture. The experiments were conducted using urban particulate matter (NIST-1648), coal fly ash (NBS-1633) and six CANMET certified reference materials (Till-2, Till-3, Till-4, LKSD-1, LKSD-2 and LKSD-4), in two laboratories (Health Canada and Environment Canada) using different microwave digestion systems and different ICP-MS instruments. Our modified microwaveassisted nitric acid digestion method improved recoveries for Pb, Zn, V, Fe and Cu approaching 'total' recoveries in the same matrices determined using Xray fluorescence (XRF) and instrumental neutron activation analysis (INAA) as reported in the certificates of analysis. Recoveries for other elements such as Cr and Ni compared well with 'near-total' recoveries yielded by traditional (non-assisted) acid digestion methods.

Trace elements, especially those associated with fine particles in airborne particulate matter (PM), may play an important role in PM adverse health effect. The aim of this paper is to characterize elements in a wide particle size range from nano (57-100 nm) to fine (100-1,000 nm) and to coarse (1,000-10,000 nm) fractions of two urban PM samples collected in Ottawa. Size-selective particle sampling was performed using a micro-orifice uniform deposit impactor, and element concentrations were determined in each different size fraction by inductively coupled plasma-mass spectroscopy. A general trend of increasing element concentration with decreasing aerodynamic diameter was observed for elements V, Mn, Ni, Cu, Zn, Se, and Cd, indicating they were predominately concentrated in the nanoparticle size range. Other elements including Fe, Sr, Mo, Sn, Sb, Ba, and Pb were predominately concentrated in the fine-size range. Increased concentration of elements in the nano and fine particle size range is significant due to their ability to penetrate into the deepest alveolar area of the lungs. This was confirmed by the calculation of median concentration diameters, which were less than 800 nm for most of the investigated elements. Particle size distribution and element correlation analysis suggest that the elements concentrated in the nano-and fine-size fractions originated mainly from vehicular combustion and emission. Long-range airborne transport and soil or road dust resuspension may also contribute. Particle size had an important effect on element bioaccessibility for the studied urban PM samples showing a general trend of increasing element bioaccessibility with decreasing particle size. These results emphasize the importance of acquiring information on nano and/or fine PM-bound elements and their bioaccessibilities for accurate element and PM exposure assessment.