Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Abstract

Laboratory experiments were carried out to examine the effects of chelating agents on heavy metal extraction from slightly contaminated dredged sediments from the port of Livorno (Italy). Ethylene diamine tetraacetate (EDTA), citric acid (CA) and humic substances (HS) were tested in two different concentrations each: 120 and 480, 500 and 2,000, 500 and 1,000 mg/l, respectively. Solubilisation of heavy metals (Cu and Zn) was observed for both EDTA and HS in the extraction kinetic experiments: 58% of the total Cu and 50% of the total Zn in the sediment were mobilised from the solid matrix using EDTA (480 mg/l) and 32% of the total Cu and 5% of the total Zn, using HS (1,000 mg/l). It was observed that solubilized metal levels were positively related to the chelating agent concentration. HS performance in the heavy metals mobilisation and phyto-toxicity tests was considered promising. HS represent an innovation in enhanced phytoextraction techniques: they can be considered an environmentally non-impacting bio-agronomic amendment. CA induced no significant effects on heavy metal mobilisation and it also negatively affects seed germination (Germination Index < 40%). Laboratory experiments with plants showed that none of the treatments significantly affected the biomass production and a trend could only be detected for the heavy metal uptake into shoots of Paspalum vaginatum sp. Transplantation of seashore paspalum is useful as a pre-treatment of contaminated dredged sediments, since it is a salt-tolerant species and it can be easily adaptable on a nutrient poor and fine textured medium.