Induced Phytoextraction/Soil Washing of Lead Using Biodegradable Chelate and Permeable Barriers

Abstract

Chelate-induced remediation has been proposed as an effective tool for the extraction of lead (Pb) from contaminated soils by plants. However, side-effects, mainly mobilization and leaching of Pb, raise environmental concerns. Biodegradable, synthetic organic chelate ethylenediaminedisuccinic acid (EDDS), and commonly used ethylenedimanetetraacetic acid (EDTA) were used for induced phytoextraction with a test plant Brassica rapa and in situ washing of soil contaminated with 1350 mg/kg of Pb. Horizontal permeable barriers were placed 20 cm deep in soil columns and tested for their ability to prevent leaching of Pb. The reactive materials in the barriers were nutrient enriched vermiculite, peat or agricultural hydrogel, and apatite. EDTA and EDDS addition increased Pb concentrations in the test plant by 158 and 89 times compared to the control, to 817 and 464 mg/kg, respectively. In EDTA treatments, approximately 25% or more of total initial soil Pb was leached in single cycle of chelate addition. In EDDS treatments, 20% of the initial Pb was leached from columns with no barrier, while barriers with vermiculite or hydrogel and apatite decreased leaching by more than 60 times, to 0.35%. 11.6% of total initial Pb was washed from the soil above the barrier with vermiculite and apatite, where almost all leached Pb was accumulated. Results indicate that use of biodegradable chelate EDDS and permeable barriers may lead to environmentally safe induced Pb phytoextraction and in situ washing of Pb.

Enhanced phytoextraction of Cu, Pb, Zn and Cd with EDTA and EDDS

“…The current results showed that the percentage of Cu phytoextracted in one phytoextraction cycle was 0.6-1.0% of the total Cu in the soil by corn and 1.9-5.3% by beans during a 30-day period of plant growth. These values were higher than the data reported by Kos and Leštan (2003b) for Pb extraction with EDDS and EDTA, and comparable with the results of Blaylock et al (1997). Blaylock et al (1997) reported that EDTA could enhance Pb uptake in B. juncea shoots (plant Pb = 15 000 mg kg -1 ), and remove 60 kg Pb ha -1 in one harvest from soil containing 600 mg kg -1 of Pb (assuming 6 000 kg ha -1 dry weight per crop).…”

Urban environmental geochemistry of trace metals

“…Some fear that this could result in groundwater pollution and that elevated concentrations of metals in plants could have ecological implications (Boyajian and Carreira, 1997). In recent years, some easily biodegradable chelates, such as EDDS (S,S-ethylenediaminedisuccinic acid), have been proposed to enhance the phytoextraction of heavy metals from contaminated soils (Grčman et al, 2003;Kos and Leštan, 2003;Tandy et al, 2004;Luo et al, 2005). At this point, the application of phytoremediation is limited, primarily due to the lengthy time requirement and the lack of an effective and safe means to dispose of the plants.…”

Bioavailability and mobility of Pb after soil treatment with different remediation methods

“…We used [S,S]-EDDS as a chelator, in a concentration of 10 mmol/kg. [S,S]-EDDS is non-toxic, naturally present in the soil, commercially produced (Jaworska et al 1999) and, most important, [S,S]-EDDS forms an easily biodegradable complex with Pb (VanDevivere et 1 cm (Kos and Leštan 2003). The materials in the reactive barrier were substrates enabling enhanced microbial activity, which promoted efficient Pb-[S,S]-EDDS biodegradation, and adsorbents to solidify and retain released Pb.…”