Non-professional paint stripping, model prediction and experimental validation of indoor dichloromethane levels.

We have experimentally quantified exposure to dichloromethane during non-professional paint stripping and validated the mathematical paint exposure model of van Veen et al. (1999). The model innovates the prediction of the dichloromethane evaporation rate and room concentration by accounting for transport in the paint stripper matrix. The experiments show that peak concentrations range from 600 to 1600 mg/m3, increasing to 2000 mg/m3 when direct sun radiation increases evaporation. A naive model prediction, using a priori parameter values from the experimental set-up and a previous experiment with alkanes, accurately predicts the upper range of the experimental values, but overpredicted four out of six experiments. Statistical fit of the two paint stripper layer parameters to the experimental data resulted in a good coincidence of predicted and experimental data. Model and experiment indicate that 10-30% of dichloromethane is immediately available for evaporation.

Variation of consumer contact with household products: a preliminary investigation.

Little information is available on product use by consumers, which severely hampers exposure estimation for consumer products. This article describes actual contact with several consumer products, specifically dishwashing detergents, cleaning products, and hair styling products. How and where products are handled, as well as the duration, frequency, and amount of use were studied by means of diaries, in-home observations, and measurements. This study addressed the question, "To what extent are frequency, duration, and amount of use associated?" Findings showed that there was a large intra- as well as interindividual variation in frequency, duration, and amount of use, with the interindividual variation being considerably larger. At the same time, results showed that, for a given activity, users tended to follow their own routine. Few relations were found among frequency, duration, and amount of use. It was concluded that among persons, frequency, duration, and amount of product act in practice as independent parameters. Diaries appear to be quite suitable for gaining insight into frequently used products. Observations of usage, recorded on video, were indispensable for obtaining particular information on product use. In addition, home visits enabled the collection of specific measurements. Although diaries and home visits are time-consuming, the combination provided insight into variation as well as relations among frequency, duration, and amount of use.

Crossing the river stone by stone: approaches for residential risk assessment for consumers.

Consumer products may contain constituents that warrant a risk analysis if they raise toxicological concern. Risk assessments are performed a priori, e.g. for pesticides and biocides, and a posteriori, to diagnose risks of contaminants. An overview is presented of residential exposure assessment and risk characterization. For exposure assessment, predictive models are used to estimate exposure concentrations. The available data on product use are used to quantify the intensity of exposure. Often, both exposure concentration and product use show high variability. Worst case assessments cope with variability and uncertainty in data poor situations by selecting 'worst case' values for exposures and exposure factors. Probabilistic models may be used to quantify and model variability and uncertainty when appropriate data is available. The Margin Of Safety approach to characterize risk is discussed. Many biocides handled by consumers are used now and then and (sub)acute exposure and toxicology will be most relevant. Users and children are generally seen as critical groups during the application and post-application phases of exposure, respectively. Still, the diversity of consumer products requires consideration of the merits of each case. We conclude that residential risk assessment is still searching for methods, data and models. Probabilistic methods appear to be useful tools, but a major challenge is to integrate them in regulatory frameworks.

Indoor air exposure to volatile compounds emitted by paints: experiment and model.

To describe the evaporation of organic solvents from paints and the resulting indoor concentrations, a mathematical model and an indoor paint experiment are presented. The model describes painting in terms of an increasing area of paint during application and two compartments of paint once applied. Evaporation of organic solvents is driven by the vapor pressure of the organic solvent. The experiment revealed concentrations of n-alkanes in indoor air, during painting, and 3 days thereafter. To compare experimental results to model predictions, model parameters were measured at the start of the experiment. Diffusional exchange between paint compartments and fraction of paint applied to the upper compartment were set by expert judgment. Model predictions and experimental results were in agreement, although the timing of the concentration peak appeared difficult to predict.

A general model for exposure and uptake from consumer products.

To assess exposure to and uptake of chemical compounds from consumer products, a general model framework is proposed. The model framework separates exposure into the components contact, potential exposure, and potential uptake rate, and establishes the relation between the three. It adds a contact function and a spatial component to other exposure modeling concepts. Before the model framework can be used, its components need to be specified. A simple diffusional model is built as an example of specifying functions for exposure and uptake. A case study of 1,1,1 trichloroethane in some shoe impregnating product, partly based on the diffusional uptake model, illustrates the inclusion of the contact component. In the latter example, the exposure is calculated for the user and then, by only modifying the contact component, for a nonuser randomly walking in the house.

Neuritic growth rate described by modeling microtubule dynamics.

A model is developed to describe neuronal elongation as a result of the polymerization of microtubules and elastic stretching of the neurites by force produced by the growth cone. The model for a single segment with a single growth cone revealed a constant elongation rate, while the concentration of tubulin in the soma rises, and the concentration of tubulin becomes constant in the growth cone. Extending the model to a neurite with a single branch point and two growth cones revealed the same results. When the assembly or the disassembly rate of microtubules is unequal in both growth cones, transient retraction of one of the terminal segments occurs, which results in complete retraction of the segment when the difference in (dis)assembly rate between the two growth cones is large enough. When the model is applied to large trees, a maximal sustainable number of terminal segments as a function of the production rate of tubulin appears. Mechanisms to stop outgrowth are discussed in relation to the establishment of synaptical contacts between cells.

Terminal and intermediate segment lengths in neuronal trees with finite length.

A basic but neglected property of neuronal trees is their finite length. This finite length restricts the length of a segment to a certain maximum. The implications of the finite length of the tree with respect to the segment length distributions of terminal and intermediate segments are shown by means of a stochastic model. In the model it is assumed that branching is governed by a Poisson process. The model shows that terminal segments are expected to be longer than intermediate segments. Terminal and intermediate segments are expected to decrease in length with increasing centrifugal order. The results are compared with data from in vivo pyramidal cells from rat brain and tissue cultured ganglion cells from chicken. A good agreement between data and model was found.