https://www.sourcewatch.org/images/2/22/McBride_-_Toxic_Metals_in_Sludge.pdf

Toxic metals in sewage sludge-amended soils: has promotion of beneficial use discounted the risks?

The responses of plants to metal toxicity. A review focusing on copper, manganese & zinc

Applications of zinc (Zn) and copper (Cu) at excessive rates may result in phytotoxicity. Experiments were conducted with mixtures of soils that were similar except for their Zn and Cu levels. The critical toxicity levels (CTL) in the soils and plants for these elements were determined. Peanut (Arachis hypogaea L.), soybean [Glycine max (L.) Merr.], corn (Zea mays L.), and rice (Oryza sativa L.) were the crops grown. One soil mixture had Mehlich 3‐extractable Zn concentrations up to 300 mg dm‐3 with no corresponding increase in soil Cu; two soil mixtures had soil Zn concentrations up to 400 and 800 mg dm‐3 with a corresponding increase in soil Cu up to 20 and 25 mg dm‐3, respectively; and four soil mixtures had no increase in soil Zn, but had Mehlich 1‐extractable Cu concentrations from 6 to 286 mg kg‐1. Under a given set of greenhouse conditions, the estimated Mehlich 3‐extractable Zn CTL was 36 mg dm‐3 for peanut, 70 mg dm‐3 for soybean, between 160 and 320 mg dm‐3 for rice, and >300 mg dm‐3 fo...

Zinc and copper toxicity in peanut, soybean, rice, and corn in soil mixtures

The properties of nanomaterials and their potential applications have been given considerable attention by researchers in various fields, especially agricultural biotechnology. However, not much has been done to evaluate the role or effect of zinc oxide nanoparticles (ZnO-NPs) in regulating physiological and biochemical processes in response to salt-induced stress. For this purpose, some callus growth traits, plant regeneration rate, mineral element (sodium, potassium, phosphorous and nitrogen) contents and changes in the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPX) in tissues of five tomato cultivars were investigated in a callus culture exposed to elevated concentrations of salt (3.0 and 6.0 g L -1 NaCl), and in the presence of zinc oxide nanoparticles (15 and 30 mg L -1 ). The relative callus growth rate was inhibited by 3.0 g L -1 NaCl; this was increased dramatically at 6.0 g L -1 . Increasing exposure to NaCl was associated with a significantly higher sodium content and SOD and GPX activities. Zinc oxide nanoparticles mitigated the effects of NaCl, and in this application of lower concentrations (15 mg L -1 ) was more effective than a higher concentration (30 mg L -1 ). This finding indicates that zinc oxide nanoparticles should be investigated further as a potential anti-stress agent in crop production. Different tomato cultivars showed different degrees of tolerance to salinity in the presence of ZnO-NPs. The cultivars Edkawy, followed by Sandpoint, were less affected by salt stress than the cultivar Anna Aasa. DOI: 10.2298/ABS151105017A Key words : Nano biotechnology, in vitro culture, protein, salinity, superoxide dismutase, glutathione peroxidase Received: November 5, 2015; Revised: February 11, 2016; Accepted: February 12, 2016; Published online: March 21, 2016 How to cite this article: Alharby HF, Metwali EMR, Fuller MP, Aldhebiani AY. Impact of application of zinc oxide nanoparticles on callus induction, plant regeneration, element content and antioxidant enzyme activity in tomato (Solanum lycopersicum Mill.) under salt stress. Arch Biol Sci. 2016;68(4):723-35.

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Impact of application of zinc oxide nanoparticles on callus induction, plant regeneration, element content and antioxidant enzyme activity in tomato (Solanum lycopersicum Mill.) under salt stress

Clarifying the connection between metal exposure and anatomical changes represents an important challenge for a better understanding of plant phytoextraction potential. A hydroponic screening experiment was carried out to evaluate the effects of combined interactions of Cd and Zn on mineral uptake (Mg, K, Ca, Na) and on the physiological and anatomical characteristics of Brassica napus L cv. Cadeli, Viking, and Navajo. Plants were exposed to 5 μM Cd (CdCl2), 10 μM Zn (ZnSO4), or both Cd + Zn, for 14 days. Cadmium exposure led to a significant reduction in root growth, shoot biomass, and chlorophyll content. After Cd-only and Cd + Zn treatment, primary root tips became thicker and pericycle cells were enlarged compared to the control and Zn-only treatment. No differences between metals were observed under UV excitation, where all treatments showed more intensive autofluorescence connected with lignin/suberin accumulation compared to control conditions. The highest concentrations of Cd and Zn were found in the roots of all tested plants, and translocation factors did not exceed the threshold of 1.0. The root mineral composition was not affected by any treatment. In the shoots, the Mg concentration slightly increased after Cd-only and Cd + Zn treatments, whereas Zn-only treatment caused a sharp decrease in Ca content. Slight increases in K were seen after the addition of Zn. Significantly higher concentrations of Na were induced by Cd- or Zn-only treatment.

Effects of Cd and Zn on physiological and anatomical properties of hydroponically grown Brassica napus plants

Zinc toxicity of peanuts (Arachis hypogaea L.), resulting from excessive amounts of Zn applied to previous crops, has been observed for many years in a limited number of peanut fields in Georgia. A tentative critical value of 12 mg/kg of Mehlich No.1 extractable soil Zn has been reported, but soil pH should be considered in establishing a more precise critical value since availability of soil Zn is affected greatly by soil acidity. A 3‐year study was conducted on a Tifton loamy sand (thermic, Plinthic Paleudults) to evaluate the relationship between soil pH and soil Zn on concentration of Zn in peanut leaves. Factorial treatments were 0, residual, medium, and high rates of Zn and soil pH levels near 5.5, 5.9, 6.2, and 6.8. Pod yields were not affected by treatments and Zn toxicity was not observed. Leaf Zn was affected more by soil pH than by soil Zn, but correlation coefficients were highest where both soil pH and soil Zn were included in the determination. A regression equation, based on soil p...

Soil zinc and pH effects on leaf zinc and the interaction of leaf calcium and zinc on zinc toxicity of peanuts.

Zinc (Zn) toxicity can be fatal to peanuts (Arachis hypogea L.) grown on high Zn soils, especially those with low pH values. The objectives of this study were to determine the influence of soil pH and soil Zn levels on Zn toxicity of peanuts and to predict the presence of Zn toxicity based on leaf or soil data. A greenhouse study was conducted with ‘Florunner’ peanuts using four soils of varying textures. Dolomitic limestone was applied to establish four pH levels ranging from 4.5-7.0 among soils. Zinc sulfate was applied at rates of 0, 10, 20 and 40 mg Zn kg−1 soil. Lime and zinc treatments were made to all soils in factorial combinations. Leaf and soil samples were taken periodically. Leaf Zn increased with increased soil Zn rates, but leaf Zn declined with increased pH levels. Leaf calcium (Ca) was reduced by soil Zn application in some cases. Leaf Zn and leaf Ca were both significantly correlated with the presence of Zn toxicity symptoms. When soil pH or soil Ca was included in models with soil Zn to predict leaf Zn from soil Zn, R-square values increased dramatically. A table was developed for the determination of target pH levels that should be reached in soils with specific soil Zn concentrations to avoid Zn toxicity problems.

J. G. Davis-Carter

Papers

Soil zinc and pH effects on leaf zinc and the interaction of leaf calcium and zinc on zinc toxicity of peanuts.

Interaction of soil zinc, calcium, and pH with zinc toxicity in peanuts