The fish in our canals popped a pill. This PhD candidate wants to do something about it
Medicine residues in rivers, such as painkillers and antidepressants, alter the behaviour of fish. UvA PhD graduate Charlie Davey investigated how much medicine residue is still being discharged into Dutch waters at the Amsterdam wastewater treatment plant. “What stood out was the large amount of ibuprofen that was still present after 97 per cent removal.”
Charlie, how did you become fascinated by the impact of our drug residues on aquatic life?
“Through studies that made global headlines a few years ago. Such as the work of American researchers who demonstrated that octopuses under the influence of MDMA (the active ingredient in ecstasy pills) start to exhibit affectionate, social behaviour. That research shows that chemicals can have the same effect on animals as they do on humans.”
“Another case is fish feminisation. This involves male fish exhibiting female characteristics and, above all, becoming infertile when they encounter the contraceptive hormone oestrogen, which ends up in ditches and rivers via the sewage system. As a result, some populations have been declining.”
“The Dutch population is using more and more medicines, and every year more than 190,000 kilograms of medicine residues end up in the sewer system per year via urine and faeces. Many people think that the medication we use is broken down by the body, but that is not always the case. Some of it ends up in the sewer system and, even after wastewater treatment, in the environment.”
The sewage treatment plant in Amsterdam-West gave you a glimpse into Amsterdam’s sewers. What did you encounter?
“What stood out was the difference in the amount of amphetamine we would expect from prescriptions versus what we saw. This substance is found in both the drug speed and in ADHD medication. A quick calculation shows that only 17 per cent of the amount of amphetamine present in the sewage can be traced back to the prescribed amount of ADHD medication. So either many Amsterdammers are using ADHD medication without a prescription, or they are using a lot of speed.”
“I didn’t look at all the substances present in the sewage water, but only at psychotropic drugs, a collective term for medication for mental disorders that result in behavioural changes. Ultimately, I was able to test 30 substances in Amsterdam’s sewage water. Substances that were common were caffeine, the painkillers ibuprofen and paracetamol, and various forms of antidepressants. After purification, paracetamol was no longer present, as it breaks down quite easily, but ibuprofen was still present. I found that interesting, given that 97 per cent of ibuprofen is removed during purification. It therefore indicates how much this painkiller is used. The antidepressant sertraline was also present in risky concentrations after purification, but this was due to its higher than average toxicity.”
What are the consequences for aquatic animals?
“Fish experience less anxiety and become overconfident when they ingest the anxiolytic sertraline. Small prey fish, which normally stay among the seaweed and rocks, start swimming in open water when sertraline is used, where they easily fall prey to larger fish. I don’t remember the exact effect of ibuprofen, but psychotropic drugs in general cause fish to become sluggish, eat less and become disoriented.”
Could this pose a risk to humans? When eating fish, for example?
“That is not unimaginable. In Israel and India, for example, it is so dry that they sometimes use sewage water to irrigate their fields and sludge from sewage treatment plants to fertilise the land. That sludge is very fertile, but it is full of contaminants. Israeli researchers have shown that potatoes grown on that land exceeded safety standards because they contained anti-epileptic medication. That is not extremely dangerous; according to a quick calculation, you would have to eat potatoes every day for two weeks to ingest one pill of medication.”
“Something similar applies to fish. A certain fish in the Black Sea may no longer be sold in the EU because of toxic substances. This is due to industry discharging waste into the Danube and Dnieper, rivers that flow into the Black Sea.”
How problematic are drug residues in our wastewater?
“I get that question a lot. Personally, I think there are bigger problems, such as the nitrogen problem and the phosphorus crisis. This leads, for example, to blue-green algae, which extracts oxygen from the water, creating so-called dead zones in the Baltic Sea. This has a greater ecological impact, including on fisheries and the economy.”
“Compared to that, psychotropic drugs in the environment are a less acute problem, which does not mean that they are not a cause for concern. One of the problems is how little we still know about them. We are only now beginning to learn more about behavioural changes in fish. Legislation often looks at ecotoxicological endpoints, such as when fish die, while behavioural changes already occur at much lower concentrations of a substance.”
“Compared to that, psychotropic drugs in the environment are a less acute problem, which does not mean that they are not a cause for concern. One of the problems is how little we still know about them. We are only now beginning to learn more about behavioural changes in fish. Legislation often looks at ecotoxicological endpoints, such as when fish die, while behavioural changes already occur at much lower concentrations of a substance.”
What are the solutions?
“There are suggestions that I discuss in my thesis. One suggestion is to go back to the drawing board and design psychotropic drugs that do break down in the environment. However, this will not be easy, because drugs such as antidepressants are designed to remain active in the brain for as long as possible. Another possibility could be to make more use of psychotherapy instead of medication, but this has some ethical questions associated with it, such as if therapeutic efficacy for the patient is maintained. Above all, we must prevent patients from stopping their medication in order to save fish in all cases.”
“Another route is to work with doctors to identify which drugs are less harmful to the environment. Together with Amsterdam UMC, I am investigating whether, in some cases, we can prescribe psychotropic drugs that break down more easily without compromising the effectiveness of the medication. In all cases, we must prevent patients from discarding their medication in inappropriate way, such as flushing unused medication down the toilet.”
“Improving sewage treatment is the most logical route, and the one I support. The costs of upgrading sewage treatment will be partly borne by pharmaceutical companies, in line with recent Urban Wastewater Treatment Directive legislation that stipulates that the polluter pays. This is the easiest way to make progress and prevent drug residues from reaching surface water. There is already a plan to improve water treatment starting from 2030. In later chapters of my thesis, I investigate some of the proposed treatment methods and agree that these will improve the situation in the rivers. We will still need to monitor how well these upgrades perform when they are built, to continue to make sure that the risk to aquatic life is minimised as much as possible.”
