ABSTRACT
The first five chapters have been concerned with the fate of chemicals in the environment and within living organisms. This chapter begins the second part of the text, in which emphasis shifts to questions about the effects that chemicals have upon individual organisms. Ecotoxicology is concerned with the harmful effects of chemicals. This chapter will address the questions of what constitutes harm and how toxicity is measured. It is important to do this before moving on to the more complex issues of Part 3, in which the crucial questions concern the relationships between toxic effects upon individuals and consequent adverse effects at the levels of population, community, and ecosystem.
