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Over 40% of the world's rivers could contain harmful levels of drugs.
Common medications, as well as illegal drugs, released into the environment can damage ecosystems and interfere with the growth and behaviour of animals and plants.
The medicines that make us well are having untold impacts on nature.
After entering the water through sewage systems, rainwater runoff and factory discharges, compounds including antidepressants, painkillers and antibiotics have been found to be exceeding safe limits in bodies of water around the world.
At these levels, the pharmaceuticals can have a significant impact on the health of organisms and ecosystems, causing behavioural change, hormone disruption and toxicity.
Alejandra Bouzas-Monroy is the lead author of a new study investigating pharmaceutical water pollution.
The PhD student says, 'This is the first truly global assessment of the impacts of single pharmaceuticals and mixtures of pharmaceuticals in riverine systems.'
'While we were expecting to find some sites where concentrations of pharmaceuticals may be of concern, we were a little surprised at the number of sites where concentrations exceeded safe values.'
'Our findings show that a very high proportion of rivers around the world are at threat from pharmaceutical pollution. We should therefore be doing much more to reduce the emissions of these substances into the environment.'
While the study investigated 61 compounds, known as active pharmaceutical ingredients (APIs), there are more than 1900 which are used in human and veterinary medicine. The study concludes that more research is needed to truly understand the effect that these compounds are having on the health of our ecosystems, as well as our own health.
Drug pollution, also known as pharmaceutical pollution, is where biologically active substances contaminate the environment and impact life. While many of these compounds are used in the treatment of human and animal health, others may be classed as illegal substances.
It primarily affects water and soil. Improper disposal of drugs, such as throwing them into landfill sites or flushing them away, allows the biologically active substances they contain to leach into the environment.
The manufacturing process of drugs also sees significant amounts of bioactive substances released as pollution, as does their use. After being taken, many active ingredients in pharmaceuticals end up being excreted into the environment, and as wastewater treatment facilities are not often designed to filter out these chemicals, they end up contaminating sewage.
When this sewage is released into waterways, or used as fertiliser, the bioactive substances they contain enter the environment, where they can have effects on all forms of life.
While many other types of pollution have been studied extensively, the impact of drug pollution is comparatively understudied.
'Widely available datasets on active pharmaceutical ingredients are becoming more common, but mainly focus on Europe, North America and China and use many different methods,' Alejandra says. 'There has also been limited assessment of their potential chronic effects.'
'Studying the effect of drug mixtures in particular is very expensive, and the equipment used to study it is not widely available outside Europe and North America.'
How a drug affects the environment depends on the compounds it contains.
For instance, a 2021 study found that cocaine being excreted in the urine of Glastonbury festivalgoers was reaching levels known to have an impact on the health of European eels in the nearby Whitelake River.
Previous research had found that eels exposed to cocaine experienced a condition similar to rhabdomyolysis, where muscle tissue breaks down and causes kidney damage. The impact of exposure lasted for at least 10 days after exposure to the drugs had stopped.
As well as damaging tissues, pharmaceuticals can also interfere with an animal's hormones. Experiments that exposed male fish to synthetic oestrogen, which is used in birth control pills, found that male minnows began to produce the female hormone vitellogenin.
Vitellogenin caused male fish to begin developing female gonads, as well as reducing sperm production and effectiveness, while female fish saw their egg development affected. While these experiments took place in an isolated lake, the level of oestrogens was similar to that found in wastewater regularly released into the environment.
Aside from physical changes, drug pollution can also cause behavioural changes. Antidepressants such as fluoxetine have been shown to reduce feeding rates in fish, whereas anti-anxiety drugs can affect shoaling and risk-taking behaviour.
Plants are also affected by pharmaceuticals. Dr Anne Jungblut, an expert in algae at the Museum, says, 'Pharmaceutical pollution often affects aquatic organisms such as algae. Some studies have shown that antibiotics can inhibit the production of chloroplasts, which carry out photosynthesis.
'This can kill the algae or harm its growth.'
Antibiotics leaching into the environment can also contribute to the development of antibiotic resistance, as bacteria adapt to tolerate doses of these compounds at non-lethal levels.
The amount of pollution in a river can vary depending on a range of factors, including the time of year, the weather and location. These can affect the amount of pollution entering a river, as well as how long it takes to break down.
Looking at drug pollution specifically, the recent study published in the journal Environmental Toxicology and Chemistry found that 43.5% of rivers had levels of pharmaceuticals above levels that reached concerning levels.
None of these rivers were in Antarctica or Australasia, as no compound investigated by the study in these areas passed the levels at which environmental impacts were possible, known as the predicted no-effect concentration point (PNEC).
This situation was true of 87% of water samples, suggesting that pharmaceutical pollution in these locations was unlikely to impact an organism's mortality or reproduction. Of those which did, sites in Africa had the highest percentage of sites where concentrations of at least one drug were above the safe limit, while North America had the lowest.
Sulfamethoxazole, an antibiotic, was the drug most frequently found to have passed safe limits in sites across Africa, North America and South America. Meanwhile, nicotine was most frequently measured to be over safe limits in Asian samples, while the beta blocker propranolol was most frequently above PNEC in Europe.
Global rivers were also tested for levels of drugs that could cause smaller impacts on wildlife, such as behavioural changes or altering the production of chlorophyll. Around the world, 11 compounds were found to be in concentrations above the safe limit, and once again this included no rivers in Antarctica or Australasia.
The diabetes drug metformin was found to most frequently have levels which could have an environmental impact, while a site in London, UK, had the highest hazard quotient (the point at which health impacts are possible) for these effects as a result of concentrations of the antidepressant amitriptyline.
Both London and Glasgow were two of the cities where hazard quotients were on average greater than one for a mixture of the drug pollutants observed in their rivers, though a stream in Tubingen, Germany, had the highest in Europe.
The highest culmulative hazard quotient in the world is found in Nairobi, Kenya, where waste disposal on a riverbank is believed to allow drugs to leach into the water.
At present, drug pollution is not something that is routinely monitored or screened out of water supplies. Specific legislation to protect rivers and other bodies of water from pharmaceuticals in nations around the world would help to kickstart a process of removing these compounds from our ecosystems.
This could include requirements to improve the disposal of pharmaceuticals so that they don't pollute the environment, and penalties for people and organisations that do.
Many high concentrations of pharmaceuticals are also found near wastewater treatment plants, as the molecules that have been excreted after use are concentrated as they pass through the facility. Improved filtration systems at these facilities would remove significant quantities of these compounds from water courses.
'Treating waste and wastewater more effectively would be one way we can lower pharmaceutical pollution levels,' Alejandra says. 'However, many of these approaches are costly to implement.'
Beyond this, active steps to remove drug pollution from the environment could also be taken. Bioremediation is where organisms, generally plants or microbes, are used to remove pollutants from an ecosystem.
'While some algae are affected by pharmaceutical pollution, some species, such as Chlamydomonas acidophila, show the potential to be used for bioremediation,' Anne says. 'There is evidence that microalgae can accumulate and degrade some pharmaceuticals, such as antibiotics, which in future could be used to treat contaminated wastewater.'
In future, algal bioreactors could become a part of wastewater treatment plants to filter out pharmaceuticals before they enter the water.
In the meantime, the researchers behind the recent study hope to continue their investigations to better understand how drug pollution is affecting the environment.
Alejandra says, 'This study has shown that the levels of concentrations found in rivers around the world are similar to or higher than levels where other researchers have reported biological disruption in the laboratory.'
'We are now starting experimental work in order to determine whether the effects we predicted are happening in the environment or not. In addition, as the monitoring study explored just a single time point, we are also embarking on an extensive study to look at seasonal differences in concentration.'