Relationship between heavy metals and dissolved organic matter released from sediment by bioturbation/bioirrigation

Organic matter (OM) is an important component of sediment. Bioturbation/bioirrigation can remobilize OM and heavy metals that were previously buried in the sediment. The remobilization of buried organic matter, thallium (Tl), cadmium (Cd), copper (Cu) and zinc (Zn) from sediment was studied in a laboratory experiment with three organisms: tubificid, chironomid larvae and loach. Results showed that bioturbation/bioirrigation promoted the release of dissolved organic matter (DOM) and dissolved Tl, Cd, Cu and Zn, but only dissolved Zn concentrations decreased with exposure time in overlying water. The presence of organisms altered the compositions of DOM released from sediment, considerably increasing the percentage of fulvic acid-like materials (FA) and humic acid-like materials (HA). In addition, bioturbation/bioirrigation accelerated the growth and reproduction of bacteria to enhance the proportion of soluble microbial byproduct-like materials (SMP). The DOM was divided into five regions in the three-dimensional excitation emission matrix (3D-EEM), and each part had different correlation with the dissolved heavy metal concentrations. Dissolved Cu had the best correlation with each of the DOM compositions, indicating that Cu in the sediment was in the organic-bound form. Furthermore, the organism type and heavy metal characteristics both played a role in influencing the remobilization of heavy metal.

Investigation of heavy metals release from sediment with bioturbation/bioirrigation

Bioturbation/bioirrigation can affect the remobilization of metals from sediments. In this study, experiments were performed to examine the effect of bioturbation/bioirrigation by different organisms on cadmium (Cd), copper (Cu), zinc (Zn) and lead (Pb) releasing from the spiked sediment. The diffusive gradient in thin films technique (DGT) revealed that at the end of exposure time, the labile heavy metals concentrations in the pore water for all metal and organisms combinations except Cu and chironomid larvae were much lower than that in the control group. However, the concentrations of heavy metals detected by the DGT were virtually indistinguishable among the treatments with tubificid, chironomid larvae and loach. The correlation analysis of heavy metals with iron (Fe) and manganese (Mn) suggested that Cd, Zn and Pb were most likely bound as Fe-Mn oxidation form in the pore water, but Cu was in other forms. After 28 d of exposure, bioturbation/bioirrigation produced a significant release of particulate heavy metals into the overlying water, especially in the treatment with loach. The bioturbation/bioirrigation impact on the Pb remobilization was less than the other three heavy metals. The effects of bioturbaiton/bioirrigation on the heavy metals remobilization in the sediment were complex that with studying the heavy metals remobilization in the sediment and water interface, the biological indicators should be recommended.