Showing papers by "Wageningen University and Research Centre published in 1997"

A total system approach to sustainable pest management

Abstract: A fundamental shift to a total system approach for crop protection is urgently needed to resolve escalating economic and environmental consequences of combating agricultural pests. Pest management strategies have long been dominated by quests for “silver bullet” products to control pest outbreaks. However, managing undesired variables in ecosystems is similar to that for other systems, including the human body and social orders. Experience in these fields substantiates the fact that therapeutic interventions into any system are effective only for short term relief because these externalities are soon “neutralized” by countermoves within the system. Long term resolutions can be achieved only by restructuring and managing these systems in ways that maximize the array of “built-in” preventive strengths, with therapeutic tactics serving strictly as backups to these natural regulators. To date, we have failed to incorporate this basic principle into the mainstream of pest management science and continue to regress into a foot race with nature. In this report, we establish why a total system approach is essential as the guiding premise of pest management and provide arguments as to how earlier attempts for change and current mainstream initiatives generally fail to follow this principle. We then draw on emerging knowledge about multitrophic level interactions and other specific findings about management of ecosystems to propose a pivotal redirection of pest management strategies that would honor this principle and, thus, be sustainable. Finally, we discuss the potential immense benefits of such a central shift in pest management philosophy.

Microbiological aspects of surfactant use for biological soil remediation

Abstract: Biodegradation of hydrophobic organic compounds in polluted soil is a process involving interactions among soil particles, pollutants, water, and micro-organisms. Surface-active agents or surfactants are compounds that may affect these interactions, and the use of these compounds may be a means of overcoming the problem of limited bioavailability of hydrophobic organic pollutants in biological soil remediation. The effects of surfactants on the physiology of micro-organisms range from inhibition of growth due to surfactant toxicity to stimulation of growth caused by the use of surfactants as a co-substrate. The most important effect of surfactants on the interactions among soil and pollutant is stimulation of mass transport of the pollutant from the soil to the aqueous phase. This can be caused by three different mechanisms: emulsification of liquid pollutant, micellar solubilisation, and facilitated transport. The importance of these mechanisms with respect to the effect of surfactants on bioavailability is reviewed for hydrophobic organic pollutants present in different physical states. The complexity of the effect of surfactants on pollutant bioavailability is reflected by the results in the literature, which range from stimulation to inhibition of desorption and biodegradation of polluting compounds. No general trends can be found in these results. Therefore, more research is necessary to make the application of surfactants a standard tool in biological soil remediation.

Catastrophic vegetation shifts and soil degradation in terrestrial grazing systems.

Abstract: It has long been recognized that alternative vegetation states may occur in terrestrial grazing systems. This phenomenon may be of great importance as small environmental fluctuations may lead to relatively sudden and irreversible jumps between vegetation states. Early theoretical studies emphasized saturation of herbivore feeding to explain multiple stable states and catastrophic behaviour. Recent studies on semi-arid grasslands and arctic salt marshes, however, relate catastrophic events in these systems to plant-soil interactions.

Beyond low fat diets.

Abstract: Low-fat diets are often advocated for weight reduction and to lower the risk of coronary heart disease and certain forms of cancer However, there is no universal agreement about the value of low-fat diets In this Clinical Debate, Connor and Connor argue in favor of the public health benefits of low-fat diets, whereas Katan, Grundy, and Willett present a different point of view

Alternate stable states and threshold effects in semi-arid grazing systems.

Abstract: Models that explain the discontinuous behaviour of semi-arid grazing systems usually emphasize herbivore feeding characteristics or plant competition as possible mechanisms. Field studies indicate, however, that plant-soil relations could be more important. We show by means of a graphical model that the interactions between water infiltration or nutrient retention and plant density potentially give rise to the existence of alternate stable vegetation states and threshold effects in semi-arid grazing systems, even without the effect of a non-linear herbivore functional response or plant competition. These interactions may trigger a positive feedback between reduced plant density and reduced resource availability, and lead to a collapse of the system. The model results are in line with well-documented observations of spatial and temporal patterns such as two-phase mosaics and stably degraded grasslands.

Variations in the predicted spatial distribution of atmospheric nitrogen deposition and their impact on carbon uptake by terrestrial ecosystems

Abstract: Widespread mobilization of nitrogen into the atmosphere from industry, agriculture, and biomass burning and its subsequent deposition have the potential to alleviate nitrogen limitation of productivity in terrestrial ecosystems, and may contribute to enhanced terrestrial carbon uptake To evaluate the importance of the spatial distribution of nitrogen deposition for carbon uptake and to better quantify its magnitude and uncertainty NO y -N deposition fields from five different three-dimensional chemical models, GCTM, GRANTOUR, IMAGES, MOGUNTIA, and ECHAM were used to drive NDEP, a perturbation model of terrestrial carbon uptake Differences in atmospheric sources of NO x -N, transport, resolution, and representation of chemistry, contribute to the distinct spatial patterns of nitrogen deposition on the global land surface; these differences lead to distinct patterns of carbon uptake that vary between 07 and 13 Gt C yr -1 globally Less than 10% of the nitrogen was deposited on forests which were most able to respond with increased carbon storage because of the wide C:N ratio of wood as well as its long lifetime Addition of NH x -N to NO y -N deposition, increased global terrestrial carbon storage to between 15 and 20 Gt C yr -1 , while the missing terrestrial sink is quite similar in magnitude Thus global air pollution appears to be an important influence on the global carbon cycle If N fertilization of the terrestrial biosphere accounts for the missing C sink or a substantial portion of it, we would expect significant reductions in its magnitude over the next century as terrestrial ecosystems become N saturated and O 3 pollution expands

A collaborative European study of personal inhalable aerosol sampler performance

Abstract: Following the adoption of new international sampling conventions for inhalable, thoracic and respirable aerosol fractions, a working group of Comite Europeen de Normalisation (CEN) drafted a standard for the performance of workplace aerosol sampling instruments. The present study was set up to verify the experimental, statistical and mathematical procedures recommended in the draft performance standard and to check that they could be applied to inhalable aerosol samplers. This was achieved by applying the tests to eight types of personal inhalable aerosol sampler commonly used for workplace monitoring throughout Europe. The study led to recommendations for revising the CEN draft standard, in order to simplify the tests and reduce their cost. However, some further work will be needed to develop simpler test facilities and methods. Several of the samplers tested were found to perform adequately with respect to the inhalable sampling convention, at least over a limited range of typical workplace conditions. In general the samplers were found to perform best in low external wind speeds, which are the test conditions thought to be closest to those normally found in indoor workplaces. The practical implementation of the CEN aerosol sampling conventions requires decisions on which sampling instruments to use, estimation of the likely impact that changing sampling methods could have on apparent exposures, and adjustment where necessary of exposure limit values. The sampler performance data obtained in this project were affected by large experimental errors, but are nevertheless a useful input to decisions on how to incorporate the CEN inhalable sampling convention into regulation, guidance and occupational hygiene practice.

Site-specific properties and irreversible vegetation changes in semi-arid grazing systems

Abstract: There is an urgent need to develop a mechanistic understanding of how site-specific properties can lead to irreversible vegetation changes. We show, by means of a bifurcation analysis of two mathematical models, how site-specific properties determine the resilience of vegetation changes in semi-arid grazing systems. The models predict that if available soil water limits plant growth, the vegetation supported by sandy soils is generally resilient to herbivore impact and rainfall fluctuations, unlike the vegetation on clayey soils. This depends on the capacity of vegetation communities to improve the structural and water-holding capacities of the soil. In contrast, if plant growth is nutrient limited, vegetation on sandy soils is generally not resilient to herbivore impact and fluctuations in external nutrient input, unlike the vegetation supported by clayey soils. This is affected by the nutrient retention capacity of vegetation communities. We stress the applicability of the general theory provided by this model to the Sahel environment. The model predictions are consistent with field observations documented in the literature.

The influences of height and age on waist circumference as an index of adiposity in adults

Abstract: OBJECTIVES: To assess the influences of height and age on the differences in waist circumference between individuals of different stature. SUBJECTS: 3319 males and 4358 females from four studies in the UK and the Netherlands. MEASUREMENTS: Waist circumference, body weight, height, and age. RESULTS: Linear regression analysis of log10 height as the independent variable on log10 waist as the dependent variable was used to determine the optimal index powers (OIP) (p) to minimize the influence of height in the relationships of waist/heightp. Six out of eight samples of men and women had OIP of height not significantly different from zero, with the remaining two groups had OIP between 0.15–0.58, indicating that height had very limited influence on the differences in waist circumference measurement between individuals. Age adjustment increased the relationship between waist and height, with OIP of 0.19–0.89 in men and 0.02–0.58 in women. Without age adjustment, height explained 0.3–3.5% and 0.1–2.5% variance in waist in men and in women respectively, and the corresponding variances were 0.4–7.5% in men and 0.0–2.6% in women with age adjustment. A similar analysis of weight and height showed the OIP of height in weight/heightp ratio ranged from 1.32–2.25 in men, and 0.87–1.74 in women without age adjustment, and from 1.47–2.24 in men and 1.25–1.96 in women with age adjustment. CONCLUSION: Height and age had limited influences on the differences in waist between Caucasian subjects of different stature. Waist alone may be used to indicate adiposity or to reflect metabolic risk factors. In contrast, the influence of height on body weight is important.

Performance of a sulfide-oxidizing expanded-bed reactor supplied with dissolved oxygen.

Abstract: The performance of a new sulfide-oxidizing, expanded-bed bioreactor is described. To stimulate the formation of well-settleable sulfur sludge, which comprises active sulfide-oxidizing bacterial biomass and elemental sulfur, the aeration of the liquid phase and the oxidation of sulfide to elemental sulfur are spatially separated. The liquid phase is aerated in a vessel and subsequently recirculated to the sulfide-oxidizing bioreactor. In this manner, turbulencies due to aeration of the liquid phase in the bioreactor are avoided. It appeared that, under autotrophic conditions, almost all biomass present in the reactor will be immobilized within the sulfur sludge which consists mainly of elemental sulfur (92%) and biomass (2.5%). The particles formed have a diameter of up to 3 mm and can easily be grinded down. Within time, the sulfur sludge obtained excellent settling properties; e.g., after 50 days of operation, 90% of the sludge settles down at a velocity above 25 m h-1 while 10% of the sludge had a sedimentation velocity higher than 108 m h-1. Because the biomass is retained in the reactor, higher sulfide loading rates may be applied than to a conventional “free-cell” suspension. The maximum sulfide-loading rate reached was 14 g HS- L-1 d-1, whereas for a free-cell suspension a maximum loading rate of 6 g HS- L-1 d-1 was found. At higher loading rates, the upward velocities of the aerated suspension became too high so that sulfur sludge accumulated in the settling zone on top of the reactor. When the influent was supplemented with volatile fatty acids, heterotrophic sulfur and sulfate reducing bacteria, and possibly also (facultatively) heterotrophic Thiobacilli, accumulated within the sludge. This led to a serious deterioration of the system; i.e., the sulfur formed was increasingly reduced to sulfide, and also the formation rate of sulfur sludge declined. © 1997 John Wiley & Sons, Inc.

SULFUR TUFT AND TURKEY TAIL:Biosynthesis and Biodegradation of Organohalogens by Basidiomycetes

Abstract: Chlorinated aliphatic and aromatic compounds are generally considered to be undesirable xenobiotic pollutants. However, the higher fungi, Basidiomycetes, have a widespread capacity for organohalogen biosynthesis. Adsorbable organic halogens (AOX) and/or low-molecular-weight halogenated compounds are produced by Basidiomycetes of 68 genera from 20 different families. Most of the 81 halogenated metabolites identified from Basidiomycetes to date are chlorinated, although brominated and iodated metabolites have also been described. Two broad categories of Basidiomycete organohalogen metabolites are the halogenated aromatic compounds and the haloaliphatic compounds. Some of these organohalogen metabolites have demonstrable physiological roles as antibiotics and as metabolites involved in lignin degradation. Basidiomycetes produce large amounts of low-molecular-weight organohalogens or adsorbable organic halogens (AOX) when grown on lignocellulosic substrates. In our view, Basidiomycetes, as decomposers of forest litter, are a major source of natural organohalogens in terrestrial environments. Basidiomycetes are also potent degraders of a wide range of chlorinated pollutants, such as bleachery effluent from kraft mills and pentachlorophenol,

Attribute Elicitation in Marketing Research: A Comparison of Three Procedures

Abstract: This article compares three attribute elicitation procedures commonlyapplied in marketing research—free elicitation (FE), hierarchicaldichotomization (HD), and Kelly's repertory grid—on type ofinformation generated, convergent validity, efficiency in datacollection, and consumers' reaction to the elicitation task On mostcriteria, RG and HD were not significantly different The maincontrasts were found between FE on the one hand and RG and HD on theother hand FE yielded more attributes, a higher proportion of abstractattributes, and a higher level of articulation and was more timeefficient FE was also evaluated more positively by respondents thanthe other two techniques Despite these differences, the threeprocedures exhibited a considerable degree of convergent validity interms of the basic categories of concepts uncovered in the elicitationprocedure Unless the marketing research technique for which theattributes are elicited requires attributes at a low level ofabstraction, the results suggest that FE is to be preferred to HD andRG

Biotransformation and biodegradation of N‐substituted aromatics in methanogenic granular sludge

Abstract: N-Substituted aromatic compounds are environmental contaminants associated with the production and use of dyes, explosives, pesticides and pharmaceuticals. In this article, we examine the potential of anaerobic granular sludge from anaerobic treatment systems towards the detoxification, transformation, and mineralization of nitroaromatic and azo compounds. Nitroaromatics and azo dyes with strong electron withdrawing are highly inhibitory to acetoclastic methanogenic bacteria. However, nitro and azo substituted aromatics are readily reductively detoxified in methanogenic consortia to their respective aromatic amines, which are several orders of magnitude less toxic. This reductive detoxification has allowed the successful operation of anaerobic reactors for the treatment of highly toxic aromatic compounds. In the course of the experiments it was discovered that some aromatic amines were mineralized. These results indicate that some N-substituted aromatic compounds can be completely mineralized and serve as a carbon and energy source for anaerobic bacteria.

Thermophilic sulphate and sulphite reduction in lab‐scale gas‐lift reactors using H2 and CO2 as energy and carbon source

Abstract: Feasibility of thermophilic (55°C) sulphate and sulphite reduction with H2 and CO2 gas-mixtures was studied in gas-lift reactors, which contained pumice particles as carrier material. Particular attention was paid to biomass retention and the competition between hydrogenotrophic sulphate-reducers and other hydrogenotrophic thermophiles. A model medium with defined mineral nutrients was used. The results of the experiments clearly demonstrate that sulphate conversion rates up to 7.5 g SO42−/L per day can be achieved. With sulphite, a reduction rate of 3.7 g S/L per day was obtained, which equals a sulphate conversion rate of 11.1 g SO42−/L per day. Under the applied conditions, a strong competition for hydrogen between hydrogenotrophic sulphate-reducers, tentatively designated as Desulfotomaculum sp., and hydrogenotrophic methanogens was observed. The outcome of the competition could not be predicted. Growth of the mixed culture was totally inhibited at an H2S concentration of 250 mg/L. Poor attachment of sulphate-reducing bacteria was observed in all experiments. The biomass concentration did not exceed 1.2 g/L, despite the presence of 50 g/L of pumice. The reason for this phenomenon remains to be understood. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng55: 807–814, 1997.

Association Between Toenail Selenium and Risk of Acute Myocardial Infarction in European Men The EURAMIC Study

Abstract: The association between selenium status and risk of acute myocardial infarction was examined in a multicenter case-control study in 10 centers from Europe and Israel in 1991-1992. Selenium in toenails was assessed for 683 nonfatal male cases with first acute myocardial infarction and 729 controls less than 70 years of age. Median toenail selenium content was 0.553 microgram/g for cases and 0.590 microgram/g for controls. After adjustment for age, center, and smoking, the odds ratio for myocardial infarction in the highest quintile of selenium as compared with the lowest was 0.63 (95 percent confidence interval 0.37-1.07, p for trend = 0.08). The observed inverse trend was somewhat stronger when the authors adjusted for vitamin E status (p = 0.05). Analysis stratified for smoking habits showed an inverse association in former smokers (odds ratio for the 75th-25th percentile contrast = 0.63 (95 percent confidence interval 0.43-0.94)), but not in current smokers (odds ratio = 0.97 (0.71-1.32)) or in those who had never smoked (odds ratio = 1.55 (0.87-2.76)). Analysis stratified by center showed a significant inverse association between selenium levels and risk of myocardial infarction for Germany (Berlin) only (75th to 25th percentile odds ratio = 0.62 (95 percent confidence interval 0.42-0.91)), which was the center with the lowest selenium levels. It appears that the increased risk of acute myocardial infarction at low levels of selenium intake is largely explained by cigarette smoking; selenium status does not appear to be an important determinant of risk of myocardial infarction at the levels observed in a large part of Europe.