This article presents an overview of the relationships between acute and chronic toxicity and ecotoxicology. The examples used come from the field of freshwater aquatic ecotoxicology although the principles are applicable to other systems.

Ecotoxicology is a combination of the terms ecology and toxicology. Ecology is the study of the relationships between plants and animals and their abiotic environment while toxicology is the study of poisons. The term ecotox-icology then may be defined as the study of the effects of poisons on ecological systems or components thereof. Components of an ecosystem include individuals, populations, communities, and the abiotic environment in which they are found. The ultimate goal of all toxicity testing is to provide data that can be used to establish biologically safe concentrations for toxicants. When sufficient data have been gathered experts in toxicology may develop a criterion for a toxicant. If criteria are incorporated into standards by regulatory agencies, they become enforceable legal limits. To that end the list of toxicity tests (listed in order from least to more complex) shown in Figure 1 have been developed so that their successful completion provides the data that can be used to develop criteria/standards.

There are advantages and disadvantages associated with each of the test methodologies shown in Figure 1. As indicated in the figure, as one moves from single species toxicity tests (which includes laboratory acute and chronic tests) to whole lake or natural system testing the complexity of the tests increases and therefore so do their expense. Generally, because of the characteristics of the tests, a tiered approach is used where testing begins with the simple tests and based on the data needs may progress across the tests. However, it is not necessary, nor is it likely that each test in the series shown in Figure 1 would be performed to evaluate the potential impact of a chemical. If funds available for testing are limited the results from the simpler tests are often used to prioritize which chemicals receive more complex testing. In many cases criteria are based only on results from acute and chronic toxicity tests performed on a variety of species.

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