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Characterization of freshwater natural dissolved organic matter (DOM): Mechanistic explanations for protective effects against metal toxicity and direct effects on organisms
Abstract Dissolved organic matter (DOM) exerts direct and indirect influences on aquatic organisms. In order to better understand how DOM causes these effects, potentiometric titration was carried out for a wide range of autochthonous and terrigenous freshwater DOM isolates. The isolates were previously characterized by absorbance and fluorescence spectroscopy. Proton binding constants (pK a) were grouped into three classes: acidic (pK a ≤5), intermediate (5<pK a ≤8.5) and basic (pK a >8.5). Generally, the proton site densities (L T) showed maximum peaks at the acidic and basic ends around pK a values of 3.5 and 10, respectively. More variably positioned peaks occurred in the intermediate pK a range. The acid–base titrations revealed the dominance of carboxylic and phenolic ligands with a trend for more autochthonous sources to have higher total L T. A summary parameter, referred to as the Proton Binding Index (PBI), was introduced to summarize chemical reactivity of DOMs based on the data of pK a and L T. Then, the already published spectroscopic data were explored and the specific absorbance coefficient at 340nm (i.e. SAC340), an index of DOM aromaticity, was found to exhibit a strong correlation with PBI. Thus, the tendencies observed in the literature that darker organic matter is more protective against metal toxicity and more effective in altering physiological processes in aquatic organisms can now be rationalized on a basis of chemical reactivity to protons.
Graphical abstract Display Omitted
Highlights SAC340 is strongly correlated with the other optical properties of DOM. A novel DOM quality measurement is proposed; the proton binding index (PBI). PBI should differentiate DOM based on strong metal binding potential. SAC340 is correlated to chemical reactivity of DOM as represented by PBI. PBI explains the tendency of darker DOM to be more protective in metal toxicity.
Characterization of freshwater natural dissolved organic matter (DOM): Mechanistic explanations for protective effects against metal toxicity and direct effects on organisms
Abstract Dissolved organic matter (DOM) exerts direct and indirect influences on aquatic organisms. In order to better understand how DOM causes these effects, potentiometric titration was carried out for a wide range of autochthonous and terrigenous freshwater DOM isolates. The isolates were previously characterized by absorbance and fluorescence spectroscopy. Proton binding constants (pK a) were grouped into three classes: acidic (pK a ≤5), intermediate (5<pK a ≤8.5) and basic (pK a >8.5). Generally, the proton site densities (L T) showed maximum peaks at the acidic and basic ends around pK a values of 3.5 and 10, respectively. More variably positioned peaks occurred in the intermediate pK a range. The acid–base titrations revealed the dominance of carboxylic and phenolic ligands with a trend for more autochthonous sources to have higher total L T. A summary parameter, referred to as the Proton Binding Index (PBI), was introduced to summarize chemical reactivity of DOMs based on the data of pK a and L T. Then, the already published spectroscopic data were explored and the specific absorbance coefficient at 340nm (i.e. SAC340), an index of DOM aromaticity, was found to exhibit a strong correlation with PBI. Thus, the tendencies observed in the literature that darker organic matter is more protective against metal toxicity and more effective in altering physiological processes in aquatic organisms can now be rationalized on a basis of chemical reactivity to protons.
Graphical abstract Display Omitted
Highlights SAC340 is strongly correlated with the other optical properties of DOM. A novel DOM quality measurement is proposed; the proton binding index (PBI). PBI should differentiate DOM based on strong metal binding potential. SAC340 is correlated to chemical reactivity of DOM as represented by PBI. PBI explains the tendency of darker DOM to be more protective in metal toxicity.
Characterization of freshwater natural dissolved organic matter (DOM): Mechanistic explanations for protective effects against metal toxicity and direct effects on organisms
Al-Reasi, Hassan A. (author) / Wood, Chris M. (author) / Smith, D. Scott (author)
Environmental International ; 59 ; 201-207
2013-06-07
7 pages
Article (Journal)
Electronic Resource
English
Dissolved Humic Substances Can Directly Affect Freshwater Organisms
| Online Contents | 2001