From Ontario, Canada to London, England, traces of illegal drugs have been found in drinking water supplies. But United Kingdom researchers were nevertheless surprised to find low levels of cocaine—along with traces of dozens of pharmaceuticals and pesticides—in shrimp from 15 sites in Suffolk, a county to the northeast of England’s capital.
“We see this often in major cities around Europe, and we do yearly monitoring on surface water levels,” Thomas Miller, a postdoctoral research associate at King’s College London and first author of a new study in Environment International, tells Smithsonian. “However, for Suffolk, a much more rural area that has a lot of agricultural land use, we were not expecting to see cocaine in every sample.”
Scientists have long been conducting research into the contaminants that permeate aquatic ecosystems. Most previous investigations have focused on levels of pollutants in the water, since it has been difficult to quantitatively measure trace contaminants in aquatic organisms themselves. But this is “a limitation,” Miller says, because if these pollutants are causing harm to wildlife, the damage will be coming from internalized chemicals. Fortunately, modern instruments have become more sensitive in recent years, making it possible for the study authors to measure contaminant levels in both surface waters and in Gammarus pulex, a freshwater crustacean.
In total, the researchers were able to detect 56 compounds from illegal drugs, pharmaceuticals and pesticides in the little critters. Cocaine was the most frequent contaminant found; it showed up in shrimp at every single site. Lidocaine, a local anaesthetic that is sometimes used to dilute cocaine, was the second most frequently detected compound. The drug ketamine was also widespread. Diazepam (also known as Valium) and alprazolam (also known as Xanax) were among the other drugs detected, as NPR’s Merrit Kennedy reports.
But how are these contaminants ending up in the water—and, subsequently, in freshwater invertebrates? Most likely through human consumption and “effluents,” the study authors write. Only some of the drugs that humans ingest get metabolized by the body; the remainder is excreted through urine and feces, and can then end up in wastewater, according to Harvard Health Publishing. Sewage treatment plants aren’t able to remove all of the chemicals from mucky water, which can lead to contaminants getting into streams and rivers.
But there are other ways that drugs infiltrate aquatic ecosystems. One is improper disposal—people flushing their unused drugs down the toilet, rather than taking them to medication collection programs. Drug manufacturing can produce pollution, and runoff from hormone and antibiotic-fed livestock and poultry can also contaminate waterways.
The scope of the problem is likely quite large. Between 1999 and 2000, for instance, the the U.S. Geological Survey analyzed water samples from 139 streams in 30 states, and found one or more chemicals in 80 percent of the streams. “The drugs identified included a witches' brew of antibiotics, antidepressants, blood thinners, heart medications (ACE inhibitors, calcium-channel blockers, digoxin), hormones (estrogen, progesterone, testosterone), and painkillers,” according to Harvard Health Publishing.
The new study, while indicative of widespread problem, raises a number of questions that the researchers cannot yet answer. Curiously, a number of pesticides that have long been banned in the U.K., including fenuron, were found in the sample, but just where they came from remains unclear.
Also unknown is the effect of all these contaminants. Concentrations of the drugs and pesticides were low, and therefore “the potential for any effect is likely to be low,” says Miller. But there have been indications that all the drugs ending up in rivers and streams can have a negative impact on aquatic animals. Last year, researchers in Italy found that European eels exposed to small concentrations of cocaine in the lab suffered from swollen muscles and fiber breakdown. The cocaine had also accumulated in the eels’ brains, gills, skin and other tissue.
It’s not just illegal drugs that pose a problem. Fish with male and female sex traits, for instance, have been found in Northeastern waterways in the U.S., and scientists think that hormones from birth control pills are driving the anomalies.
Ultimately, more research is needed to fully understand how aquatic organisms are being impacted by drug pollutants. The new study, though comprehensive, focuses on just one species in just one place, and “is actually a very small ‘snapshot’ of what is likely to be present in wildlife,” Miller says. “We need more routine monitoring of chemical contaminants in wildlife so that we can prioritise compounds of concern and better protect our environment.”