This course will cover the general aspects of ecosystems and environmental toxicology of different contaminants. Environmental toxicology studies the interaction between different contaminants and organisms (including humans), and thus the integration of biology and chemistry is a must. In this course, the general principles of ecosystem dynamics and different classes of contaminants (such as metals, organic contaminants, radionuclides, and emerging chemicals of concerns) will be first introduced. The environmental transport, bioaccumulation and bioavailability, and toxicological assessments of these contaminants will then be thoroughly evaluated and compared. Emphasis will be placed on the ‘interface’ of different environmental (or biological) matrixes. Different mathematical or empirical models used to study the transport, bioaccumulation, and toxicity of contaminants will be introduced. Finally, the more applied aspects of environmental toxicology will be discussed using real case examples in Hong Kong or elsewhere. The course will also provide basic framework to conduct realistic environmental risk assessments of different contaminants in the environments.