Effect of EDTA and Citric acid on soil enzyme activities and phytoextraction of lead by sun flower and Indian mustard from a contaminated soil

Chelate induced-phytoextraction is one of the methods for remediation of heavy metal contaminated soils that have been attracted a lot of attention in the past decade. So far more attentions have been placed to effects of chelating agents on heavy metal solubility in soil and their uptake by plants, while there are less information about their side effects on soil environment and organisms. Soil enzyme activities can be suitable indicators to assess soil recovery after different remediation processes. The aim of this study was to evaluate the effects of EDTA and Citric acid (CA) on soil enzyme activities as well as lead (Pb) uptake by Indian mustard and sun flower.
Material and This study was conducted in a completely randomized design with factorial arrangement and three replications in greenhouse condition. The experimental factors were chelating agent treatments and plant types. The chelating agent treatments were including Control (without chelating agent), EDTA3 and EDTA5 (3 and 5 mmol EDTA per kg dry soil), CA3 and CA5 (3 and 5 mmol CA per kg dry soil). The plant species were Indian mustard (Brassica juncea) and sun flower (Helianthus annus). Also additional treatment (without Pb and without chelating agent) was considered to evaluate the effect of Pb on plant dry weight and soil enzymes activities (NP treatment).
The results showed that EDTA was more effective than CA for increasing available Pb concentration. Unexpectedly, the addition of CA into soil significantly decreased available Pb concentration compared with the control treatment. The results showed that between two studied chelating agents, the EDTA was appropriate for increasing Pb uptake by shoots and CA was appropriate for increasing Pb uptake by roots. The highest Pb uptake by root (2.99 mg Pb per pot) was observed in Indian mustard using 5 mmol CA per kg dry soil. Also the highest Pb uptake by shoot (1.74 mg Pb per pot) was obtained by Indian mustard with EDTA3 treatment. The results showed that soil treated with EDTA led to hormesis effect on dehydrogenase and phosphomonoestrase activity, GMea and TEA indices. The EDTA5 treatment decreased GMea and TEA indices while, the EDTA3 treatment increased these indices compared with the control treatment. The addition of both concentration of CA into soil significantly and considerably increased the studied soil enzyme activities as well as GMea and TEA indices compared with the control treatment.
In EDTA3 treatment the shoot Pb uptake amount was higher than control treatment and, furthermore, it improved GMea and TEA indices. The EDTA5 treatment had lower efficiency than EDTA3 in increasing of shoot Pb uptake and also it decreased GMea and TEA indices compared with the control treatment. The addition of CA into soil was probably more suitable option for Pb phytostabilization in the studied soil and also considerably increased TEA and GMea indices compared with the control and NP treatments.