The major chemical pollutions or accidents presented in this article do not occur often, but the damage can be enormous when they do. Assessing the environmental impact of these types of events is difficult and complex due to the wide range of potentially toxic substances that may be released and the high degree of variability found in natural environment. As illustrated in the case of Minamata, Sandoz, and Aznalcollar, not just a single substance but also chemical mixtures or environmental conditions such as anoxic sediment can determine the scale of the ecological damage. In many cases, neither ecological nor toxicological data are available. Interactions among chemical, environmental, and biological factors will also influence the scale of ecological damage. As illustrated by the Minamata, Exxon Valdez, and Aznalcollar cases, the effects of pollution or accidents on ecosystems would be delayed and prolonged. The consequences of such disastrous events suggest the importance of the inclusion for long-term and indirect effects in addition to short-term effects when assessing or predicting ecological impacts of such catastrophic events.
The aftermath of such catastrophic events have represented a valuable opportunity to learn from misfortune. The scientific investigation of the aftermath in those highly contaminated areas can help us understand the environment, how it responds to catastrophic events, and how it recovers from the catastrophic events. As illustrated by Minamata, integrating a variety of patchy data regarding chemical release, environmental monitoring, and fishery statistics would provide insight into interpreting damage to the environment caused by chemical pollution. Long-term monitoring of the contaminated environment including residue levels in biota is an effective approach for initially assessing damage to an ecosystem, as was clearly demonstrated by the Minamata case. Monitoring of the habitats and species combined with contaminant levels in the area will provide valuable information to understand ecotoxicological impacts on ecosystems. Applying strategies learnt from the case histories could help with the design of both chemical and ecological monitoring program to improve the understanding of the relationship between ecological damage and chemical pollution and planning effective remediation approaches.
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