Freshwater shrimp kept for twenty hours at a caffeine concentration detected in highly polluted rivers spent less time in the dark than shrimp kept at ordinary background levels, and that shift was ab
A study from the University of Bonn reveals that freshwater shrimp exposed to caffeine levels found in polluted rivers exhibit altered behavior, specifically spending less time in the dark. This suggests that common water pollutants can disrupt the natural survival instincts of aquatic species.
Why it matters
Understanding how chemical pollutants affect animal behavior is crucial for assessing the long-term health of river ecosystems and biodiversity.
The high tanks held 10,000 nanograms of caffeine per litre and the low tanks held 100, two levels chosen because both occur in real rivers. There was no caffeine-free group at all, so what the experiment measures is the distance between those two numbers.
By Life Signs · Edited by Christy Jeremia
Published September 12, 2026 · How we edit
How much caffeine does it take to change the way a river animal handles the risk of being eaten? In a laboratory in Bonn the figure on the label was 10,000 nanograms per litre, a level that has been detected in highly polluted rivers. After twenty hours at that concentration the animals spent less of a five-minute test in the dark than animals held at a hundredth of it.
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