Retention Of Mn Research Articles

Dietary Manganese for Dry and Lactating Holstein Cows

Apparent digestibility and retention of Mn by dairy cows was used to compare 2 sources of Mn and to estimate Mn requirements. In experiment 1, Holstein cows at dry-off (60 d prepartum) were fed a basal diet with no supplemental Mn (43mg of Mn/kg of dry matter) and received a daily bolus of 0 or 200mg/d supplemental Mn from MnSO4 or from Mn-Met (6 cows per treatment) until parturition. Approximately 30 d before parturition, cows were moved to metabolism stalls for total collection of feces and urine. No differences were observed between Mn sources, but apparent absorption of Mn (6.4 vs. 2.3%) tended to be greater, and apparent retention of Mn (44 vs. 12mg/d) was greater, for cows given supplemental Mn compared with control cows. In the second experiment, apparent Mn digestibility data from 8 experiments conducted with lactating dairy cows (39 dietary treatments and 160 observations) were combined with data from experiment 1. The regression equation of intake of digestible Mn on Mn intake (i.e., Lucas test) was as follows: intake of digestible Mn (mg/d) = −151 + 0.26×Mn intake (mg/d). Based on that equation, Mn intake had to equal 580mg/d to meet the metabolic fecal Mn requirement. The corresponding dietary concentration, assuming dry matter intakes of 21 and 12kg/d for lactating and dry cows, respectively, were 28 and 49mg/kg dry matter. These concentrations are approximately 1.6 and 2.7 times higher than those needed to meet the Mn requirements for lactating and dry cows, respectively, as calculated using the 2001 National Research Council dairy requirements model.

Absorption and Retention of Trace Minerals in Adult Horses

AbstractAbsorption and retention of Cu, Mn, and Zn were compared when feeding diets supplemented with oxide, sulfate, or organic-chelated forms of the minerals. Six mature Miniature Horses were used in the replicated 3 × 3 Latin square-designed experiment. The experiment was conducted in three 17-d periods, consisting of 10 d of diet adaptation followed by a 7-d total fecal and urine collection. Horses were fed a diet of 40% coastal Bermudagrass and 60% concentrate formulated to meet the energy, protein, Ca, and P requirements for maintenance of mature horses. Copper, Mn, and Zn were supplemented to provide 140 to 180% of the NRC (1989) recommended dietary concentrations for these minerals and were supplied in oxide, sulfate, and organic-chelate forms. Following total collections of feces and urine, feed, fecal, and urine samples were processed and analyzed for Cu, Mn, and Zn concentrations by atomic absorption spectrophotometry. Absorption of Cu, Mn, and Zn in all forms was low compared with previous studies, but systemic retention of these minerals was high. The cause of this disparity is unknown, although experimental error is unlikely. There were no differences in the absorption or retention of Cu, Mn, and Zn among the three forms of mineral supplements. Mature, idle horses may not be appropriate animals in which to evaluate absorption of various forms of trace minerals.

Efficiency of natural calcite precipitation compared to lake marl application used for water quality improvement in an eutrophic lake

Since the 1980s, several in-lake restoration methods for eutrophied lakes have been developed based on artificially induced calcite precipitation and lime additions. The aim of these measures is to improve water quality and reduce the incidence of cyanobacterial blooms by increasing P adsorption and removal through natural calcite precipitation. The authors compared the relative efficiencies of lake marl application and natural calcite precipitation in immobilizing P, Mn and Fe in Lake Arendsee, northeastern Germany, and their subsequent value as a tool for managing eutrophication. Microprobe investigations of element distributions in calcite minerals of laminae precipitated annually during several years before and two years following the restoration suggest that recently grown biogenic calcites were more efficient at the co-precipitation and immobilization of P, Fe and Mn. The lake marl applied as 16% calcite/water mixture proved unsuitable as a restoration tool because of its coarse grain size mainly in the range of 20–1000 μm and associated organic matter which reduced its suspension time and sorption reaction rates in the water column. In Lake Arendsee or in similar eutrophic hardwater lakes with fast internal P recycling by rapid degradation of autochthonous organic matter in the water column and at the sediment surface (sedimentary TOC:TP ratios of 200 or more), biogenic calcites provide almost permanent P, Fe and Mn retention in the sediments. The study shows that epilimnetic additions of pure CaCO 3 seed crystals comparable to natural calcite precipitation are the most effective for improving water quality. Small CaCO 3 crystals exhibit a larger reactive surface, and thus, incorporate adsorbed dissolved nutrients and trace metals more rapidly during growth. However, in-lake water quality management strategies work best only if external point and non-point nutrient sources are reduced or diverted.

Amino acid-chelate: a better source of Zn, Mn and Cu for rainbow trout, Oncorhynchus mykiss

This study aimed to evaluate the amino acid-chelated trace elements as dietary supplement to rainbow trout. Three diets were formulated containing trace elements either from the inorganic salt (SF) or amino acid-chelate (AM). Diets 1 (SF) and 2 (AM) contained the same amount of trace elements from inorganic and amino acid-chelates, respectively. Diet 3 (AM-Hf) was added with trace elements from amino acid-chelatex at one-half of their levels in Diets 1 and 2. Each diet was fed for 15 weeks to three groups of 30 fish each, with an average weight of 1.52±0.21 g. Growth of fish was not affected by the treatment ( P>0.05). However, bone ( P<0.01) and liver ( P<0.05) Cu contents were higher in the AM than the SF group. Similarly, hematocrit level ( P<0.05) and alkaline phosphatase (ALP) activity ( P<0.01) were higher in the chelate-fed fish. Further, DNA polymerase and CuZnSOD expression in the AM group was highly upregulated ( P<0.05) compared to the SF fed fish as quantified by RT-PCR. Absorption and whole body retention of Mn and Zn from the AM were higher ( P<0.05) than the inorganic salt. Half supplementation of those fed the elements from AM was at par with the full provision from the inorganic source tested.

Manganese alters mitochodrial integrity in the hearts of swine marginally deficient in magnesium.

It was previously reported that pigs marginally deficient in magnesium (Mg) and fed diets high in manganese (Mn) died suddenly with signs of sudden cardiac death. Manganese, which has properties similar to Mg, may exacerbate Mg-deficiency and be accumulated by mitochondria resulting in ultrastructural damage. The objective of this study was to determine whether deaths of the type previously observed were mediated by adverse interactions of Mn and Mg resulting in ultrastructural damage to the myocardium, alterations in electrocardiographic recordings and tissue retention of Mn, Mg and calcium (Ca). Forty-eight pigs were fed one of six diets in a 2 X 3 factorial arrangement of Mg (100 or 1000 mg Mg/kg) and Mn (5, 50 or 500 mg Mn/kg) for 8 weeks. Left ventricle muscle samples were collected for examination by transmission electron microscopy. No differences in heart muscle ultrastructure were observed between pigs fed low and adequate dietary Mg. However, marked myocardial necrosis and mitochondrial swelling were observed in pigs fed high dietary Mn when combined with low Mg. Feeding low dietary Mg elevated minimum (P < 0.01), maximum (P < 0.05) and average (P < 0.001) heart rates. Low dietary Mg resulted in a 55% probability of a ventricular beat being recorded (P = 0.05) and lower Mg (P < 0.02) and Ca (P < 0.04) contents in heart atria and ventricles. These results suggest that high Mn, when fed in combination with low Mg, disrupts mitochondrial ultrastructure and is associated with the sudden deaths previously reported.

Absorção e translocação de manganês por plantas de soja micorrizadas, sob doses crescentes deste nutriente

A toxidez de Mn pode ser atenuada, em algumas situações, pela micorrização das plantas. Mecanismos diretos e indiretos podem estar envolvidos nesse processo. Este trabalho visou avaliar o efeito intrínseco do fungo micorrízico arbuscular (FMA) na absorção e translocação de Mn por plantas de soja. Inicialmente, testaram-se três espécies de FMA quanto à capacidade de propiciar crescimento das plantas sob excesso de Mn. Glomus macrocarpum foi a mais eficiente em proteger as plantas contra o excesso de Mn, resultado da maior retenção de Mn nas raízes e menor translocação para a parte aérea. A simbiose com Gigaspora margarita foi ineficiente e limitou o desenvolvimento das plantas. Num segundo experimento, empregaram-se um cultivar tolerante e outro sensível ao excesso de Mn, em associação ou não com G. macrocarpum. Pretendeu-se verificar ocorrência de oxidação de Mn nas raízes das plantas micorrizadas, sob excesso de Mn. Não houve efeito da micorrização na oxidação de Mn nas raízes, mas na dose de 15 mg kg-1 de Mn, as plantas micorrizadas tiveram maior teor de Mn nas raízes. Houve efeito do cultivar, tendo o tolerante apresentado maior oxidação de Mn nas raízes.

High available phosphorus corn and phytase in layer diets

High available phosphorus corn (HAP) developed using the low phytic acid 1-1 (lpal-1) allele of the corn LPA1 gene containing 0.27% P, with 0.17% nonphytate P (NPP), was compared to near isogenic normal corn (LPA1), which contained 0.23% P and 0.05% NPP. Five levels of NPP from either HAPC or normal corn (0.40, 0.35, 0.30, 0.25 and 0.20% + 300 phytase units (FTU)/kg microbial phytase) were combined in a 2 x 5 factorial experiment for a total of 10 dietary treatments. Each dietary treatment was fed to eight replicate cages with five Hy-Line W-36 hens per replicate cage from 20 to 40 wk of age. Feed consumption and egg production were not significantly affected by dietary NPP level or corn type. Feed conversion ratio (g feed:g egg mass) was improved at the 0.35% NPP level (1.856) compared to the other levels of NPP--0.40, 0.30, 0.25, and 0.20% + phytase having feed conversion ratios of 1.872, 1.905, 1.930, and 1.898, respectively. Egg weight and egg mass decreased significantly as dietary NPP decreased; diets with 0.20% NPP plus phytase had equal egg mass to the 0.35 and 0.40% NPP diets. A significant corn type x NPP interaction effect was observed for egg weight, such that within the HAP corn diets, egg weight decreased more markedly at the 0.25% NPP levels compared to the normal corn 0.25% NPP diets. Specific gravity was not affected by dietary treatment, but percent dry shell was improved at the lower AP levels and with phytase treatment. Dietary NPP level and corn type had no significant effect on bone ash. Excreta levels of total phosphorus decreased significantly as dietary NPP decreased and were lower in the HAP corn excreta compared to normal corn excreta. Total P, Ca, Zn, Cu, and Mn retention were significantly affected by NPP level and corn type. HAP corn reduced Ca, Zn, Cu, and Mn retention compared to normal corn; this negative effect was alleviated by phytase supplementation to HAP corn diets. HAP corn allowed less dicalcium phosphate supplementation in layer diets compared to normal corn while supporting equal egg production. Phytase supplementation of low NPP diets had no significant positive effects on egg production parameters in either corn type diets.

Dietary Calcium and Non-phytin Phosphorus Interaction on Growth, Bone Mineralization and Mineral Retention in Broiler Starter Chicks

An experiment was conducted to study the requirement of calcium (Ca) and non-phytin phosphorus (NPP) in commercial broilers during starter phase. Seven hundred and twenty day-old Vencob male broiler chicks were randomly distributed into 144 stainless steel battery brooders, 5 birds in each. Four levels each of Ca (6, 7, 8, and 9 g/kg) and NPP (3, 3.5, 4, and 4.5 g/kg diet) were fed in a factorial design in a corn-soya basal diet. Levels of dicalcium phosphate and oyster shell grit were adjusted to obtain the desired levels of Ca and NPP. Each diet was fed ad libidum to chicks in 9 battery brooders from one d to 21 d of age. Body weight gain and feed intake were depressed (p 6 g/kg) and NPP (>3 g/kg) levels. The leg abnormality score decreased (p 2:1, Ca and NPP). Similarly, the retention of Zn, Mn, and Fe in liver was significantly higher (p<0.01) at lower levels of Ca and NPP tested. Results from this study indicate that the commercial broilers do not require more than 3 g NPP and 6g Ca/kg diet during starter phase (up to 21 d of age) for optimum weight gain, feed efficiency and utilization of Ca, P, Zn, Mn, Fe and Cu. However, the requirements of these minerals for optimum bone mineralization were higher than the levels suggested above.

Efficacy of supplementation of a phytase-producing bacterial culture on the performance and nutrient use of broiler chickens fed corn-soybean meal diets

We evaluated the efficacy of supplementation of active Mitsuokella jalaludinii culture (AMJC) on the growth performance, nutrient use, and mineral concentrations in tibia bone and plasma of broiler chickens fed corn-soybean meal diets. Dietary treatments included low-nonphytate P (NPP) feed (containing 0.24% and 0.232% NPP for chicks from 1 to 21 and 22 to 42 d of age, respectively), low-NPP feed added with different levels of AMJC (equivalent to 250, 500, 750, and 1,000 U phytase/kg of feed), and normal-NPP feed (containing 0.46 and 0.354% NPP for chicks from 1 to 21 and 22 to 42 d of age, respectively). Supplementation of AMJC to low-NPP feed increased (P < 0.05) weight gain and feed intake and decreased (P < 0.05) feed:gain ratio of chickens during the whole experiment (Days 1 to 42). Supplementation of AMJC increased (P < 0.05) the AME value, digestibility of DM and CP, and retention of P, Ca, and Cu. Mn retention in broilers was only increased (P < 0.05) by AMJC supplementation from 18 to 20 d of age, and Zn retention was improved (P < 0.05) only at a high level of AMJC (equivalent to 1,000 U phytase/kg of feed) supplementation. Chicks fed low-NPP feed added with AMJC had similar tibia ash percentages as those fed the normal-NPP diet. Generally, supplementing AMJC to low-NPP feed increased (P < 0.05) Ca, decreased significantly (P < 0.05) Mn and Cu, but did not affect Zn and P concentrations in tibia ash. Supplementing AMJC also increased (P < 0.05) plasma P but had no effect on plasma Ca or Mn. Plasma Zn concentration was increased only when a high level of AMJC (equivalent to 1,000 U phytase/kg of feed) was used. In conclusion, AMJC supplementation to low-NPP feed improved growth performance; AME value; digestibility of CP and DM; use of Ca, P, and Cu; and bone mineralization.

On-line pre-concentration of Cr(III) and Mn(II) in FI-FAAS: A critical study involving interference effects and analytical use of an immobilized 8-hydroxyquinoline minicolumn.

A flow injection system with a pre-concentration minicolumn based on a chelating resin was coupled to a flame atomic absorption spectrometer. The focus of this work was the investigation of interference effects and the analytical applicability of the azo-immobilized 8-hydroxyquinoline on controlled-pore glass for the determination of Cr and Mn in mussel and non-fat milk powder. All studied concomitants affected the retention of Cr(III). These effects are probably related to the formation of hydroxo-complexes at the optimum pH range 9.0-10. The positive effect caused by Ca(II) was exploited to increase the retention of Cr(III) species and to improve the slope by 70%. The interferences on Mn(II) retention were less severe. The quantification of Cr and Mn was performed by standard additions. The proposed methodology was validated by analysis of three certified reference materials of mussels (Cr and Mn) and non-fat milk powder (Mn) with a mean relative percent error of <6.5% and mean relative standard deviation of <13%. Chromium and Mn were determined in typical Chilean mussels samples, and Mn was determined in non-fat milk powder samples. Results agreed at the 95% confidence level with those obtained by electrothermal atomic absorption spectrometry (ETAAS) using graphite furnace atomization. The method detection limits for a 30 s pre-concentration time were 0.9 and 1.1 micro g L(-1) for Mn, and 2.2 and 2.5 micro g L(-1) for Cr in acid digested solutions of mussel and non-fat milk, respectively. The methodology is simple, fast (sampling frequency 60-72 h(-1)), reliable, of low cost, and can be applied to the determination of traces of Cr (> or =0.18 micro g g(-1)) and Mn (> or =0.6 micro g g(-1)) in mussel samples, and Mn (> or =0.37 micro g g(-1)) in non-fat milk powder.

Processes controlling the retention and release of manganese in the organic-rich catchment of Loch Bradan, SW Scotland

Loch Bradan, a drinking water reservoir in SW Scotland, frequently exhibits unacceptably high dissolved Mn concentrations. Both the surrounding catchment and the loch sediments are potential sources of Mn to the loch water. This study focused on the catchment soils, which are peaty, and found that redox cycling was an important process with respect to retention of Mn in the top sections (0–15 cm). Under more reducing conditions, reduction to Mn(II) and subsequent complexation by humic substances was observed at greater depth in some soil profiles. Complexation by humic substances is important because lateral water flow can remove soluble complexes and indeed this study observed that about 50% of Mn was humic-complexed in the stream waters feeding into the loch. It was particularly evident that the soil profile with the lowest Mn inventory exhibited the greatest extent of humification and that the remaining Mn was predominantly in a non-easily reducible form.

Bioavailability of amino acid-chelated and glass-embedded manganese to rainbow trout, Oncorhynchus mykiss (Walbaum), fingerlings

Feeding experiments were conducted to determine the bioavailability of new types of manganese (Mn) supplement to rainbow trout fingerlings. Two levels of Mn (7 and 14 mg kg−1 diet) were supplemented to diets using either manganese sulphate (Mn-S), glass-embedded Mn (Mn-Gl), or amino acid-chelated Mn (Mn-Am); more than one acid was used to chelate the metal. Rainbow trout weighing 1.30 g on average were fed the experimental diets for 12 weeks. Absorption of Mn from various compounds was evaluated using larger fish (105 g on average) fed the experimental diets. Growth was higher in the group supplemented with Mn-Am at both levels. Whole-body Mn content in fish fed the diet supplemented with Mn-Am was significantly higher than the other sources. Bone Mn accumulation was significantly higher in treatments with 14 mg Mn kg−1 diet from all sources, except Mn-Gl. At 7 mg kg−1, absorption from Mn-Am was significantly higher than from Mn-Gl and Mn-S. Mn retention from both levels of Mn-Am supplementation was significantly higher (P < 0.05) than the rest. The results indicated that amino acid-chelated Mn provided more bioavailable nutrient than Mn-S and Mn-Gl. Further, availability of Mn from Mn-Gl is equivalent to that of Mn-S.

Processes of nickel and cobalt uptake by a manganese oxide forming sediment in Pinal Creek, Globe mining district, Arizona.

A series of column experiments was conducted using manganese oxide coated sediments collected from the hyporheic zone in Pinal Creek (AZ), a metal-contaminated stream, to study the uptake and retention of Mn, Ni, and Co. Experimental variables included the absence (abiotic) and presence (biotic) of active Mn-oxidizing bacteria, the absence and presence of dissolved Mn, and sediment manganese oxide content. Uptake of Mn under biotic conditions was between 8 and 39% higher than under abiotic conditions. Continuous uptake of Mn due to biotic oxidation was evident from extraction of column sediments. Manganese uptake is hypothesized to initially occur as adsorption, which led to subsequent surface and/or microbial oxidation. Complete breakthrough of Ni within 100 pore volumes indicated no process of continuous uptake and was modeled as an equilibrium adsorption process. Nickel uptake in the presence of dissolved Mn was 67-100% reversible. Sediment extractions suggest that Ni uptake occurred through weak and strong adsorption. Continuous uptake of cobalt increased with sediment manganese oxide content, and Co uptake was up to 75% greater under biotic than abiotic conditions. Cobalt uptake was controlled by both existing and newly formed manganese oxides. Only a small amount of Co uptake was reversible (10-25%). XANES spectral analysis indicated that most Co(II) was oxidized to Co(III) and probably incorporated structurally into manganese oxides. Although manganese oxides were the primary phase controlling uptake and retention of Mn, Ni, and Co, the mechanisms varied among the metals.

Filtration artifacts caused by overloading membrane filters.

The conventional practice of using 0.45 or 0.40 microm membranes to distinguish between the particulate and dissolved phases in natural waters neglects the importance of colloids. Many of the colloids in natural waters pass through 0.45 or 0.40 microm membranes, but a significant fraction at the upper end of the colloidal particle size range is retained. Membrane clogging during filtration decreases the effective pore size and can cause the retention of increasing amounts of colloids. This filtration artifact can cause serious errors in sampling and in assigning trace metals to various particle size classes. We evaluated the effect of membrane loading for two common membrane types (0.45 microm Millipore Durapore and 0.40 microm Nuclepore) on the retention of colloidal Fe, Al, Mn, and OM in three Connecticut rivers. In addition, we used a 1.0 microm Nuclepore membrane to estimate the amount of colloids in the 0.40-1.0 microm size fraction that are retained by membranes during conventional filtration. All samples were collected with clean techniques, and all filtrations were carried out in a class 100 clean room. A peristaltic pump, set at an initial flow rate of 120 mL/min, was used to pump samples through 47 mm diameter inline Teflon filter holders. Back pressure and flow rate were monitored during filtration, and both are good indicators for the onset of membrane clogging. The results show a consistent correlation between increasing back pressure and decreasing concentration of colloidal Fe and sometimes Al, Mn, and OM in the filtrate for all membrane types. Although the shape of the loading-retention curves varied dramatically by site and by membrane type, the essential relationship between back pressure, flow rate, and filtration artifacts during membrane clogging remained the same.

Test of the first-order removal model for metal retention in a young constructed wetland

The first-order removal model is widely used in constructed wetland design. The suitability of this model was tested to predict metal retention in a young constructed wetland receiving agricultural and urban runoff. During two years, water samples for total and dissolved metal analyses were collected every third day at both the inlet and the outlet. The wetland retained metals best during summer and fall whereas during winter the retention of metals was significantly lower. The first-order removal model predicted Fe and Mn retention in the spring and dissolved Zn retention from spring to fall in both years. During those periods, hydraulic retention times (HRTs) greater than 7 days provided maximum retention for Fe, Mn, and dissolved Zn. However, first-order removal models failed to fit summer, fall and winter data for almost every metal under investigation (Fe, Mn, dissolved Cu, dissolved As) suggesting that HRTs (<1–25 days) did not affect metal retention during these seasons. The metal loading to the wetland was low and the input of metals through internal loading may be more significant consequently decreasing the metal retention. Therefore, the first-order removal model is inadequate to predict metal retention on a seasonal basis. Models used to design constructed wetlands under cold climates must consider seasonal changes that affect biological as well as hydrological variables.

Changes in dissolved and total Fe and Mn in a young constructed wetland: Implications for retention performance

Surface-flow wetlands are generally considered sinks for Fe and Mn but they may also export and affect the partitioning of these metals. This study was undertaken to evaluate the effect of a young constructed wetland on the retention and transformation of both dissolved and particulate Fe and Mn. Duplicate water samples were collected every three days at the inlet and outlet structures of the Monahan Wetland, Kanata, Ontario, from spring of 1997 to 1999. While on a yearly basis the wetland showed significant retention of the dissolved phase, the retention of total Fe and Mn was poor. There were strong seasonal differences in retention and, during the winter, the wetland was a source. The wetland transformed dissolved into particulate Fe and Mn from spring to fall whereas during the winter, dissolved Fe and Mn were released. Changes in pH, alkalinity and temperature could explain 11% and 40% of the outlet variation in the ratio of dissolved to total Fe and Mn respectively. Furthermore, from spring to late summer, planktonic algal biomass was negatively related to the ratio of dissolved to total Fe and Mn implying a role in Fe and Mn transformations in young wetlands where emergent and submerged vegetation have yet to dominate the system.

Manganese absorption and retention in rats is affected by the type of dietary fat.

There is evidence that manganese (Mn) metabolism may be altered by the form and amount of dietary fat. Also, iron (Fe) absorption is greater with saturated fats, as compared to polyunsaturated fatty acids (PUFAs). The absorption of Fe and Mn are interrelated in many aspects; therefore, the form of dietary fat may indirectly alter Mn absorption. The reported studies were conducted to determine whether saturated fat, as compared to unsaturated fat, affected Mn absorption, retention, and metabolism. In experiment I, adult rats were fed diets containing either 0.7 or 100.4 microg/g Mn with the fat source as high-linoleic safflower oil or stearic acid. After 2 wk of equilibration, the animals were fed a test meal of 54Mn followed by whole-body counting for 10 d. Manganese absorption was significantly (p < 0.05) lower in the stearic acid group (0.9-4.8%) than in the safflower oil group (20-33.8%); however, the biological half-life was shorter in the safflower oil group. Retention of 54Mn and total Mn was always significantly (p < 0.05) greater in the safflower oil group when dietary Mn was low, but it was the same when dietary Mn was high. In experiment II, weanling rats were fed 1.3, 39.3, or 174.6 microg Mn/g and either stearate, high-oleic safflower oil or high-linoleic safflower oil for 8 wk. Long-term feeding of the stearate and low Mn-containing diet resulted in a significant (p < 0.0001) reduction in heart superoxide dismutase activity and kidney and liver Mn concentrations compared to the other diets. These data show that stearic acid inhibitits Mn absorption, but it may not inhibit Mn retention when dietary Mn is high.

Absorbed Mn&lt;SUP&gt;2+&lt;/SUP&gt; and Mn redox cycling in Iberian continental margin sediments (northeast Atlantic Ocean)

Although Mn 2+ sorption has been investigated extensively in the laboratory, the role of Mn 2+ sorption in natural marine sediments remains speculative. Our objectives were to study (1) the role of Mn 2+ sorption in the redox cycling of Mn, (2) to quantify Mn cycling and (3) to identify its rate-determining factors at the Iberian margin. Profiles of pore water Mn 2+ , adsorbed Mn 2+ and solid phase Mn were measured together with benthic oxygen fluxes along three transects across the margin from the shelf to the deep sea as well as in the Nazere Canyon. In the profiles, peaks of adsorbed Mn 2 were observed in-between those of solid phase Mn and pore water Mn 2+ , We propose that upon Mn reduction, the produced Mn 2+ is adsorbed onto adjacent Mn oxide or oxyhydroxide surfaces. Available adsorption-sites diminish and/or saturate as Mn reduction continues, upon which Mn 2+ is released into the pore water. Mn redox chemistry is controlled by the organic carbon flux to the sediment. A simple steady state model was formulated that includes Mn 2+ sorption as a combination of an instantaneous reversible equilibrium process and a first-order kinetic reaction. Model derived, depth integrated rates of Mn reduction as well as Mn 2+ desorption and oxidation rates range between 1 and 35 pmoles m -2 d -1 . Mn cycling is most intense at moderate carbon fluxes. Moreover, Mn cycling is enhanced at higher deposition fluxes of Mn oxide in the canyon. Budgets based on the model indicate that adsorbed Mn 2+ is an important redox intermediate between Mn oxide and pore water Mn 2+ in the reduced sediment layer. Adsorption of Mn 2+ restrains the efflux of dissolved Mn 2+ into the water column, by lowering the pore water gradient at stations with a thin oxidation zone. There, adsorbed Mn 2+ enhances the retention of Mn 2+ in the sediment column.

Influence of induced salinity and sodicity on manganese sorption in vertisols and aridisols

Salinity and sodicity effects on manganese (Mn) sorption in a mixed sodium‐calcium (Na‐Ca) soil system were studied. Soil samples were taken at 0–30 cm depth from Vertisols (El‐Hosh and El‐Suleimi) and Aridisols (El‐Laota) at three sites in Gezira scheme (Sudan). No Mn was applied to these soils. Prior to analysis the soils were equilibrated with NaCl‐CaCL2 mixed salt solutions to attain SAR values at different salt concentrations. The results indicated that saline soils sorbed less Mn and had higher equilibrium Mn concentrations. Sodic soils retained more Mn but had low equilibrium concentrations. Sodicity had a pronounced effect only on increasing Mn retention at higher SAR values. Salinity tended to alleviate sodicity effects on Mn retention, but soluble salts that increased soil pH decreased Mn concentration.

多段表面処理シリカ粒子添加によるポリカーボネート複合系の熱安定効果と衝撃強度の向上

The thermal stability and recyclability of Polycarbonate resin (PC) composites filled with silica particles which are surface-treated with polyhydric phenol agents has been investigated. The composites were evaluated after molding 4 consecutive times. For the composites containing 1.5wt% silica particles treated with polyhydric phenol, the number-average molecular weight (Mn) of PC in the composites, measured by gel permeation chromatography, decreased from 24300 to 21800 after 4 injection molding cycles, while the unfilled PC resin control decreased to 21000.These results suggest that the PC molecule depolymerized during the injection molding process due to the thermal energy and stress. On the other hand, we found that the surface treatment of silica particles with polyhydric phenol reduced the decrease in PC Izod impact strength to 1/5 that of the neat PC resin. In addition, we studied the effects of multistage surface treatment of silica particles using two phases and three phases with benzophenone, silane-coupling agents. Three phase multistage treated silica particles resulted in higher Mn retention than those containing a single phase with polyhydric phenol.The magnitude of the activation energies (ΔE) related to the thermal degradation of the composites were evaluated by thermo-gravimetry. ΔE increased in the following order: neat PC, composite with the two-phase multistage and that with the three-phase multistage.These findings suggest that the addition of multistage surface-treated particles in PC improved the stability of PC composites. This implies that surface treatment may be an effective method in the recycle of PC resin composites.