Availability and plant uptake of heavy metals in EDTA-assisted phytoremediation of soil and composted biosolids

AbstractHeavy metals should be removed in soil for the safety of the environment, and phytoremediation, which is the use of plants to remove contaminants from the environment, can be useful in rehabilitating polluted sites. Chelating agents such as ethylenediamine tetraacetic acid (EDTA) have been used in different situations in phytoremediation to enhance the extraction of heavy metals by plants from soil. The objectives of the study were (1) to assess the availability of heavy metals in soil injected with biosolids and in composted biosolids with or without EDTA amendment, (2) to determine the efficacy of EDTA on uptake of heavy metals by sunflower plants from soil with biosolids and composted biosolids, and (3) to investigate whether EDTA applied in the previous season can reduce growth of the next crop. A laboratory and two greenhouse experiments were conducted at Kansas State University. In the laboratory, five EDTA doses were applied into the flasks with 5 g of either soil injected with biosolids (soil) or composted biosolids (compost). The soil and EDTA solution in flasks were shaken by electronic shaker for 4 h. The solution was decanted 2 h after shaking and then tested for the concentration of heavy metals by inductively coupled plasma emission spectrometry (ICP-ES). In the greenhouse, sunflower (Helianthus annuus) plants were grown in soil with biosolids and in the composted biosolids. At the flowering stage, EDTA salt at 0, 1.0, and 2.0 g/kg soil or compost was applied. Plant organs were separated and dried at the end of the trial. The concentrations of heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) were analyzed using ICP-ES. After harvesting the first greenhouse experiment and extraction of the roots, the pots were refilled with the same soil or compost and five sunflower seeds were sown to establish a second greenhouse experiment. The emergence of seedlings and plant growth was determined. In the laboratory experiment, heavy metal concentration in the solution was increased by EDTA in both soil with biosolids and the composted biosolids. The solution from composted biosolids which received EDTA had a higher concentration of heavy metals than solution from soil injected with biosolids. EDTA increased the accumulation of Cd and Ni in the roots of plants grown in the composted biosolids. Essential heavy metal (Cu, Fe, Mn, Zn) concentrations were increased in the organs of the plants grown in the composted biosolids where EDTA at 2.0 g/kg soil was applied. The concentrations of all seven heavy metals in the plant organs were not affected by EDTA in soil injected with biosolids. The high EDTA dose of 2.0 g/kg soil reduced seedling emergence and height of the plants grown in the composted biosolids

Phytoremediation of soil contaminated with heavy metals: a technology for rehabilitation of the environment

This paper reviews the chemical behaviour of heavy metals in soil, the effect of heavy metals on plants and humans, and describes phytoremediation, which is the use of green plants to remove soil contaminants. The physiological processes that support bio-accumulation of heavy metals by plants are also described

EDTA assisted phytorremediation of a Pb contamined soil: metal leaching and uptake by jack beans Lixiviação e absorção de Pb pelo feijão-de-porco assistido pela aplicação de EDTA no solo

Lead (Pb) is one of the main soil contaminants. It is also of difficult phytoremediation due to its low solubility and high retention on soil particles. EDTA application to soil is a strategy to increase heavy metal phytoextraction, but such chelants usually cause phytotoxicity and metal leaching side effects. Therefore, these research work objectives were to evaluate the effects of single (0.5 g kg-1) and split (0.25 + 0.25 g kg-1) EDTA application on Pb uptake by jack beans (Canavalia ensiformis L.) as well as on Pb vertical movement in a Pb contaminated soil material. Two sets of experiments were carried out under greenhouse conditions: in the first one, plants were grown in 3L-pots filled with a Pb-contaminated soil to evaluate Pb uptake by plants; for the second experiment, PVC-columns (42 cm height) were used to evaluate soil Pb leaching: the upper half-column (20 cm) was filled up with Pb-contaminated soil (1800 mg kg-1) whereas the lower half-column (20 cm) was filled with clean soil. Ten 60 mm-rainfalls with a duration of five hours were simulated by dropping distilled water on the top of columns, and leachates were collected for chemical analysis. Plants did not show any visual Pb toxicity symptoms or reduction in dry matter yield. Nevertheless, Pb uptake by jack beans regarded as total plant Pb accumulation was higher in EDTA-treated plants. Vertical Pb movement was observed mostly for the single EDTA application. EDTA addition to the soil favor Pb-phytoextraction by jack beans and the split EDTA application decrease the metal leaching, indicating less risk of environmental contamination.<br>O chumbo (Pb) é um dos principais contaminantes de solo. Os processos de remediação são dificultados devido à alta retenção do elemento às partículas do solo. A utilização do EDTA para aumentar a fitoextração dos metais do solo tem apresentado bons resultados. Contudo, os quelantes podem causar efeitos indesejáveis como a fitotoxidez e a lixiviação do metal. Nesse sentido, avaliou-se o efeito da aplicação única (0,5 g kg-1) e parcelada de EDTA (0,25 + 0,25 g kg-1) na absorção de Pb pelas plantas de feijão-de-porco (Canavalia ensiformis L.) e na movimentação vertical de Pb em solo contaminado, sob condições de casa de vegetação. Em um experimento, as plantas foram crescidas em vasos contendo 3 L de solo contaminado por Pb. No outro, utilizaram-se colunas de PVC com 42 cm de altura, preenchendo-se os primeiros 20 cm com solo contaminado com 1800 mg kg-1de Pb, seguido de outros 20 cm, com amostra de solo não contaminado. Nesse experimento, foram feitas dez lixiviações com água em volume equivalente a uma chuva de 60 mm cada. As plantas não apresentaram sintomas visuais de toxicidade de Pb, nem diferença na produção de massa seca do feijão em função dos tratamentos aplicados. No entanto, a absorção de Pb foi superior para as plantas que receberam EDTA. Houve movimentação vertical de Pb no solo, principalmente devido à aplicação única de EDTA. A adição de EDTA ao solo auxilia a fitoextração de Pb por plantas de feijão-de-porco e que o parcelamento do EDTA diminui a lixiviação do metal, mostrando se menos agressivo ao ambiente