Researchers have known for more than a decade that the pharmaceuticals we consume tend to turn up secondhand in wildlife. Sometimes this can have horrible effects.

Chemical hormones in birth control pills, for instance, pass into the urine and are released via municipal sewage plants into the environment, where they can become potent endocrine disruptors. These drugs alter the reproductive physiology and behavior of fish downstream, with impacts including feminized or intersex males.

But so far, society’s reaction has largely been a collective shrug: Those are fish, not people. Why should we care? Attempts to limit drug pollution have mostly gone nowhere.

A new study in the journal Food Chemistry should shake us out of our complacency. Chemical analyst M. Abdul Mottaleb and his team at Northwest Missouri State University went to fish counters at local supermarkets and purchased fillets of 14 different species. Then they tested them for the presence of several human pharmaceuticals, including the antihistamine found in medications like Benadryl, and the antianxiety compound found in medications like Valium.

The results: Eleven of 14 fish servings contained elevated levels of the two drugs.

Moreover, the fish weren’t just freshwater species, such as catfish or its Asian cousin swai, which might predictably pick up wastewater treatment byproducts in river habitats. Saltwater fish including mullet, cod, red snapper, ocean perch, bay scallops, mahimahi, Atlantic salmon, sole, and Spanish mackerel were just as likely to be contaminated.

(Photo: UGA College of Ag and Environmental Sciences/Flickr)

So while eating fresh fish may well boost your levels of healthy omega-3 fatty acids, this study suggests that it could also mean unwittingly consuming a cocktail of unintended drugs (not to mention mercury, PCBs, and other pollutants).

One puzzling aspect of the study, Mottaleb said, was that many of the fish specimens came from Thailand, Vietnam, and China, countries that are notorious for illegal fishing but not normally associated with heavy pharmaceutical use.

But prescription drug consumption is rapidly increasing as those countries adopt Western lifestyles, said Kathryn Arnold, a University of York ecologist who was not involved in the new study. Many Asian nations have also become generic drug producers but have few or no regulations on what pharmaceutical manufacturers dump into the environment.

The level of drugs found in the study was relatively small in human terms: You are not going to treat your anxiety or your runny nose by consuming fish. Arnold calculated that in a normal meal of any of these fish, even the highest concentrations detected would still yield less than a thousandth of the normal therapeutic dose for either drug.

Unintentionally consuming multiple drugs with the same effect could still pose a health risk, and some drugs are dangerous if taken together. The antianxiety drug diazepam, for instance, shouldn’t be combined with a long list of other prescription drugs because it alters their effectiveness. But “it’s a slim risk,” Arnold said.

“For me the greater worry is for fish-eating wildlife,” she added, animals like cormorants or leopard seals “whose entire diet consists of fish.”

The concentration of pharmaceuticals in any single meal is very small. But as these animals dine on the same prey fish day after day, the contaminants accumulate in their bodies, Arnold said, “and they weren’t designed to be eating any of these drugs.”

A drug that is beneficial in one species can have astonishing and unpredictable effects in another. In India in the 1990s, for instance, farmers began administering the drug diclofenac to relieve arthritis symptoms in cattle. But that drug causes fatal kidney failure in vultures, and because vultures scavenge on dead cattle, one of the largest vulture populations in the world plummeted 99 percent in just five years. Today, three vulture species are still flirting with extinction.

Effects on individual species can also cascade through entire ecosystems. Researchers in Canada recently concluded a long-term experiment in which they added human contraceptive by-products at typical levels into a small, isolated lake. Because of the disruption to their reproductive lives, fathead minnows, a common prey fish, vanished within two years. After four years, slimy sculpin, another prey species, were down to 1 percent of their former numbers.

The devastation worked its way up the food chain to lake trout, the top predator, which diminished as much as 42 percent over the seven-year study.

Removing drug residues from wastewater treatment plant effluent is extremely expensive, especially for developing countries that haven’t yet built even the most rudimentary sewage treatment. But in almost every ecosystem, humans are at the top of the food chain. What happens to the plant and wildlife nearby will ultimately happen to us.

Think about that (and let your lawmakers know what you think) next time you step up to the seafood counter or reach for a prescription drug.