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At least 415 records · Page 23Linked to original sources
PubMed2004

Adaptation of soil biological nitrification to heavy metals.

The adaptive response of soil biological nitrification to Zn and Pb was assessed using an in situ method we have developed. The method is based on reinoculating a sterilized metal contaminated soil with the same soil that is either uncontaminated or has been incubated with metal. This approach excludes the potentially confounding effects of metal aging reactions in soils. We found added Zn concentrations which gave rise to a decrease in nitrification to 50% that of the uncontaminated soil (i.e. EC50) of 210 mg/kg for communities not previously exposed to Zn and 850 mg/kg for communities exposed to Zn for 17 months, indicating that significant adaptation of the community to Zn had occurred. Similarly, this protocol was able to demonstrate adaptation of soil biological nitrification to Pb, with EC50 values of 1960 and 3150 mg/kg for the unexposed and exposed treatments, respectively. Exposure of unadapted and adapted microbial communities to a combination of Zn and Cd showed that the presence of Cd did not lead to greater toxicity in either community. Adapted communities were not more sensitive to decreases in soil pH than unadapted communities. Prior exposure to Zn was found to confer significantly greater tolerance of the community to Pb. Prior exposure to Pb similarly conferred significantly greater tolerance of the community to Zn. Implications of the adaptive capacity of soil microbes to the development of critical threshold values for heavy metals in soil based on ecotoxicity assessments are discussed.

Adaptation, Physiological↗
PubMed2006

Evidence of altered gene flow, mutation rate, and genetic diversity in redbreast sunfish from a pulp-mill-contaminated river.

To determine effects of pulp mill effluent on population genetic structure, redbreast sunfish (Lepomis auritus) were collected from several sites along the Pigeon River, NC, as well as from reference sites. Previous studies found effects on molecular, biochemical, physiological, population, and community level endpoints in these populations. The population genetic structure of these fish was determined using the randomly amplified polymorphic DNA (RAPD) technique. The level of genetic diversity was higher in the Pigeon River populations than in the reference populations. Genetic distances among populations could not be explained by drainage patterns and may have been altered by contaminant exposure. Phylogeographic analysis, maximum likelihood analysis, and assignment tests suggested that there were fewer emigrants and more immigrants in the contaminated sites than in the reference sites, suggesting that the contaminated sites may harbor "sinklike" populations. Finally, a "terminal branch amplitype" analysis (neighbor-joining and minimum-spanning trees) and maximum likelihood analysis indicated that there may be an elevated mutation rate in the polluted sites. Thus, the genetic diversity (within and among populations) in the Pigeon River populations may have been affected by altered gene flow and mutational processes as a result of pulp mill effluent discharge.

Animals↗
PubMedDate not supplied

Ring-testing and field-validation of a terrestrial model ecosystem (TME)--an instrument for testing potentially harmful substances: effects of carbendazim on enchytraeids.

The effects of the fungicide carbendazim (applied in the formulation Derosal) on enchytraeids were determined in Terrestrial Model Ecosystem (TME) tests and field-validation studies. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) taken from a grassland or, in one case, from an arable site. The TMEs were taken from the same site where the respective field study was performed. The tests were performed in Amsterdam (The Netherlands), Bangor (Wales, England), Coimbra (Portugal) and Flörsheim (Germany). Concerning the enchytraeid overall abundance and the number of species, differences between sampling points and differences between the TME tests and the respective field-validation studies were not found in the controls. Generally, a high variability of data which reduced the probability of determining statistically significant differences was determined. Effects of the model chemical carbendazim were determined for the overall abundance of enchytraeids and the number of enchytraeid species. The clearest dose-response relationship was found for the abundance of the genus Fridericia. The abundance of the genera Achaeta and Enchytraeus was not affected. Effects were most pronounced 8 and 16 weeks after application of the test chemical. The observed effects appeared not to differ between the TME tests and the respective field-validation studies. Due to the high variability of data NOEC-values could often not be determined. The EC50-values derived from the TME pre-test, TME ring-test and field-validation study indicate that the reproducibility (i.e. the variation between the partners) of the EC50-values was reasonable, although different soils were used at the different sites. The EC50-values for effects of carbendazim on enchytraeid abundance ranged between 0.5 and 28.4 kg a.i./ha (corresponding to 0.7-37.8 mg/kg), on the number of species between 7.2 and 87.4 kg a.i./ha (9.5-116.2 mg/kg) and on the abundance of Fridericia between 0.7 and 18.6 kg a.i./ha (0.9-24.7 mg/kg). Since one specific taxon has the potential to be more sensitive for a chemical stressor than other taxa, it is recommended to include investigations on the species level in the assessment of TME or field studies.

Animals↗
PubMed2004

Migration of birds as an indicator of broad-scale environmental condition.

The migration of Neotropical birds may provide a robust measure of changing environmental condition along the migratory route. I review previous work on assessing broad-scale stopover quality in the eastern United States and discuss how future research can aid regional environmental assessment. Scientists can quantify how environmental changes affect the migratory system, and then monitor for those effects on migrant abundance from year to year. The cyclical nature of migration provides a constant re-evaluation of habitat quality and spatial distribution by migrant birds. Avian monitoring programs can detect changes in migrant abundance. Migrating birds may thus provide a living sensor of environmental change, enabling broad-scale environmental assessments to detect and address habitat degradation early on, allowing local managers to prioritize restoration efforts accordingly. Understanding the environmental factors driving stopover selection, and how birds move between stopovers during migration, is an important first step.

Animals↗
PubMed2004

Assessing development pressure in the Chesapeake Bay watershed: an evaluation of two land-use change models.

Natural resource lands in the Chesapeake Bay watershed are increasingly susceptible to conversion into developed land uses, particularly as the demand for residential development grows. We assessed development pressure in the Baltimore-Washington, DC region, one of the major urban and suburban centers in the watershed. We explored the utility of two modeling approaches for forecasting future development trends and patterns by comparing results from a cellular automata model, SLEUTH (slope, land use, excluded land, urban extent, transportation), and a supply/demand/allocation model, the Western Futures Model. SLEUTH can be classified as a land-cover change model and produces projections on the basis of historic trends of changes in the extent and patterns of developed land and future land protection scenarios. The Western Futures Model derives forecasts from historic trends in housing units, a U.S. Census variable, and exogenously supplied future population projections. Each approach has strengths and weaknesses, and combining the two has advantages and limitations.

Baltimore↗
PubMed2004

Criteria to assess and select sites for long-term avian monitoring in an urbanizing landscape.

A methodology was developed to prioritize the suitability of sites for long-term monitoring of avian populations, including vulnerable species, both to enhance assessment of changes in ecological resources and to facilitate land-use planning at the regional scale. This paper argues that a successful monitoring program begins with a site prioritization procedure that integrates scores based on spatial controls with ecological and socio-economic indicators, particularly those dependent on community involvement. The evaluation strategy in this study combines 1) spatial controls such as land ownership and accessibility, with 2) biological and habitat indicators such as vulnerable species and habitat connectivity, and 3) community and agency variables such as volunteer commitment and agency priorities. In total, a set of ten indicators was identified. This strategy was applied to predominantly agricultural landscapes, which are experiencing increasing human pressures, in three sub-watersheds of the Credit River, Southern Ontario. Specifically, bird populations were recorded during the breeding seasons of 2000-2002 in nine land units or habitat types including marsh, deciduous forest, and grasslands as mapped by Credit Valley Conservation (CVC) following Ecological Land Classification (ELC) guidelines. CVC selected sites for long-term monitoring in 2002 and the relationships between the scored (or ranked) sites and the selected long-term monitoring sites are discussed.

Agriculture↗
PubMed2001

The global impact of HIV/AIDS.

The scale of the human immunodeficiency virus (HIV)/AIDS epidemic has exceeded all expectations since its identification 20 years ago. Globally, an estimated 36 million people are currently living with HIV, and some 20 million people have already died, with the worst of the epidemic centred on sub-Saharan Africa. But just as the spread of HIV has been greater than predicted, so too has been its impact on social capital, population structure and economic growth. Responding to AIDS on a scale commensurate with the epidemic is a global imperative, and the tools for an effective response are known. Nothing less than a sustained social mobilization is necessary to combat one of the most serious crises facing human development.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Widespread amphibian extinctions from epidemic disease driven by global warming.

As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with 'very high confidence' (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.

Altitude↗
PubMed2000

Modelling in tumour biology part 1: modelling concepts and structures.

Our strategies for the treatment of cancer are constrained by our incomplete understanding of tumour biology and behaviour, and by the enormous complexity and resilience to therapeutic perturbation found in the biological world. We are obliged to simplify this complexity through the use of models and mechanistic explanations. In the first of these papers, we consider the nature of modelling mechanisms available to clinical researchers and the extent to which we rely upon them in our understanding of the nature and behaviour of tumours. In the second part, we will consider specifically how models help us to develop more effective strategies for cancer therapy.

Algorithms↗
PubMed1996

Association between mild, routine exercise and improved insulin dynamics and glucose control in obese adolescents.

The association between mild routine exercise and glucose homeostasis, insulin dynamics, and risk factors for coronary artery disease was investigated in obese adolescent males. Subjects (n = 7; mean +/- SD age 13.3 +/- 1.4 yr) were tested before and after 15 wk of supervised mild intensity exercise. Serum glucose (GLU), insulin (IN), and C-peptide (CP) were measured in response to a mixed meal before and after the 15 wk period. Weight, body composition, peak oxygen uptake (peak VO2), resting blood pressure (BP), and blood lipid levels were also assessed pre- and post-training. After training, percent fat and body weight were not decreased compared to the initial values. Relative changes (p < or = 0.02) in mean values for GLU and peptides after training were: fasting GLU, -15%; total GLU response, -15%; peak IN response, -51%; total IN response, -46%; peak CP response, +55%; and total CP response, +53%. Following training, the subjects did not have an increased peak VO2, but showed consistent reductions in systolic BP and LDL-cholesterol (p < 0.05). Increases in hepatic insulin clearance (decreased insulin levels but increased CP levels) might be training adaptations unique to low intensity exercise or to obese youth. Decreased insulin levels with concurrent decreases in resting blood pressure and the LDL-cholesterol levels suggest that mild exercise training may reduce health risk factors without weight loss in the obese adolescent male.

Adolescent↗
PubMed1996

Comparison of prediction models for the compression force on the lumbosacral disc.

The main objective of this research was to compare three representative methods of predicting the compressive forces on the lumbosacral disc: LP-based model, double LP-based model, and EMG-assisted model. Two subjects simulated lifting tasks that are frequently performed in the refractories industry of Korea, in which vertical and lateral distances, and weight of load were varied. To calculate the L5/S1 compressive forces, EMG signals from six trunk muscles were measured, and postural data and locations of load were recorded using the Motion Analysis System. The EMG-assisted model was shown to reflect well all three factors considered here, whereas the compressive forces from the two LP-based models were only significantly affected by weight of load. In addition, low lifting index (LI) values were observed for relatively high L5/S1 compressive forces from the EMG-assisted model, suggesting that the 1991 NIOSH lifting equations may not fully evaluate the risk of dynamic asymmetric lifting tasks.

Adult↗
PubMed2006

HIV epidemic in Estonia in the third decade of the AIDS era.

This article describes current trends of HIV/AIDS and related conditions in Estonia, with the aim of highlighting key determinants in transmission dynamics and risk groups, problems and barriers of combating HIV/AIDS, and possible implications for prevention and control. Throughout the transition period Estonia has experienced major changes in political, economic, and social structure which all have contributed to increased violence, high-risk sexual behaviour, and substance abuse. Incidences of hepatitis B, C and sexually transmitted infections (STIs) increased in the early 1990s. HIV outbreaks were first detected among injecting drug users (IDUs) in 2000 and are still concentrated among this population group. High rates of sexual risk behaviour and inadequate knowledge regarding prevention of disease transmission in Estonia emphasizes the threat of a sex-related and STI facilitated driven HIV epidemic. To prevent further spread of HIV it is necessary to implement harm reduction interventions among IDUs. However, without effective management of socioeconomic and administrative barriers to health care and other services, an explicit policy on drugs will not reach marginalized groups and will not be able to prevent a further spread of these interrelated epidemics.

Adolescent↗