Field crops for phytoremediation of metal-contaminated land. A review

Abstract

The use of higher plants to remediate contaminated land is known as phytoremediation, a term coined 15 years ago. Among green technologies addressed to metal pollution, phytoextraction has received increasing attention starting from the discovery of hyperaccumulator plants, which are able to concentrate high levels of specific metals in the above-ground harvestable biomass. The small shoot and root growth of these plants and the absence of their commercially available seeds have stimulated study on biomass species, including herbaceous field crops. We review here the results of a bibliographical survey from 1995 to 2009 in CAB abstracts on phytoremediation and heavy metals for crop species, citations of which have greatly increased, especially after 2001. Apart from the most frequently cited Brassica juncea ( L.) Czern., which is often referred to as an hyperaccumulator of various metals, studies mainly focus on Helianthus annuus L., Zea mays L. and Brassica napus L., the last also having the greatest annual increase in number of citations. Field crops may compensate their low metal concentration by a greater biomass yield, but available data from in situ experiments are currently very few. The use of amendments or chelators is often tested in the field to improve metal recovery, allowing above-normal concentrations to be reached. Values for Zn exceeding 1,000 mg kg(-1) are found in Brassica spp., Phaseolus vulgaris L. and Zea mays, and Cu higher than 500 mg kg(-1) in Zea mays, Phaseolus vulgaris and Sorghum bicolor (L.) Moench. Lead greater than 1,000 mg kg(-1) is measured in Festuca spp. and various Fabaceae. Arsenic has values higher than 200 mg kg(-1) in sorghum and soybean, whereas Cd concentrations are generally lower than 50 mg kg(-1). Assisted phytoextraction is currently facilitated by the availability of low-toxic and highly degradable chelators, such as EDDS and nitrilotriacetate. Currently, several experimental attempts are being made to improve plant growth and metal uptake, and results are being achieved from the application of organic acids, auxins, humic acids and mycorrhization. The phytoremediation efficiency of field crops is rarely high, but their greater growth potential compared with hyperaccumulators should be considered positively, in that they can establish a dense green canopy in polluted soil, improving the landscape and reducing the mobility of pollutants through water, wind erosion and water percolation

Detection of heavy metals in common vegetables at Varaždin City Market, Croatia

“…However, of the three samples with high Zn content, only in the sample of cabbage with the highest Zn concentration (198.0 mg kg -1 ) was the concentration of Mn (19.5 mg kg -1 ) within the critical deficiency range. Regarding the nonessential heavy metals, the concentrations of As, Cd, Cr, and Pb were below the corresponding plant toxicity thresholds (15) and the concentrations of Hg were below the limit of phytotoxic effects in food crops (30).…”

“…The critical toxicity concentrations in dry weight are as follows: for Cu above 20-30 mg kg -1 (in leaves of crops), for Mn 200-5300 mg kg -1 (in shoots), for Ni above 10-50 mg kg -1 (in crops), and for Zn from 100 to above 300 mg kg -1 (in leaves of crops) (19). The concentrations of non-essential As, Cd, Cr, and Pb were compared with plant toxicity thresholds of 20, 5-10, 1-2, and 10-20 mg kg -1 , respectively (15). The concentrations of Hg were compared with a limit for phytotoxic effects in food crops of 1 mg kg -1 (30).…”

Nutritional and biochemical changes induced by lead in sunflower (Helianthus annuus L.)

“…Lamhamdi et al (2013) found that proline contents increased in leaves of T. aestivum and S. oleracea when the plants were exposed to increasing Pb concentrations. According to Verbruggen and Hermans (2008), proline contents may vary among species, and their values are up to 100 times higher in stressed plants than those in control ones. Proline accumulation is also related to stress tolerance, and concentrations of this amino acid are usually higher in tolerant than in sensitive plants (ASHRAF;FOOLAD, 2007).…”

“…When soil contains large amounts of metals, their uptake by plants is mainly affected by the bioavailability fraction (VAMERALI et al, 2010). In the case of lead, the uptake occurs either in an ionic form (Pb 2+ ) or via a passive mechanism (KABATA-PENDIAS; PENDIAS, 2011).…”

Phytofiltration of Arsenic and Cadmium From the Water Environment UsingMicranthemum Umbrosum(J.F. Gmel) S.F. Blake As A Hyperaccumulator

“…The fact that their translocation factors were less than 1 indicated partial immobilization of As in their roots and a low conveyance of As to the shoots. This immobilization reduces the phytoavailability of contaminants from the environment (Vamerali et al 2010). Pteris vittata L. has shown the highest ability to accumulate and 5 translocate As from root to shoot (Ma et al 2001).…”