What Do We Know About Metal Recycling Rates?

The recycling of metals is widely viewed as a fruitful sustainability strategy, but little information is available on the degree to which recycling is actually taking place. This article provides an overview on the current knowledge of recycling rates for 60 metals. We propose various recycling metrics, discuss relevant aspects of recycling processes, and present current estimates on global end‐of‐life recycling rates (EOL‐RR; i.e., the percentage of a metal in discards that is actually recycled), recycled content (RC), and old scrap ratios (OSRs; i.e., the share of old scrap in the total scrap flow). Because of increases in metal use over time and long metal in‐use lifetimes, many RC values are low and will remain so for the foreseeable future. Because of relatively low efficiencies in the collection and processing of most discarded products, inherent limitations in recycling processes, and the fact that primary material is often relatively abundant and low‐cost (which thereby keeps down the price of scrap), many EOL‐RRs are very low: Only for 18 metals (silver, aluminum, gold, cobalt, chromium, copper, iron, manganese, niobium, nickel, lead, palladium, platinum, rhenium, rhodium, tin, titanium, and zinc) is the EOL‐RR above 50% at present. Only for niobium, lead, and ruthenium is the RC above 50%, although 16 metals are in the 25% to 50% range. Thirteen metals have an OSR greater than 50%. These estimates may be used in considerations of whether recycling efficiencies can be improved; which metric could best encourage improved effectiveness in recycling; and an improved understanding of the dependence of recycling on economics, technology, and other factors.     

Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin

doi:10.1111/j.1741‐2358.2009.00333.x
Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth.     

Ascorbic acid enhancement of organogenesis in tobacco callus

The effect of ascorbic acid on growth and shoot formation in callus cultures of tobacco (Nicotiana tabacum L.) was investigated, using young (4–12 subcultures) and old (more than 30 subcultures) tissue. It was found that ascorbate, at levels of 4–8×10^-4M, enhanced shoot formation in both young and old callus. Treatment with ascorbate also speeded up the shoot-forming process. In addition, ascorbate completely reversed the inhibition of shoot formation by gibberellic acid in young callus, but was less effective in old callus.     

Effects of external NaCl on the growth of Atriplex amnicola and the ion relations and carbohydrate status of the leaves

Abstract Atriplex amnicola, was grown in nutrient solution cultures with concentrations of NaCl up to 750 mol m^?3. The growth optimum was at 25–50 mol m^?3 NaCl and growth was 10–15% of that value at 750 mol m^?3 NaCl. Sodium chloride at 200 mol m^?3 and higher reduced the rate of leaf extension and increased the time taken for a leaf to reach its maximal length. Concentrations of Na⁺, K⁺ and Mg²⁺ in leaves of different ages were investigated for plants grown at 25, 200 and 400 mol m^?3 NaCl. Although leaves of plants grown at 200 and 400 mol m^?3 NaCl had high Na⁺ concentrations at young developmental stages, much of this Na⁺ was located in the salt bladders. Leaves excluding bladders had low Na⁺ concentrations when young, but very high in Na⁺ when old. In contrast to Na⁺, K⁺ concentrations were similar in bladders and leaves excluding bladders. Concentrations of K⁺ were higher in the rapidly expanding than in the old leaves. At 400 mol m^?3 NaCl, the K⁺:Na⁺ ratios of the leaves excluding bladders were 0.4–0.6 and 0.1 for rapidly expanding and oldest leaves, respectively. The Na⁺ content in moles per leaf, excluding bladders, increased linearly with the age of the leaves; concurrent increases in succulence were closely correlated with the Na ⁺ concentration in the leaves excluding the bladders. Soluble sugars and starch in leaves, stems and buds were determined at dusk and dawn. There was a pronounced diurnal fluctation in concentrations of carbohydrates. During the night, most plant parts showed large decreases in starch and sugar. Concentrations of carbohydrates in most plant organs were similar for plants grown at 25 and 400 mol m^?3 NaCl. One notable exception was buds at dusk, where sugar and starch concentrations were 30–35% less in plants grown at 400 mol m^?3 NaCl than in plants grown at 25 mol m^?3 NaCl. The data indicate that the growth of A. amnicola at 400 mol m^?3 NaCl is not limited by the availability of photosynthate in the plant as a whole. However, there could have been a growth limitation due to inadequate organic solutes for osmotic regulation.     

Stand characteristics and biodiversity indicators along the productivity gradient in boreal forests: Defining a critical set of indicators for the monitoring of habitat nature quality

Abstract

We quantified the effects of anthropogenic disturbances on the structure and biodiversity of boreal forests on acidic soils and created a statistically supported rational set of indicators to monitor the stand “naturalness”. For that, we surveyed various traits of tree layer, understory, herb layer, forest floor and several widely accepted biodiversity epiphytic indicators in 252 old‐aged boreal stands in Estonia, mostly dominated by Scots pine or Norway spruce. Multifactorial general linear model analyses showed that many forest characteristics and potential indicators were confounded by the gradient of soil productivity (reflected by the forest site type), local biogeographic gradients and also by stand age. Considering confounding effects, boreal forests in a near‐natural state have more large‐diameter trees (diameter at breast height >40 cm) and larger variety of diameter classes, higher proportion of spruce or deciduous trees, a larger amount of coarse woody debris in various stages, a more closed tree canopy and denser understory than managed mature forests. By increasing light availability above the field layer, forest management indirectly increases the coverage of herbs and lichens on the forest floor but reduces the alpha‐ and beta‐diversity of herbs and the proportion of graminoids. Human disturbances reduce the relative incidence of many commonly accepted biodiversity indicators such as indicator lichens, woodpeckers, wood‐dwelling insects or fungi on trees. The test for the predictive power of characteristics reacting on disturbance revealed that only a fraction of them appeared to be included in a diagnostic easy‐to‐apply set of indicators to assess the nature quality of boreal forest: the amount of dead wood, the proportion of deciduous trees, the presence of specially shaped trees and woodpeckers and, as an indicator of disturbances, the forest herb Melampyrum pratensis. Many of these indicators have already been implemented in practice.     

Tree functional traits as predictors of microburst-associated treefalls in tropical wet forests

On 19 May 2018, a microburst caused 600 isolated forest gaps in a Costa Rican tropical forest. We surveyed fallen and standing trees within gaps to determine whether certain variables are associated with treefalls. Our results highlight considerations for future research to understand the impacts of microbursts in tropical forests.     

Liana communities exhibit different species composition,diversity and community structure across forest types in the Congo Basin

Lianas are poorly characterized for central African forests. We quantify variation in liana composition, diversity and community structure in different forest types in the Yangambi Man and Biosphere Reserve, Democratic Republic of Congo. These attributes of liana assemblages were examined in 12 1-ha plots, randomly demarcated within regrowth forest, old growth monodominant forest, old growth mixed forest and old growth edge forest. Using a combination of multivariate and univariate community analyses, we visualize the patterns of these liana assemblage attributes and/or test for their significant differences across forest types. The combined 12 1-ha area contains 2,638 lianas (≥2 cm diameter) representing 105 species, 49 genera and 22 families. Liana species composition differed significantly across forest types. Taxonomic diversity was higher in old growth mixed forests compared to old growth monodominant and regrowth forests. Trait diversity was higher than expected in the regrowth forest as opposed to the rest of forest types. Similarly, the regrowth forest differed from the rest of forest types in the pattern of liana species ecological traits and diameter frequency distribution. The regrowth forest was also less densely populated in lianas and had lower liana total basal area than the rest of forest types. We speculate that the mechanism of liana competitive exclusion by dominant tree species is mainly responsible for the lower liana species diversity in monodominant compared to mixed forests. We attribute variation in liana community structure between regrowth and old growth forests mostly to short development time of size hierarchies.     

Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate

The aim of the present study was to investigate the responses of Merkel cells that are numerous in the palatine rugae, due to the continuous mechanical stimulation exerted by the palatal plate. Forty golden hamsters were used in this experiment. The palatal plate was made of adhesive resin and it was set on the palate of the animal. To exert a continuous pressure, a 0.8?mm elevation on the internal surface of the palatal plate was created at the middle portion of the fourth palatine ruga. Thereafter, the number of Merkel cells in the mucosa was calculated by immunohistochemical observation. Morphological changes of Merkel cells were examined by electron microscopy. There was significant difference among the control and any of the treated groups on the number of CK20 positive Merkel cells (p?<?0.05) and that numbers were decreased at the sites where continuous mechanical stimulation was exerted. Degeneration of the cytoplasm mitochondria and nerve endings, and a decrease in both the number of neurosecretory granules and cytoplasmic processes were observed. Furthermore, the presence of nuclear chromatin aggregation and fragmentation was recognized. The continuous mechanical stimulation by the palatal plate affected the responses of Merkel cells and nerve endings, thus inducing a decrease in the number of Merkel cells. A portion of these changes was also associated with the expression of apoptosis.