Arsenic in freshwater systems: Influence of eutrophication on occurrence, distribution, speciation, and bioaccumulation

Arsenic exists in a variety of chemical forms, and microbial metabolism results in the occurrence of thermodynamically unstable arsenite (As III) and methylarsenic compounds in freshwaters (rivers and lakes). The inorganic forms (As V and As III) and the methylated forms (methylarsonic acid; MMAA V and dimethylarsinic acid; DMAA V) are the main species of As in freshwaters while the bulk of the total dissolved As is inorganic species. Although the predominant forms of methylarsenic compounds are consistently DMAA V followed by MMAA V, the DMAA III and MMAA III species have also been found in freshwaters. Several observations have revealed that phytoplankton activities are responsible for the seasonal variations of methylarsenic compounds in freshwaters. Although it was unclear if the occurrences of methylarsenic compounds were from the breakdown of larger molecules or the end-products of phytoplankton biosynthesis, recent studies have revealed that less toxic As-glutathione complexes are intermediates in the biosynthesis of organoarsenic compounds by phytoplankton. Recent studies have also revealed that eutrophication plays an important role in the production, distribution, and cycling of methylarsenic compounds in freshwaters. In this review, the recent reports on the influence of eutrophication on distribution, speciation, and bioaccumulation in freshwaters are discussed. © 2011 Elsevier Ltd

Analysis of the proteinaceous components of the organic matrix of calcitic sclerites from the soft coral Sinularia sp.

An organic matrix consisting of a protein-polysaccharide complex is generally accepted as an important medium for the calcification process. While the role this "calcified organic matrix" plays in the calcification process has long been appreciated, the complex mixture of proteins that is induced and assembled during the mineral phase of calcification remains uncharacterized in many organisms. Thus, we investigated organic matrices from the calcitic sclerites of a soft coral, Sinularia sp., and used a proteomic approach to identify the functional matrix proteins that might be involved in the biocalcification process. We purified eight organic matrix proteins and performed in-gel digestion using trypsin. The tryptic peptides were separated by nano-liquid chromatography (nano-LC) and analyzed by tandem mass spectrometry (MS/MS) using a matrix-assisted laser desorption/ionization (MALDI) - time-of-flight-time-of-flight (TOF-TOF) mass spectrometer. Periodic acid Schiff staining of an SDS-PAGE gel indicated that four proteins were glycosylated. We identified several proteins, including a form of actin, from which we identified a total of 183 potential peptides. Our findings suggest that many of those peptides may contribute to biocalcification in soft corals

Mathematical analysis of a measles transmission dynamics model in Bangladesh with double dose vaccination

Although the availability of the measles vaccine, it is still epidemic in many countries globally, including Bangladesh. Eradication of measles needs to keep the basic reproduction number less than one (i.e.R01) epidemic occurs. While using the Routh-Hurwitz criteria, the equilibria are found to be locally asymptotically stable under the former condition on R0. The partial rank correlation coefficients (PRCCs), a global sensitivity analysis method is used to compute R0 and measles prevalence (I∗) with respect to the estimated and fitted model parameters. We found that the transmission rate (β) had the most significant influence on measles prevalence. Numerical simulations were carried out to commissions our analytical outcomes. These findings show that how progression rate, transmission rate and double dose vaccination rate affect the dynamics of measles prevalence. The information that we generate from this study may help government and public health professionals in making strategies to deal with the omissions of a measles outbreak and thus control and prevent an epidemic in Bangladesh

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. © 2011 Elsevier Ltd

Bioaccumulation, biotransformation and trophic transfer of arsenic in the aquatic food chain

The occurrence, distribution, speciation, and biotransformation of arsenic in aquatic environment (marine and freshwater) have been studied extensively by several research groups during last couple of decades. However, most of those studies have been conducted in marine waters, and the results are available in a number of reviews. Speciation, bioaccumulation, and biotransformation of arsenic in freshwaters have been studied in recent years. Although inorganic arsenic (iAs) species dominates in both marine and freshwaters, it is biotransformed to methyl and organoarsenic species by aquatic organisms. Phytoplankton is considered as a major food source for the organisms of higher trophic levels in the aquatic food chain, and this autotrophic organism plays important role in biotransformation and distribution of arsenic species in the aquatic environment. Bioaccumulation and biotransformation of arsenic by phytoplankton, and trophic transfer of arsenic in marine and freshwater food chains have been important concerns because of possible human health effects of the toxic metalloid from dietary intake. To-date, most of the studies on arsenic biotransformation, speciation, and trophic transfer have focused on marine environments; little is known about these processes in freshwater systems. This article has been reviewed the bioaccumulation, biotransformation, and trophic transfer of arsenic in marine and freshwater food chain. © 2012 Elsevier Inc

Arsenic accumulation in rice (Oryza sativa L.): Human exposure through food chain

Although human exposure to arsenic is thought to be caused mainly through arsenic-contaminated underground drinking water, the use of this water for irrigation enhances the possibility of arsenic uptake into crop plants. Rice is the staple food grain in Bangladesh. Arsenic content in straw, grain and husk of rice is especially important since paddy fields are extensively irrigated with underground water having high level of arsenic concentration. However, straw and husk are widely used as cattle feed. Arsenic concentration in rice grain was 0.5±0.02 mg kg-1 with the highest concentrations being in grains grown on soil treated with 40 mg As kg-1 soil. With the average rice consumption between 400 and 650 g/day by typical adults in the arsenic-affected areas of Bangladesh, the intake of arsenic through rice stood at 0.20-0.35 mg/day. With a daily consumption of 4 L drinking water, arsenic intake through drinking water stands at 0.2 mg/day. Moreover, when the rice plant was grown in 60 mg of As kg-1 soil, arsenic concentrations in rice straw were 20.6±0.52 at panicle initiation stage and 23.7±0.44 at maturity stage, whereas it was 1.6±0.20 mg kg-1 in husk. Cattle drink a considerable amount of water. So alike human beings, arsenic gets deposited into cattle body through rice straw and husk as well as from drinking water which in turn finds a route into the human body. Arsenic intake in human body from rice and cattle could be potentially important and it exists in addition to that from drinking water. Therefore, a hypothesis has been put forward elucidating the possible food chain pathways through which arsenic may enter into human body. © 2007 Elsevier Inc. All rights reserved

Comparative study of Bacillus clausii and multistrain probiotics in the management of acute diarrhoea in children

Background: Diarrhoea is the second most common cause of under-five mortality especially in developing world. Many studies have been conducted so far using different probiotic strains with variable outcome. So, the aim of the present study was to compare the clinical efficacy of Bacillus clausii and multi strain probiotic formulation as adjunct treatment of acute diarrhoea.Methods: This prospective single blind randomized controlled clinical trial included 300 infants and children between 6 months to 6 years of age admitted in a tertiary care hospital Sylhet, Bangladesh with acute watery diarrhoea having varied dehydration status ranging from no to severe dehydration excluding shocked state. Cases were randomly assigned to three groups which were group I (n=100) comprised of children who were treated with standard treatment (according to WHO guideline) only as control group, group II (n=100) who received standard treatment plus Bacillus clausii and group III (n=100) who received standard treatment plus multi strain probiotic formulation (Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus acidophilus, Lactobacillus bulgaricus, Bifidobacterium breve, Bifidobacterium infantis, Streptococcus thermophilus). Primary outcome variables were duration, frequency of diarrhoea and consistency of stool. Secondary outcome variable was duration of hospital stay.Results: Mean duration of diarrhoea was significantly shorter (p=0.001) in group III (2.62 days) compared to group I (3.26 days) and group II (3.22 days). Frequency of diarrhoea was significantly lower on day 3 of probiotic administration in group III (p 0.05) in group II in comparison to group I and group III.Conclusions: Multistrain probiotic formulation is effective in reducing the duration, frequency of diarrhoea and duration of hospital stay