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H van der Voet

Publications and source records attributed to H van der Voet.

11 recordsLinked to original sources
PubMed2006

Analysis of multivariate extreme intakes of food chemicals.

A recently published multivariate Extreme Value Theory (EVT) model is applied to the estimation of population risks associated with dietary intake of pesticides. The objective is to quantify the acute risk of pesticide intake above a threshold and relate it to the consumption of specific primary food products. As an example daily intakes of a pesticide from three foods are considered. The method models and extrapolates simultaneous intakes of pesticide, and estimates probability of exceeding unobserved large intakes. Multivariate analysis was helpful in identifying whether the avoidance of certain food combinations would reduce the likelihood of exceeding a threshold. We argue that the presented method can be an important contribution to exposure assessment studies.

Databases, Factual↗
PubMed2005

Integrated statistical analysis of cDNA microarray and NIR spectroscopic data applied to a hemp dataset.

Both cDNA microarray and spectroscopic data provide indirect information about the chemical compounds present in the biological tissue under consideration. In this paper simple univariate and bivariate measures are used to investigate correlations between both types of high dimensional analyses. A large dataset of 42 hemp samples on which 3456 cDNA clones and 351 NIR wavelengths have been measured, was analyzed using graphical representations. For this purpose we propose clustered correlation and clustered discrimination images. Large, tissue-related differences are seen to dominate the cDNA-NIR correlation structure but smaller, more difficult to detect, variety-related differences can be found at specific cDNA clone/NIR wavelength combinations.

Algorithms↗
PubMed2003

Introduction to the Monte Carlo project and the approach to the validation of probabilistic models of dietary exposure to selected food chemicals.

The Monte Carlo project was established to allow an international collaborative effort to define conceptual models for food chemical and nutrient exposure, to define and validate the software code to govern these models, to provide new or reconstructed databases for validation studies, and to use the new software code to complete validation modelling. Models were considered valid when they provided exposure estimates (e(a)) that could be shown not to underestimate the true exposure (e(b)), but at the same time are more realistic than the currently used conservative estimates (e(c)). Thus, validation required e(b) </= e(a)<e(c). In the case of pesticides, validation involved the collection of duplicate diets from 500 infants for pesticide analysis. In the case of intense sweeteners, a new consumption dataset was created among prescreened high consumers of intense sweeteners by recording, at brand level, all foods and beverages ingested over 12 days. In the case of nutrients and additives, existing databases were modified to minimize uncertainty over the model parameters. In most instances, it was possible to generate probabilistic models that fulfilled the validation criteria.

Diet↗
PubMed2003

Validation of a probabilistic model of dietary exposure to selected pesticides in Dutch infants.

A probabilistic model for dietary exposure to pesticides was validated. For this, we evaluated the agreement of dietary exposure to six pesticides as estimated with the model with exposures measured in duplicate diet samples (='real intake') and those calculated with the point estimate. To calculate the exposure with the model and point estimate, consumption data of the duplicate diet survey and pesticide residue measurements from Dutch monitoring programmes in 2000 and 2001 were used. The model was considered validated when the outcome was both higher than the real intake and lower than the point estimate. Results showed that exposures estimated with the model were closer to the real intake than those of the point estimate, and that the model outcome was lower than the point estimate. Furthermore, it was shown that the probabilistic approach can address the exposure to a pesticide via the consumption of different food products, while the point estimate only estimates the exposure through the consumption of one product. The model validated is a valuable asset when estimating the dietary exposure to pesticides in both the authorization of new pesticides and the evaluation of exposures using monitoring data.

Diet↗
PubMed2000

Identification of the SAAT gene involved in strawberry flavor biogenesis by use of DNA microarrays.

Fruit flavor is a result of a complex mixture of numerous compounds. The formation of these compounds is closely correlated with the metabolic changes occurring during fruit maturation. Here, we describe the use of DNA microarrays and appropriate statistical analyses to dissect a complex developmental process. In doing so, we have identified a novel strawberry alcohol acyltransferase (SAAT) gene that plays a crucial role in flavor biogenesis in ripening fruit. Volatile esters are quantitatively and qualitatively the most important compounds providing fruity odors. Biochemical evidence for involvement of the SAAT gene in formation of fruity esters is provided by characterizing the recombinant protein expressed in Escherichia coli. The SAAT enzyme showed maximum activity with aliphatic medium-chain alcohols, whose corresponding esters are major components of strawberry volatiles. The enzyme was capable of utilizing short- and medium-chain, branched, and aromatic acyl-CoA molecules as cosubstrates. The results suggest that the formation of volatile esters in fruit is subject to the availability of acyl-CoA molecules and alcohol substrates and is dictated by the temporal expression pattern of the SAAT gene(s) and substrate specificity of the SAAT enzyme(s).

Acyltransferases↗
PubMed1999

Optimizing the balance between false positive and false negative error probabilities of confirmatory methods for the detection of veterinary drug residues.

GC-MS data on veterinary drug residues in bovine urine are used for controlling the illegal practice of fattening cattle. According to current detection criteria, peak patterns of preferably four ions should agree within 10 or 20% from a corresponding standard pattern. These criteria are rigid, rather arbitrary and do not match daily practice. A new model, based on multivariate modeling of log peak abundance ratios, provides a theoretical basis for the identification of analytes and optimizes the balance between the avoidance of false positives and false negatives. The performance of the model is demonstrated on data provided by five laboratories, each supplying GC-MS measurements on the detection of clenbuterol, dienestrol and 19 beta-nortestosterone in urine. The proposed model shows a better performance than confirmation by using the current criteria and provides a statistical basis for inspection criteria in terms of error probabilities.

Animals↗
PubMed1997

A feasibility study of accelerated fractionation in radiotherapy of carcinoma of the urinary bladder.

PURPOSE: To establish the shortest possible overall treatment time, with respect to acute and late toxicity, in which a radiation dose of 66 Gy in 2 Gy/fraction can be administered to the urinary bladder. METHODS AND MATERIALS: In a stepwise fashion the overall treatment time of our routinely used conventional treatment schedule (66 Gy in 2 Gy/fraction in 6.5 weeks) was reduced to 5 weeks (Step 1) and then 4 weeks (Step 2). Shortening of the overall treatment time was obtained by giving two daily fractions during the last part of the treatment. The interfraction interval was a minimum of 6 h. Toxicity was scored according to a modified scheme of the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer. Fifteen patients received the 5-week schedule and 25 patients received the 4-week schedule. RESULTS: Note that feasibility was very good for the 5-week schedule. No Grade > or = 3 acute bowel or bladder toxicity was seen in these patients. Severe late complications did not occur. In the 4-week schedule, acute bladder toxicity was unaffected but acute bowel toxicity was considerably increased. Of the 25 patients, 16 suffered from Grade 3 toxicity, 3 from Grade 4, and 1 from Grade 5 toxicity. Actuarial analysis at 3 years showed a 31% incidence of Grade 4 late bladder complications. CONCLUSION: It is concluded that the 5-week schedule is well tolerated. In contrast, the 4-week schedule shows unacceptable acute bowel toxicity and an increased incidence of late bladder complications (p = 0.043).

Aged↗
PubMed1993

A risk-assessment model for toxic exposure of small mammalian carnivores to cadmium in contaminated natural environments.

A model is presented to assess the risk of cadmium toxicity in mammalian wildlife in contaminated environments. The target-organ load was used as a hazard indicator and animals were considered to be at risk when a critical value, i.e. the lowest-observed-adverse-effect level (LOAEL), was attained or exceeded. The model was developed for Sorex araneus, a small mammalian predator with a high potential of attaining the critical target-organ load. Model parameter values were estimated from both explicit analysis of original field data and from theoretical considerations. A submodel was derived from linear regression of data concerning 36 field sites to predict the bioconcentration of cadmium in earthworms, an important food item of small mammalian carnivores. In addition to soil cadmium concentration several soil factors affecting cadmium bioavailability were included in the submodel. A second submodel was developed to predict target-organ load from a non-linear age-dependent regression of data on 63 predators from two different field sites. A separate theoretical model was constructed for the prediction of target-organ load as a function of pollutant ingestion, assimilation rates, and internal partitioning. The risk of cadmium exposure was assessed by estimating the EC50 value, the environmental effect concentration of a toxic substance in soil at which 50% of an adult population of predators would attain a target-organ load equal to or higher than the LOAEL. The model allows one to establish availability-differentiated soil quality standards with regard to cadmium pollution in natural environments. It predicts an exponential increase of the risk of hazardous exposure of terrestrial wildlife in areas sensitive to increasing levels of soil acidification ('chemical time bomb effect').

Animals↗
PubMed1992

A dose-effect relationship for the effect of deltamethrin on a linyphiid spider population in winter wheat.

The relationship between application rate and effect of deltamethrin (Decis) on a linyphiid spider population was studied in relation to ambient physical factors. A field experiment using five application rates and a control was conducted in winter wheat plots. The aim was to determine application rates that allowed for determination of negative as well as positive effects of physical factors on arthropod toxicity using pitfall traps. Several physical variables were measured in the crop canopy and deltamethrin deposition was determined at ground level. The use of Before-After-Control-Impact design (BACI) time series analysis for characterization of instantaneous pesticide effects and velocity of recovery, relative to the application rate sprayed was evaluated. An initial reduction in spider catches ranging from 58% to 85% percent for sprayed concentrations of 0.25 to 4 g active ingredient per hectare (ai ha-1) was observed, followed by exponential recovery with a half-life time of 2.8 days for all treatments. The effects observed in this study were relatively mild compared to other field-experiments. It was concluded that an application rate near 0.25 g ai ha-1 deltamethrin (i.e., one twentieth of the recommended rate) would be sufficient to study the relationship between physical factors and the effects of deltamethrin. BACI time series analysis was shown to be a useful technique for characterizing short-term pesticide effects.

Animals↗
PubMed1983

On-line diode array UV-visible spectrometry in screening for drugs and drug metabolites by high-performance liquid chromatography.

The direct coupling of a multi-channel diode array UV-visible spectrophotometer to a powerful reversed-phase HPLC separation system is considered, especially for use in qualitative analysis, e.g., screening/identification of drugs and drug metabolites. The approach is illustrated by the screening for metabolites of butoprozine and ticlopidine directly in human and rat bile.

Amiodarone↗