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S Nayar

Publications and source records attributed to S Nayar.

At least 19 recordsLinked to original sources
PubMed2006

Environmental effects of dredging on sediment nutrients, carbon and granulometry in a tropical estuary.

This monitoring study encompassed a period prior to dredging, during dredging and post dredging between July 1999 to June 2000 in Ponggol estuary located along the northeastern coast of Singapore. Mean concentrations of sediment nutrients in mg x Kg(-1) (+/- standard error of means) prior to dredging, during dredging and post dredging were 9.75 +/- 4.24, 8.18 +/- 4.29 and 11.46 +/- 4.74 for ammonium, 0.08 +/- 0.05, 0.06 +/- 0.02 and 0.09 +/- 0.01 for nitrite, 0.04 +/- 0.04, 0.11 +/- 0.17 and 0.25 +/- 0.30 for nitrate, 4.83 +/- 3.48, 0.77 +/- 0.48 and 8.33 +/- 9.73 for phosphate respectively. Pre dredge, dredge and post dredge levels of total carbon (TC) were 18.5 +/- 3.7, 20.2 +/- 3.5 and 34.6 +/- 12.0, of total organic carbon (TOC) were 10.5 +/- 2.9, 19.5 +/- 3.6 and 34.6 +/- 12.0 and of total inorganic carbon (TIC) were 7.9 +/- 1.0, 0.7 +/- 0.4 and non detectable in the sediments, respectively. Both, sediment nutrients and carbon registered lower concentrations with onset of dredging, with the exception of nitrate and TOC. A shift in sedimentary carbon from inorganic carbon to organic carbon was also observed with the onset of the dredging activities when the organically enriched historically contaminated layer was exposed. Sediment granulometry showed that the sediments in the estuary were predominantly silt and clay prior to dredging, which changed to sand with onset of dredging. Silt load in the sediments was highest post-dredge. Sediment nutrients and sediment organic carbon were observed to associate with the finer fractions (silt and clay) of sediments. Finer fractions of sediments get resuspended during a dredging event and are dispersed spatially as the result of tides and water movements. Prior to this study, the potential for nutrient release and sediment granulometry due to dredging have been suggested, but there have been few studies of it, especially in the tropics. The baseline information gathered from this study could be used to work out effective management strategies to protect similar tropical ecosystems elsewhere, should there be no other alternative to dredging.

Carbon↗
PubMed2006

Spatio-temporal fluxes in particulate organic carbon in a tropical coastal lagoon.

Temporal and spatial variations in particulate organic carbon (POC) in relation to primary production, chlorophyll a, phaeophytin, plankton abundance, secondary production and suspended particulate matter (SPM) were studied monthly for 1 year from April 1996 to March 1997 in a shallow tropical coastal lagoon on the southwest coast of India. Though temporal variations in all components were significant, spatial variabilities were not statistically significant. POC values range from 200 to 5690 mg C m(3) h(-1), while primary production, chlorophyll a, and phaeophytin varied between 0.02 and 14.53 mg C m(-3) h(-1), 0.87 and 23.11 mg m(-3) and 3.02 and 30.581 mg m(-3), respectively. Phytoplankton and zooplankton abundance varied from 0.01 to 655.5 x 10(5) no m(-3) and negligible to 7.08 x 10(5) no m(-3) respectively; secondary production from 10 to 490 mg C m(-3) and SPM between 0.38 and 74.43 x 10(4) mg m(-3) during this study. Temporally, postmonsoon months were observed to have the highest concentrations of POC in the lagoon waters. The bulk of the POC pool in the lagoon was composed of secondary producers (72%), followed by chlorophyll a (21%), phaeophytin (7%) and suspended particulate matter of inorganic origin (< 0.1%).

Animals↗
PubMed2005

Environmental impacts of diesel fuel on bacteria and phytoplankton in a tropical estuary assessed using in situ mesocosms.

Dissolved or dispersed petroleum hydrocarbon concentrations (DDPH) were monitored in Ponggol estuary, Singapore, fortnightly from July 1999 to June 2000. DDPH concentrations ranged from 4.4 to 248.9 microg l(-1) and 0.4 to 1099.7 microg l(-1) for surface and subsurface waters, respectively and with mean concentrations of 41.01 microg l(-1) in the water column. Absorbed or adsorbed petroleum hydrocarbon (AAPH) concentrations measured in sediments ranged from 20.6 to 541.0 mg kg(-1), with mean concentrations of 148.23 mg kg(-1). In situ mesocosm studies of bacteria and phytoplankton were based on field monitoring of environmentally measured concentrations of petroleum hydrocarbons, using diesel fuel as the source of contaminant. The mesocosm comprised of 25 L clear polycarbonate carboys incubated in situ for 6 days. Water and sediments from a clean site with undetectable levels of petroleum hydrocarbons were used in controls. The treatment mesocosms comprised of mean and highest concentrations of DDPH and AAPH. The study revealed signs of acute toxicity to autotrophs viz., phytoplankton and autotrophic bacteria in treatments simulating concentrations of diesel fuel found in the sediments. A stimulatory effect was seen at lower concentrations. Bacterial heterotrophs responded positively to all concentrations of diesel fuel because of the abundance of a carbon source, reduced grazing pressure and reduced competition for nutrients from phytoplankton.

Amidines↗
PubMed2004

Environmental impact of heavy metals from dredged and resuspended sediments on phytoplankton and bacteria assessed in in situ mesocosms.

Past and on-going reclamation, dredging, construction and shipping activities impact Ponggol Estuary, located on the northeastern coast of Singapore. Tin, lead, nickel, cadmium, and copper in particulate and dissolved fractions and sediments ranged from ND (undetectable)-92 ppm, ND-303.2 ppm, ND-2818.4 ppm, ND-74.4 ppm and ND-1117.7 ppm, respectively. Intensive dredging activity during the monitoring period may have led to the resuspension and bioavailability of particulate metals. This was tested by the exposure of phytoplankton and bacteria in mesocosms to previously measured environmental levels of heavy metals and the contaminated sediments with the highest heavy metal concentrations from one of the impacted sites. The results showed significant copper toxicity to phytoplankton and autotrophic bacteria, followed by nickel and lead at all concentrations tested. Enhanced rates of heterotrophic bacterial production and total bacterial abundance were observed in treatments with higher metal concentrations. Among the various treatments, particulate and sediment metal concentrations were significantly different from those of the control. Mesocosms using contaminated sediments with the highest metal concentrations compared with the control showed a bioavailability of metals that resulted in the inhibition of phytoplankton and autotrophic bacteria. High concentrations of copper (5.52-11.35 mg L(-1)) and nickel (2.42-2.71 mg L(-1)) observed in the aqueous phase of treatment mesocosms, and attributed to release from the contaminated sediments could account for the toxicity to phytoplankton and autotrophic bacteria.

Bacteria↗
PubMed2003

In situ microcosms to study the impact of heavy metals resuspended by dredging on periphyton in a tropical estuary.

Ponggol estuary, located on the northeastern coast of Singapore, is heavily impacted by reclamation, dredging, construction and shipping. Tin, lead, nickel, cadmium, copper and zinc in the particulate and dissolved fraction and in sediments were monitored biweekly in the estuary from July 1999 to June 2000. The concentrations of tin, lead, nickel, cadmium, copper and zinc were observed to range from ND-92 ppm, ND-303 ppm, ND-2818 ppm, ND-74 ppm, ND-1117 ppm and ND-137000 ppm, respectively, in the dissolved, particulate and sediments fractions. Intensive dredging activity occurred during the monitoring period, and this may have led to the resuspension and increased bioavailability of particulate metals. Periphytic algae were established on glass slides and exposed to previously measured environmental levels of heavy metals using in situ estuarine microcosms. The toxicity of heavy metals in various fractions to periphytic algae was assessed from the changes in their chlorophyll a content. Cadmium had the least significant effect followed by lead, zinc, nickel, tin and copper at all concentrations tested. A reduction in periphyton biomass (with respect to controls) of 95-100% was observed for treatments with metals in particulate form. In addition, exposure to contaminated sediments for 3 days significantly decreased chlorophyll a by 90-99% compared to controls. High concentrations of zinc (9893-17240 mg l(-1)), copper (5-11 mg l(-1)) and cadmium (1-1.8 mg l(-1)) recorded in the aqueous phase of treatment microcosms, and attributed to release from the contaminated sediments, could account for the toxicity to periphyton.

Analysis of Variance↗
PubMed2001

UDP-galactose 4-epimerase from Escherichia coli: equilibrium unfolding studies.

UDP-galactose 4-epimerase from Escherichia coli is a homodimer of 39 kDa subunit with non-covalently bound NAD acting as cofactor. The enzyme can be reversibly reactivated after denaturation and dissociation using 8 M urea at pH 7.0. There is a strong affinity between the cofactor and the refolded molecule as no extraneous NAD is required for its reactivation. Results from equilibrium denaturation using parameters like catalytic activity, circular-dichroism, fluorescence emission (both intrinsic and with extraneous fluorophore 1-aniline 8-naphthalene sulphonic acid), 'reductive inhibition' (associated with orientation of NAD on the native enzyme surface), elution profile from size-exclusion HPLC and light scattering have been compiled here. These show that inactivation, integrity of secondary, tertiary and quaternary structures have different transition mid-points suggestive of non-cooperative transition. The unfolding process may be broadly resolved into three parts: an active dimeric holoenzyme with 50% of its original secondary structure at 2.5 M urea; an active monomeric holoenzyme at 3 M urea with only 40% of secondary structure and finally further denaturation by 6 M urea leads to an inactive equilibrium unfolded state with only 20% of residual secondary structure. Thermodynamical parameters associated with some transitions have been quantitated. The results have been discussed with the X-ray crystallographic structure of the enzyme.

Binding Sites↗
PubMed1999

Prevalence of sputum-positive pulmonary tuberculosis in tribal and non-tribal populations of the Ashti and Karanja tahsils in Wardha district, Maharashtra State, India.

SETTING: Ashti and Karanja tahsils, Wardha district, Maharashtra State, Central India. OBJECTIVE: To find and compare the prevalence of bacillary positive pulmonary tuberculosis amongst the different tribes and in the non-tribal population. DESIGN: Prevalence study of pulmonary tuberculosis by house-to-house survey of symptoms among tribal (n = 20596) and non-tribal (n = 93 670) populations aged 5 years and over, between September 1989 and November 1990. RESULTS: The prevalence of smear and/or culture-positive tuberculosis/100000 population was 133 in the tribal and 144 in the non-tribal population. The difference in prevalence of symptomatic individuals and sputum-positive cases among the tribal and the non-tribal populations was statistically significant only in the symptomatic individuals/100000 (P = 0.01). The prevalence of cases in both groups was higher in males than females; however this difference was significant only in the tribal group (P = 0.05). Only two of the 46 tribes encountered, the Mana and Pawara tribes, showed a high prevalence, of 730 and 612/100000, respectively. The three other tribes with positive cases (the Gond group) had prevalences comparable to that of the nontribal population. CONCLUSION: The prevalence of tuberculosis in tribal people was comparable to that of the non-tribal population.

Adolescent↗
PubMed1997

UDP-galactose 4-epimerase from Escherichia coli: existence of a catalytic monomer.

UDP-galactose 4-epimerase from Escherichia coli is a homodimer of molecular mass 39 kDa/subunit and requires NAD as a co-factor. X-ray crystallographic studies indicate two pyridine nucleotide co-factor-binding sites of the dimeric molecule situated in a symmetry-oriented manner. Size-exclusion HPLC of an equilibrium intermediate at 3 M urea suggests a monomeric holoenzyme structure that is catalytically active. Ultracentrifugal studies of the native enzyme in a 5-20% sucrose gradient at low protein concentration also indicate existence of a catalytic monomer. The monomer resembles the dimeric protein in stability and most of its physico-chemical properties.

Anilino Naphthalenesulfonates↗
PubMed1997

A study of ocular morbidity among elderly population in a rural area of central India.

A cross-sectional study was conducted in five randomly selected villages in Wardha district of Maharashtra state to study the magnitude and factors related to the prevalence of ocular diseases among the elderly population. A total of 903 persons above 50 years were screened. The prevalence of low vision was 32% while that of blindness was 12.2%. Ocular morbidity rate was 1.21 lesions per elderly person and it increased significantly with increasing age (p < 0.001). Ocular diseases were found to be more prevalent among males, low socio-economic status group and landless labourers (p < 0.001). There was a high prevalence of refractive errors (40.8%), cataract (40.4%), aphakia (11.1%) followed by pterygium (5.2%), glaucoma (3.1%) and corneal opacities (3%). Prevalence of diseases of the lens and iris increased significantly with increasing age (p < 0.001). There is a need to evolve strategies for reducing the burden of ocular diseases and improve geriatric eye health under the existing infrastructure of health care delivery in our country.

Aged↗
PubMed1996

Association of endogenous steroid levels with high and low density lipoprotein concentrations in the human maternal-fetoplacental unit at term.

OBJECTIVE: To determine the concentrations of high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), estradiol (E2), dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) in both maternal and venous cord blood upon delivery at term; to determine the degree of association between lipoprotein cholesterol concentrations and concentrations of selected steroid hormones, thus indicating correlations between regulatory mechanisms mediating steroid biosynthesis and cholesterol homeostasis in the maternal-fetoplacental unit; and to determine the efficacy of both heparin-manganese precipitation and agarose-gel electrophoresis techniques for quantitation of HDL-C and LDL-C in fetal and maternal plasma. STUDY DESIGNS: Steroids were quantitated by radioimmunoassay in maternal and umbilical cord venous blood collected from 56 patients upon delivery. Correlation analysis and ANOVA were utilized to determine the degree of association between quantitative parameters in the total study population and differences in regard to fetal sex, respectively. RESULTS: Values determined for all parameters measured fell within previously established normal ranges. HDL-C concentrations in the cord blood of female newborns were higher than those of males, while LDL-C concentrations were unchanged in regard to fetal sex. Concentrations of both LDL-C and all steroids measured in the maternal periphery were unchanged in regard to fetal sex, but HDL-C concentrations were higher in plasma of women bearing female fetuses. Further, LDL-C levels in cord blood positively correlated with maternal DHEAS levels and negatively correlated with maternal E2 levels. Cord E2 concentrations correlated highly with cord levels of both DHEA and DHEAS, and maternal E2 levels correlated, although to a lesser degree, with maternal DHEA concentrations. CONCLUSION: The results indicated both positive and negative correlations of lipoprotein cholesterol levels with concentrations of the various steroid hormones associated with human pregnancy and illustrate the complicated interplay of mechanisms regulating steroid/lipoprotein metabolism in the maternal-fetoplacental unit. Changes in lipoprotein levels in the maternal-fetoplacental unit may suggest changes in steroid metabolism associated with fetal sex. Both heparin-manganese precipitation and agarose-gel electrophoresis techniques proved adequate for the quantitation of plasma lipoprotein cholesterol in both maternal and fetal plasma.

Adolescent↗
PubMed1996

Magnitude of acute respiratory infections in under five children.

A community based study was carried out in a rural area of Wardha district in Maharastra to measure the incidence of acute respiratory infections among children below 5 years age. 384 under five children were followed up fortnightly for one calendar year to estimate the incidence of acute respiratory infections (ARI). There were 1298 episodes of ARI averaging 3.67 episodes/child/year. The incidence of lower respiratory infections was 0.07 episodes/child/year. The incidence of ARI was found to be closely associated with nutritional status of the child, socio-economic status of the family, maternal literacy status and family size. Environmental factors like type of house, ventilation and fuel used for cooking were found to influence the incidence of ARI.

Acute Disease↗
PubMed1994

Oscillating behavior of carbohydrate granule formation and dinitrogen fixation in the cyanobacterium Cyanothece sp. strain ATCC 51142.

It has been shown that some aerobic, unicellular, diazotrophic cyanobacteria temporally separate photosynthetic O2 evolution and oxygen-sensitive N2 fixation. Cyanothece sp. ATCC strain 51142 is an aerobic, unicellular, diazotrophic cyanobacterium that fixes N2 during discrete periods of its cell cycle. When the bacteria are maintained under diurnal light-dark cycles, N2 fixation occurs in the dark. Similar cycling is observed in continuous light, implicating a circadian rhythm. Under N2-fixing conditions, large inclusion granules form between the thylakoid membranes. Maximum granulation, as observed by electron microscopy, occurs before the onset of N2 fixation, and the granules decrease in number during the period of N2 fixation. The granules can be purified from cell homogenates by differential centrifugation. Biochemical analyses of the granules indicate that these structures are primarily carbohydrate, with some protein. Further analyses of the carbohydrate have shown that it is a glucose polymer with some characteristics of glycogen. It is proposed that N2 fixation is driven by energy and reducing power stored in these inclusion granules. Cyanothece sp. strain ATCC 51142 represents an excellent experimental organism for the study of the protective mechanisms of nitrogenase, metabolic events in cyanobacteria under normal and stress conditions, the partitioning of resources between growth and storage, and biological rhythms.

Carbohydrate Metabolism↗
PubMed1994

Epidemiological aspects of visual impairment above 50 years in a rural area.

A cross-sectional survey was conducted in 5 villages in central India to find out the extent, causes and epidemiological factors for visual impairment among 903 individuals aged above 50 years; 44.3% of them were visually impaired (29.4% with low vision and 14.9% blind). Age-specific visual impairment increased at a rate of 13.2% with each decade of advancing age. Landless labourers suffered more from visual impairment than other occupational groups (p < 0.05). Socioeconomic and literacy status of the population did not significantly influence the prevalence of visual impairment. Major causes of visual impairment were cataract (48.5%), refractive errors (24.5%), age-related macular degeneration (10%), glaucoma (6.8%), and others (10.2%). In view of the high prevalence of visual impairment among the elderly individuals, it is necessary to intensify our efforts in motivating them for early detection and treatment.

Aged↗
PubMed1990

Vitamin A intake and vitamin A deficiency in rural children.

The prevalence of vitamin A deficiency was estimated in 366 rural children in the age group of 1 to 15 years. In a systematically selected subsample of 90 children, the dietary intake of vitamin A was assessed. The prevalence of vitamin A deficiency signs ranged from 24.1 to 34.8%. The adequacy of dietary intake of vitamin A ranged from 8 to 12% when compared with the recommended dietary allowance. The dietary intake of children with and without vitamin A deficiency was not different (p greater than 0.05). The main source of beta carotene in the diet was cereals accounting for 47.9% of the total beta carotene intake.

Adolescent↗