Mercury contamination and life history traits of Allis shad <Emphasis Type="Italic">Alosa alosa</Emphasis> (Linnaeus, 1758) and Twaite shad <Emphasis Type="Italic">Alosa fallax</Emphasis> (Lacépède, 1803) in the Gironde estuary (South West France)

Mercury concentration [Hg] was assessed in 20 adult Allis shad Alosa alosa (54–59 cm) and 20 adult Twaite shad Alosa fallax (36–44 cm) collected during their spawning migration in the Dordogne and the Garonne rivers (France). [Hg] was measured in the gills, dorsal muscle, liver and kidney. Twaite shad exhibited higher [Hg] than Allis shad. Median [Hg] values were [Hg]_Gills = 0.33 μg g⁻¹ (dw), [Hg]_Muscle = 1.22 μg g⁻¹, [Hg]_Liver = 1.99 μg g⁻¹, [Hg]_Kidney = 1.93 μg g⁻¹ for Twaite shad and [Hg]_Gills = 0.06 μg g⁻¹, [Hg]_Muscle = 0.20 μg g⁻¹, [Hg]_Liver = 1.18 μg g⁻¹, [Hg]_Kidney = 1.08 μg g⁻¹ for Allis shad. In order to understand such differences, we investigated some life history traits of the two species: migratory history, age (3–6 years), size at age (an expression of growth) and the number of spawning events (0–2 events). The difference in estuarine residence time between the juveniles of both species, which was assumed to influence [Hg], was investigated using otolith Sr:Ca ratio. The microchemical analysis revealed a significant difference in the residence time of juveniles in the estuary (medians are 21 d and 10 d for Twaite shad and Allis shad, respectively) but this residence time seems too short to influence [Hg] (Allis shad: r _spearman < 0.128; Twaite shad: r _spearman < −0.340). As both species show the same age structure, the influence of age on [Hg] was negligible. The literature shows that the differences in growth and in the number of spawning events reported in our study are in favour of a higher [Hg] for Twaite shad than for Allis shad. Although trophic status was not investigated here, the literature reveals that it is another factor that could produce higher [Hg] in Twaite shad, since its diet includes higher trophic levels than Allis shad. Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot Fish and diadromy in Europe (ecology, management, conservation)     

Silver Nanoparticles as a New Solid-Phase Adsorbent and Its Application to Preconcentration and Determination of Lead from Biological Samples

A new, simple, and fast method for preconcentration and determination of trace amount of lead from biological samples was developed by modified silver nanoparticle-based solid-phase extraction technique and graphite furnace atomic absorption spectrometry. In this study, morin was used as a complexing agent. Some factors influencing the recovery of lead including pH, sample flow rate, type, flow rate, and least amount of the eluent for elution of the lead from silver nanoparticles were studied and optimized. Under the optimum conditions, the detection limit of this method was 68 ng L⁻¹, and the relative standard deviation was 4.1% (n = 10, c = 20 μg L⁻¹). The developed procedure was validated by the analysis of certified reference material and applied to the recovery and determination of lead in biological samples.     

Selenium and Mercury in Native and Introduced Fish Species of Patagonian Lakes,Argentina

A survey of mercury (Hg) and selenium (Se) contents was performed in fish collected from lakes located in two National Parks of the northern patagonian Andean range. Two native species, catfish (Diplomystes viedmensis) and creole perch (Percichthys trucha), and three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis), were caught from lakes Nahuel Huapi, Moreno, Traful, Espejo Chico, and Guillelmo belonging to Nahuel Huapi National Park and from lakes Futalaufquen and Rivadavia, Los Alerces National Park. In lake Moreno, fish diet items were analyzed and rainbow trout grown in a farm. Hg and Se were measured in muscle and liver tissues by instrumental neutron activation analysis. The average concentrations in muscle of Hg for all species, ages, and lakes are between 0.4 to 1.0 μg g⁻¹ dry weight (DW) with a few fish, mainly native, exceeding the United States Environmental Protection Agency health advisory for freshwater fish limited consumption, and from 0.8 to 1.5 μg g⁻¹ DW for Se. Average concentrations in liver of Hg in all species range from 0.4 to 0.9 μg g⁻¹ DW. Brown trout, the top predator in these lakes, showed the lowest average Hg burden in both tissues. Se concentrations in the liver of brown and rainbow trout, up to 279 μg g⁻¹ DW, are higher than those expected for nearly pristine lakes, exceeding 20 μg g⁻¹ DW, the threshold concentration associated with Se toxicity. These species show lower Hg contents in muscle, suggesting a possible detoxification of Hg by a Se-rich diet. Creole perch and velvet catfish livers have lower Se concentrations, with a narrower span of values (2.3 to 8.5 μg g⁻¹ and 3.3 to 5.5 μg g⁻¹ DW respectively).     

Electrochemical properties of heme-protein in lauric acid films and its application as a biosensor

In this research, the enhancement of electron-transfer activity of hemoglobin (Hb) in lauric acid film was investigated for the first time. This type of composite film was made on a glassy carbon electrode by a casting method. Cyclic voltammetric result of the modified electrode displays a well-defined redox peak, which was attributed to the direct electrochemical response of Hb. Our results illustrate that Hb exchange electrons directly with electrode and exhibits the characteristics of peroxidase. When we use this modified electrode as a biosensor, it gives excellent performance in the electrocatalytic reduction of hydrogen peroxide (H₂O₂). The parameters such as pH and applied potential of the biosensor influencing in H₂O₂ detection were optimized carefully. Through the optimal conditions, the proposed biosensor shows the linear range for H₂O₂ determination was from 1×10⁻⁵ to 1.25×10⁻⁴ mol L⁻¹ with a detection limit of 1×10⁻⁷ mol L⁻¹. The biosensor retained more than 90% of the initial response after 14 d.     

Amberlite IR-120 Modified with 8-Hydroxyquinoline as Efficient Adsorbent for Solid-Phase Extraction and Flame Atomic Absorption Determination of Trace Amounts of Some Metal Ions

In this study, a solid-phase extraction method combined with atomic absorption spectrometry for extraction, preconcentration, and determination of iron (Fe³⁺), copper (Cu²⁺), and lead (Pb²⁺) ions at trace levels in water samples has been reported. The influences of effective parameters such as flow rate, pH, eluent conditions (type, volume, and concentration), sample volumes, and interference of matrix ions on metal ions recoveries were studied. Under optimized conditions, the limits of detection were found in the range of 0.7–2.2 μg L⁻¹, while preconcentration factors for Fe³⁺, Cu²⁺, and Pb²⁺ ions were found to be 166, 200, and 250, respectively, and loading half time (t _1/2) values were less than 2 min for all analyte ions. The proposed procedure was applied for the determination of metal ions in different water samples with recovery of >94.4% and relative standard deviation less than 4.4% for N = 5.     

Greater nitrogen and/or phosphorus availability increase plant species’ cover and diversity at a High Arctic polar semidesert

Enhanced nitrogen (N) deposition at high latitudes is a circumpolar phenomenon. Low soil phosphorus (P), however, may limit vegetation responses to increased N inputs. From 2000 to 2002, the effects of N at 0, 0.5 (a rate occurring in Greenland and Iceland) and 5 (equivalent to deposition in areas of Europe) g N m⁻² a⁻¹ and P (0.1 g m⁻² a⁻¹) treatments on plant species’ cover and diversity were determined at a polar semidesert site (ambient deposition c 0.1 g N m⁻² a⁻¹) in Svalbard (79°N). The largest response was to combined 5 g N plus 1 g P m⁻² a⁻¹, where cover of Saxifraga oppositifolia increased c fourfold, density of Salix polaris leaves c ninefold, seedlings of several ‘new’ species (Draba oxycarpa, Saxifraga caespitosa, Sagina nivalis) were established and ‘immigration’ of Bryum arcticum and ‘extinction’ of Schistidium apocarpum were observed. There were fewer, less pronounced, effects on the plant community at 0.5 g N m⁻² a⁻¹. Low P availability did indeed appear to restrict vegetation response to N. There was a trend for plant species’ richness and diversity to increase with 1 g P m⁻² a⁻¹ at 0 and 0.5 g N m⁻² a⁻¹, but not at 5 g N m⁻². Plant species showed individualistic responses so that generalisation by functional type was not possible. Such increased colonisation by moss species of bare soil, and greater densities of previously unrecorded angiosperm seedlings, are not usually observed in more closed (subarctic) tundra as a response to N and P additions. These changes are likely to influence significantly nutrient cycles, whole system carbon budgets and surface energy and water balances. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Modeling and Mapping of Atmospheric Mercury Deposition in Adirondack Park,New York

The Adirondacks of New York State, USA is a region that is sensitive to atmospheric mercury (Hg) deposition. In this study, we estimated atmospheric Hg deposition to the Adirondacks using a new scheme that combined numerical modeling and limited experimental data. The majority of the land cover in the Adirondacks is forested with 47% of the total area deciduous, 20% coniferous and 10% mixed. We used litterfall plus throughfall deposition as the total atmospheric Hg deposition to coniferous and deciduous forests during the leaf-on period, and wet Hg deposition plus modeled atmospheric dry Hg deposition as the total Hg deposition to the deciduous forest during the leaf-off period and for the non-forested areas year-around. To estimate atmospheric dry Hg deposition we used the Big Leaf model. The average atmospheric Hg deposition to the Adirondacks was estimated as 17.4 g m yr with a range of −3.7–46.0 g m yr. Atmospheric Hg dry deposition (370 kg yr) was found to be more important than wet deposition (210 kg yr) to the entire Adirondacks (2.4 million ha). The spatial pattern showed a large variation in atmospheric Hg deposition with scattered areas in the eastern Adirondacks having total Hg deposition greater than 30 μg m⁻² yr⁻¹, while the southwestern and the northern areas received Hg deposition ranging from 25–30 μg m⁻² yr⁻¹.     

Mercury accumulation in sediment cores and along food chains in two regions of the Brazilian Pantanal

The Pantanal is a 140,000 km² floodplain wetland stretching acrosswestern Brazil and parts of Bolivia and Paraguay. Gold mining withmercury (Hg) amalgamation has thrived since 1980 along its northern rim. We quantified Hg accumulation in sediment cores (N = 5) and food chainsin this general region of the northern Pantanal and in a reference region,200 km deeper into the wetland (Acurizal). Cores were dated with²¹⁰Pb and ¹³⁷Cs using direct gamma-assay. Total Hg wasanalyzed by cold-vapor atomic fluorescence using a gold-meshpre-concentration trap. Average pre-1940 Hg accumulation in cores wasnot significantly different (N = 5, p= 0.14) between both regions andcomparable with rates calculated for global reference sites. Post gold-rushHg (post-1980) deposition averaged 55 ± 11.3 g m^-2yr^-1 in the northern impacted region and was more than 1.5 timeshigher than the post-1980 rate in Acurizal, implying a regional Hg effectof gold mining. Post-1980 Hg accumulation in Acurizal, in turn, was 2.1times the rate reported for a global reference during that time period,suggesting an additional basin-wide effect over such reference sites. Bycombining our core data with assessments of the size of the impacted areaand the amount of Hg released to the region since 1980, we estimated thatonly 2–8% of this Hg was recovered as a sedimentary signal. Theremainder of the Hg was lost to the atmosphere, downstream areas, orstored in biota. Hg concentrations in surface sediments in the northernPantanal (45.5 ± 5.5 ng g_dry ^-1) were significantlyhigher than those in our reference region (29.1 ± 0.7ng g_dry ^-1). Hg levels in primary producers were alsoelevated in the northern Pantanal. Eichhornia crassipes rootscontained 2.7–3.0 times more mercury than shoots in both regions and Salvinia auriculata, suggested as a biological monitor for Hg pollution,contained almost four times more mercury in the northern Pantanal (90.7± 9.1 ng g_dry ^-1) than in Acurizal (24.5 ± 3.3ng g_dry ^-1). Plant grazers and scavengers, such as apple snails(Pomacea sp.) and adult water beetles (Fam. Hydrophilidae), werelow in Hg, confirming previous data showing that the channeling of mercuryfrom lower to higher trophic levels along herbivorous links was inefficientcompared to transfer along carnivorous links. Collections of 12–16individuals of four species of Characidae (Aphyocharax sp., Tetragonopterus sp., Serrasalmus spiropleura and Pygocentrisnattereri) in both regions showed elevated Hg body burdens in bothpiranhas S. spiropleura and P. nattereri from the northernPantanal (149.9 ± 84.2 and 302.2 ± 159.1ng g_dry ^-1, respectively). Fish length for each species was notstatistically different between regions. P. nattereri length correlatedsignificantly (p<0.001) with Hg content in both regions, but the slopeof the regression in the northern Pantanal was 2.6 times the slope for theAcurizal collection, indicating an elevated rate of biomagnification in theHg-impacted region. Signals of Hg use in mining can be quantified insediment core chronologies and biological tissues, although species atdifferent trophic levels show dissimilar impacts. Mechanisms involved in Hgmagnification along food chains deserve more attention, particularly intropical regions where the threat of chronic exposure to this neurotoxinmay have the greatest implications for biodiversity.     

Zinc,Manganese, Calcium,Copper, and Cadmium Level in Scalp Hair Samples of Schizophrenic Patients

The purpose of the study was to determine the concentration of trace elements present in scalp hair sample of schizophrenic patients and to find out the relationship between trace elements level and nutritional status or socioeconomic factors. The study was conducted among 30 schizophrenic male patients and 30 healthy male volunteers. Patients were recruited from Bangabandhu Sheikh Mujib Medical University by random sampling. Hair trace element concentrations were determined by flame atomic absorption spectroscopy and analyzed by independent t test, Pearson’s correlation analysis, regression analysis, and analysis of variance (ANOVA). Mn, Zn, Ca, Cu, and Cd concentrations of schizophrenic patients were 3.8 ± 2.31 μg/gm, 171.6 ± 59.04 μg/gm, 396.23 ± 157.83 μg/gm, 15.40 ± 5.68 μg/gm, and 1.14 ± 0.89 μg/gm of hair sample, while those of control subjects were 4.4 ± 2.32 μg/gm, 199.16 ± 27.85 μg/gm, 620.9 ± 181.55 μg/gm, 12.23 ± 4.56 μg/gm, and 0.47 ± 0.32 μg/gm of hair sample, respectively. The hair concentration of Zn and Ca decreased significantly (p = 0.024; p = 0.000, respectively) and the concentration of Cu and Cd increased significantly (p = 0.021; p = 0.000, respectively) in schizophrenic patients while the concentration of Mn (p = 0.321) remain unchanged. Socioeconomic data reveals that most of the patients were poor, middle-aged and divorced. Mean body mass indices (BMIs) of the control group (22.26 ± 1.91 kg/m²) and the patient group (20.42 ± 3.16 kg/m²) were within the normal range (18.5−25.0 kg/m²). Pearson’s correlation analysis suggested that only Ca concentration of patients had a significant positive correlation with the BMI (r = 0.597; p = 0.000) which was further justified from the regression analysis (R ² = 44%; t = 3.59; p = 0.002) and one-way ANOVA test (F = 3.62; p = 0.015). A significant decrease in the hair concentration of Zn and Ca as well as a significant increase in the hair concentration of Cu and Cd in schizophrenic patients than that of its control group was observed which may provide prognostic tool for the diagnosis and treatment of this disease. However, further work with larger population is suggested to examine the exact correlation between trace element level and the degree of disorder.     

Effect of Scalp and Facial Hair on Air Displacement Plethysmography Estimates of Percentage of Body Fat

Objective: The objective of this study was to determine the effect of body hair (scalp and facial) on air displacement plethysmography (BOD POD) estimates of percentage of body fat. Research Methods and Procedures: A total of 25 men (31.4 ± 8.0 years, 83.4 ± 12.2 kg, 181.8 ± 6.9 cm) agreed to grow a beard for 3 weeks to participate in the study. Total body density (g/cm³) and percentage of body fat were evaluated by BOD POD. To observe the effect of trapped isothermal air in body hair, BOD POD measures were performed in four conditions: criterion method (the beard was shaven and a swimcap was worn), facial hair and swimcap, facial hair and no swimcap, and no facial hair and no swimcap_. Results: The presence of only a beard (facial hair and swimcap) resulted in a significant underestimation of percentage of body fat (16.2%, 1.0618 g/cm³) vs. the criterion method (17.1%, 1.0597 g/cm³, p < 0.001). The effect of scalp hair (no swim cap worn) resulted in a significant underestimation in percentage of body fat relative to the criterion method, either with facial hair (facial hair and no swimcap; 14.8%, 1.0649 g/cm³) or without facial hair (no facial hair and no swimcap; 14.8%, 1.0650 g/cm³, p < 0.001 for both). Discussion: A significant underestimation of percentage of body fat was observed with the presence of facial hair (～1%) and scalp hair (～2.3%). This underestimation in percentage of body fat may be caused by the effect of trapped isothermal air in body hair on body‐volume estimates. Thus, excess facial hair should be kept to a minimum and a swimcap should be worn at all times to ensure accurate estimates of body fat when using the BOD POD.     

137Cs mobility in soils and its long-term effect on the external radiation exposure

To predict the external gamma-dose rate of Chernobyl-derived ¹³⁷Cs for a period of about 100 years after its deposition, the vertical distribution of radiocesium in several meadow soils in the Chernobyl area and in Germany was determined, and the corresponding residence half-times of this radionuclide in the various soil layers were evaluated using a compartment model. The resulting residence half-times were subsequently used to calculate the vertical distribution of ¹³⁷Cs in the soil as a function of time and finally to predict the external gamma-dose rates in air for these sites at various times. A regression analysis of the data obtained showed that the time dependence of the relative gamma-dose rate in air D(t) at the Chernobyl sites can be described by an exponential equation D(t) = a + b ⋅ exp(–t/c), where t is the time after deposition. For the ten German sites the best fit was obtained using the two-exponential equation D(t) = a ⋅ exp(–t/b) + c ⋅ exp(–t/d). The gamma-dose rate of ¹³⁷Cs at the Chernobyl sites decreases significantly more slowly with time than at the German sites. This means that after e.g. 30 years the mean relative gamma-dose rate at the German sites will have decreased from 100% (corresponding to an infinite plane source on a smooth surface) to 9% (95% confidence interval 8%–10%), while at the sites in the Chernobyl area it will have decreased only to 21% (20%–23%). This difference is the result of the longer residence half-times of ¹³⁷Cs in the soils at the Chernobyl sites. All results are compared with estimates from earlier studies. Received: 16 October 1996 / Accepted in revised form: 28 November 1996     

Response of nutrient dynamics of decomposing pine (Pinus massoniana) needles to simulated N deposition in a disturbed and a rehabilitated forest in tropical China

The effects of simulated N deposition on changes in mass, C, N and P of decomposing pine (Pinus massoniana) needles in a disturbed and a rehabilitated forest in tropical China were studied during a 24-month period. The objective of the study was to test the hypothesis that litter decomposition in a disturbed forest is more sensitive to N deposition rate than litter decomposition in a rehabilitated forest due to the relatively low nutrient status in the former as a result of constant human disturbance (harvesting understory and litter). The litterbag method and N treatments (control, no N addition; low-N, 5 g N m⁻² year⁻¹; medium-N, 10 g N m⁻² year⁻¹) were employed to evaluate decomposition. The results revealed that N addition increased (positive effect) mass loss rate and C release rate but suppressed (negative effect) the release rate of N and P from decomposing needles in both disturbed and rehabilitated forests. The enhanced needle decomposition rate by N addition was significantly related to the reduction in the C/N ratio in decomposing needles. However, N availability is not the sole factor limiting needle decomposition in both disturbed and rehabilitated forests. The positive effect was more sensitive to the N addition rate in the rehabilitated forest than in the disturbed forest, however the reverse was true for the negative effect. These results suggest that nutrient status could be one of the important factors in controlling the response of litter decomposition and its nutrient release to elevated N deposition in reforested ecosystems in the study region.     

Optimization of culture conditions and continuous production of chitosan by the fungi,Absidia coerulea

The production of chitosan from the mycelia ofAbsidia coerulea was studied to improve cell growth and chitosan productivity. Culture conditions were optimized in batch cultivation (pH 4.5 agitator speed of 250 rpm, and aeration rate of, 2 vvm) and the maximum chitosan concentration achieved was 2.3 g/L under optimized conditions. Continuous culture was carried out successfully by the formation of new growth spots under optimized conditions, with a chitosan productivity of 0.052 gL⁻¹ h⁻¹, which is the highest value to date, and was obtained at a dilution rate of 0.05 h⁻¹. Cell chitosan concentrations reached about 14% in the steady state, which is similar to that achieved in batch culture. This study shows that for the continuous culture ofAbsidia coerulea it is vital to control the medium composition.     

Production of 1,3-Propanediol by Clostridium butyricum VPI 3266 in continuous cultures with high yield and productivity

The effects of dilution rate and substrate feed concentration on continuous glycerol fermentation by Clostridium butyricum VPI 3266, a natural 1,3-propanediol producer, were evaluated in this work. A high and constant 1,3-propanediol yield (around 0.65 mol/mol), close to the theoretical value, was obtained irrespective of substrate feed concentration or dilution rate. Improvement of 1,3-propanediol volumetric productivity was achieved by increasing the dilution rate, at a fixed feed substrate concentration of 30, 60 or 70 g l⁻¹. Higher 1,3-propanediol final concentrations and volumetric productivities were also obtained when glycerol feed concentration was increased from 30 to 60 g l⁻¹, at D=0.05–0.3 h⁻¹, and from 60–70 g l⁻¹, at D=0.05 and 0.1 h⁻¹·30 g l⁻¹ of 1,3-propanediol and the highest reported value of productivity, 10.3 g l⁻¹ h⁻¹, was achieved at D=0.30 h⁻¹ and 60 g l⁻¹ of feed glycerol. A switch to an acetate/butyrate ratio higher than one was observed for 60 g l⁻¹ of feed glycerol and a dilution rate higher than 0.10 h⁻¹; moreover, at D=0.30 h⁻¹ 3-hydroxypropionaldehyde accumulation was observed for the first time in the fermentation broth of C. butyricum.     

Ethanol production from hardwood spent sulfite liquor using an adapted strain of Pichia stipitis

Conditions have been optimized for fermentation of pretreated hardwood spent sulfite liquor (HSSL) using an adapted strain of Pichia stipitis. The pretreatments, consisting of boiling and overliming with Ca(OH)₂ of HSSL, to partially remove inhibitors, and adaptation of the yeast strain to HSSL, were both critical for a successful fermentation. Ethanol concentration was increased from 6.7 to 20.2 g l⁻¹ using adapted P. stipitis (A) and pretreated HSSL. The maximum ethanol yield (Y _p/s) and productivity (Q _p) were 0.41 g g⁻¹ and 0.44 g l⁻¹ h⁻¹, respectively, at an oxygen transfer rate of 2.0 mmol O₂ l⁻¹ h⁻¹. The optimized results with this strain were compared to those of other xylose-fermenting yeasts and Saccharomyces cerevisiae (SSL-acclimatized) currently used at an industrial plant for the fermentation of spent sulfite liquor. Journal of Industrial Microbiology & Biotechnology (2001) 26, 145–150. Received 23 June 2000/ Accepted in revised form 21 October 2000     

Production of chum salmon cystatin from the recombinant <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> optimized using response surface methodology

Chum salmon cystatin was overexpressed on Saccharomyces cerevisiae YPH 499. At first, the culture condition for the production of recombinant chum salmon cystatin (RC) by S. cerevisiae YPH 499 was optimized in a shake flask using response surface methodology. Three independent variables; medium pH, inducing time, and the amount of inducing assistant, were analyzed to get the optimal condition for the production of RC. The results were fitted to a second-order polynomial equation, in which the determination coefficient (R ²) was 0.904. The highest RC production in a shake flask, 0.57 U/mL was obtained at 5.7 of medium pH, 6.7 h of inducing time, and 5.6 g/L of inducing assistant. Based on the results of shake flask, the effects of agitation and aeration rates on the production of RC by S. cerevisiae YPH 499 were determined for scaleup in a fermentor. The highest production of RC in a fermentor, 0.56 U/mL was obtained at 350 rpm of agitation rate and 1.0 vvm of aeration rate. RC at 100 μg/g showed the highest inhibitory activity against the autolysis of Alaska pollock surimi based on the analysis of TCA-soluble peptides.     

Kinetic spectrophotometric method for the determination of ramipril in pharmaceutical formulations

The objective of this research was to develop a kinetic spectrophotometric method for determination of ramipril in pure form and pharmaceutical formulations. The method was based on the reaction of carboxylic acid group of the drug with a mixture of potassium iodate (KIO₃) and potassium iodide (KI) in aqueous medium at room temperature. The reaction is followed spectrophotometrically by measuring the increase in absorbance at 352 nm as a function of time. The initial-rate and fixed-time methods were adopted for constructing the calibration curves. Both the calibration curves were linear in the concentration range of 10.0–70.0 μg mL⁻¹. The detection limits were 0.02μg mL⁻¹ and 0.15-μg mL⁻¹ for initial rate and fixed time methods, respectively. The proposed methods are validated statistically and through recovery studies. The point and interval hypothesis tests have been performed confirming that there is no significant difference between the proposed methods and the reference method. The experimental true bias of all samples is less than ±2%. The methods have been successfully applied to the determination of ramipril in tablets and capsules. Published: October 27, 2005     

Optimization of fed-batch fermentation for xylitol production by Candida tropicalis

Xylitol, a functional sweetener, was produced from xylose by biological conversion using Candida tropicalis ATCC 13803. Based on a two-substrate fermentation using glucose for cell growth and xylose for xylitol production, fed-batch fermentations were undertaken to increase the final xylitol concentration. The effects of xylose and xylitol on xylitol production rate were studied to determine the optimum concentrations for fed-batch fermentation. Xylose concentration in the medium (100 g l⁻¹) and less than 200 g l⁻¹ total xylose plus xylitol concentration were determined as optimum for maximum xylitol production rate and xylitol yield. Increasing the concentrations of xylose and xylitol decreased the rate and yield of xylitol production and the specific cell growth rate, probably because of an increase in osmotic stress that would interfere with xylose transport, xylitol flux to secretion to cell metabolism. The feeding rate of xylose solution during the fed-batch mode of operation was determined by using the mass balance equations and kinetic parameters involved in the equations in order to increase final xylitol concentration without affecting xylitol and productivity. The optimized fed-batch fermentation resulted in 187 g l⁻¹ xylitol concentration, 0.75 g xylitol g xylose⁻¹ xylitol yield and 3.9 g xylitol l⁻¹ h⁻¹ volumetric productivity. Journal of Industrial Microbiology & Biotechnology (2002) 29, 16–19 doi:10.1038/sj.jim.7000257 Received 15 October 2001/ Accepted in revised form 30 March 2002     

Optimization of probiotic and lactic acid production by Lactobacillus plantarum in submerged bioreactor systems

Biomass and lactic acid production by a Lactobacillus plantarum strain isolated from Serrano cheese, a microorganism traditionally used in foods and recognized as a potent probiotic, was optimized. Optimization procedures were carried out in submerged batch bioreactors using cheese whey as the main carbon source. Sequential experimental Plackett–Burman designs followed by central composite design (CCD) were used to assess the influence of temperature, pH, stirring, aeration rate, and concentrations of lactose, peptone, and yeast extract on biomass and lactic acid production. Results showed that temperature, pH, aeration rate, lactose, and peptone were the most influential variables for biomass formation. Under optimized conditions, the CCD for temperature and aeration rate showed that the model predicted maximal biomass production of 14.30 g l⁻¹ (dw) of L. plantarum. At the central point of the CCD, a biomass of 10.2 g l⁻¹ (dw), with conversion rates of 0.10 g of cell g⁻¹ lactose and 1.08 g lactic acid g⁻¹ lactose (w/w), was obtained. These results provide useful information about the optimal cultivation conditions for growing L. plantarum in batch bioreactors in order to boost biomass to be used as industrial probiotic and to obtain high yields of conversion of lactose to lactic acid.     

Investigation of mercury concentrations in fur of phocid seals using stable isotopes as tracers of trophic levels and geographical regions

Recent studies have shown that the complementary analysis of mercury (Hg) concentrations and stable isotopic ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) can be useful for investigating the trophic influence on the Hg exposure and accumulation in marine top predators. In this study, we propose to evaluate the interspecies variability of Hg concentrations in phocids from polar areas and to compare Hg bioaccumulation between both hemispheres. Mercury concentrations, δ¹⁵N and δ¹³C were measured in fur from 85 individuals representing 7 phocidae species, a Ross seal (Ommatophoca rossii), Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophagus), harbour seals (Phoca vitulina), grey seals (Halichoerus grypus), ringed seals (Pusa hispida) and a bearded seal (Erignathus barbatus), from Greenland, Denmark and Antarctica. Our results showed a positive correlation between Hg concentrations and δ¹⁵N values among all individuals. Seals from the Northern ecosystems displayed greater Hg concentrations, δ¹⁵N and δ¹³C values than those from the Southern waters. Those geographical differences in Hg and stable isotopes values were likely due to higher environmental Hg concentrations and somewhat greater number of steps in Arctic food webs. Moreover, dissimilarities in feeding habits among species were shown through δ¹⁵N and δ¹³C analysis, resulting in an important interspecific variation in fur Hg concentrations. A trophic segregation was observed between crabeater seals and the other species, resulting from the very specific diet of krill of this species and leading to the lowest observed Hg concentrations.