Compound amino acids added in media improved Solanum nigrum L. phytoremediating CD-PAHS contaminated soil

Amendments and bioaugmentation enhanced phytoremediation and micro-ecology for PAHs and heavy metals co-contaminated soils

Co-existence of polycyclic aromatic hydrocarbons (PAHs) and multi-metals challenges the decontamination of large-scale contaminated sites. This study aims to comprehensively evaluate the remediation potential of intensified phytoremediation in coping with complex co-contaminated soils. Results showed that the removal of PAHs and heavy metals is time-dependent, pollution-relevant, and plant-specific. Removal of sixteen PAHs by Medicago sativa L. (37.3%) was significantly higher than that of Solanum nigrum L. (20.7%) after 30 days. S. nigrum L. removed higher amounts of Cd than Zn and Pb, while M. sativa L. uptake more Zn. Nevertheless, amendments and microbial agents significantly increased the phytoremediation efficiency of pollutants and shortened the gap between plants. Cd removal and PAHs dissipation reached up to 80% and 90% after 90 days for both plants. Heavy metal stability in soil was promoted after the intensified phytoremediation. Plant lipid peroxidation was alleviated, regulated by changed antioxidant defense systems (superoxide dismutase, peroxidase, catalase). Soil enzyme activities including dehydrogenase, urease, and catalase increased up to 5-fold. Soil bacterial diversity and structure were changed, being largely composed of Proteobacteria, Actinobacteria, Patescibacteria, Bacteroidetes, and Firmicutes. These findings provide a green and sustainable approach to decontaminating complex-polluted environments with comprehensive improvement of soil health.

The effects of different electrode materials on seed germination of Solanum nigrum L. and its Cd accumulation in soil

The effects of different electrode on Solanum nigrum L. seed germination were determined. The result showed that germination percentage (GP) of seeds in treatment T2 (titanium electrode) was 26.6% higher than in control (CK, without electric field). High potassium and calcium concentrations were beneficial for seed enzymatic activity in treatment T2, which could partly explain the increase in GP. Cd accumulation (μg/pot) in S. nigrum treated with any electric field was significantly higher (p<0.05) than in CK without electric field. Specifically, Cd accumulation under the treatment T3 (stainless steel electrode) was the highest both in roots and shoots; this accumulation in shoots and roots were 74.7 % and 67.4 % higher for stainless steel than in CK. This increase must have been associated with a higher Cd concentration in plants and did not exert a significant effect on the biomass. In particular, Cd concentrations in roots and shoots under stainless steel treatment were both significantly higher than in CK (p<0.05), which had to be related to the higher available Cd concentration in the soil in the middle region. Furthermore, it could be attributed to altered soil pH and other soil properties. Moreover, none of the biomasses were significantly affected (p<0.05) by different electrode materials compared to CK.

Strong accumulation capacity of hyperaccumulator Solanum nigrum L. for low or insoluble Cd compounds in soil and its implication for phytoremediation

This experiment is to explore whether one hyperaccumulator shows the strongly accumulative capacities for low or insoluble Cd compounds in soil. Soil potting experiment was conducted to analyze the accumulation capacity of Solanum nigrum L. for 10 different Cd compounds under two levels. The results clearly indicated: The Cd concentrations of shoots and roots were very high for different Cd compounds in soils even with low or insoluble Cd compounds compared with easily soluble Cd in the treatments of soil contaminated with Cd at different concentrations. Furthermore, the EFs and TFs were all larger than 1 either. Based on the results, although the bioavailabilities of some Cd compounds in soil were lower, S. nigrum's ability to accumulate them was still very strong. Phytoremediation may be widely used to treat with soil contaminated by different cadmium compounds. In addition, the total Cd content is also very important in evaluating the risk of Cd contamination in soil. Thus, phytoextraction is promising.

Assessment of nutrients effect on the bioaccessibility of Cd and Cu in contaminated soil

Soil is considered as a sink for heavy metals. Human health is severely affected by the continuous intake of toxic heavy metals even in a very low concentration. In the present experiment, we determined the influence of nutritional status including control (fasted condition), glucose (fed state), plant protein (fed state), animal protein (fed state) and calcium (fed state) on soil cadmium (Cd) and copper (Cu) bioaccessibility using physiologically-based extraction test (PBET) method together with simulator of the human intestinal microbial ecosystem (SHIME) model. The bioaccessibility of Cd was 1.06-73.58%, 0.44-54.79% and 0-17.78% and Cu was 3.81-67.32%, 4.98-71.14%, and 0-17.54% in the phase-I, phase-II and Phase-III respectively (in this study gastric phase, small intestinal phase and colon phase were considered as phase-I, phase-II and Phase-III respectively). The outcomes showed that, the average Cd bioaccessibility was higher with animal protein addition compared with other treatments in different phases. So, the effect of animal protein on Cd bioaccessibility was higher than other treatments in the phase-I, phase-II and phase-III. Due to the addition of plant protein, the higher average bioaccessibility of Cu was noticed in phase-I and phase-II in comparison to other treatments. However, in phase-III, the higher average bioaccessibility of Cu was found due to control treatment comparing with other treatments. Therefore, the influence of plant protein was higher than other nutrients on Cu bioaccessibility in the phase-I and phase-II. Moreover, other nutrients showed variable influence on Cd and Cu bioaccessibility. So, nutritional status has a significant effect on bioaccessibility as well as human health risk assessment.

Glycine transformation induces repartition of cadmium and lead in soil constituents

Heavy metal stress in soil accelerates the plant root exudation of organic ligands. The degradation of exudate ligands can be fundamental to controlling the complexation of heavy metals. However, this process remains poorly understood. Here, we investigated the relationship between the transformation of glycine, a representative amino acid exudate, and cadmium/lead mobility in soils. Two 48-h incubation experiments were conducted after glycine addition to the soils. Parameters related to glycine distribution and degradation, Cd/Pb mobility, and the formation of glycine-Cd complex were analyzed. Glycine addition gradually decreased the Cd and Pb mobility throughout the 48-h incubation. By the end of the experiment, the CaCl₂-extracted Cd and Pb concentrations decreased by 63.5% and 43.6%, respectively. The glycine mineralization was strong in the first 6 h, as indicated by a sharp decrease in CO₂ efflux rates from 10.04 ± 0.62 to 3.51 ± 0.07 mg C-CO₂ kg^-1 soil h^-1. The mineralization rates notably decreased after 6 h. The comparisons of dissolved organic carbon and hydrolyzable amino acid contents indicated that glycine mineralization in solution (95.6%) was much stronger than that in soil solids (49.3%). At the end of incubation, 0.22 mmol kg^-1 glycine remained in soil solids. The remaining glycine provided sufficient sorption sites for Cd²⁺ and Pb²⁺, resulting in enhanced metal fixation via complexation. Comparisons of zeta potentials supported the formation of the glycine-Cd complex. The Cd and Pb immobilization processes could be attributed to metal-glycine complex formation, sorption re-equilibrium, and glycine degradation. These findings emphasize that the biogeochemical processes of glycine, derived from root exudates or protein degradation products, increased the sorption of heavy metals to soils and thus reduced their toxicity to plants.

Effect and mechanism of commonly used four nitrogen fertilizers and three organic fertilizers on Solanum nigrum L. hyperaccumulating Cd

Solanum nigrum L. is a hyperaccumulator and shows very high phytoremediation potential for Cd-contaminated soil. Fertilizer addition to soil is an effective pathway to improve Cd hyperaccumulation. This article compared the strengthening roles of commonly used four nitrogen fertilizers with three organic fertilizers on S. nigrum hyperaccumulating Cd at the same total nitrogen level. The results showed that Cd concentrations in roots and shoots of S. nigrum were not affected by the addition of inorganic nitrogen like NH₄HCO₃, NH₄Cl, (NH₄)₂SO₄, and CH₄N₂O compared with the control without nitrogen addition. However, Cd concentrations in S. nigrum roots and shoots were significantly decreased (p < 0.05) when the organic nitrogen was added in the form of chicken manure, pig manure, and commercial organic fertilizer (by 15.6% and 15.1%, 30.1% and 23.6%, 20.3% and 16.8%, respectively). On the other hand, of all nitrogen treatments, the addition of (NH₄)₂SO₄ and CH₄N₂O to the soil enormously increased S. nigrum biomass, i.e., S. nigrum shoot biomass increased 2.0- and 2.1-fold compared with the control. Correspondingly, Cd loads in S. nigrum shoots were also the highest in former two treatments and amounted to 79.91 μg pot^-1 and 80.17 μg pot^-1, respectively. Compared with the control, the addition of three organic fertilizers significantly increased (p < 0.05) pH and decreased (p < 0.05) available Cd concentrations in the soil, which could be the main reasons for their negative effects on S. nigrum accumulating Cd. (NH₄)₂SO₄ and CH₄N₂O significantly increased S. nigrum biomasses and exerted no effects on the available soil Cd concentration, which made them more better fertilizers in practice. In general, the same fertilizer may show different effects on different hyperaccumulators. The selection of fertilizer should be decided in accordance with the specific conditions in the phytoremediation practice of contaminated soil.

Ornamental hyperaccumulator Mirabilis jalapa L. phytoremediating combine contaminated soil enhanced by some chelators and surfactants

Mirabilis jalapa L. is an ornamental plant of the composite family, which was found hyperaccumulating Cd. Due to its larger biomass, developed root system, root exudation, and microbial interactions, certain organic pollutants in its rhizosphere can be effectively degraded. Thus, M. jalapacan be used to co-remediate heavy metal and organic pollutant co-contaminated soil. The aim of this paper is to explore the remediation capacity of M. jalapa for Cd-PAHs co-contaminated soil in the presence of five chelators or surfactants. The concentrations of Cd and PAHs in collected soil samples were 0.85 mg kg^-1 Cd and 1.138 mg kg^-1 PAHs (16 kinds of priority control polycyclic aromatic hydrocarbons by USEPA). The chelators or surfactants of EDTA, EGTA, CA, TW80, and SA were respectively spiked to the pots according to the experiment design at 1 month before the plant harvested. The results showed that the capacity of Cd in shoot of M. jalapa was 7.99 μg pot^-1 without any addition (CK4, M. jalapa in original soil without amendment). However, Cd capacity in shoot of M. jalapa was increased (p < 0.05) by 31.7%, 181.7%, and 107.4% in treatment of R_EGTA, R_CA and R_{EGTA + SA}, respectively. As for the degradation of PAHs in soil, there was no significant decrease (p < 0.05) in the treatment of CK2 (original soil spiked with 0.9 SA without M. jalapa), CK3 (original soil spiked with 0.3 TW80 without M. jalapa), and CK4 compared to the control CK1 (original soil without M. jalapa and amendment). When amendments were added to soils with M. jalapa,the PAHs concentrations in soils significantly decreased (p < 0.05) by 21.7%, 23.8%, 27.0%, 19.8%, 21.8%, 31.2%, and 25.5% for the treatment of R_{EDTA + SA}, R_{EDTA + T80}, R_{EGTA + SA}, R_{EGTA + T80}, R_{CA + T80}, R_{SA + T80 + EDTA}, and R_{SA + T80 + CA}, respectively. Basically, Cd capacity in shoot of M. jalapa was improved by chelators. PAHs degradation was caused by the existence of surfactants in rhizosphere of M. jalapa. But the roles of different chelators or surfactants were quite distinct. In short, the Cd capacity in the shoot and PAHs degradation in the rhizosphere of M. jalapa in the treatment of R_{EGTA + SA} were all significantly increased (p < 0.05), which was more practical for M. jalapa phytoremediating Cd-PAHs co-contaminated soil.

Ectopic expression of SaNRAMP3 from Sedum alfredii enhanced cadmium root-to-shoot transport in Brassica juncea

SaNRAMP3 gene cloned from a Zn/Cd hyperaccumulator Sedum alfredii was ectopicly expressed in Brassica juncea, a fast-growing and high-biomass crop plant. In a tissue culture experiment, transgenic plants were grown on MS medium with 0, 25, 50, 100, 200 μM Cd. It was shown that, at the same Cd treatment, the Cd tolerance of transgenic plants had no significant difference with those of wild-type plants (WT). However, the shoot Cd content and accumulation were improved significantly while the root Cd content and accumulation were descended significantly by SaNRAMP3 gene expression, which obviously enhanced the Cd root-to-shoot translocation factor (TF). In the hydroponic experiment, plants were cultured in nutrition solution with 0, 2.5, 25 μM Cd. Data showed that the Cd tolerance of transgenic plants had no significant difference with that of WT under the same Cd exposure. Whereas, the shoot Cd content and accumulation was increased 1.43-1.81 times and the TF was enhanced 3.09-3.51 times by SaNRAMP3 gene expression. Those results indicated that ectopic expression of SaNRAMP3 in B. juncea didn't lead to Cd sensitivity, but enhanced Cd root-to-shoot transport, so that increased shoot Cd accumulation. This study provided a possibility to improve phytoextraction efficiency of heavy metal through gene engineering.

Enhanced phytoremediation of cadmium and/or benzo(a)pyrene contaminated soil by hyperaccumlator Solanum nigrum L

The role of same amendment on phytoremediating different level contaminated soils is seldom known. Soil pot culture experiment was used to compare the strengthening roles of cysteine (CY), EDTA, salicylic acid (Sa), and Tween 80 (TW) on hyperaccumulator Solanum nigrum L. phytoremediating higher level of single cadmium (Cd) or Benzo(a)pyrene (BAP) and their co-contaminated soils. Results showed that the Cd capacities (ug pot^-1) in shoots of S. nigrum in the combined treatment T_{0.1EDTA+0.9CY} were the highest for the 5 and 15 mg kg^-1 Cd contaminated soils. When S. nigrum remediating co-contaminated soils with higher levels of Cd and BAP, that is, 5 mg kg^-1 Cd + 1 mg kg^-1 BAP and 15 mg kg^-1 Cd + 2 mg kg^-1 BAP, the treatment T_{0.9CY+0.9Sa+0.3TW} showed the best enhancing remediation role. This results were different with co-contaminated soil with 0.771 mg kg^-1 Cd + 0.024 mg kg^-1 BAP. These results may tell us that the combine used of CY, SA, and TW were more useful for the contaminated soils with higher level of Cd and/or BAP. In the combined treatments of Sa+TW, CY was better than EDTA.

Hyperaccumulating potential of Bidens pilosa L. for Cd and elucidation of its translocation behavior based on cell membrane permeability

Phytoremediation with the use of hyperaccumulating plant species to remove excess trace metals from contaminated soil and water is considered a cost-effective non-invasive technique. Over 400 plant taxa worldwide have been identified as natural hyperaccumulators, but only very few are reported to hyperaccumulate Cd. Bidens pilosa L. is a newly found, promising Cd hyperaccumulator, although its potential to accumulate Cd and mechanism of this process are not yet well known. This paper was aimed at exploring hyperaccumulation capacity of B. pilosa for Cd, and its translocation behavior related to cell membrane permeability. The highest Cd concentration in shoots of B. pilosa grown in soil was 405.91 mg kg^-1 and of that cultured in nutrient solution 1651.68 mg kg^-1, indicating very high accumulation potential. Cd concentrations in the root, stem, leaf, and shoot of B. pilosa cultured in nutrient solution were all much higher than those in soil, while biomass development was considerably lower. This resulted in lesser differences between Cd maximum accumulation loads in the shoot (462 and 365 μg pot^-1) and in the root (100 and 96 μg pot^-1) of B. pilosa grown in solution and in soil, respectively. Relative electric conductivity (REC), K⁺ relative permeability ratio, and MDA (malondialdehyde) contents, which are major indices expressing cell membrane permeability, appeared to be closely related to Cd translocation and accumulation. The relative molecular mechanism of Cd accumulation/translocation in B. pilosa was found of importance and needs to be elucidated.

Remediation of heavy metal contaminated soils by using Solanum nigrum: A review

Heavy metals are among the major environmental pollutants and the accumulation of these metals in soils is of great concern in agricultural production due to the toxic effects on crop growth and food quality. Phytoremediation is a promising technique which is being considered as an alternative and low-cost technology for the remediation of metal-contaminated soils. Solanum nigrum is widely studied for the remediation of heavy metal-contaminated soils owing to its ability for metal uptake and tolerance. S. nigrum can tolerate excess amount of certain metals through different mechanism including enhancing the activities of antioxidant enzymes and metal deposition in non-active parts of the plant. An overview of heavy metal uptake and tolerance in S. nigrum is given. Both endophytic and soil microorganisms can play a role in enhancing metal tolerance in S. nigrum. Additionally, optimization of soil management practices and exogenous application of amendments can also be used to enhance metal uptake and tolerance in this plant. The main objective of the present review is to highlight and discuss the recent progresses in using S. nigrum for remediation of metal contaminated soils.