Small amounts of cocaine, pesticides and other contaminants have been detected in U.K. freshwater shrimp.

"We found that the most frequently detected compounds were illicit drugs, including cocaine and ketamine and a banned pesticide, fenuron," said King's College London environmental toxicologist Thomas Miller.

He added: "For many of these, the potential for any effect is likely to be low."

For years, scientists have found trace amounts of illicit drugs, pharmaceuticals and pesticides in drinking water around the world. A newer area of study is looking at how these chemicals impact wildlife living in these ecosystems.

"Pharmaceuticals and personal care products and pesticides and these types of illicit drugs have been detected in surface waters all over the world, because when we use them, our waste isn't always treated properly, and so they come out in rivers and streams," Emma Rosi, an aquatic ecologist at the Cary Institute of Ecosystem Studies who has done similar studies, tells NPR.

"We detect these compounds in the environment because people use them, and the things that we use in our everyday lives end up getting into the environment," she says. "What's very worrying is we don't know what the effects are, the ecological effects."

The researchers from King's College London and the University of Suffolk collected samples of Gammarus pulex shrimp in 15 locations in the county of Suffolk, northeast of London. They tested the shrimp for a wide range of pharmaceuticals, pesticides and illicit drugs.

Cocaine was found in samples at every single site. The researchers' paper, published recently in Environment International, says the concentration of cocaine did not fluctuate much between sites, "showing widespread contamination."

Lidocaine, which is used as a local anesthetic and sometimes in tandem with cocaine, was the second most common substance found. The study also detected ketamine, alprazolam and diazepam.

"Such regular occurrence of illicit drugs in wildlife was surprising. We might expect to see these in urban areas such as London, but not in smaller and more rural catchments," Leon Barron, a forensic scientist at King's who worked on this study, said in a statement.

The researchers also found traces of pesticides that are currently banned in the U.K., such as fenuron. Barron added: "The presence of pesticides which have long been banned in the UK also poses a particular challenge as the sources of these remain unclear."

Pesticides can enter the water system through runoff, and their health impact can vary. "Whether these contaminants pose a health risk depends on how toxic the pesticides are, how much is in the water, and how much exposure occurs on a daily basis," according to the U.S. Environmental Protection Agency.

The drugs and pharmaceuticals may be entering the water system through wastewater facilities, among other avenues.

Rosi concluded in a paper published last year that more than 60 pharmaceutical compounds could be detected in aquatic invertebrates and spiders in streams near Melbourne, Australia. In the Nature Communications study, her team also found that animals higher up the food chain like platypuses and gray trout "could in principle be exposed to certain drugs in their diets at levels comparable (up to 50%) to prescribed human doses."

Last year, researchers found traces of oxycodone in bay mussels in Washington state's Puget Sound.

In 2015, researchers in Ontario found that drinking water there was contaminated with small amounts of cocaine, which appeared to come from a nearby wastewater treatment plant. And in 2016, scientists found numerous drugs, including amphetamine, in streams around Baltimore.

The mix of pharmaceutical traces found in water sources is worrying for the same reason that doctors are careful about not mixing certain drugs in humans, Rosi says — because they could have adverse reactions.

"I've done research in lab settings where we have exposed aquatic organisms like invertebrates to various types of pharmaceuticals," Rosi adds, saying that they have found that the compounds can disrupt growth rates and have other negative effects.

One major way to prevent pharmaceuticals from getting into waterways is to properly dispose of them through a drug takeback program, rather than flushing them down the toilet. The EPA has guidelines for disposing of medications here, and you can find a public disposal location for pharmaceuticals here.

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