Micronutrient deficiencies in maternity and child health: a review of environmental and social context and implications for Malawi

It is well documented that micronutrient malnutrition is of increasing concern in the developing world, resulting in poor health and high rates of mortality and morbidity. During pregnancy, deficiency of iron and zinc can produce cognitive and growth impairment of the foetus, which may continue into infancy. Iron and zinc are essential micronutrients for both plant growth and human nutrition. Despite significant work in the areas of soil fertility, crop biofortification and dietary interventions, the problems of micronutrient deficiencies persist in Africa. There is a need to examine why communities have not embraced intervention strategies which may offer health benefits. Bottom-up, interdisciplinary approaches are required to effectively study the relationships between local communities and their environment, and to assess the impact their behaviour has on the cycling of micronutrients within the soil–plant–human system. From a detailed consideration of diverse influencing factors, a methodological model is suggested for studying the barriers to improving micronutrient uptake within rural communities. It combines environmental understanding with health and social factors, emphasising the need for and potential benefits of understanding and coherence in true interdisciplinary working.     

Concurrent nitrate and Fe(III) reduction during anaerobic biodegradation of phenols in a sandstone aquifer

The biodegradation of phenols (5, 60, 600 mg l⁻¹) under anaerobic conditions (nitrate enriched and unamended) was studied in laboratory microcosms with sandstone material and groundwater from within an anaerobic ammonium plume in an aquifer. The aqueous phase was sampled and analyzed for phenols and selected redox sensitive parameters on a regular basis. An experiment with sandstone material from specific depth intervals from a vertical profile across the ammonium plume was also conducted. The miniature microcosms used in this experiment were sacrificed for sampling for phenols and selected redox sensitive parameters at the end of the experiment. The sandstone material was characterized with respect to oxidation and reduction potential and Fe(II) and Fe(III) speciation prior to use for all microcosms and at the end of the experiments for selected microcosms.The redox conditions in the anaerobic microcosms were mixed nitrate and Fe(III) reducing. Nitrate and Fe(III) were apparently the dominant electron acceptors at high and low nitrate concentrations, respectively. When biomass growth is taken into account, nitrate and Fe(III) reduction constituted sufficient electron acceptor capacity for the mineralization of the phenols observed to be degraded even at an initial phenols concentration of 60 mg l⁻¹ (high) in an unamended microcosm, whereas nitrate reduction alone is unlikely to have provided sufficient electron acceptor capacity for the observed degradation of the phenols in the unamended microcosm.For microcosm systems, with solid aquifer materials, dissolution of organic substances from the solid material may occur. A quantitative determination of the speciation (mineral types and quantity) of electron acceptors associated with the solids, at levels relevant for degradation of specific organic compounds in aquifers, cannot always be obtained. Hence, complete mass balances of electron acceptor consumption for specific organic compounds degradation are difficult to confine. For aquifer materials with low initial Fe(II) content, Fe(II) determinations on solids and in aqueous phase samples may provide valuable information on Fe(III) reduction. However, in microcosms with natural sediments and where electron acceptors are associated with the sediments, complete mass-balances for substrates and electron acceptors are not likely to be obtained.     

Redox reactions of iron and manganese oxides in complex systems

• Mechanisms of redox reactions of Fe- and Mn-oxides were discussed. • Oxidative reactions of Mn- and Fe-oxides in complex systems were reviewed. • Reductive reaction of Fe(II)/iron oxides in complex systems was examined. • Future research on examining the redox reactivity in complex systems was suggested. Conspectus Redox reactions of Fe- and Mn-oxides play important roles in the fate and transformation of many contaminants in natural environments. Due to experimental and analytical challenges associated with complex environments, there has been a limited understanding of the reaction kinetics and mechanisms in actual environmental systems, and most of the studies so far have only focused on simple model systems. To bridge the gap between simple model systems and complex environmental systems, it is necessary to increase the complexity of model systems and examine both the involved interaction mechanisms and how the interactions affected contaminant transformation. In this Account, we primarily focused on (1) the oxidative reactivity of Mn- and Fe-oxides and (2) the reductive reactivity of Fe(II)/iron oxides in complex model systems toward contaminant degradation. The effects of common metal ions such as Mn²⁺ , Ca²⁺, Ni²⁺, Cr³⁺ and Cu²⁺, ligands such as small anionic ligands and natural organic matter (NOM), and second metal oxides such as Al, Si and Ti oxides on the redox reactivity of the systems are briefly summarized.     

Effect of metals on a siderophore producing bacterial isolate and its implications on microbial assisted bioremediation of metal contaminated soils

A bacterial isolate producing siderophore under iron limiting conditions, was isolated from mangroves of Goa. Based on morphological, biochemical, chemotaxonomical and 16S rDNA studies, the isolate was identified as Bacillus amyloliquefaciens NAR38.1. Preliminary characterization of the siderophore indicated it to be catecholate type with dihydroxy benzoate as the core component. Optimum siderophore production was observed at pH 7 in mineral salts medium (MSM) without any added iron with glucose as the carbon source. Addition of NaCl in the growth medium showed considerable decrease in siderophore production above 2% NaCl. Fe⁺² and Fe⁺³ below 2 μM and 40 μM concentrations respectively, induced siderophore production, above which the production was repressed. Binding studies of the siderophore with Fe⁺² and Fe⁺³ indicated its high affinity towards Fe⁺³. The siderophore concentration in the extracellular medium was enhanced when MSM was amended with essential metals Zn, Co, Mo and Mn, however, decreased with Cu, while the concentration was reduced with abiotic metals As, Pb, Al and Cd. Significant increase in extracellular siderophore production was observed with Pb and Al at concentrations of 50 μM and above. The effect of metals on siderophore production was completely mitigated in presence of Fe. The results implicate effect of metals on the efficiency of siderophore production by bacteria for potential application in bioremediation of metal contaminated iron deficient soils especially in the microbial assisted phytoremediation processes.     

Effect of external iron and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake in rice (Oryza sativa L.)

This study was conducted to investigate the effect of external iron status and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake. Rice seedlings (Oryza sativa L.) were used as model plant, and were grown in artificially contaminated sandy soils irrigated with Murashige and Skoog (MS) culture solution. Arsenate uptake in roots and shoots of rice seedlings were affected significantly (p > 0.05) while dimethylarsinic acid (DMAA) was not by the additional iron and chelating ligand treatments. Regardless of iron concentrations in the soil solution, HIDS increased arsenic uptake for roots more than EDTA and EDDS. Chelating ligands and arsenic species also influenced iron uptake in rice roots. Irrespective of arsenic species, HIDS was found to be more effective in the increase of iron bioavailability and uptake in rice roots compared to other chelants. There was a significant positive correlation (r = 0.78, p < 0.05) between arsenate and iron concentrations in the roots of rice seedlings grown with or without additional iron indicating that arsenate inhibit iron uptake. In contrast, there was no correlation between iron and DMAA uptake in roots. Poor correlation between iron and arsenic in shoots indicated that iron uptake in shoots was neither affected by additional iron nor by arsenic species. Compared to the control, chelating ligands increased iron uptake in shoots of rice seedlings significantly (p < 0.05). Regardless of additional iron and arsenic species, iron uptake in rice shoots did not differed among EDTA, EDDS, and HIDS treatments.     

Geochemical and microbiological processes contributing to the transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated aquifer material

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a potential human carcinogen, and its contamination of subsurface environments is a significant threat to public health. This study investigated abiotic and biological degradation of RDX in contaminated aquifer material. Anoxic batch systems were started with and without pre-aeration of aquifer material to distinguish initial biological RDX reduction from abiotic RDX reduction. Aerating the sediment eliminated chemical reductants in the native aquifer sediment, primarily Fe(II) sorbed to mineral surfaces. RDX (50 μM) was completely reduced and transformed to ring cleavage products when excess concentrations (2 mM) of acetate or lactate were provided as the electron donor for aerated sediment. RDX was reduced concurrently with Fe(III) when acetate was provided, while RDX, Fe(III), and sulfate were reduced simultaneously with lactate amendment. Betaproteobacteria were the dominant microorganisms associated with RDX and Fe(III)/sulfate reduction. In particular, Rhodoferax spp. increased from 21% to 35% and from 28% to 60% after biostimulation by acetate and lactate, respectively. Rarefaction analyses demonstrated that microbial diversity decreased in electron-donor-amended systems with active RDX degradation. Although significant amounts of Fe(III) and/or sulfate were reduced after biostimulation, solid-phase reactive minerals such as magnetite or ferrous sulfides were not observed, suggesting that RDX reduction in the aquifer sediment is due to Fe(II) adsorbed to solid surfaces as a result of Fe(III)-reducing microbial activity. These results suggest that both biotic and abiotic processes play an important role in RDX reduction under in situ conditions.     

3—（H—酸偶氮）—4—（羟基）—苯磺酸与铁显色反应研究应用

研究了新试剂３—（Ｈ—酸偶氮）—４—（羟基）—苯磺酸（ＨＡＨＢＳ）与铁的显色反应,在ＮＨ４Ａｃ（ｐＨ＝ ７．０）缓冲介质中,ＨＡＨＢＳ和Ｆｅ（Ⅲ）可生成３∶１ 稳定络合物,λｍａｘ ＝ ５５０ ｎｍ ,ε＝ ４．８９×１０４Ｌ·ｍ ｏｌ－ １·ｃｍ － １,铁含量在０～０．６ ｍ ｇ／Ｌ内符合比耳定律。方法用于环境水样中铁的测定,结果令人满意。     

海藻酸钠凝胶球去除单宁酸和没食子酸的研究

采用海藻酸钠-钙凝胶球、海藻酸钠-钙-铁(Ⅲ)凝胶球、海藻酸钠-铁(Ⅲ)凝胶球对水体中单宁酸和没食子酸进行吸附实验研究。结果表明,对50mL(50mg/L)的模拟污水进行吸附,海藻酸钠-铁凝胶球和海藻酸钠-钙-铁(Ⅲ)凝胶球的吸附效果优于海藻酸钠-钙凝胶球,吸附120min后,使用Fe(Ⅲ)凝胶球对单宁酸的去除率可达97%,对没食子酸的去除率可达99%,对两种物质的吸附量分别为8.0、8.3mg/g,使用海藻酸钠-钙-铁(Ⅲ)凝胶球对单宁酸、没食子酸的去除率可达84%和97%,对两种物质的吸附量分别为7.0、8.0 mg/g。饱和吸附后海藻酸钠-钙-铁(Ⅲ)凝胶球可以再生利用,对单宁酸的去除效果随着降解再生次数的增加而降低。     

Oxidation catalyst of iron oxide suppressing dioxin formation in polyethylene combustion

A new iron oxide catalyst, which has a superior oxidation activity in carbon monoxide and polyethylene (PE) combustion, was synthesized by an aqueous solution reaction. Catalytic oxidation of carbon monoxide over six kinds of hematite obtained from the goethite was done using a microcatalytic pulse reactor, and the composition of the hematite with the highest oxidation activity was determined. With the aim of suppressing dioxin formation on combustion, incineration tests of solid wastes in PE refuse bags with and without the goethite were carried out using a commercial semibatch-type incinerator with a combustion chamber of 6.2 m³. The result confirmed that the concentration of dioxins in the flue gas decreased considerably when the refuse was incinerated in PE bags manufactured with goethite. Received: July 24, 2000 / Accepted: October 18, 2000