PRINCIPLES OF ENVIRONMENTAL TOXICOLOGY AND CONTAMINATION (PART II)

Table of Contents

1. Index
2. UNIT 5 - Transport and fate of contaminants in the environment
3. UNIT 6 - Principles of toxicokinetics and toxicodynamics
4. UNIT 7 - Biotransformation
5. UNIT 8 - Toxicity Testing
   1. Introduction
   2. Dose-response relationships
   3. Test design and test species
   4. Indicator species
   5. Model organisms
   6. Biomarkers and monitoring studies
6. Glossary of key terms associated with environmental toxicology

Model organisms

A model organism is a species that has been widely studied and hence is biologically, anatomically and physiologically well-known. Commonly, these species are easy to maintain and breed in laboratory conditions and have particular experimental advantages that make them a model for ecotoxicological studies. The diversity of reported data about such organisms considering different season-dependent characteristics in field studies or controlled conditions in laboratory studies makes them more attractive to use in study and reinforce results-comparison between different studies. Taking into account the diversity of available data, model organisms can be used to improve the knowledge about other species (including humans) that are more difficult to study directly.

Different types of model organisms can be considered attending the advantages of their use and the purpose of the study.

To illustrate this section, see the following video:
https://www.youtube.com/watch?v=scI_1pRfHSo

Genetic model organisms

These are species that are amenable to genetic analysis considering characteristics such as large number of breeding and short generation time, which enables multigenerational studies. Generally, many different mutants are available and highly detailed genetic maps can be created. (Examples: baker's yeast Saccharomyces cerevisiae, the fruit fly Drosophila melanogaster and the nematode worm Caenorhabditis elegans).

Experimental model organisms

Although these species may not be genetically amenable for research, they have other experimental advantages, namely production of robust embryos that can easily be manipulated and used in developmental biology studies (Examples: the chicken and the African clawed frog Xenopus laevis).

Genomic model organism

Regardless of their genetic or experimental advantages and disadvantages, certain species are chosen as model organism because of their position in the evolutionary tree or due to some advantage characteristic of their genome that enable comparisons between species and identify conservative pathways of genetically different groups. Mice have been extensively used to establish disease models by mimicking the gene defects seen in humans, and these models can be used to test the efficacy of new drugs. Another recognized model organism is zebrafish (Danio rerio), which shows a high sensitivity for disruption during developmental process, with conserved teratogenic mechanisms compared with humans and other mammals.