When Frank Sinatra threw “three coins in a fountain,” Old Blue Eyes may have endangered fish swimming in those waters. In an experiment, copper-contaminated waters blocked fishes’ ability to smell the odor released by other fish when in danger.

However, people willing to spend a bit more on their wishes don’t stifle fishes’ senses. The metal nickel didn’t seem to block the detection of danger signaling scents released by fish during a predator attack.

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“Our research shows that copper affects the function of a specific type of olfactory neurons in fish, preventing them from detecting important olfactory signals used to detect fish injured by predation,” said Bill Dew of the University of Lethbridge in Canada in a press release. “This means that fish in an environment contaminated with copper would not be able to detect compounds released during a predation event and potentially not avoid predators, while fish in a nickel contaminated environment would be able to detect these compounds and undertake predator-avoidance behaviors.”

Dew used fathead minnows in his experiment. Dew’s study will be presented today at a meeting of the Society for Experimental Biology.

Copper contamination can occur when hopeful humans toss pennies into natural wells. For example, in Bermuda, tourists make wishes before throwing coins into deep cave pools filled with salty water, reported the National Oceanic and Atmospheric Administration. The copper in the coins dissolves rapidly in salt water and results in toxic levels of copper in the pools.

Copper mining and its byproducts can contaminate water with copper, as well. Copper mines and waste from the operations can pollute water with so much metal that the water turns turquoise blue. Runoff of copper-based fungicides from farms and vineyards also can pollute waterways.

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Humans need to be wary of copper contamination too, warns the U.S. Environmental Protection Agency. People can suffer liver and kidney damage after drinking copper polluted water over the long term, and gastrointestinal problems over the short term.

IMAGES: Stream stained turqouise-blue as it emerges from the spoilings or tailings piles of copper ore at Jerome, Arizona (©Andrew Dunn, Wikimedia Commons)

Piles of copper coins from a wishing well pool in a Bermuda cave. (Bermuda Deep Water Caves 2011 Exploration, NOAA-OER)