Prescribing for shrimps

Shrimps kept in sea water laced with the level of fluoxetine currently found in their natural habitat change their behaviour. Instead of seeking cover from predators under rocks, they swim towards light. So human drugs may trigger behaviour changes which could unbalance the ecosystem.

What happens to all the medication we prescribe? It’s a challenge to find out.

As we know, a lot isn’t ever taken. In one survey, only 18% of people said they completed courses of antibiotics. Unused pharmaceuticals should be returned to a pharmacy. They are then incinerated. In hospital, end of problem. But in the community, probably only 25% of unused prescriptions find their way back to a pharmacist. People usually throw unwanted medication into the household waste or flush it down the toilet.

Either way, it can end up in the environment.

Household waste goes to the dump. Landfill sites in UK have rubber liners, so their contents are contained. But inevitably there are leaks, so chemicals seep into ground water. Once there, they may decompose into who-knows-what-possibly-toxic compounds.

Any drug, whether excreted through the kidneys or the gut or thrown into a British toilet, goes to a sewage treatment works. There, waste water is treated to make it safe to discharge into the environment. These processes also treat water from industry and agriculture, so they have to cope with a huge range of contaminants, some potentially very toxic and in large concentrations. Once treated, the solids (sludge) and the cleaned-up water are discharged onto the land or into rivers or the sea. Any chemicals they still contain may then find their way to the reservoirs and aquifers. That’s where most of our drinking water come from; further treatment makes it safe to drink.

Until very recently drugs were the least of the Drinking Water Inspectorate’s concerns. DWI was far more worried about particles – no-one wants murk in their glass of water – than heavy metals and pathogenic micro-organisms . But twenty years ago someone started asking other questions. And scientists started doing tests.

In clinical practice, levels of anticonvulsants, performance-enhancing drugs and illegal substances are routinely measured, but it’s a different matter to test drinking water for tiny quantities of the thousands of drugs we prescribe, let alone their metabolites. Nevertheless the evidence that exists is reassuring. Though many drugs can be detected in treated water, they have never been found at anything near a harmful level.

Research has asked other interesting questions. Can you trace the usage of drugs in a community through their concentrations in waste water? By looking at prescribing data for an area it is possible to estimate the likely consumption of those medications. It is much more difficult to hazard a guess about over-the-counter pharmaceuticals, and almost impossible to calculate usage of illicit drugs. But it has proved possible to estimate communities’ usage of some drugs from the concentrations in their sewers. The cocaine levels in waste water from different districts of Barcelona provide useful information about patterns of cocaine consumption in the city.

There are complications. Heavy rains can overwhelm sewage treatment plants and when raw sewage is discharged, drug levels will be higher. The level in our environment of drugs such as antihypertensives is steady throughout the year round. But what about drugs which are used very widely for a brief time? Just as far more thyme and sage appear in American sewers at Thanksgiving, waste water will reflect events. Had the bird flu pandemic turned serious, how much Tamiflu would have reached our water, and what effect might it have had? We don’t know. Will micro-organisms exposed to the antibiotics which remain in treated water develop resistance? We don’t know. Meanwhile, one way or another, from agriculture, from landfill, from leaky sewers, from treated water, we are dumping an ever more complex soup of pharmacologically active chemicals into our environment.

And we aren’t the only living things on the planet. India’s vulture population has plummeted since vets started prescribing diclofenac for cattle. It turns out that cow carcasses contain enough diclofenac for vultures to develop renal failure. It is now well established that ‘endocrine disruptors’ – which come from many sources besides HRT– can affect the sexual development of amphibians, reptiles and fish. It’s not just the anglers who are concerned. And remember those shrimps, putting their lives at risk by swimming towards the light.

Here in Britain our drinking water may be free of other people’s Prozac, but the volume of prescriptions goes ever upwards. What can we do about it? The less that goes into the environment the better, which probably means developing water treatment processes specifically designed to remove medications. A campaign to explain to people why they should return unwanted drugs to pharmacies would help. And what happens to shrimps and vultures should matter to us. We aren’t just prescribing for Mrs Jones; we are also prescribing for shrimps.

Dr Alex Ford of the University of Portsmouth describes his work on shrimps here.

This article first appeared in The Sessional GP magazine in August 2011.

2 Responses

  1. Since I wrote this article in 2012, further experiments, by Dr Alex Ford and others, have shown that antidepressants in concentrations found in environmental waters can affect molluscs as well as crustaceans and fish. Meanwhile more and more medications are dispensed.
  2. 23rd June 2020 Viral material from Covid-19 can be detected in waste water. Since February Singapore has been sampling waste water from foreign workers' dormitories and correlated the level of viral material with the prevalence of infection in the dormitories. Potentially very useful for identifying local outbreaks of infection, for monitoring population spread and for assessing how effectively it is being managed.

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