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Whether sipping a cappuccino or tossing back an energy drink, people turn to caffeine as the world’s most popular stimulant.

What these devotees may not appreciate is that caffeine passed through the human body and flushed down the toilet is making its way through wastewater treatment plants and into the ocean—with potentially troubling results.

“Exposing marine organisms to caffeine raises very significant concerns,” says Luís Vieira, lead author of a new study that summarizes global research on caffeine in marine waters.

Vieira conducted the study as a caffeine-craving ecotoxicologist at the University of Aveiro in Portugal. “I’m guilty: two to three coffees per day,” he says. “No Red Bull.”

Marine pollution is a widely studied field, which includes investigating the impact of pharmaceuticals and plastics. Caffeine, a natural psychoactive substance that affects mental function, has received relatively little attention, yet can affect marine life in several ways. Caffeine has been found in a wide range of wild fish, from the common silver-biddy of Saudi Arabia’s Red Sea to South Africa’s striped bonito.

In lab studies, researchers have exposed marine life such as algae, clams, mussels, worms, urchins, and small crustaceans to caffeine levels consistent with those recorded in the ocean. Their experiments showed negative impacts related to reproduction and development, growth, metabolic activity, and cellular damage.

Additional research is needed to see if the lab results are repeated in the ocean, Vieira says, and to determine how caffeine may react with other pollutants.

An estimated average of five percent of caffeine consumed by humans is excreted, the study says. Caffeine is not as persistent in the environment as other pollutants such as dioxins and PCBs, but it has a reported half-life in ocean water of 100 to 240 days.

“Because we’re constantly releasing or excreting it, aquatic species in the receiving environment are exposed in perpetuity,” says Peter Ross, a water pollution researcher with the Raincoast Conservation Foundation in British Columbia.

Caffeine levels are expected to be higher in estuaries as well as in urban and heavily touristed areas. Coastal marine zones that are shallow or feature poor tidal flushing are also at greater risk.

The higher the level of waste treatment, the better the chance of removing caffeine. Realistically, that is society’s best bet for reducing the amount entering our oceans.

No one dares challenge the public’s insatiable thirst for caffeine.

“People love their coffee, tea, and caffeinated colas,” says Ross, who did not participate in the study. “You’ll run into a social backlash.”