This thesis presents the development, evaluation, and application of a generalized toxicokinetic model for mixtures of chemicals. Humans are exposed to mixtures of chemicals that are found together in multiple exposure media (soil, food, and air), and at levels that have been shown to cause adverse effects due to toxic interactions. Although several physiologically based toxicokinetic (PBTK) models exist for different environmental chemicals, using them in assessing risks to co-occurring contaminants is often impractical. This is especially true for the case of toxic metals, where half-lives in the human body span days (e.g. arsenic), months (e.g. methylmercury), and decades (e.g. lead, cadmium). Several differences in the formulation of these models exist with respect to (a) physiological structure (e.g. body tissue volumes and blood flow ratios), (b) general modeling assumptions (e.g. for transport and transformation of the chemicals within the body), and (c) exposure-relevant parameters. Since assumptions made for one metal or metal compound can be incompatible with the assumptions made for another metal, current formulations are inadequate for use in assessing health risks from mixtures of toxic metals. Further complications arise when assessing risks of both metals and nonmetals, which also interact at the toxicokinetic and toxicodynamic levels. The issues of consistent representation of physiology and chemical interactions across different classes of chemicals such as mixtures of metals and mixtures of metals and organics are addressed through the development of a Generalized Toxicokinetic Model for Mixtures of chemicals (GTMM). The GTMM resolves inconsistencies by standardizing the physiology across all models, and by allowing simulations of different models to be done simultaneously. It has been implemented as a set of modules in Matlab and as a user-oriented graphical interface in Matlab-Simulink. The GTMM has been evaluated with multiple existing PBTK models for individual chemicals, and the results demonstrate that the GTMM produces identical results as the original published formulations. Subsequently, the GTMM has been applied to different problems relevant to population risk assessment.

Toxicokinetics in Risk Assessment discusses the noncancer risk assessment process and its reliance on uncertainty factors in order to facilitate the continued study and refinement of the scientific basis for health risk assessment. This text clearly demonstrates the application of physiologically-based pharmacokinetic (PBPK) modeling in human healt

Many health risk assessments develop exposure limits for chemicals, intended to protect the general population, including sensitive subpopulations. Critical toxicokinetic and toxicodynamic determinants of toxicity vary among subgroups of populations, thus making some of them potentially more susceptible than the general population to the health effects of chemicals. This chapter focuses on toxicokinetics and reviews the current computational approaches to address the issue of interindividual variability for health risk assessments. These approaches include individual-based PBPK modeling, P-bounds modeling, Monte Carlo simulation, and Markov Chain Monte Carlo simulation, each of which has different data requirements regarding input parameters. The advantage of these computational approaches is that they allow predictions of variables that cannot be easily accessed or measured in susceptible subpopulations with the available methodologies. Thus, the resulting simulations are useful in characterizing the magnitude of interindividual variability in the human health assessment of chemicals.

Ecotoxicology Modeling is a comprehensive and well-documented text providing a collection of computational methods to the ecotoxicologists primarily interested in the study of the adverse effects of chemicals, their mechanisms of action and/or their environmental fate and behavior. Avoiding mathematical jargon, the book presents numerous case studies to enable the reader to understand the interest but also the limitations of linear and nonlinear models in ecotoxicology. Written by an international team of scientists, Ecotoxicology Modeling is of primary interest to those whose research or professional activity is directly concerned with the development and application of models in ecotoxicology. It is also intended to provide the graduate and post-graduate students with a clear and accessible text covering the main types of modeling approaches used in environmental sciences.

In the last decade and a half, great progress has been made in the development of concepts and models for mixture toxicity, both in human and environmental toxicology. However, due to their different protection goals, developments have often progressed in parallel but with little integration. Arguably the first book to clearly link ecotoxicology an

Physiologically Based Pharmacokinetic (PBPK) Modeling: Methods and Applications in Toxicology and Risk Assessment presents foundational principles, advanced techniques and applications of PBPK modeling. Contributions from experts in PBPK modeling cover topics such as pharmacokinetic principles, classical physiological models, the application of physiological models for dose-response and risk assessment, the use of in vitro information, and in silico methods. With end-of-chapter exercises that allow readers to practice and learn the skills associated with PBPK modeling, dose-response, and its applications to safety and risk assessments, this book is a foundational resource that provides practical coverage of PBPK modeling for graduate students, academics, researchers, and more. - Provides end-of-chapter exercises to teach hands-on computational tools used in toxicology - Supplies computer code and explanations and includes examples of applied models used in regulatory toxicology and research - Authored by expert editors and contributors who are among the best PBPK modelers in the world

Explore this comprehensive discussion of the application of physiologically- and physicochemical-based models to guide drug delivery edited by leading experts in the field Drug Delivery Approaches: Perspectives from Pharmacokinetics and Pharmacodynamics delivers a thorough discussion of drug delivery options to achieve target profiles and approaches as defined by physical and pharmacokinetic models. The book offers an overview of drug absorption and physiological models, chapters on oral delivery routes with a focus on both PBPK and multiple dosage form options. It also provides an explanation of the pharmacokinetics of the formulation of drugs delivered by systemic transdermal routes. The distinguished editors have included practical and accessible resources that address the biological and delivery approaches to pulmonary and mucosal delivery of drugs. Emergency care settings are also described, with explorations of the relationship between parenteral infusion profiles and PK/PD. The future of drug delivery is addressed via discussions of virtual experiments to elucidate mechanisms and approaches to drug delivery and personalized medicine. Readers will also benefit from the inclusion of: A thorough introduction to the utility of mathematical models in drug development and delivery An exploration of the techniques and applications of physiologically based models to drug delivery Discussions of oral delivery and pharmacokinetic models and oral site-directed delivery A review of integrated transdermal delivery and pharmacokinetics in development An examination of virtual experiment methods for integrating pharmacokinetic, pharmacodynamic, and drug delivery mechanisms Alternative endpoints to pharmacokinetics for topical delivery Perfect for researchers, industrial scientists, graduate students, and postdoctoral students in the area of pharmaceutical science and engineering, Drug Delivery Approaches: Perspectives from Pharmacokinetics and Pharmacodynamics will also earn a place in the libraries of formulators, pharmacokineticists, and clinical pharmacologists.