The role of bacterial and algal exopolymeric substances in iron chemistry

© 2015 Elsevier B.V. It is widely accepted that the complexation of iron (Fe) with organic compounds is the primary factor that regulates Fe reactivity and its bioavailability to phytoplankton in the open ocean. Despite considerable efforts to unravel the provenance of the many organic ligands present in the 'ligand soup' and their contribution to Fe chemistry, much of this pool remains largely unresolved. Bacteria and phytoplankton are known to release exopolymeric substances (EPS) for a variety of functions and it is known that this material has metal binding properties. However, the contribution that bacterial and algal EPS makes to Fe biogeochemistry is not well documented. This study revealed that both bacterial and algal EPS contain functional components known to bind Fe (uronic acid, saccharides) and details the molecular weight distribution of the EPS. It is also demonstrated that components of the EPS have a high affinity for Fe-binding, in some cases similar to that of bacterial siderophores (~KFe'L 1012) and that this material greatly enhances Fe solubility (and, possibly, Fe oxyhydroxide reactivity via prevention of aggregation) in seawater. However, EPS may also accelerate Fe(II) oxidation and thus Fe(II) removal from the system. Our findings indicate that, in remote ocean regions, bacterial and algal EPS could play a significant role in the biogeochemical cycling of Fe and their contribution should be considered to further our understanding of the dynamics of Fe-limited oceans

Socio-Cultural Factors Challenging Development Interventions in Cattle Production in the Remote Areas of Vietnam

The northwest highlands of Vietnam are characterized by high altitude, low infrastructure, and low population densities composed of a wide diversity of different ethnic groups. Their socio-cultural characteristics strongly influence their lifestyle and production systems, including agricultural activities. The majority of these people have suffered from slow economic development, with the highest poverty rate in the country. This is a real need for plausible interventions where behavioral changes of smallholders throughout local value chains would be a critical foundation. Our project implemented in this context of development in the Northwest highlands of Vietnam aims to understand the role of socio-cultural factors in cattle production systems in order to propose and examine feasible technical and marketing interventions to improve local grazing-based cattle production. Data on farmers and other actors (collectors, slaughterhouses, retailers and consumers) in local cattle value chains of two selected provinces (Son La and Dien Bien) were collected at the beginning of the project via a baseline survey. In addition, different group discussions with farmers were conducted until the end of the project to monitor the project’s progress and changes created through its interventions. We found that such behavioral changes cannot be motivated by development interventions per se without integrating an understanding of socio-cultural factors (i.e. ethnicity, geographical location and grazing-practices)

Can Tourism Promote Inclusive Growth? Supply Chains, Ownership and Employment in Ha Long Bay, Vietnam

Inclusive growth is contested yet adopted by the World Bank to reduce poverty and inequality through rapid economic growth. Research has tested inclusive growth in sectors including agriculture, but few studies apply it to tourism which is significant for many developing countries. The paper interrogates tourism-led inclusive growth: supply chain, economic linkages/leakage, ownership, employment and expenditure. It draws from fieldwork in Vietnam where tourism has rapidly developed with partial economic benefits for local communities, but does not appear to fall within the inclusive growth paradigm. It is unclear if tourism-led growth will become any more inclusive in the short-to-medium term

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Kinetics of Cu(II) reduction by natural organic matter

The kinetics of Cu(II) reduction by Suwannee River fulvic acid (SRFA) at concentrations from 0.25 to 8 mg L−1 have been investigated in 2 mM NaHCO3 and 0.7 M NaCl at pH 8.0. In the absence of oxygen, SRFA reduced Cu(II) to Cu(I) in a biphasic manner, with initial rapid formation of Cu(I) followed by a much slower increase in Cu(I) concentration over time. When present, oxygen only had a noticeable effect on Cu(I) concentrations in the second phase of the reduction process and at high [SRFA]. In both the absence and presence of oxygen, the rate of Cu(I) generation increased with increasing [SRFA]. At 8 mg L−1 [SRFA], nearly 75% of the 0.4 μM Cu(II) initially present was reduced to Cu(I) after 20 min, although the yield of Cu(I) relative to [SRFA] decreased at [SRFA] \u3e 1 mg L−1. Two plausible kinetic modeling approaches were found to satisfactorily describe the experimental data over a range of [SRFA]. Despite some uncertainty as to which approach is correct, common features of both approaches were complexation of Cu(II) by SRFA and reduction of Cu(II) by two different electron donor groups within SRFA: a relatively labile electron donor (with a concentration of 1.1 × 10−4 equiv of e− (g of SRFA)−1) that reduced Cu(II) relatively rapidly and a less labile donor (with a concentration of 3.1 × 10−4 equiv of e− (g of SRFA)−1) that reduced Cu(II) more slowly

The effect of dissolved natural organic matter on the rate of removal of ferrous iron in fresh waters

The ease of removal of iron in water treatment is determined principally by the form of iron present. If iron is complexed to natural organic matter (NOM) and present in dissolved form, it is quite difficult to remove by conventional deep-bed filtration methods while if present as particulate iron oxyhydroxides it is readily removed. A major source of iron in reservoirs is the benthic sediments which, on becoming anoxic, release ferrous iron (Fe(II)) to the water column. This Fe(II) may either bind to NOM and be retained in dissolved form or may form inorganic hydroxyl complexes which oxidize to Fe(III) species which typically precipitate rapidly. In this paper, we report on studies of the kinetics of Fe(II) removal from solution in the presence and absence of the IHSS standard Suwannee River Fulvic Acid (SRFA). Oxidation of inorganic Fe(II) by oxygen is negligible at low pH but addition of organics changes the kinetics of removal of Fe(II) remarkably, reducing the half life of Fe(II) from hours to minutes. Increasing the concentration of SRFA also enhances the degree of Fe(II) removal. Experimental results obtained over a wide range of conditions are successfully described using a kinetic model which accounts for the transformations between Fe(II) and Fe(III) species

Kinetic Modeling Assisted Analysis of Vitamin C‑Mediated Copper Redox Transformations in Aqueous Solutions

The kinetics of oxidation of micromolar concentrations of ascorbic acid (AA) catalyzed by Cu(II) in solutions representative of biological and environmental aqueous systems has been investigated in both the presence and absence of oxygen. The results reveal that the reaction between AA and Cu(II) is a relatively complex set of redox processes whereby Cu(II) initially oxidizes AA yielding the intermediate ascorbate radical (A•–) and Cu(I). The rate constant for this reaction was determined to have a lower limit of 2.2 × 104 M–1 s–1. Oxygen was found to play a critical role in mediating the Cu(II)/Cu(I) redox cycle and the oxidation reactions of AA and its oxidized forms. Among these processes, the oxidation of the ascorbate radical by molecular oxygen was identified to play a key role in the consumption of ascorbic acid, despite being a slow reaction. The rate constant for this reaction (A•−+O2→DHA+O2•−) was determined for the first time with a calculated value of 54 ± 8 M–1 s–1. The kinetic model developed satisfactorily describes the Cu/AA/O2 system over a range of conditions including different concentrations of NaCl (0.2 and 0.7 M) and pH (7.4 and 8.1). Appropriate adjustments to the rate constant for the reaction between Cu(I) and O2 were found to account for the influence of the chloride ions and pH on the kinetics of the process. Additionally, the presence of Cu(III) as the primary oxidant resulting from the interaction between Cu(I) and H2O2 in the Cu(II)/AA system was confirmed, along with the coexistence of HO•, possibly due to an equilibrium established between Cu(III) and HO•

Kinetics of Fe(III) precipitation in aqueous solutions at pH 6.0–9.5 and 25 °C

The kinetics of Fe(III) precipitation in synthetic buffered waters have been investigated over the pH range 6.0–9.5 using a combination of visible spectrophotometry, 55Fe radiometry combined with ion-pair solvent extraction of chelated iron and numerical modeling. The rate of precipitation, which is first order with respect to both dissolved and total inorganic ferric species, varies by nearly two orders of magnitude with a maximum rate constant of 16 ± 1.5 × 106 M−1 s−1 at a pH of around 8.0. Our results support the existence of the dissolved neutral species, Fe(OH)30, and suggest that it is the dominant precursor in Fe(III) polymerization and subsequent precipitation at circumneutral pH. The intrinsic rate constant of precipitation of Fe(OH)30was calculated to be allowing us to predict rates of Fe(III) precipitation in the pH range 6.0–9.5. The value of this rate constant, and the variation in the precipitation rate constant over the pH range considered, are consistent with a mechanism in which the kinetics of iron precipitation are controlled by rates of water exchange in dissolved iron hydrolysis species

Kinetics of Cu(II) Reduction by Natural Organic Matter

The kinetics of Cu­(II) reduction by Suwannee River fulvic acid (SRFA) at concentrations from 0.25 to 8 mg L^–1 have been investigated in 2 mM NaHCO₃ and 0.7 M NaCl at pH 8.0. In the absence of oxygen, SRFA reduced Cu­(II) to Cu­(I) in a biphasic manner, with initial rapid formation of Cu­(I) followed by a much slower increase in Cu­(I) concentration over time. When present, oxygen only had a noticeable effect on Cu­(I) concentrations in the second phase of the reduction process and at high [SRFA]. In both the absence and presence of oxygen, the rate of Cu­(I) generation increased with increasing [SRFA]. At 8 mg L^–1 [SRFA], nearly 75% of the 0.4 μM Cu­(II) initially present was reduced to Cu­(I) after 20 min, although the yield of Cu­(I) relative to [SRFA] decreased at [SRFA] > 1 mg L^–1. Two plausible kinetic modeling approaches were found to satisfactorily describe the experimental data over a range of [SRFA]. Despite some uncertainty as to which approach is correct, common features of both approaches were complexation of Cu­(II) by SRFA and reduction of Cu­(II) by two different electron donor groups within SRFA: a relatively labile electron donor (with a concentration of 1.1 × 10^–4 equiv of e^– (g of SRFA)⁻¹) that reduced Cu­(II) relatively rapidly and a less labile donor (with a concentration of 3.1 × 10^–4 equiv of e^– (g of SRFA)⁻¹) that reduced Cu­(II) more slowly