Investigation of trace element mobility in river sediments using ICP-OES

In this study, the column method was used to determine the leachable trace metals present in selected river sediments. In addition the sediments were investigated using a shaker method and these two methods were compared for reliability. For both these methods extract solutions associated with a sequential extraction method were used. However, the sediments were only subjected to one extractant solution and not to the whole sequential procedure. The river sediments were also subjected to a digestion procedure to determine the total trace metal content. Simulated pollution experiments were performed where the sediments were also spiked to give known concentrations of trace metals. These results were very useful, especially in cases where certain trace metals were not currently present in river sediments. From the results achieved in this study the general trace metal status of the sediments can be established. From the results achieved it was established that in the case of the less impacted rivers (Crocodile and Olifants Rivers) only slight changes in the river conditions are needed to mobilise the trace metals present. From the results of the Blesbokspruit it was seen that urgent attention is needed to prevent further damage to the system. Water SA Vol. 31 (2) 2005: pp.183-19

On-line Determination of Hydrochloric Acid in Process Effluent Streams by Potentiometric Sequential Injection Acid-Base Titration

An on-line potentiometric sequential injection acid-base system for the titration of a hydrochloric acid solution with a standard sodium hydroxide solution in process effluent streams is proposed. A solution of 0.1 mol/l sodium chloride is used as carrier. The sample is sandwiched between two titrants in a holding coil, with the volume of the first base being twice to that of the second one and channeled by flow reversal through a reaction coil to the potentiometric sensor. A linear relationship between peak width and logarithm of the hydrochloric acid concentration was obtained in the range 0.025 mol/l - 0.05 mol/l of hydrochloric acid when a solution of 0.001 mol/l sodium hydroxide was used for the titration. Samples from process effluent streams were used to evaluate the feasibility of the method with that of an automated and manual titration. The results showed good agreement between the different methods. The percentage relative standard deviation (RSD %) was found to be less than 0.22. The sample frequency is 30 samples per hour. South African Journal of Chemistry Vol.55 2002: 43-5

Translocation of zeatin riboside and zeatin in soybean explants

Soybean explants consisting of a leaf, one or more young pods, and a subtending piece of stem were given a 1-h pulse of 3 H (ring-labeled)-zeatin riboside (ZR) or -zeatin (Z), via the base of the stem, followed by a 24-h incubation. At the end of the pulse, about 55% of the soluble 3 H was in the leaf blades, 11% in the petiole, 30% in the stem, 2% in the carpels, 0.1% in the seed coats, and 0.08% in the embryos. After 24 h, the percentages were 58, 7, 26, 6, 2, and 0.3, respectively. During this period, the total soluble 3 H decreased by 84%, the remainder being bound to “insoluble” material. The 3 H-cytokinin was rapidly converted to diverse metabolites including adenosine and adenine. At the end of the 1-h pulse, appreciable percentages (1–16%) of the total soluble 3 H in the seed coats chromatographed with ZR (or dihydro ZR) and with the 5′-phosphate of ZR, but these percentages declined markedly at 24 h. No distinct peaks of 3 H corresponded to known metabolites in the soluble extracts of embryos, and at 24 h, the 3 H equivalent to ZR must have been less than 0.0006% of the 3 H-ZR supplied. The bound 3 H corresponded to adenine and guanine in DNA and RNA. In contrast to cytokinin, 3 H-adenosine given as a pulse was readily translocated into the seed coats and embryos. Thus, cytokinin (ZR and Z) flowing up through the xylem from the root system does not readily enter the embryo (though metabolites such as adenosine could), and the seeds clearly do not compete with the leaves for this supply of cytokinin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45929/1/344_2005_Article_BF02042255.pd

Spatio-temporal Models of Lymphangiogenesis in Wound Healing

Several studies suggest that one possible cause of impaired wound healing is failed or insufficient lymphangiogenesis, that is the formation of new lymphatic capillaries. Although many mathematical models have been developed to describe the formation of blood capillaries (angiogenesis), very few have been proposed for the regeneration of the lymphatic network. Lymphangiogenesis is a markedly different process from angiogenesis, occurring at different times and in response to different chemical stimuli. Two main hypotheses have been proposed: 1) lymphatic capillaries sprout from existing interrupted ones at the edge of the wound in analogy to the blood angiogenesis case; 2) lymphatic endothelial cells first pool in the wound region following the lymph flow and then, once sufficiently populated, start to form a network. Here we present two PDE models describing lymphangiogenesis according to these two different hypotheses. Further, we include the effect of advection due to interstitial flow and lymph flow coming from open capillaries. The variables represent different cell densities and growth factor concentrations, and where possible the parameters are estimated from biological data. The models are then solved numerically and the results are compared with the available biological literature.Comment: 29 pages, 9 Figures, 6 Tables (39 figure files in total

The Bifidobacterium dentium Bd1 Genome Sequence Reflects Its Genetic Adaptation to the Human Oral Cavity

Bifidobacteria, one of the relatively dominant components of the human intestinal microbiota, are considered one of the key groups of beneficial intestinal bacteria (probiotic bacteria). However, in addition to health-promoting taxa, the genus Bifidobacterium also includes Bifidobacterium dentium, an opportunistic cariogenic pathogen. The genetic basis for the ability of B. dentium to survive in the oral cavity and contribute to caries development is not understood. The genome of B. dentium Bd1, a strain isolated from dental caries, was sequenced to completion to uncover a single circular 2,636,368 base pair chromosome with 2,143 predicted open reading frames. Annotation of the genome sequence revealed multiple ways in which B. dentium has adapted to the oral environment through specialized nutrient acquisition, defences against antimicrobials, and gene products that increase fitness and competitiveness within the oral niche. B. dentium Bd1 was shown to metabolize a wide variety of carbohydrates, consistent with genome-based predictions, while colonization and persistence factors implicated in tissue adhesion, acid tolerance, and the metabolism of human saliva-derived compounds were also identified. Global transcriptome analysis demonstrated that many of the genes encoding these predicted traits are highly expressed under relevant physiological conditions. This is the first report to identify, through various genomic approaches, specific genetic adaptations of a Bifidobacterium taxon, Bifidobacterium dentium Bd1, to a lifestyle as a cariogenic microorganism in the oral cavity. In silico analysis and comparative genomic hybridization experiments clearly reveal a high level of genome conservation among various B. dentium strains. The data indicate that the genome of this opportunistic cariogen has evolved through a very limited number of horizontal gene acquisition events, highlighting the narrow boundaries that separate commensals from opportunistic pathogens

Determination of Total Iron as Fe(II) in Multivitamins, Haematinics and Natural Waters using a Sequential Injection (SIA) System

The determination of total iron in pharmaceutical products and natural waters as Fe(II) using a sequential injection system was investigated. A cadmium reductor consisting of cadmium granules was used to reduce Fe (III) to Fe (II). The Fe (II) was then determined (by its reaction with 1,10 Phenanthroline) as a [Fe(phen)32+] complex at 515 nm with a UV/Vis spectrophotometer. The linear range of the system is between 1 and 60 mg/l with a detection limit of 0.18 mg/l. The proposed system is suitable for the determination of total iron as Fe(II) in pharmaceutical products and natural waters at a rate of 24 samples/hour with a relative standard deviation of less than 2.5%. Statistical comparison between the proposed sequential injection (SIA) system, certified values and the standard methods (Inductively Coupled Plasma {ICP} and UV/Vis spectrophotometry) revealed that there is no significant difference at the 95% confidence level. South African Journal of Chemistry Vol.53(3) 2000: 191-20

An improved technique for the determination of oxidised nitrogen in natural waters with a Sequential Injection Analysis (SIA) system

An SIA system is proposed for the determination of oxidised nitrogen (nitrate + nitrite as N) in natural waters. A cadmium reductor, made of cadmium granules closely packed in a glass column reduces the nitrate to nitrite. The reduced nitrate and the nitrite present in the water samples is diazotised in the SIA system with sulphanilamide and coupled with N - (1-napthyl) ethylene diammoniumdichloride to form a highly coloured azo dye which is detected at 540 nm with a UV/Vis spectrophotometer. The proposed system is fully computerised and is able to monitor total oxidised nitrogen as nitrite at a frequency of 36 samples per hour with a standard deviation of < 1.2%. The calibration curve is linear up to 5 mg/l with a detection limit of 0.01 mg/l. WaterSA Vol.27(3) 2001: 355-36