Chapter 29

• Ecotoxicology is the study of the fate and effects of toxic substances on an ecosystem.
• Chemodynamics is, in essence, the study of chemical release, distribution, degradation, and fate in the environment.
• A chemical can enter any of the four matrices: the atmosphere by evaporation, the lithosphere by adsorption, the hydrosphere by dissolution, or the biosphere by absorption, inhalation, or ingestion (depending on the species). Once in a matrix, the toxicant can enter another matrix by these methods.
• The biological availability (or bioavailability) of a chemical is the portion of the total quantity of chemical present that is potentially available for uptake by organisms.
• Pollution may result in a cascade of events, beginning with effects on homeostasis in individuals and extending through populations, communities, ecosystems, and landscapes.
• Terrestrial toxicology is the science of the exposure to and effects of toxic compounds in terrestrial ecosystems.
• Aquatic toxicology is the study of effects of anthropogenic chemicals on organisms in the aquatic environment.

Ecotoxicology is the study of contaminants in the biosphere and their effects on constituents of the biosphere. It has an overarching goal of explaining and predicting effect or exposure phenomena at several levels of biological organization (Figure 29–1). Relevant effects to nonhuman targets range from biomolecular to global. As the need to predict major effects to populations, communities, ecosystems, and other higher level entities has become increasingly apparent, more cause–effect models relevant to these higher levels of biological organization are added to the conventional set of toxicology models applied by pioneering ecotoxicologists. Contaminant chemical form, phase association, and movement among components of the biosphere are also central issues in ecotoxicology because they determine exposure, bioavailability, and realized dose.

###### Figure 29-1

Ecological scales relevant to ecotoxicology. Solely biological scales relevant to ecotoxicology range from the molecular to the community levels: solely abiotic scales range from the chemical to the entire habitat. Biotic and abiotic components are usually combined at levels above the ecological community and habitat. The ecological community and physicochemical habitat combine to form the ecosystem. Ecological systems can be considered at the landscape scale, that is, the combination of marine, freshwater, and terrestrial systems at a river's mouth. Recently, the continental and biospheric scales have become relevant as in the cases of ozone depletion, acid precipitation, and global warming.

Relevant exposure routes are the conventional ingestion, inhalation, and dermal absorption. But, unique features of exposure pathways must be accommodated for species that ingest a wide range of materials using distinct feeding mechanisms, breathe gaseous or liquid media using different structures, and come into dermal contact with a variety of gaseous, liquid, and solid media.

Prediction of oral exposure can be limited because species feed on different materials; however, conventional principles about oral bioavailability remain relevant. Many techniques applied to determining human oral bioavailability are available to the ecotoxicologist. As an ...

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