Chemical exposure modelling

Field Applicability Testing (FAT) Workshop. In March 1982, the EPA Office of Research and Development convened a workshop with the specific objectives to (1) assess the state of knowledge on determining the field applicability of laboratory bioassay tests, toxicity studies, microcosm studies, and mathematical chemical exposure models (i.e., the extent to which these methods have been tested/compared with field data), and (2) recommend research objectives and priorities to advance the current level of field testing. Workshop attendees included representatives from EPA research laboratories, universities, and private industry. 

Exposure Modeling Committee Report. Testing for the Field Applicability of Chemical Exposure Models. Proc. Workshop on Field Applicability Testing. U.S. EPA, Athens, GA.,... 

MESOCHEM Chemical Atmospheric and Hazard Assessment System Impell Corporation Becky Cropper 300 Tristate Internat l Suite 400 Lincolnshire, IL 60069 (312) 940-2090 Software for atmospheric dispersion and chemical exposure assessment. A plume dispersion model. 

Dr. Richard Walentowicz provided the EPA CD-ROM disk entitled Exposure Models Library and Integrated Model Evaluation System" with other reference material. Lester Wittenberg of the Center for Chemical Process Safety, AIChE was particularly helpful in providing a chenncal industry perspective and reference material as was Dr. Steven Arendt of JBF Associates, Inc. Drs. David Hesse of Battelle Columbus Laboratories and Vinod Mubayi of Brookhaven National Laboratory were very helpful in providing material on the chemical consequence codes. 

Working groups were organized with specific responsibility to assess the utility and limits of four different methods (or tools) currently used by EPA and industry for evaluating hazards posed by toxic chemicals (1) laboratory toxicity data, (2) microcosm test data, (3) site-specific data, and (4) chemical fate and exposure model results. The Exposure Modeling Committee (3.) report presented an assessment of the current extent of field model testing and recommendations for future testing efforts. 

To conclude, a combination of both modeling and measuring procedures should be the most appropriate and wise recommendation for assessing chemical exposure in environmental scenarios. 

Fate and exposure analyses. The multimedia transport and transformation model is a dynamic model that can be used to assess time-varying concentrations of contaminants that are placed in soil layers at a time-zero concentration or contaminants released continuously to air, soil, or water. This model is used for determining the distribution of a chemical in the environmental compartments. An overview of the partitioning among the liquid, solid and/or gas phases of individual compartments is presented in Fig. 7. The exposure model encompasses... 

Besides the LCA approach, also risk assessment can be performed analysing the chemical compounds or modelling via predictive exposure models. Both types of approaches have their justification to measure environmental concentrations of chemicals in the environment with laboratory measurement is still the most reliable way for determination. But it goes along with the disadvantage of high investments concerning time and money. Besides that laboratory approaches are limited in terms of space and time, and in consequence, the survey of many micro-pollutants and their... 

Nowadays, best practice is to combine both modelling and analysis of chemicals for an appropriate assessment of chemical exposure in environmental scenarios. Future research activities should focus on the development of reliable analytical methods at trace level concentrations. 

The PBPK model development for a chemical is preceded by the definition of the problem, which in toxicology may often be related to the apparent complex nature of toxicity. Examples of such apparent complex toxic responses include nonlinearity in dose-response, sex and species differences in tissue response, differential response of tissues to chemical exposure, qualitatively and/or quantitatively difference responses for the same cumulative dose administered by different routes and scenarios, and so on. In these instances, PBPK modeling studies can be utilized to evaluate the pharmacokinetic basis of the apparent complex nature of toxicity induced by the chemical. One of the values of PBPK modeling, in fact, is that accurate description of target tissue dose often resolves behavior that appears complex at the administered dose level. 

Note Risks from activities are actuarial and much more certain than those associated with chemical exposures, which are estimated using regulatory models. Risks of cancer are assumed to equate to risks of death. Lifetime risk will be about 70 times higher if risks do not change substantially from year to year. 

The European Commission s Joint Research Centre (on behalf of DG S ANCO) has started a project known as European Information System on Risks from Chemicals Released from Consumer Products/Articles (EIS-ChemRisks) (EU 2004), which is designed as a network to collect exposure data, exposure factors, exposure models, and health-related data. The overall objective is to develop tools and reference data to enable harmonized exposure assessment procedures in the EU. A toolbox has been designed to collect exposure information from four reference systems to systematically support exposure assessors in the EU ... 

CEM TF. 2004. Consumer Exposure Modelling Tools. Ispra, European Commission, Joint Research Centre, Institute for Health and Consumer Protection, Physical and Chemical Exposure Unit, Exposure Modelling Sector, http //cem.jrc.it/cemdb/qstart.php... 

EU. 2004. European information system on risks from chemicals released from consumer products/aiticles. Consumer exposure modelling task force. Bmssels, European Commission, Joint Research Centre, http // www.jrc.cec.eu.int/eis-chemrisks/... 

Activation of innate or acquired immunity Chemical interactions with biological systems or biomolecules T cell sensitization Clinical outcomes/relevant route of exposure models... 

Public concern about industrial chemical exposures might also be misguided. The EPA typically uses mathematical dispersion models to calculate human exposure to chemicals released into the air by major stationary sources like factories and power plants. There is little evidence that the models are predictive. In one experiment, a tracer gas was released from the Alaska pipeline terminus at Valdez. Actual exposure, as measured by personal exposure badges, was compared with the predictions of the EPA dispersion model. The statistical correlation between them was near zero (— 0.01), meaning the predictions were worthless (Wallace 1993, 137-38). 

Estimating environmental concentrations of chemicals using fate and exposure models. Brussels, European Centre for Ecotoxicology and Toxicology of Chemicals (Technical Report No. 50). 

This chapter will focus on PM ambient concentrations, which are key variables for exposure models, and are generally obtained by direct measurements in air quality monitoring stations. However, depending on the location and dimension of the region to be studied, monitoring data could not be sufficient to characterise PM levels or to perform population exposure estimations. Numerical models complement and improve the information provided by measured concentration data. These models simulate the changes of pollutant concentrations in the air using a set of mathematical equations that translate the chemical and physical processes in the atmosphere. 

Mathematical construction of physical/ chemical processes that predict the range and probability density distribution of an exposure model outcome (e.g. predicted distribution of personal exposures within a study population)... 

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