School of Biological Sciences
Natural Resources: depletion, pollution and toxicology
[ BIOL202 Home | Aquabiology at Liverpool ]
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School of Biological Sciences |
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Natural Resources: depletion, pollution and toxicology[ BIOL202 Home | Aquabiology at Liverpool ] |
Ecotoxicology is the branch of toxicology concerned with the study of toxic effects, caused by natural or synthetic pollutants, to the constituents of ecosystems, animal, vegetable or microbial in an integral context.
Ecotoxicology as a subject area came to prominence in the 1950s and 60s after the publishing of Rachel Carson’s book (Silent Spring) on the impact of pesticides such as DDT. Further impetus was provided by problems arising from spills of chemicals and oil. This generated the need for the ‘competent authorities’ ie. Government in all its forms to predict and evaluate the nature and significance of ecological effects resulting from the deliberate or accidental introduction of toxic substances to the environment.
As a result of decades of work, there are now established procedures for establishing the fate and effects of substances introduced into the environment and in many components of ecosystems. However, since many aspects of this are difficult and complex, there is much ongoing research into areas such as sediments and the toxicity of complex mixtures.
Laboratory ecological tests are designed to evaluate both acute and chronic effects. Laboratory acute tests are designed to evaluate effects resulting from short-term (a few days) exposure to relatively high concentrations of a test substance. Typically, the end-point of the test is mortality. Chronic tests are designed to evaluate effects from longer-term (several weeks) exposure to relatively low concentrations of a test substance. End points of the test are usually mortality, reduction of growth or reproductive performance or both.
Similar principles apply to tests with both terrestrial and aquatic organisms. Groups of the test organism are exposed to a range of concentrations of the test substance (often arranged in a geometric series of concentrations) for a pre-determined period. At intervals and at termination of the exposure period, the groups are scored for effects.
The results of the scoring exercise are analysed statistically to determine the concentrations which, it is predicted, would result in a given magnitude of effect over a particular exposure period. In acute toxicity tests, LC50 or EC50 values are determined. These values represent the concentration which it is calculated that 50% of the exposed animals would die (LC50) or otherwise being affected if a different end-point criterion is being used (EC50). These values are usually prefixed by the duration of the exposure period (often 48hrs).
Thus the results from a series of tests could be used to predict that exposure to a solution of a toxic substance (eg a solution of copper) at a concentration of 5 mg l-1 would resulted in the death of 50% of the test organisms (eg Daphnia) after 48 hrs exposure. Statistical procedures for calculating the value from acute toxicity test data include probit analysis (REF??).
Ecotoxicological studies are designed to form part of the process for predicting the likely hazard associated with the manufacture, transport, use or disposal of a substance. It contributes to environmental exposure assessment through the determination of concentrations resulting from chemical application in field experiments that are designed to represent either realistic application conditions or ‘worst-cases’.
Assessing toxicity of a substance can be achieved using one of two approaches:
1 Prediction on the basis of its molecular structure using Quantitative Structure Activity Relationships (QSARs)
2 Measurement using model test systems
Test systems used to measure the toxicity of a substance range from relatively simple laboratory tests to more complex field tests involving natural or semi-natural communities.
Laboratory tests are designed to evaluate both chronic and acute tests. Chronic tests are designed to effects resulting from longer-term (usually several weeks)
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