Speciation of heavy metals in landfill leachate: a review

This review focuses on the speciation methods of heavy metals present in landfill leachate, emphasizing their physical and chemical fractionations. The objective was to critically analyze existing literature concerning metal species in landfill leachate, a topic of limited investigation with less than 30 detailed samples analyzed across fewer than 15 landfills. Utilizing a combination of various speciation techniques, including physical fractionation (particulate, colloidal, dissolved) and chemical fractionation (organic and inorganic complexes, free metal ions), the study highlights the significance of colloids and complexes in determining the behavior of heavy metals in leachate. Results consistently indicate that the free metal ion represents a minor fraction, usually below 30% and often less than 10% of the total metal concentration. This has crucial implications for sampling methodologies and the assessment of metal content in leachate, particularly concerning treatment processes, toxicity evaluations, and potential environmental migration into aquifers. Therefore, the study advocates for the establishment of standardized procedures to enhance the understanding and management of heavy metal contamination in landfill leachate.