Assessing the potential of Khayasenegalensis in phytoremediation of heavy metals under borehole water and tannery effluent irrigation

Khayasenegalensis was planted on soil irrigated with tannery effluent and borehole water for duration of three months. Plant samples were collected after harvest and soil samples were collected before planting and after harvesting. Atomic Absorption Spectroscopy (AAS) was used to determine the concentration of heavy metals in the planting media and plant tissues. The aim was to establish the phytoremediation potential of Khayasenegalensis under these conditions. After harvesting, a noticeable decrease in the concentrations of Cd, Cr, Cu Ni, Pb and Zn in the media was observed from the initial values. The highest levels of Cd (5.53±0.56mg/kg), Cr (13.99±0.82mg/kg), Pb(10.6110.61±0.57mg/kg, Ni (8.33±2.78mg/kg)and Zn(25.72±0.00 mg/kg) accumulation were found in the roots, whereas the highest Cu (7.29±1.80mg/kg) concentrations was observed in the shoot. The roots of Khayasenegalensis were found to be suitable for the phytostabilization heavy metals in both the tannery effluent and borehole water irrigated media. In addition, Cd, Cr, Cu, Ni and Pb mainly accumulated in the Khayasenegalensisroots. The results of translocation factors (TF) and bioconcentration factors (BCF) of Khayasenegalensis for heavy metals revealed that Khayasenegalensis is an excluder plant for Cd, Cr, Pb, Ni and Zn and a potential accumulator plant for Cu serving as an ideal remediation plant for this metal. Furthermore, the increasing heavy metal contents in soil that have been irrigated with tannery effluent resulted in the accumulation of these metals inKhayasenegalensis.

Phytoextraction of Lead: Its Feasibility, Constraints and Concerns

Aims: With lead being one of the most common soil contaminants and phytoextraction has been reported as a prospective method for remediation of lead-contaminated soil, this review aims to examine the feasibility of lead phytoextraction as well as its constraints and concerns. Study Design: This is a literature review. Methodology: Peer-reviewed papers were sourced from scholarly databases. The papers included in the review were mainly those about phytoextraction of lead, particularly with the shoot, soil and root concentrations of lead mentioned as well as the bioconcentration and translocation factors stated. Besides, papers discussing the limits, for instance, the duration of lead phytoextraction, and concerns of the approach were also included. Results: This review found only 11 plants have been reported to accumulate lead in shoots at nominal threshold of near or above 1,000 mg Pb/kg dry weight and in certain cases, soil amendment was required to achieve this. Only two of the plants had bioconcentration factor > 1 and another two had translocation factor > 1. None of the plants fulfilled all three criteria of a successful hyperaccumulator, indicating the constraints and a lack of feasibility of lead phytoextraction. Besides, lead phytoextraction has been predicted to require significant amount of time, hence increasing the risk of exposure to lead. Conclusion: This review highlights that lead phytoextraction may not be feasible for the remediation of lead-contaminated soil. It recommends phytostabilization as a more viable alternative to immobilize lead in rhizosphere and reduce lead exposure.

Hydroponic Phytoremediation of Ni, Co, and Pb by Iris Sibirica L.

Heavy metal pollution in mine wastelands is quite severe. Iris sibirica L., an emergent wetland plant, is characterized by an ability to survive under high stress of heavy metals. This study aimed to explore the phytoremediation ability of nickel (Ni), cobalt (Co), and lead (Pb) by Iris sibirica L. under hydroponic conditions. A series of tests were conducted at different metal stress conditions to evaluate the phytoextraction and tolerance of Iris sibirica L. The concentrations of Ni, Co, and Pb in plant shoots reached their highest values in 500 mg L−1 treatments, where they were 6.55%, 23.64%, and 79.24% higher than those in 300 mg L−1, respectively. The same concentrations in roots also reached their peak in 500 mg L−1 treatments, where they were 5.52%, 33.02%, and 70.15% higher than those in 300 mg L−1, respectively. Bioconcentration factors (BCF) for Ni, Co, and Pb revealed the phytoextraction ability of Iris sibirica L., and the translocation factors (TCF) showed that Ni may be most easily translocated in the plant, followed by Co and Pb. This study indicates that, compared with Ni and Co, Iris sibirica L. is more suitable for the phytoremediation of Pb-contaminated metal mine wastelands.

Response of Iron and Cadmium on Yield and Yield Components of Rice and Translocation in Grain: Health Risk Estimation

Rice consumption is a major dietary source of Cd and poses a potential threat to human health. The aims of this study were to examine the influence of Fe and Cd application on yield and yield components, dynamics of Cd in pore water, translocation factors, daily dietary intake, and estimation of human health risks. A pot experiment was performed under glasshouse conditions where rice cultivars (Langi and Quest) were cultivated in two dissimilar soils under different levels of Cd (0, 1.0, and 3.0 mg kg−1) and Fe (0, 1.0, and 2.0 g kg−1). The results showed that variation in two rice cultivars in terms of yield and yield-related components was dose dependent. Cadmium concentration in soil pore water was decreased over time and increased with increasing Cd levels but decreased with Fe application. Translocation factors (TFs) from root to straw (TFroot-straw) or straw to husk (TFstraw-husk) were higher than root to grain (TFroot-grain) or straw to grain (TFstraw-grain). The Quest cultivar had 20% lower Cd than the Langi cultivar. Application of Fe at the rate of 1 and 2 g kg−1 soil reduced Cd by 23 and 46%, respectively. Average daily intake (ADI) of Cd exceeded the permissible limit (5.8 × 10−3 mg −1 kg−1 bw per week) when rice plant subjected 1 and 3 mg kg−1 Cd stress with or without Fe application. Results also indicated that ADI value was lower in the Quest cultivar as compared to the Langi cultivar. Estimation of human health risk revealed that the non-carcinogenic risks (HQ > 1) and carcinogenic risks (CR > 1.0 × 10−4) increased with increasing Cd levels in the soil. The application of Fe decreased the human health risks from rice consumption which is more pronounced in Fe 2.0 than in Fe1.0 treatments. The rice cultivar grown in soil-1 (pH 4.6) showed the highest health risks as compared to soil-2 (pH 6.6) and the Quest cultivar had lower health risks than the Langi cultivar.

Metal accumulation capacity in indigenous Alaska vegetation growing on military training lands

Permafrost thawing could increase soil contaminant mobilization in the environment. Our objective was to quantify metal accumulation capacities for plant species and functional groups common to Alaskan military training ranges where elevated soil metal concentrations were likely to occur. Plant species across multiple military training range sites were collected. Metal content in shoots and roots was compared to soil metal concentrations to calculate bioconcentration and translocation factors. On average, grasses accumulated greater concentrations of Cr, Cu, Ni, Pb, Sb, and Zn relative to forbs or shrubs, and bioconcentrated greater concentrations of Ni and Pb. Shrubs bioconcentrated greater concentrations of Sb. Translocation to shoots was greatest among the forbs. Three native plants were identified as candidate species for use in metal phytostabilization applications. Elymus macrourus, a grass, bioconcentrated substantial concentrations of Cu, Pb, and Zn in roots with low translocation to shoots. Elaeagnus commutata, a shrub, bioconcentrated the greatest amounts of Sb, Ni, and Cr, with a low translocation factor. Solidago decumbens bio-concentrated the greatest amount of Sb among the forbs and translocated the least amount of metals. A combination of forb, shrub, and grass will likely enhance phytostabilization of heavy metals in interior Alaska soils through increased functional group diversity.

Effects of Cattails and Hydraulic Loading on Heavy Metal Removal from Closed Mine Drainage by Pilot-Scale Constructed Wetlands

This study demonstrated heavy metal removal from neutral mine drainage of a closed mine in Kyoto prefecture in pilot-scale constructed wetlands (CWs). The CWs filled with loamy soil and limestone were unplanted or planted with cattails. The hydraulic retention time (HRT) in the CWs was shortened gradually from 3.8 days to 1.2 days during 3.5 months of operation. A short HRT of 1.2 days in the CWs was sufficient to achieve the effluent standard for Cd (0.03 mg/L). The unplanted and the cattail-planted CWs reduced the average concentrations of Cd from 0.031 to 0.01 and 0.005 mg/L, Zn from 0.52 to 0.14 and 0.08 mg/L, Cu from 0.07 to 0.04 and 0.03 mg/L, and As from 0.011 to 0.006 and 0.006 mg/L, respectively. Heavy metals were removed mainly by adsorption to the soil in both CWs. The biological concentration factors in cattails were over 2 for Cd, Zn, and Cu. The translocation factors of cattails for all metals were 0.5–0.81. Sulfate-reducing bacteria (SRB) belonging to Deltaproteobacteria were detected only from soil in the planted CW. Although cattails were a minor sink, the plants contributed to metal removal by rhizofiltration and incubation of SRB, possibly producing sulfide precipitates in the rhizosphere.

Long-Term Irrigation with Treated Municipal Wastewater from the Wadi-Musa Region: Soil Heavy Metal Accumulation, Uptake and Partitioning in Olive Trees

Utilization of treated wastewater (TWW) for agricultural purposes has grown over the past few years because of limited available water resources. This study was performed to assess the long-term irrigation of treated wastewater from the Wadi-Musa region on the accumulation of heavy metals in soil and their uptake and translocation to various parts of olive trees. Fifteen year old trees that had been grown and irrigated with treated wastewater resources since their establishment were used in this study. Irrigation water, soil, and plant samples (root, stem bark, leaves, fruits) were collected and chemically analyzed for their heavy metal content. Accumulation of heavy metals in irrigation water and soil were found to be within the acceptable range for the safe use of treated wastewater according to the standards of the WHO. However, long-term and continuous irrigation with TWW resulted in significant accumulation of heavy metals in plant parts when compared to their levels in irrigation water and soil. Uptake of metals was consistent among plant parts with the highest concentrations for Fe, Mn, Pb and Zn, and the lowest concentrations for Ni, Cr and Cd. Assessment of the bioaccumulation factor (BFC) and translocation factors (TF) of heavy metals into different plant parts indicated selective absorption and partitioning of these heavy metals into different plant parts. High BCF values were observed for Fe, Cu and Ni in roots and fruits, and Fe, Mn, Cd and Pb in leaves. Translocation factors of metal ions were variable among plant parts. Fruits had the highest TF for Cu, Cd and Zn metals, and the lowest for Mn and Fe, while leaves have the highest TF for Fe, Zn and Mn and the lowest for Cd and Pb. The results of this study indicate that olive trees are heavy metal accumulators, caution should be considered in long-term use of TWW and periodic assessment of possible hazards, especially on fruits and oil quality is required.

Effects of Optimized Water Management on the Uptake and Translocation of Cadmium and Arsenic in Oryza Sativa L. In Two Contaminated Soils

Pot experiments were conducted to identify the most efficient water management strategy for reducing Cd and As accumulations and amino acid (AA) synthesis in rice in two soils with different Cd and As contents. A treatment consisting of five days of flooding followed by three days of drainage (F5D3, repeated every eight days) was identified as the most effective treatment for simultaneously decreasing Cd and As in grains, with reductions of grain Cd and As contents of more than 80.0% and 73.1%, respectively, compared with either a drained treatment or a flooded treatment alone; this is probably related to the high efficiency of the F5D3 treatment in reducing dissolved Cd and As according to its minimum “trade-off value”, due to the variations in grain Cd and As contents were significantly correlated with the variations in soil solution Cd (R2 = 0.98) and As (R2 = 0.92, p = 0.0001) concentrations. Additionally, grain Cd content was also significantly related to the organs Cd contents (especially root Cd content, R2 = 0.99) and the root-to-shoot Cd translocation factors (R2 = 0.99), whereas grain As content was significantly related to soil Eh (R2=-0.82, p = 0.003) and pH (R2 = 0.88, p = 0.0008). The AA contents in organs under the F5D3 treatment were lower than those under the Flooded and Drained treatments. These results indicated that the F5D3 treatment was the most effective water management strategy for simultaneously reducing grain Cd and As contents and AA synthesis in rice, which was probably due to there being no need for rice to synthesize abundant AAs to chelate metal ions.

Toxic Metals (As, Cd, Ni, Pb) Impact in the Most Common Medicinal Plant (Mentha piperita)

This study aimed to evaluate the behavior of Mentha piperita under Cd, Pb, Ni, and As soil contamination and their transfer from soil in plants as well as translocation in the roots/stems/leaves system compared with a control without metal addition. The mint seedlings were exposed for a three-month period using two metal mixtures in the same concentrations such as AsCd and AsCdNiPb (23.7 mg/kg As, 5 mg/kg Cd, 136 mg/kg Ni, and 95 mg/kg Pb). The results of metal concentration in plants showed that Cd, Ni, and Pb were accumulated in different parts of the plant, except for As. In plants organs, the order of metal accumulation was roots > stems > leaves. No significant impact on the growth, development, and chlorophyll content compared to the control was observed in the first month of exposure. After three months of exposure, phytotoxic effects occurred. Generally, the transfer coefficients and translocation factors values were less than 1, indicating that Mentha piperita immobilized the metals in root. The laboratory experiments highlighted that for a short period of time, Mentha piperita has the capacity to stabilize the metals at the root level and was a metal-tolerant plant when using a garden rich-substrate.