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Effects of chelates (EDTA, EDDS, NTA) on Phytoavailability of HMs (As, Cd, Cu, Pb, Zn) using Ryegrass (Lolium multiflorum)


 This paper summarises a study of the application of the synthetic chelate ethylenediaminetetraacetic acid (EDTA), and the natural chelates ethylenediamine-N,N-disuccinic acid (EDDS) and nitrilotriacetate (NTA) to enhance ryegrass uptake of the heavy metal(oid)s (HMs) (As, Cd, Cu, Pb and Zn) from contaminated soils in mining sites. The study compares the effects of these chelates (EDTA, EDDS and NTA) on the phytoavailability of HMs (As, Cd, Cu, Pb, Zn) using ryegrass (Lolium multiflorum) through the single addition and sequential addition methods. The results show that application of EDTA, EDDS and NTA significantly increases ryegrass’s (Lolium multiflorum) shoot uptake of some HMs when compared with no EDTA, EDDS or NTA application, particularly through sequential chelate treatment (EDTA 0.5:1 + 0.5:1; NTA 0.5:1 + 0.5:1; EDDS 0.5:1 + 0.5:1). EDTA 0.5:1 + 0.5:1 was more effective at increasing the concentration of Pb in shoots than were the other chelates (EDDS and NTA) and controls. Moreover, the concentrations of Zn in the shoots of ryegrass in LH significantly increased with the application of split dose (0.5:1 + 0.5:1). The plants displayed symptoms of toxicity including yellow and necrotic leaves at the end of the experiment. The selected chelates (EDTA, EDDS and NTA) led to a significant decrease in plant biomass (yield) 28 days after transfer with a maximum decrease in EDTA treatment (0.5:1 + 0.5:1) soils. This decrease was 3.43-fold in HT, 3-fold in LH and 1.59-fold, respectively, relative to the control. HM concentration and dissolved organic carbon (DOC) in pore water, provided an explanation for why fresh weight was significantly reduced with application of chelates in sequential dose (EDTA 0.5:1 + 0.5:1 and NTA 0.5:1 + 0.5:1).