Trace elements in agroecosystems and impacts on the environment

Trace elements mean elements present at low concentrations (mg kg-1 or less) in agroecosystems. Some trace elements, including copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), molybdenum (Mo), and boron (B) are essential to plant growth and are called micronutrients. Except for B, these elements are also heavy metals, and are toxic to plants at high concentrations. Some trace elements, such as cobalt (Co) and selenium (Se), are not essential to plant growth but are required by animals and human beings. Other trace elements such as cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), mercury (Hg), and arsenic (As) have toxic effects on living organisms and are often considered as contaminants. Trace elements in an agroecosystem are either inherited from soil parent materials or inputs through human activities. Soil contamination with heavy metals and toxic elements due to parent materials or point sources often occurs in a limited area and is easy to identify. Repeated use of metal-enriched chemicals, fertilizers, and organic amendments such as sewage sludge as well as wastewater may cause contamination at a large scale. A good example is the increased concentration of Cu and Zn in soils under long-term production of citrus and other fruit crops. Many chemical processes are involved in the transformation of trace elements in soils, but precipitation-dissolution, adsorption-desorption, and complexation are the most important processes controlling bioavailability and mobility of trace elements in soils. Both deficiency and toxicity of trace elements occur in agroecosystems. Application of trace elements in fertilizers is effective in correcting micronutrient deficiencies for crop production, whereas remediation of soils contaminated with metals is still costly and difficult although phytoremediation appears promising as a cost-effective approach. Soil microorganisms are the first living organisms subjected to the impacts of metal contamination. Being responsive and sensitive, changes in microbial biomass, activity, and community structure as a result of increased metal concentration in soil may be used as indicators of soil contamination or soil environmental quality. Future research needs to focus on the balance of trace elements in an agroecosystem, elaboration of soil chemical and biochemical parameters that can be used to diagnose soil contamination with or deficiency in trace elements, and quantification of trace metal transport from an agroecosystem to the environment.

Staining of tissue sections for electron microscopy with heavy metals. II. Application of solutions containing lead and barium

Descriptions of three heavy metal stains and methods of application to tissue sections for electron microscopy are presented. Lead hydroxide stains rather selectively two types of particles in liver: those associated with the endoplasmic reticulum and containing ribonucleic acid and other somewhat larger particles. Barium hydroxide emphasizes certain bodies within vesicles of the Golgi region of hepatic cells. Alkalized lead acetate is useful as a general stain, as are also lead and barium hydroxides.

The fine structure of elastic fibers

The fine structure of developing elastic fibers in bovine ligamentum nuchae and rat flexor digital tendon was examined. Elastic fibers were found to contain two distinct morphologic components in sections stained with uranyl acetate and lead. These components are 100 A fibrils and a central, almost amorphous nonstaining area. During development, the first identifiable elastic fibers are composed of aggregates of fine fibrils approximately 100 A in diameter. With advancing age, somewhat amorphous regions appear surrounded by these fibrils. These regions increase in prominence until in mature elastic fibers they are the predominant structure surrounded by a mantle of 100 A fibrils. Specific staining characteristics for each of the two components of the elastic fiber as well as for the collagen fibrils in these tissues can be demonstrated after staining with lead, uranyl acetate, or phosphotungstic acid. The 100 A fibrils stain with both uranyl acetate and lead, whereas the central regions of the elastic fibers stain only with phosphotungstic acid. Collagen fibrils stain with uranyl acetate or phosphotungstic acid, but not with lead. These staining reactions imply either a chemical or an organizational difference in these structures. The significance and possible nature of the two morphologic components of the elastic fiber remain to be elucidated.

Occupational exposures to metals as risk factors for Parkinson's disease

In a population-based case-control study, we investigated the potential role of occupational exposure to iron, copper, manganese, mercury, zinc, and lead as risk factors for Parkinson's disease (PD). Concurrently recruited, nondemented patients (n = 144) with idiopathic PD and controls (n = 464) consisting of men and women > or =50 years of age, frequency-matched for age (within 5 years), race, and sex were enrolled. All had primary medical care at Henry Ford Health System in urban/suburban metropolitan Detroit. Subjects were given an extensive risk-factor questionnaire detailing actual worksite conditions of all jobs held for more than 6 months from age 18 onward. An industrial hygienist, blinded to the case-control status of subjects, rated occupational exposure to each of the metals of interest. When adjusted for sex, race, age, and smoking status, we found in those with more than 20 years' exposure a significantly increased association with PD for copper (OR = 2.49, 95% CI = 1.06, 5.89) and manganese (OR = 10.61, 95% CI = 1.06, 105.83). For more than 20 years' exposure to combinations of lead-copper (OR = 5.24, 95% CI = 1.59, 17.21), lead-iron (OR = 2.83, 95% CI = 1.07, 7.50), and iron-copper (OR = 3.69, 95% CI = 1.40, 9.71), there was a greater association with PD than with any of these metals alone. These findings suggest that chronic exposure to these metals is associated with PD, and that they may act alone or together over time to help produce the disease.

The beginning of pattern formation in the Drosophila compound eye: the morphogenetic furrow and the second mitotic wave

Events in the morphogenetic furrow set the stage for all subsequent compound eye development in Drosophila. The periodic pattern of the adult eye begins in the furrow with the spaced initiation of ommatidial rudiments, the preclusters. A wave of mitosis closely follows the furrow. A cell-by-cell analysis reveals details of these events. Early stages of ommatidial assembly can be resolved using a lead sulfide stain. Overt ommatidial organization begins in the morphogenetic furrow as cells gather into periodically spaced concentric aggregates. A stereotyped sequence of cell rearrangements converts these aggregates into preclusters. In the furrow, new rows of ommatidia are initiated at the equator and grow as new clusters are added to the peripheral ends. Mitotic labeling using BrdU feeds shows that all cells not incorporated into a precluster divide. BrdU injections show that cells divide roughly simultaneously between two adjacent rows of ommatidia.

Molecular mechanism of heavy metals (Lead, Chromium, Arsenic, Mercury, Nickel and Cadmium) - induced hepatotoxicity - A review

Heavy metals pose a serious threat if they go beyond permissible limits in our bodies. Much heavy metal's viz. Lead, Chromium, Arsenic, Mercury, Nickel, and Cadmium pose a serious threat when they go beyond permissible limits and cause hepatotoxicity. They cause the generation of ROS which in turn causes numerous injuries and undesirable changes in the liver. Epidemiological studies have shown an increase in the levels of such heavy metals in the environment posing a serious threat to human health. Epigenetic alterations have been seen in the event of exposure to such heavy metals. Apoptosis, caspase activation as well as ultrastructural changes in the hepatocytes have also been seen due to heavy metals. Inflammation involving TNF-alpha, pro-inflammatory cytokines, MAPK, ERK pathways have been seen in the event of heavy metal hepatotoxicity. All these have shown that these heavy metals pose a serious threat to human health in particular and the environment as a whole.

Simultaneous removal of heavy-metal ions in wastewater samples using nano-alumina modified with 2,4-dinitrophenylhydrazine

2,4-Dinitrophenylhydrazine (DNPH) immobilized on sodium dodecyl sulfate coated nano-alumina was developed for the removal of metal cations Pb(II), Cd(II), Cr(III), Co(II), Ni(II) and Mn(II) from water samples. The research results displayed that adsorbent has the highest adsorption capacity for Pb(II), Cr(III) and Cd(II) in ions mixture system. Optimal experimental conditions including pH, adsorbent dosage and contact time have been established. Langmuir and Freundlich isotherm models were applied to analyze the experimental data. The best interpretation for the experimental data was given by the Freundlich adsorption isotherm equation for Mn(II), Pb(II), Cr(III) and Cd(II) ions and by Langmuir isotherm equation for Ni(II) and Co(II) ions. Desorption experiments by elution of the adsorbent with a mixture of nitric acid and methanol show that the modified alumina nanoparticles could be reused without significant losses of its initial properties even after three adsorption-desorption cycles. Thus, modified nano-alumina with DNPH is favorable and useful for the removal of these metal ions, and the high adsorption capacity makes it a good promising candidate material for Pb(II),Cr(III) and Cd(II) removal.

The vascular system as a target of metal toxicity

Vascular system function involves complex interactions among the vascular endothelium, smooth muscle, the immune system, and the nervous system. The toxic metals cadmium (Cd), arsenic (As), and lead (Pb) can target the vascular system in a variety of ways, ranging from hemorrhagic injury to subtle pathogenic remodeling and metabolic changes. Acute Cd exposure results in hemorrhagic injury to the testis, although some strains of animals are resistant to this effect. A comparison of Cd-sensitive with Cd-resistant mouse strains showed that expression of the Slc39a8 gene, encoding the ZIP8 transporter, in the testis vasculature endothelium is responsible for this difference. Endogenously, ZIP8 is a Mn(2+)/HCO(3)(-)symporter that may also contribute to Cd damage in the kidney. Chronic Cd exposure is associated with various cardiovascular disorders such as hypertension and cardiomyopathy and it is reported to have both carcinogenic and anticarcinogenic activities. At noncytotoxic concentrations of 10-100nM, Cd can inhibit chemotaxis and tube formation of vascular endothelial cells. These angiostatic effects may be mediated through disruption of vascular endothelial cadherin, a Ca(2+)-dependent cell adhesion molecule. With regard to As, ingestion of water containing disease-promoting concentrations of As promotes capillarization of the liver sinusoidal endothelium. Because capillarization is a hallmark precursor for liver fibrosis and contributes to an imbalance of lipid metabolism, this As effect on hepatic endothelial cells may be a pathogenic mechanism underlying As-related vascular diseases. With regard to Pb, perinatal exposure may cause sustained elevations in adult blood pressure, and genetically susceptible animals may show enhanced sensitivity to this effect. Taken together, these data indicate that the vascular system is a critical target of metal toxicity and that actions of metals on the vascular system may play important roles in mediating the pathophysiologic effects of metals in specific target organs.

Transport adenosine triphosphatase cytochemistry. II. Cytochemical localization of ouabin-sensitive, potassium-dependent phosphatase activity in the secretory epithelium of the avian salt gland

A cytochemical procedure is described for the ultrastructural localization of K-dependent, ouabain-sensitive nitrophenyl phosphatase activity in avian salt gland. Cryostat sections (50 µ) of paraformaldehyde-fixed tissue were incubated in a kinetically defined medium containing: 5 mM p-nitrophenyl phosphate, 10 mM MgCl2, 10 mM KCl, 100 mM Tris-HCl buffer (pH 8.5 or 9.0) and 20 mM SrCl2 to precipitate hydrolyzed phosphate. After incubation at room temperature, the sections were treated with Pb(NO3)2 to convert SrPi to PbPi precipitates for visualization in the electron microscope. Reaction product was localized on the cytoplasmic side of the secretory cell lateral and basal plasma membranes. Little, if any, reaction product was associated with the apical surfaces of the secretory cells or with endothelial surfaces of capillaries. Appropriate control experiments indicated that deposition of reaction product was dependent on Mg and K and was sensitive to ouabain. Furthermore, nonenzymatic hydrolysis of nitrophenyl phosphate did not occur in the medium, and deposition of artifactually produced precipitates did not resemble deposition of enzymatically produced precipitates. The relationship of this localization to transport adenosine triphosphatase cytochemistry is discussed, and the physiologic implications of the localization for tracing the route of active Na transport in the salt gland are considered.

A simplified lead oxide cadaver injection technique

A simple, inexpensive injectable substance is reported for analysis of the arterial circulation in fresh human or animal cadavers. The technique is a modification of that reported by Salmon in 1936 and utilizes lead oxide and gelatin. This combination is highly radiopaque; it perfuses the small radicles of the vascular tree and sets to a firm rubbery consistency to fascilitate dissection.

Lead toxicity in plants: Impacts and remediation

Lead (Pb) is the second most toxic heavy metal after arsenic (As), which has no role in biological systems. Pb toxicity causes a range of damages to plants from germination to yield formation; however, its toxicity is both time and concentration dependent. Its exposure at higher rates disturbs the plant water and nutritional relations and causes oxidative damages to plants. Reduced rate of seed germination and plant growth under stress is mainly due to Pb interference with enzymatic activities, membrane damage and stomatal closure because of induction of absicic acid and negative correlation of Pb with potassium in plants. Pb induced structural changes in photosynthetic apparatus and reduced biosynthesis of chlorophyll pigments cause retardation of carbon metabolism. In this review, the noxious effects of Pb on germination, stand establishment, growth, water relations, nutrient uptake and assimilation, ultra-structural and oxidative damages, carbon metabolism and enzymatic activities in plants are reported. The Pb dynamics in soil rhizosphere and role of remediation strategies i.e. physical, chemical and biological to decontaminate the Pb polluted soils has also been described. Among them, biological strategies, including phytoremediation, microbe-assisted remediation and remediation by organic amendments, are cost effective and environmentally sound remedies for cleaning Pb contaminated soils. Use of organic manures and some agricultural practices have the potential to harvest better crops yield of good quality form Pb contaminated soils.

Adsorption mechanism of cadmium on microplastics and their desorption behavior in sediment and gut environments: The roles of water pH, lead ions, natural organic matter and phenanthrene

Microplastics (MPs) in aquatic systems can act as a vector for various toxic contaminants, such as metal ions. Although some studies have investigated the adsorption characteristics of metal ions on MPs, the desorption behaviors of metal ions from MPs in different environments are largely unknown. Here, the adsorption of cadmium (Cd(II)) onto five different types of MPs were compared to examine the relationship between the surface characteristics and the adsorption properties of MPs. Our results showed that polyamide had the highest Cd(II) adsorption capability with a value of 1.70 ± 0.04 mg/g, followed by polyvinyl chloride (1.04 ± 0.03 mg/g), polystyrene (0.76 ± 0.02 mg/g), acrylonitrile butadiene styrene (0.65 ± 0.02 mg/g) and polyethylene terephthalate (0.25 ± 0.01 mg/g). The specific surface area and total pore volume were closely correlated with the adsorption capacity of the MPs, and the π-π interaction, electrostatic interaction and oxygen-containing functional groups played crucial roles in the adsorption of Cd(II) onto the MPs. The sorption capabilities of Cd(II) onto the MPs first increased and then decreased with increasing solution pH from 2.0 to 9.0. In addition, the adsorption capacities were suppressed with the presence of lead ions (20-80 mg/L), while the coexistence of phenanthrene had a minor impact. Interestingly, the presence of humic acid promoted the desorption of Cd(II) from the MPs both in the synthetic earthworm gut and in the sediment system. A higher desorption rate was observed in the simulated gut environment, suggesting that metal-contaminated MPs would pose higher ecological risks to macroinvertebrates. Overall, our findings provide a better understanding of the sorption mechanism of Cd(II) onto MPs and the desorption behavior under different environmental conditions in aquatic ecosystems.

Sugar-Poly(para-phenylene ethynylene) Conjugates as Sensory Materials: Efficient Quenching by Hg2+ and Pb2+ Ions

Three polar poly(para-phenylene ethynylene)s (PPE) were synthesized by utilizing the Heck-Sonogashira protocol. Two of the PPEs carry beta-glucopyranose substituents. Depending upon the linker used between the glycol units and the backbone, the fluorescence of these PPEs can be quenched by Hg2+ and Pb2+ to a varying degree. Monomeric model compounds that are substituted with only one glucose unit are not efficiently quenched. The presence of many glucose substituents in one PPE assembly led to a large increase in the binding constant to Hg2+ and quenching of the fluorescence was amplified.

Individual and combined toxicogenetic effects of microplastics and heavy metals (Cd, Pb, and Zn) perturb gut microbiota homeostasis and gonadal development in marine medaka (Oryzias melastigma)

Currently, microplastics (MPs) attracted increased attention for their ubiquity and toxic properties. In this study, marine medaka was used to explore the individual and combined toxicity of heavy metals (HMs) and MPs on intestinal bacteria and gonadal development. After exposure to environmentally relevant concentrations of MPs and HMs, significant alterations of intestinal microbiota were found. The MPs treatment reduced the diversity and abundance of intestinal microbiota, while the HMs and MPs-HMs treatments increased them, which were confirmed by the abundance changes of Proteobacteria. According to the KEGG analysis, the metabolism and environmental information processing (EIP) pathways in the microbial community were significantly affected. This study showed that the MPs-HMs treatment caused a higher pollution load on the gut of the marine medaka, and triggered more significant changes of specific bacterial species and gut function in the males. However, during the gonadal development, HMs and MPs-HMs treatments resulted in empty follicles (EF) and follicular atresia (FA), and altered the gene expression levels related to hypothalamic-pituitary-gonadal (HPG) axis. In short, this study demonstrated that the reproductive disturbance was mainly due to HMs, but the combination of MPs and HMs did not strengthen the risk to the gonad development of the marine medaka.