TOXICITY AND BIOAVAILABILITY OF HEAVY METALS (IN SiNGLE AND COMBINED METAL SOLUTIONS) IN THE PRESENCE OF HUMIC ACIDS

摘要

The complexation of heavy metals with humic acids (HA), as an important parameter that may alter the bioavailability and toxicity of heavy metals, was investigated in this study. The toxicity of heavy metals in the absence and in the presence of HA was investigated using the photobacterium Vibrio fischeri (Microtox test) as a test organism, while the metal species and the complexation capacity of HA were predicted using model WinHumicV for speciation modeling. In particular, this study included the investigation of the effect of HA on the toxicity of copper, zinc and lead, and the effect of HA on the toxicity of combined heavy metals solutions, as well. The results obtained from toxicity testing showed that the toxicities of copper and lead were generally comparable, while the toxicity of zinc was lower than the ones of the other two metals. The toxicity of copper decreased with the addition of HA, the toxicity of zinc remained almost constant, whereas the toxicity of lead increased. Furthermore, the interactive effects between copper and zinc and between zinc and lead were synergistic, while the interactive effect between lead and copper towards bacterium V. fischeri was additive. It was found that the mode of interaction depended on the type of pair of metals and not on the concentrations tested. The addition of HA resulted in most cases in a decrease of the toxic effect of the combined solutions, due to the formation of complexes of HA with metals (as concluded from the use of model WinhumicV). The application of model WinhumicV for the prediction of metal species that were present in the solutions showed that the toxicity of heavy metals depended not only on the free metal ion species concentration, but on different metal species that may also be bioavailable.