Effects of electric fields on Cd accumulation and photosynthesis in Zea mays seedlings

Evaluation of electrokinetic-assisted phytoremediation efficiency of dibutyl phthalate contaminated soil by maize (Zea mays L.) under different electric field intensities

The excessive accumulation of dibutyl phthalate (DBP) in soil poses a serious threat to soil ecosystems and crop safety production. Electrokinetic-assisted phytoremediation (EKPR) has been considered as a potential technology for remediating organic contaminated soils. In order to investigate the effect of different electric fields on removal efficiency of DBP, three kinds of electric fields were set up in this study (1 V·cm-1, 2 V·cm-1 and 3 V·cm-1). The results showed that 59 % of DBP in soil was removed by maize (Zea mays L.) within 20 d in low-intensity electric field (1 V·cm-1), and the accumulation of DBP in maize tissues decreased significantly compared to the non-electrified treatment group. Interestingly, it could be observed that the low-intensity electric field could maintain ion homeostasis and improve the photosynthetic efficiency of the plant, thereby relieving the inhibition of DBP on plant growth and increasing the chlorophyll content (94.1 %) of maize. However, the removal efficiency of DBP by maize decreased significantly under the medium-intensity (2 V·cm-1) and high-intensity electric field (3 V·cm-1). Moreover, the important roles of soil enzyme and rhizosphere bacterial community in low-electric field were also investigated and discussed. This study provided a new perspective for exploring the mechanism of removing DBP through EKPR.

Effects of willow and Sedum alfredii Hance planting patterns on phytoremediation efficiency under AC electric field

Heavy metal contamination to soil is tricky due to its difficult removal, long retention time, and biomagnified toxicity. The green and low-cost phytoremediation with electric field treatment and planting pattern selection is an emerging and more effective approach to remove heavy metals from soils. In this study, alternating current (AC) electric field-assisted phytoremediation was examined with different planting patterns, i.e., monoculture willow (Salix sp.), monoculture Sedum alfredii Hance, and interplanting of willow and S. alfredii. AC electric field greatly increased phytoremediation efficiency to soil cadmium (Cd) regardless of planting patterns, either single plant species of willow or S. alfredii. The Cd removal capacity of willow and S. alfredii raises apparently under 0.5 V cm-1 AC electric field. Under different planting patterns of AC electric field treatment, Cd accumulation in the whole plant by interplanting was 5.63 times higher than monoculture willow, but only 0.75 times as high as monoculture S. alfredii. The results showed that AC electric field-assisted interplanting of willow and S. alfredii is a promising remediation technique for efficiently clean-up Cd-contaminated soil.

Kochia scoparia L., a newfound candidate halophyte, for phytoremediation of cadmium-contaminated saline soils

In recent years, heavy metal pollution in saline soil is increasingly severe due to the rapid development of industry and agriculture. Halophytes can survive at higher concentrations of salt and heavy metal, which make them suitable candidates for the phytoremediation of heavy metals in saline soils. In the present study, the halophyte plant Kochia scoparia (L.) Schrad. seedlings were exposed to different doses of Cd (0, 5, 10, 30 mg/kg) and NaCl (0, 200, 400, 800 mM) to explore its tolerance and phytoremediation ability for Cd. There was no significant toxic effect of Cd on the K. scoparia seedlings. NaCl reduced the biomass of K. scoparia compared with the control, but did not show any visible toxic symptom. Furthermore, Cd accumulation in K. scoparia is mainly distributed in the shoot; especially when exposed to low-Cd (5 mg/kg) treatment, the accumulation of Cd in the shoots was up to 5.42-22.25 mg/kg, which was 3.18-53.4 times of that in the roots. Moreover, the contents of glutathione and oxalate in plants increased gradually with the increase of NaCl concentration. Under the treatment of 800 mM NaCl without Cd, the content of glutathione reached the highest 51.21 μg/g, and the proportion of oxalate reached the highest 28.76% under the treatment of 30 mg/kg Cd with 400 Mm NaCl. Finally, we also found the significant alterations of cadmium chemical forms in rhizosphere soil with the addition of NaCl. Overall, K. scoparia could be an efficient and valuable candidate for the phytoextraction of low-Cd (5 mg/kg)-contaminated saline soil.

Kosteletzkya pentacarpos: A Potential Halophyte Candidate for Phytoremediation in the Meta(loid)s Polluted Saline Soils

Kosteletzkya pentacarpos (L.) Ledebour is a perennial facultative halophyte species from the Malvacea family that grows in coastal areas with high amounts of salt. The tolerance of K. pentacarpos to the high concentration of salt (0.5–1.5% salinity range of coastal saline land) has been widely studied for decades. Nowadays, with the dramatic development of the economy and urbanization, in addition to the salt, the accumulation of mate(loid)s in coastal soil is increasing, which is threatening the survival of halophyte species as well as the balance of wetland ecosystems. Recently, the capacity of K. pentacarpos to cope with either single heavy metal stress or a combination of multiple meta(loid) toxicities was studied. Hence, this review focused on summarizing the physiological and biochemical behaviors of K. pentacarpos that has been simultaneously exposed to the combination of several meta(loid) toxicities. How the salt accumulated by K. pentacarpos impacts the response to meta(loid) stress was discussed. We conclude that as a potential candidate for phytoremediation, K. pentacarpos was able to cope with various environmental constrains such as multiple meta(loid) stresses due to its relative tolerance to meta(loid) toxicity.

Risk assessment of bioavailable heavy metals in the water and sediments in the Yongding New River, North China

To explore the pollution status of heavy metals and potential risks in the Yongding New River of Tianjin, China, a comparative study of concentrations of heavy metals (Cd, Cr, Cu, Pb, Zn, As, and Hg) in surface sediments from submerged areas (SA), fluctuant flooded district (FFD), and non-flooded district (NFD) was conducted. In the present study, a modified three-stage European Community Bureau of Reference sequential extraction procedure and EDTA-Na₂ single extraction were used to determine the heavy metal distribution in different sediment samples. Results showed that Cd was the metal with the highest contamination level compared to a background value of Tianjin soils, particularly in SA, followed by As. The concentrations of Cr, Pb, Cu, and Zn were relatively higher in upstream. Cu and Pb had higher bioavailability when compared with the other metals, indicating the two metals were easier to be mobilized. The Pearson correlation coefficient is applied to assess the degree of correlation between heavy metals. As, Cu, Zn, and Hg had the strong correlation, implying they may have common sources. Human activity in the riparian such as agricultural production, vehicle, and burning coal increased inputs of heavy metals in the surface sediments and influenced their distribution spatially. Besides, we also calculated geo-accumulation indexes (I_geo) and eco-risk index to assess the degree of risk of heavy metals in sediments. The I_geo were higher in SA than in FFD and NFD. Based on I_geo and potential eco-risk index, Cd has the highest risk, followed by As and Hg.