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Biomedical subjects

Mark Nieuwenhuijsen

Publications and source records attributed to Mark Nieuwenhuijsen.

6 recordsLinked to original sources
PubMed2006

New developments in exposure assessment: the impact on the practice of health risk assessment and epidemiological studies.

The field of exposure assessment has matured significantly over the past 10-15 years. Dozens of studies have measured the concentrations of numerous chemicals in many media to which humans are exposed. Others have catalogued the various exposure pathways and identified typical values which can be used in the exposure calculations for the general population such as amount of water or soil ingested per day or the percent of a chemical than can pass through the skin. In addition, studies of the duration of exposure for many tasks (e.g. showering, jogging, working in the office) have been conducted which allow for more general descriptions of the likely range of exposures. All of this information, as well as the development of new and better models (e.g. air dispersion or groundwater models), allow for better estimates of exposure. In addition to identifying better exposure factors, and better mathematical models for predicting the aerial distribution of chemicals, the conduct of simulation studies and dose-reconstruction studies can offer extraordinary opportunities for filling in data gaps regarding historical exposures which are critical to improving the power of epidemiology studies. The use of probabilistic techniques such as Monte Carlo analysis and Bayesian statistics have revolutionized the practice of exposure assessment and has greatly enhanced the quality of the risk characterization. Lastly, the field of epidemiology is about to undergo a sea change with respect to the exposure component because each year better environmental and exposure models, statistical techniques and new biological monitoring techniques are being introduced. This paper reviews these techniques and discusses where additional research is likely to pay a significant dividend. Exposure assessment techniques are now available which can significantly improve the quality of epidemiology and health risk assessment studies and vastly improve their usefulness. As more quantitative exposure components can now be incorporated into these studies, they can be better used to identify safe levels of exposure using customary risk assessment methodologies. Examples are drawn from both environmental and occupational studies illustrating how these techniques have been used to better understand exposure to specific chemicals. Some thoughts are also presented on what lessons have been learned about conducting exposure assessment for health risk assessments and epidemiological studies.

Bayes Theorem↗
PubMed2006

Indoor time-microenvironment-activity patterns in seven regions of Europe.

Personal exposure to environmental substances is largely determined by time-microenvironment-activity patterns while moving across locations or microenvironments. Therefore, time-microenvironment-activity data are particularly useful in modeling exposure. We investigated determinants of workday time-microenvironment-activity patterns of the adult urban population in seven European cities. The EXPOLIS study assessed workday time-microenvironment-activity patterns among a total of 1427 subjects (age 19-60 years) in Helsinki (Finland), Athens (Greece), Basel (Switzerland), Grenoble (France), Milan (Italy), Prague (Czech Republic), and Oxford (UK). Subjects completed time-microenvironment-activity diaries during two working days. We present time spent indoors--at home, at work, and elsewhere, and time exposed to tobacco smoke indoors for all cities. The contribution of sociodemographic factors has been assessed using regression models. More than 90% of the variance in indoor time-microenvironment-activity patterns originated from differences between and within subjects rather than between cities. The most common factors that were associated with indoor time-microenvironment-activity patterns, with similar contributions in all cities, were the specific work status, employment status, whether the participants were living alone, and whether the participants had children at home. Gender and season were associated with indoor time-microenvironment-activity patterns as well but the effects were rather heterogeneous across the seven cities. Exposure to second-hand tobacco smoke differed substantially across these cities. The heterogeneity of these factors across cities may reflect city-specific characteristics but selection biases in the sampled local populations may also explain part of the findings. Determinants of time-microenvironment-activity patterns need to be taken into account in exposure assessment, epidemiological analyses, exposure simulations, as well as in the development of preventive strategies that focus on time-microenvironment-activity patterns that ultimately determine exposures.

Activities of Daily Living↗
PubMed2006

Assessment of uncertainty in a probabilistic model of consumer exposure to pesticide residues in food.

The assessment of consumer exposure to pesticides is an important part of pesticide regulation. Probabilistic modelling allows analysis of uncertainty and variability in risk assessments. The output of any assessment will be influenced by the characteristics and uncertainty of the inputs, model structure and assumptions. While the use of probabilistic models is well established in the United States, in Europe problems of low acceptance, sparse data and lack of guidelines are slowing the development. The analyses in the current paper focused on the dietary pathway and the exposure of UK toddlers. Three single food, single pesticide case studies were used to parameterize a simple probabilistic model built in Crystal Ball. Data on dietary consumption patterns were extracted from National Diet and Nutrition Surveys, and levels of pesticide active ingredients in foods were collected from Pesticide Residues Committee monitoring. The effect of uncertainty on the exposure estimate was analysed using scenarios, reflecting different assumptions related to sources of uncertainty. The most influential uncertainty issue was the distribution type used to represent input variables. Other sources that most affected model output were non-detects, unit-to-unit variability and processing. Specifying correlation between variables was found to have little effect on exposure estimates. The findings have important implications for how probabilistic modelling should be conducted, communicated and used by policy and decision makers as part of consumer risk assessment of pesticides.

Body Weight↗
PubMed2005

Diagnostic model for sensitization in workers exposed to occupational high molecular weight allergens.

BACKGROUND: Occupational allergy has great impact on workers exposed to high molecular weight (HMW) allergens. The present study is aimed to develop and validate a generic diagnostic model for sensitization to HMW allergens, defined as positive IgE. METHODS: The model was developed in pooled data from Dutch laboratory animal (LA) workers and bakers using logistic regression analysis. Validity was assessed internally by bootstrapping procedure, and externally in British LA workers. RESULTS: The model included working hours/week, work-related symptoms, total IgE, and IgE to common allergen. Significant interactions between the type of work and the predictors resulted in different scores for LA workers and bakers. Internal and external validation showed that the model was satisfactorily calibrated and discriminated between workers at high and low risk of being sensitized. CONCLUSIONS: It is possible to develop a generic model for sensitization to occupational HMW allergens. However, the weighing of predictors differs across specific work environments.

Adult↗
PubMed2002

Lung lining liquid modifies PM(2.5) in favor of particle aggregation: a protective mechanism.

The health effects of particle inhalation including urban air pollution and tobacco smoke comprise a significant public health concern worldwide, although the mechanisms by which inhaled particles cause premature deaths remain undetermined. In this study, we assessed the physicochemical interactions of fine airborne particles (PM(2.5)) and lung lining liquid using scanning electron microscopy, atomic force microscopy, and X-ray photon spectroscopy. We provide experimental evidence to show that lung lining liquid modifies the chemistry and attractive forces at the surface of PM(2.5), which leads to enhanced particle aggregation. We propose that this is an important protective mechanism that aids particle clearance in the lung.

Air Pollution↗