Abstract
Dissolved organic matter (DOM) plays an important role in the environment by influencing the transport and distribution of organic and inorganic components through different processes: the retention, mobilization, and bio-availability of potentially toxic elements (PTEs). The aim of the present study is to examine the dimensional characterization of humic acids (HA) extracted from soil matrix, as well as to analyze the metal distribution among different ligand classes. The molecular size distribution of the HA extract from soil showed three dimensional classes: 52 KDa, 4.5 KDa, and 900 Da. HPSEC-ICP-MS measurements demonstrated that the dimensional classes, relative to first two fractions, bind the largest part of metals. The complexing capacity of HA was evaluated to assess the pollutants mobility in the environmental system. In particular, cadmium (Cd) and copper (Cu) complexation was investigated due to the great concern regarding their bio-availability and toxicity in natural waters. The complexing capacity of HA solution (20 mg/L) was measured by titration using a high-performance size exclusion chromatography (HP-SEC) coupled to an inductively coupled mass spectrometry (ICP-MS). Results obtained by this technique are compared with those obtained by anodic stripping voltammetry (ASV) to investigate the effects of kinetic lability of complexes on measurements carried by HPSEC-ICP-MS. In this study, results of ligand concentrations and stability constants obtained via the two techniques are assessed considering the detection window associated to the applied analytical methodology. Results obtained using the two analytical techniques showed that Cd is complexed by two classes of ligands. However, the ligand concentration values obtained using the two techniques are different, because the detection window associated to the two methodologies; the complexing capacity, which was obtained as sum of the two classes of ligands, were 33 nmol/L and 9 nmol/L for ASV and HPSEC-ICP-MS, respectively. The copper complexing capacities determined by the two methodologies are comparable: 166 and 139 nmol/L for ASV and HPSEC-ICP-MS, respectively. However, the results of Cu titration differ for the two techniques, highlighting only one class of ligands when ASV was used, and two classes when HPSEC-ICP-MS was employed. Differences on results obtained by the two techniques are explained considering the kinetic lability of complexes; the results show that, differently from previous studies, also Cu complexes can be kinetically labile, if one technique with high reaction time is used, as well some cadmium complexes are sufficient stable to be determined by HPSEC-ICP-MS.
Highlights
The development of an adequate monitoring program for toxic elements and the determination of tolerable effects require knowledge on the interaction of metals with abiotic and biotic factors, on their bio-availability and the mechanisms of metal penetration into living organisms; larger part of these processes are directly dependent from the chemical speciation of elements [1]
Differences on results obtained by the two techniques are explained considering the kinetic lability of complexes; the results show that, differently from previous studies, Cu complexes can be kinetically labile, if one technique with high reaction time is used, as well some cadmium complexes are sufficient stable to be determined by HPSEC-inductively coupled mass spectrometry (ICP-MS)
The peak number 4 cannot be attributed to a humic substances (HS) because of its small dimension, as it is lower than the inferior limit of the column used
Summary
The development of an adequate monitoring program for toxic elements and the determination of tolerable effects require knowledge on the interaction of metals with abiotic and biotic factors, on their bio-availability and the mechanisms of metal penetration into living organisms; larger part of these processes are directly dependent from the chemical speciation of elements [1]. One of the main characteristics of HS is their ability to interact with metal ions, oxides, hydroxides, mineral, and organic compounds that influence metal speciation, bioavailability, toxicity, and mobility in the environment [3,4]. The ability of HS complexation and their surface-active properties can influence the processes that control the sedimentation, bioavailability, and speciation of metals in the environment, even if they are present at trace concentrations. It has been demonstrated that HS can contribute to the reduction of metal concentrations (e.g., aluminum, Cr(VI)) [6,7] and element toxicity in water (e.g., arsenic, zinc, lead) [8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
