Shien-Tsong Ho

Chemical binding of heavy metals in anoxic river sediments.

Acid volatile sulfides (AVS) in sediments are available for binding with divalent cationic metals through the formation of insoluble metal-sulfide complexes, thereby controlling the metal bioavailability and subsequent toxicity to benthic biocommunities. However, when the molar concentrations of simultaneously extracted metals (SEM) were greater than AVS, the unexpectedly low or nondetectable levels of metal in pore water could also be found. Thus, except AVS, additional binding phases in sediments were supposed to provide the binding sites for SEM. The aims of this study are to realize the spatial distribution of AVS, SEM, and other binding phases of heavy metals in anoxic sediments of the Ell-Ren river and to elucidate what may be the main additional binding phases except AVS in the anoxic river sediments. By comparing the spatial distributions of SEM/ AVS ratio with various binding phases in extremely anoxic sediments (redox potential was between -115 and -208 mV), both organic matter and carbonates could be considered to be the main additional binding phases of SEM other than AVS. In addition, AVS appeared to have the priority to bind with SEM. By comparing the binding phases of heavy metals before and after AVS extraction, it could be found that Fe-oxides could also be considered to be the main additional binding phase associated with Zn in slightly anoxic sediments (redox potential was between -50 and -130mV), while organic matter with Cu being the next.

Correlation analyses on binding behavior of heavy metals with sediment matrices.

This article presents the amounts of heavy metals bound to the sediment matrices (carbonates, Fe-oxides, Mn-oxides, and organic matter), the correlations between any two heavy-metal binding fractions, and the correlations between sediment matrices and their heavy-metal binding fractions. Data consisted of 313 sets obtained from five main rivers (located in southern Taiwan) were analyzed by statistical methods. Among six heavy metals analyzed (Zn, Cu. Pb, Ni, Cr, and Co), the statistical results show that Zn is primarily bound to organic matter, and Cr is primarily bound to Fe-oxides. Principal component analysis (PCA) and correlation analysis (CA) result in significant correlations between carbonates bound Ni and carbonates bound Cr, Fe-oxides bound Ni and Fe-oxides bound Cr, and Mn-oxides bound Cu and Mn-oxides bound Cr. From linear regression results, the levels of the six heavy metals bound to either organic matter or Fe-oxides is moderately dependent on the contents of organic matter or Fe-oxides, especially true for Cr and Pb. According to slope values of linear regression, Cu and Cr have the highest specific binding amounts (SBA) to organic matter and Fe-oxides, respectively. A significant correlation between organic matter and organically bound heavy metals implied that organic matter contained in the sediments of the Potzu river and the Yenshui river can be adequately used as a normalizing agent. However, the six heavy metals bound to either carbonates or Mn-oxides do not correlate with carbonates or Mn-oxides. The obtained results also imply that competitions of various sediment phases in association with heavy metals occur, and organic matter and Fe-oxides are more accessible to heavy metals than other sediment phases.

Multivariate correlations of geochemical binding phases of heavy metals in contaminated river sediment.

Distributions of geochemical binding phases of seven heavy metals (Cr, Cu, Co, Zn, Ni, Pb, and Cd) in sediment cores taken from six heavily polluted sites of the Ell-Ren River in Southern Taiwan were studied. Sequential extraction procedures (SEP) were used to determine the variations of heavy metal binding phases (exchangeable, bound to carbonates, bound to manganese-oxides, bound to iron-oxides, and bound to organic matter) in different sediment depths. Multivariate analyses were used to explore the correlations among these geochemical binding phases of heavy metals. Results showed that the total amounts of various binding phases of heavy metals significantly varied with sediment depth, but their binding behaviors in various phases did not significantly change with depth. The organic matter content in the sediments increased with increasing Fe-oxide content. In addition, the binding affinities of carbonates with Zn, Pb, and Ni were higher than the affinities of carbonates with the other heavy metals. The binding affinity of Fe-oxides with Cr was higher than the affinities of Fe-oxides with the other heavy metals. Both correlation matrixes and principal component analyses demonstrated that distributions of Cu, Zn, Ni, and Cd had significant correlations with each other in both different depth horizons and various geochemical binding phases. The results indicate that these heavy metals might be discharged from the same pollution sources in the past, and also showed stable geochemical binding behaviors with the high silt sediment. However, Co had a poor correlation with the other six heavy metals in various binding phases, except with organic matter. Binding behaviors of Pb in the phases of bound to carbonates and exchangeable were different from the other six heavy metals. Cu was inversly correlated with the other six heavy metals in its binding behavior with reducible phases (Fe-/Mn-oxides).

Distribution of heavy metals in contaminated river sediment.

ABSTRACT Sediment was collected from the Ell-Ren River for analysis, to assess the influence of geochemical components in the sediment on remobilization of heavy metals into pore water and on distribution of each heavy metal in five geochemical phases (exchangeable, carbonates, Mn-oxides, Fe-oxides, and organic matters (OM)) in the sediment. Average distribution coefficients, the ratio of heavy metal in pore water to total extractable heavy metal (TEHM), were found in the decreasing order of Co, Zn, Cd, Ni, Pb, Cr, and Cu. Each of the seven heavy metals in five geochemical phases correlated positively with OM but, except for Cd, did not correlate with Fe-oxides. Pb, Zn, Ni, and Cr in pore water correlated negatively with carbonates and Mn-oxides in the sediment, and again did not correlate with Fe-oxides. Significant correlations were also observed between Zn, Cd, Ni, Pb, and Cr in pore water and OM. Principal component analysis results illustrate that the geochemical behavior of different forms of Zn, Pb, Cr, Cu, Ni, and Cd (TEHM, heavy metal in five geochemical phases, and heavy metal in pore water) in association with OM is similar.

Remobilizations of lead, nickel and copper from ELL‐REN river sediment fractions affected by EDTA, DTPA and EGTA

Batch tests were performed to illustrate the remobilization abilities of three chelating agents (EDTA, DTPA, and EGTA) on lead, nickel and copper, as well as sequential extraction method was used to realize the variation and transformation of these metals contents in sediment binding fractions. Both EDTA and DTPA had high remobilization effects at neutral pH conditions, and their remobilization effects were increased by their increasing doses. The remobilizations of lead and nickel were mainly transferred from both “bound to carbonates”; and “bound to Fe/Mn oxides”; fractions. However, the remobilization of copper were remarkably transferred from “bound to organic matter”; fraction.