Valves and Bivalves

It appears a Polish city has a particularly clever way of sensing pollution in their water supply and closing valves. With bivalves.

Natural Sensors

It appears that the city of Poznań, in western Poland, has an intriguing method of assaying and controlling their water supply. ^{[1] [2] [3] [4] [5] [6]} They’re partly worried about terrorist attacks on the water supply, but also about bacterial contamination. And, being in an old East-Bloc nation, the occasional heavy metal contaminant, like chromium. It’s a problem, having to test for so many things at once!

They came upon an intriguing solution, involving local mussels. They normally are very sensitive to a variety of pollutants, which cause them to close their shells. So 8 mussels are recruited, glued to a station where they will be fed and enjoy a stream of local water. However, as shown here, a magnet on a spring is glued (harmlessly) to their shell.

If more than 4 out of the 8 mussels no longer care for the taste of the water and close their shells, then a computer closes off the water supply. The bivalves control the valves. (The story does not say what the city does for water in that eventuality.)

(NB: Tom Scott’s video is a bit more skeptical, but to satisfy that skepticism he got to talk to the staff of the water treatment plant. The shutdown criterion is a bit more complex: 6/8 mollucs closed, all within 4 minutes, and overall activity drops below 25%. Probably a couple other things, too. As Scott is careful to express clearly, this is one part of a defense in depth, along with other mechanical and chemical detectors.)

After a few months, the mussels become too accustomed to their new lives and are thus returned to the wild and replaced by new mussels. At least on the surface, it sounds remarkably humane, as well as clever.

This is apparently the practice in 50 water plants in Poland, as well as 1 in Russia. (Apparently several American cities use bluegills for a similar purpose?) Of course, the mussels won’t tell you which pollutant offends them, but it’s a good first-line defense.

The Weekend Conclusion

Bivalves control valves.

Yeah, that crummy little joke was pretty much the whole reason for this post.

(Ceterum censeo, Trump incarcerandam esse.)

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Notes & References

1: J Kotke, “Eight Clams Control This Polish City’s Water Supply”, Kotke.org, 2024-Dec-31. Downloaded 2025-Jan-04. ↩

2: A Micu, “In Poznan, Poland, eight clams get to decide if people in the city get water or not”, ZME Science, 2020-Dec-28. Downloaded 2024-Jan-04. ↩

3: Unknown Author, “How clams help keep Polish water clean”, The Economist, 2021-Jan-21. NB: Link is to a Wayback Machine that may, or may not, get you past the paywall if you’re judicious enough on disabling javascript. ↩

4: C Giamo, “These Hardworking Mussels Monitor Poland’s Drinking Water”, Atlas Obscura, 2024-Jun-14. ↩

5: J Pelka, “Fat Kathy (Gruba Kaśka)”, Polish Shorts film collection. Also available full-length on YouTube.↩

6: T Scott, “Is Poland’s tap water really protected by clams?”, Tom Scott’s YouTube Channel, 2022-Oct-31. ↩