Modified diatomite for soil remediation and its implications for heavy metal absorption in Calendula officinalis.

BACKGROUND: Among different adsorbents, natural and inorganic compounds such as diatomite are important and advantageous in terms of high efficiency and cost-effectiveness, and function in stabilizing heavy metals in the environment. Calendula officinalis, a plant known as a high accumulator of heavy metals, was cultivated in soil treated with varying concentrations of modified diatomite to demonstrate the efficiency of modified diatomite in stabilizating of heavy metals in soils, RESULTS: The modification of diatomite aimed to enhance Calendula officinalis adsorptive properties, particularly towards heavy metals such as lead (Pb), Zinc (Zn), Chromium (Cr), Nickle (Ni), and Copper (Cu), common contaminants in industrial soils. The experimental design included both control and treated soil samples, with assessments at regular intervals. Modified diatomite significantly decreased the bioaccumulation of heavy metals in contaminated soils except Zn, evidenced by decreased DTPA extractable heavy metals in soil and also heavy metal concentrations in plant tissues. Using 10% modified diatomite decreased 91% Pb and Cu, 78% Cr, and 79% Ni concentration of plants compared to the control treatment. The highest concentration of Zn in plant tissue was observed in 2.5% modified diatomite treatment. Remarkably, the application of modified diatomite also appeared to improve the nutrient profile of the soil, leading to enhanced uptake of key nutrients like phosphorus (P) 1.18%, and potassium (K) 79.6% in shoots and 82.3% in roots in Calendula officinalis. Consequently, treated plants exhibited improved growth characteristics, including shoots and roots height of 16.98% and 12.8% respectively, and shoots fresh and dry weight of 48.5% and 50.2% respectively., compared to those in untreated, contaminated soil. CONCLUSION: The findings suggest promising implications for using such amendments in ecological restoration and sustainable agriculture, particularly in areas impacted by industrial pollution.

Ecotoxicological impact of butisanstar and clopyralid herbicides on soil microbial respiration and the enzymatic activities.

The application of herbicides in soil has been noted for its detrimental effect on the soil microbial community, crucial for various biochemical processes. This study provides a comprehensive assessment of the impact of butisanstar and clopyralid herbicides, both individually and in combination at different dosage (recommended field dose (RFD), ½, 2 and 5-times RFD). The assessment focuses on soil basal respiration (SBR), cumulative microbial respiration (CMR), and the activities dehydrogenase (DH), catalase (CAT), urease, acid and alkaline phosphatases (Ac-P and Alk-P) enzymes, along with their variations on days 10, 30, 60, and 90 post-herbicide application. Results indicate that, although herbicides, even at lower doses of RFD, demonstrate inhibitory effects on DH, CAT, and microbial respiration, they paradoxically lead to a significant enhancement in urease and phosphatase activities, even at higher doses. The inhibitory/enhancing intensity varies based on herbicide type, incubation period, and dosage. Co-application of herbicides manifests synergistic effects compared to individual applications. The most notable inhibitory effects on DH, CAT, and SBR are observed on the 30th day, coinciding with the highest activities of urease and phosphatases on the same day. The persistent inability to restore respiration and enzyme activities to initial soil (control) levels emphasizes the lasting adverse and inhibitory effects of herbicides, especially clopyralid, over the long term. It becomes apparent that soil microorganisms require an extended duration to decompose and acclimate to the presence of herbicides. Consequently, these agrochemical compounds pose a potential risk to crucial biochemical processes, such as nutrient cycling, ultimately impacting crop production.

The beneficial effects of bare and CMC-supported α-FeOOH, Fe3O4, and α-Fe2O3 nanoparticles on growth, nutrient content, and essential oil of summer savory (Satureja hortensis L.) under Cd, Pb and Zn stresses.

This research studies the impacts of iron oxide nanoparticles (FeONPs) on alleviating the toxic effects of cadmium (Cd), lead (Pb), and zinc (Zn) on summer savory (Satureja hortensis L.). Different types of soil additives, including bare and carboxymethylcellulose (CMC)-supported hematite (α-Fe2O3), goethite (α-FeOOH), and magnetite (Fe3O4), were applied at three rates (0, 0.25, and 0.5% w/w) to a Cd, Pb, and Zn-contaminated soil sample. The experimental results showed that the application of FeONPs increased plant height, dry weights of shoot and root, and yield and content of essential oil. Bare and CMC-supported FeONPs increased the content of K, P, and Fe in the aerial parts of summer savory. However, these soil additives reduced the contents of Cd, Pb, and Zn in plant tissues. CMC-supported FeONPs proved to be more efficient additives in diminishing the toxic effects of Cd, Pb, and Zn in summer savory compared to their bare forms. Bare and CMC-supported goethite NPs were able to restrict the uptake of Cd, Pb, and Zn by summer savory roots in the metal-contaminated soil. The application of CMC-supported goethite at an application dose of 0.5% (w/w) increased shoot dry weight, shoot concentrations of K, P, and Fe, and yield of essential oil by about 62.6, 76.6, 77.1, 210, and 230%, respectively. Conversely, they reduced shoot concentrations of Cd, Pb, and Zn by about 64.6, 68.7, and 40.6%, respectively, compared to the control. These are significant results and indicate that CMC-supported goethite is likely to be the most effective soil additive in diminishing the toxicity of Cd, Pb, and Zn to metal-stressed summer savory.

The effect of petroleum levels on some soil biological properties under phytoremediation and bioaugmentation.

With the development of industries and excessive use of petroleum compounds, petroleum pollution has become a serious threat to the environment. The aim of this study was to the effect of petroleum levels on the biological activities of soil affected by phytoremediation and bioaugmentation. A surface soil sample was collected from the polluted areas around Bandar Abbas Oil Refinery Company, and the petroleum-degrading bacteria were isolated. M. yunnanensis (native) was selected among the isolated colonies for further experiment. The used soil in this study was a surface soil collected from Baghu region of Bandar Abbas, Sothern Iran, and treatments were added to soil samples. To evaluate removal of petroleum levels (0, 4, and 8%) from the soil by phytoremediation (control, sorghum, barley, and bermudagrass) and bioaugmentation (control, A. brasilense (non-native) and M. yunnanensis) and bioaugmented phytoremediation, a factorial pot experiment with completely randomized design and three replications was performed. The results demonstrated that sorghum and bermudagrass were more resistant than barley to the toxic effects of petroleum. Positive effect of bacteria on dry weight in polluted soil was greater than in the non-polluted soil. The degradation of petroleum reaches 77% in sorghum + M. yunanesis + 4% petroleum. Plants had stronger ability to degrade total petroleum hydrocarbon (TPH), while bacteria could better degrade polyaromatic hydrocarbons (PAHs). Application of bacteria and plants stimulated soil biological characteristics (dehydrogenase, arylsulfatase, lipase, bacterial population, and respiration) in polluted soil. Among measured enzymes, dehydrogenase exhibited a stronger response to petroleum levels. Four-percent level had greater irritating effect on soil biological properties. Plants and bacteria rely on differences in biological properties to attain synergy in petroleum degradation. Results indicated that M. yunnanensis has a high ability to remove petroleum from soil, and plants enhance the efficiency of this bacterium.

The effects of non-stabilised and Na-carboxymethylcellulose-stabilised iron oxide nanoparticles on remediation of Co-contaminated soils.

A pot experiment was carried out to evaluate the efficiency of six types of non-stabilised and Na-carboxymethylcellulose (CMC)-stabilised iron oxide nanoparticles (α-FeOOH, α-Fe2O3, and Fe3O4) on the immobilisation of cobalt (Co) in a soil spiked with different concentrations of it (5, 25, 65, 125, 185 mg kg-1). Amendments were added to soil samples at the rate of 0.5%, and the samples incubated for 60-days. The addition of amendments significantly decreased the concentrations of DTPA-Co and MgCl2-Co, compared with the unamended control. The highest decrease in concentration of DTPA-Co and MgCl2-Co was obtained by the application of CMC-stabilised Fe3O4 (MC) when the concentration of soil total Co was low (5 and 25 mg kg-1) and by the use of CMC-stabilised α-FeOOH (GC) when the concentration of soil total Co was high (65, 125, and 185 mg kg-1), as compared to the control. CMC-stabilised iron oxide nanoparticles were more effective than non-stabilised nanoparticles in the immobilisation of Co. To investigate the effectiveness of iron oxide amendments on the chemical species of Co in the soil spiked with 65 mg kg-1 of this metal, sequential extraction was performed. The concentration of EXCH (exchangeable) and CARB (carbonate) bound fractions decreased significantly after treatment by different amendments. In particular, GC reduced the concentration of EXCH and CARB bound fractions by 20.87, and 17.52%, respectively, compared with the control. Also amendments significantly increased the concentration of FeMn-OX (Fe-Mn oxides), and OM (organic matter) bound, and RES (residual) fractions.

Lead and cadmium-resistant bacterial species isolated from heavy metal-contaminated soils show plant growth-promoting traits.

Application of metal-resistant rhizobacteria is a promising approach for detoxification and bioremediation of contaminated soils. In order to isolate, identify, and characterize lead and cadmium-resistant bacteria, nearly 30 soil samples were collected from heavy metal-contaminated sites, and five resistant bacterial strains were isolated and identified based on their cultural, physiological, biochemical, and molecular characteristics as Enterobacter cloacae, Enterobacter kobei, Bacillus cereus, Rhizobium pusense, and Agrobacterium tumefaciens. The nucleotide information of these strains is available in GenBank under the accession numbers of MH327251, MH327252, MH327253, MH327254, and MK123361, respectively. The minimum inhibitory concentrations (MICs) against lead and cadmium differed for each isolate and the isolates showed higher MIC against lead (3500 µg ml-1) than cadmium (100 µg ml-1). Assessment of the heavy metal degradation capacity of the species showed 10-60% and 5-40% reduction in concentrations of lead and cadmium, respectively. The highest ability for P-solubilization was measured for the R. pusense, A. tumefaciens, and B. cereus species, while the R. pusense and B. cereus species had the capability to solubilize potassium. The studied species also had the ability to produce indole acetic acid (IAA) and/or hydrogen cyanide production (HCN). Inoculation of ornamental cabbage cultivated in a heavy metal-contaminated soil with the isolated species significantly increased biomass and Pb and Cd uptake of the plant. With respect to plant growth promoting and heavy metal-resistant traits of the studied species, it is concluded that these species can have great significance in bioremediation and management of environmental pollution.

Assessing the phytoavailability of arsenic and phosphorus to corn plant after the addition of an acrylic copolymer to polluted soils.

Soil pollution by arsenic increases the potential risk of arsenic entrance into the food chain. The usefulness of maleic anhydride- styrene- acrylic acid copolymer on the mobility and phytoavailability of arsenic was evaluated. Treatments were the concentrations of acrylic copolymer (0, 0.05, 0.10, and 0.20% w/w) and the concentrations of soil total arsenic (0, 6, 12, 24, 48, and 96 mg kg-1). Sodium arsenate was added in appropriate amounts to subsamples of an uncontaminated soil to give contaminated soils with different levels of arsenic. The contaminated soils were subjected to a greenhouse experiment using corn as the test crop. The results showed that contamination of soil by arsenic increased the concentrations of soil available arsenic, root and aerial parts arsenic. By the use of acrylic copolymer, the concentration of available arsenic in the soil and the accumulation of arsenic in the root and aerial parts of the corn plant decreased but the dry weights of the root and aerial parts increased significantly. When the concentration of soil total arsenic was 96 mg kg-1, the application of copolymer at the concentration of 0.20% w/w reduced the concentrations of arsenic in soil, root, and aerial parts by 62.53, 43.65, and 37.00% respectively, indicating that application of acrylic copolymer immobilized arsenic in soils.