You can find a list of published articles with pictures about the worst ecological crises here:
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Hungary toxic sludge
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The Aral Sea problem
The Aral Sea problem - part II
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Bhopal disaster
Bhopal disaster - part II
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The Black Death
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The Chernobyl nuclear disaster
The Chernobyl nuclear disaster - part II
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Easter Island deforestation
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The Great Sparrow
The Great Sparrow - part II
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Deepwater Horizon oil spill
Deepwater Horizon oil spill - part II
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London smog
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Fukushima nuclear accident
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Exxon Valdez oil spill
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Pollution in China
Pollution in China - part II
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