Metal availability, soil nutrient, and enzyme activity in response to application of organic amendments in Cd-contaminated soil

Effects of tea infusion on selenium uptake in grapevine

Increased selenium (Se) content in fruits can supply Se in human body, but the effects of teas on the Se uptake in fruit trees are unknown. The effects of infusions of four teas (green, black, dark, and white) on the Se uptake of grapevine were studied to promote the Se uptake in fruit trees in this study. However, only black tea infusion increased the biomass, photosynthetic pigment content, superoxide dismutase (SOD) activity, peroxidase (POD) activity, and soluble protein content of grapevine. Except for white tea infusion, other tea infusions also increased the catalase (CAT) activity of grapevine. Furthermore, the tea infusions increased the activities of adenosine triphosphate sulfurase (ATPS) and adenosine 5'-phosphosulfate reductase (APR), and decreased the activities of serine acetyltransferase (SAT) and selenocysteine methyltransferase (SMT). Only the dark and white tea infusions increased the shoot total Se content by 86.53% and 23.32%, respectively (compared with the control), and also increased the shoot inorganic Se content and shoot organic Se content. Notably, four tea infusions decreased the organic Se proportion and increased the inorganic Se proportion in grapevine. Correlation and grey relational analyses showed that the root total Se content, ATPS activity, and ARP activity were closely associated with the shoot total Se content. The principal component and cluster analyses also showed that the ATPS activity, APR activity, root total Se content, and shoot total Se content were classified into one category. These findings show that black tea infusion can promote grapevine growth, while dark and white tea infusions can promote the Se uptake in grapevine.

Enhanced simultaneous removal of phosphate and ammonium from swine wastewater using magnetic magnesium-loaded Chinese herbal medicine residues: Performance, mechanism, and resource utilization

Magnetic magnesium (Mg)-loaded Chinese herbal medicine residues (MM-TCMRs) were fabricated to simultaneously remove and recover phosphate and ammonium from wastewater. The MM-TCMRs exhibited larger specific surfaces and rougher structures with massive spherical particles than those of original residues. They could be separated by adjusting the magnetic field. The phosphate and ammonium adsorption by MM-TCMRs were matched with the pseudo-second-order model, while the Langmuir model yielded the maximum adsorption capacities of 635.35 and 615.57 mg g-1, respectively. Struvite precipitation on the MM-TCMRs surface was the primary removal mechanism with electrostatic attraction, ligand exchange, intra-particle diffusion, and ion exchange also involved. The recyclability of MM-TCMRs confirmed their good structural stability. More importantly, the nutrient-loaded MM-TCMRs enhanced alfalfa growth and improved soil fertility in planting experiments. Collectively, the MM-TCMRs are promising candidates for nutrient removal and recovery from wastewater.

Spirulina platensis improves growth, oil content, and antioxidant activitiy of rosemary plant under cadmium and lead stress

In the present study, a pot experiment was conducted to investigate the response of rosemary (Rosmarinus officinalis L.) plants to foliar application of Spirulina platensis at 0.0, 0.1, 0.2, and 0.4%; soil irrigation with heavy metals (Cd nitrate, Pb acetate, and Cd + Pb, each at 100 ppm), and Spirulina platensis at 0.1% + heavy metals. Spirulina platensis significantly improved growth parameters, oil yield/fed, photosynthetic pigments, and activity of superoxide dismutase (SOD), glutathione reductase (GR), catalase (CAT), and polyphenol oxidase (PPO) with a maximum promoting effect at 0.2% algal extract. On the other hand, heavy metal stress reduced growth criteria, photosynthetic pigments, and oil yield, while, significantly increased levels of antioxidant enzymes (SOD, CAT, GR) and corresponding non-enzymatic antioxidants (ascorbic acid, total antioxidant capacity, phenolics and flavonoids). Bioaccumulation factor (BF) and translocation factor (TF) indicated that Cd and Pb accumulated largely in the roots, with little transfer to the shoots. Nevertheless, compared with heavy metal treatments, S. platensis at 0.1% significantly increasing growth parameters, oil content, photosynthetic pigments, and the activity of non-enzymatic and enzymatic antioxidants, while, slightly reduced TF of Cd and Pb, alleviated membrane lipid peroxidation, and significantly lowered the content of malondialdehyde, hydrogen peroxide, and indole acetic acid oxidase (IAAO) activity in heavy metal (Cd, Pb, and Cd + Pb)-treated rosemary plants.

Insights into the inhibition effects of Cd on soil enzyme activities: From spatial microscale to macroscale

Cd is a heavy metal with high toxicity and adverse influence on the activities of soil enzymes. However, how Cd toxicity varies with the microenvironment or different regions needs further investigation. In this study, 17 soil samples were collected from different locations in China. Each soil sample was divided into two parts in accordance with aggregate size, macroaggregate fraction (> 250 µm) and microaggregate fraction (< 250 µm). The inhibitory effects of Cd on three soil enzymes were analyzed. Results showed that on the microscale, the inhibitory effect of Cd in macroaggregates was significantly stronger than that in microaggregates. Moreover, the inhibitory effect of Cd varied obviously across different regions, with the greatest effects being observed in soils from northeast China. This result indicates that the temperature and precipitation played a synergistic role in the Cd inhibition effects. The Cd inhibition ratios showed significantly negative correlations with clay content and positive correlations with pH value and organic carbon content, indicating that soil clay, pH and organic carbon were the main factors determining the Cd inhibition ratios on enzyme activities. This suggests that factors on the microscale and macroscale should be considered in addressing Cd pollution in soils.

Effect of the direct use of biomass in agricultural soil on heavy metals __ activation or immobilization?

In recent years, the biomass was directly used extensively in agriculture due to its low cost and convenience. Increasingly serious soil pollution of heavy metals may pose threats and risks to human health. Directly addition of biomass to soil may affect the bioavailability and content of heavy metals. Here, we reviewed the impact of direct application of oil cake, manure, sewage sludge, straw and municipal waste to soil on the form and concentration of heavy metals in soil, and also emphasized the role of biomass in soil heavy metals remediation. Heavy metals can be activated in a short term by the content of heavy metals in biomass, the production of low-molecular-weight organic acids by biomass application, and the oxidation of sulfides (except for ammoniation). However, heavy metals in soil can be immobilized by humic substances. These can be produced by biomass during a long-term application to soil. Moreover, the degree of immobilization depended on the kind of biomass. Biomass contaminated by heavy metals cannot be returned to the field directly. Therefore, Mitigating the activation of heavy metals in the early stage of biomass application is meaningful, especially for application of these biomass such as straw, sewage sludge and municipal waste. Future researches should focus on the heavy metal control on direct use of biomass in agricultural.

Enhanced uptake of Cd, Cr, and Cu in Catharanthus roseus (L.) G.Don by Bacillus cereus: application of moss and compost to reduce metal availability

Heavy metals (HMs) being the notorious and toxic are being introduced into the environment credited to natural and anthropogenic activities. The use of ornamental plants is being ignored as potential candidates for HMs phytoremediation. In this study, pot experiments were conducted on Catharanthus roseus (L.) G.Don to evaluate selected heavy metals tolerance and accumulation potential with reference to the bacterial endophyte (Bacillus cereus) and organic amendments (moss and compost at 5% v/v). Results indicated improvement in uptake of Cd (230 mg kg^-1), Cu (229 mg kg^-1), and Cr (458 mg kg^-1) by C. roseus with B. cereus. The concentration of Ni and Pb was found highest in controls (without strain) that were 420 and 904 mg kg^-1, respectively. Conversely, the addition of organic amendments enhanced biomass production, as compared to controls, 441, 471, and 763% by peat moss (T3), compost (T4), and peat moss + compost + inoculum treatments (T6), respectively, while reduction of plant HMs content was observed. Microbial-aided phytoremediation/phytoextraction could be a potential method for removal of Cd, Cr, and Cu, while organic amendments can significantly improve plant growth in the presence of heavy metals.

Influence of Pseudomonas japonica and organic amendments on the growth and metal tolerance of Celosia argentea L

In this study, a pot experiment was piloted in a greenhouse to evaluate the potential of Celosia argentea var. cristata L. for tolerating/accumulating heavy metals in synthetic wastewater in the presence of Pseudomonas japonica and organic amendment, i.e., moss and compost. Two-week-old seedlings were transferred to pots, and after 4 weeks, the bacterial strain was inoculated, then watered with synthetic wastewater for 5 weeks and harvested after 9 weeks. After harvesting, physiological and biochemical parameters, as well as metal contents of plants, were quantified. The results indicated highest growth and biomass production in moss- and compost-associated plants while highest metal uptake has been found in the presence of P. japonica and synthetic wastewater-irrigated plants. Synthetic wastewater-irrigated plants have shown highest Pb uptake of 2899 mg kg^-1 DW, while with P. japonica in soil those plants have shown highest Cd, Cu, Ni, and Cr uptake of 962, 1479, 1042, and 956 mg kg^-1 DW, respectively. The production of antioxidant enzymes, i.e., catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and glutathione-s-transferase (GST), was high in P. japonica-amended plants because of increased uptake of metals. It is concluded that moss and compost have improved growth while P. japonica improved metal accumulation and translocation to aerial parts with little involvement in plant growth.

N-Fertilizer (Urea) Enhances the Phytoextraction of Cadmium through Solanum nigrum L

Heavy metal contamination is currently a major environmental concern, as most agricultural land is being polluted from municipal discharge. Among various other pollutants, cadmium (Cd), one of the most harmful heavy metals, enters into the food chain through the irrigation of crops with an industrial effluent. In the present study, a pot experiment was designed to assess the effect of different nitrogen (N)-fertilizer forms in the phytoremediation of Cd through Solanum nigrum L. Two types of N fertilizers (NH₄NO₃ and urea) were applied to the soil in different ratios (0:0, 100:0, 0:100, and 50:50 of NH₄NO₃ and urea, individually) along with different Cd levels (0, 25, and 50 mg kg⁻¹). The plants were harvested 70 days after sowing the seeds in pots. Cadmium contamination significantly inhibited the growth of leaves and roots of S. nigrum plants. Cadmium contamination also induced oxidative stress; however, the application of N-fertilizers increased the plant biomass by inhibiting oxidative stress and enhancing antioxidants’ enzymatic activities. The greatest plant growth was observed in the urea-treated plants compared with the NH₄NO₃-treated plants. In addition, urea-fed plants also accumulated higher Cd concentrations than NH₄NO₃-fed plants. It is concluded that urea is helpful for better growth of S. nigrum under Cd stress. Thus, an optimum concentration of N-fertilizers might be effective in the phytoremediation of heavy metals through S. nigrum.

Phytostabilization of Cd and Pb in Highly Polluted Farmland Soils Using Ramie and Amendments

In-situ remediation of heavy-metal-contaminated soil in farmland using phytostabilization combined with soil amendments is a low-cost and effective technology for soil pollution remediation. In this study, coconut shell biochar (CB, 0.1% and 0.5%), organic fertilizer (OF, 3.0%), and Fe-Si-Ca material (IS, 3.0%) were used to enhance the phytostabilization effect of ramie (Boehmeria nivea L.) on Cd and Pb in highly polluted soils collected at Dabaoshan (DB) and Yangshuo (YS) mine sites. Results showed that simultaneous application of CB, OF, and IS amendments (0.1% CB + 3.0% OF + 3.0% IS and 0.5% CB + 3.0% OF + 3.0% IS, DB-T5 and DB-T6) could significantly increase soil pH, reduce the concentrations of CaCl₂-extractable Cd and Pb, and increase the contents of Ca, P, S, and Si in DB soil. Under these two treatments, the growth of ramie was significantly improved, its photosynthesis was enhanced, and its levels of Cd and Pb were reduced, in comparison with the control (DB-CK). After applying DB-T5 and DB-T6, the concentrations of Cd and Pb in roots were decreased by 97.7–100% and 64.6–77.9%, while in shoots they were decreased by up to 100% and 92.9–100%, respectively. In YS-T4 (0.5% CB + 3.0% OF), the concentrations of Cd and Pb in roots were decreased by 39.5% and 46.0%, and in shoots they were decreased by 44.7% and 88.3%. We posit that phytostabilization using ramie and amendments could reduce the Cd and Pb bioavailability in the soil mainly through rhizosphere immobilization and plant absorption. In summary, this study suggests that the use of tolerant plant ramie and simultaneous application of coconut shell biochar, organic fertilizer, and Fe-Si-Ca materials is an effective stabilization strategy that can reduce Cd and Pb availabilities in soil. Ultimately, this strategy may reduce the exposure risk of crops to heavy metal pollution in farmland.