Complexation of Dissolved Organic Matter with Trace Metal Ions in Natural Waters

Toxic metals (Ni2+, Pb2+, Hg2+) binding affinity of dissolved organic matter (DOM) derived from different ages municipal landfill leachate

“…Figure 2 shows the changes in fluorescence spectra of DOM samples before and after complexation titrations. This was the result of complexation of metal with fluorophores present in DOM which can alter the DOM fluorescence intensity (Mostofa et al 2013). Decreasing fluorescence intensities (in RU) after addition of metals were observed for each sample.…”

“…The excitation-emission maxima of L-3 was at 355/436 nm and it was shifted at 355/436-442 nm, 355/436-446 nm and 355-450/436-526 , respectively. These red shifts might be contributed by the formation of metal complexes with fluorophores or functional groups (Mostofa et al 2013) that also resulted in reduced fluorescence intensities.…”

The mechanism behind the DOM effects on methylmercury photodegradation

“…In contrast, much weaker interactions (K 0 DOM = 1010.7±1.0 L/kg) are observed at Hg/DOM ratios above approximately 10 lg Hg/mg DOM, coherently with Hg binding to oxygen functional groups [8]. The second issue is that p-electrons are loosely bound and they are highly susceptible to radiative excitation [7]. The ligand-to-metal charge transfer could be triggered by the photolysis of the complex H 3 CHg + DOM (where the "" indicates electron donation), which could take place as follows (Eq.…”

“…A couple of considerations may help in shedding some light over this issue and could provide scope for further research in the field. The first issue is the formation of p-electron bonding systems between CH 3 Hg + [Hg 1+ = 1s22s22p63s23p64s23d104p65s24d105p66s14f145d10] and DOM (CH 3 Hg-DOM), through electron donation from the functional groups of high molecular weight DOM to an empty sorbital of CH 3 Hg + (ligand-to-metal charge transfer) [7]. Note that the p-electron bonding system is not formed with low-molecular-weight DOM, because the formed complex would not be stable enough.…”

“…(2)) would not occur, because irradiated Hg cannot release its outer electron from the s-orbital and also because of the high availability of hydrated electrons in waters under the light condition [7,10]. The occurrence of inorganic compounds can also be important: for instance, increasing salinity can decrease the photodegradation of CH 3 Hg + by several processes [3], including: (1) the scavenging of HO • by bromide (the main HO• scavenger in seawater) [7,10] and (2) the different speciation of the CH 3 Hg + cation in seawater compared to freshwater. In seawater, the formation of stable complexes/ ion pairs with anions such as Cl-and Br-may hinder the formation of the photolabile species H 3 CHg + DOM.…”