What happens when I flush a pill down the toilet? And why should I care?
[Finnish version: click here]
Trace amounts of medications have been found in drinking water in various places. Are there effects on health? Some media are alarmist, but the most accurate answer basically is that we simply do not know yet (WHO,CWA, CBS, New Scientist).
Although it is only human to be worried about humans, the effects on the wider ecosystem may be much larger. A small amount in purified water means a larger amount in the non-purified source water. Again, there are alarming case studies where large amounts of medicine-related hormones have had biological effects on fish populations. However, on the whole no one really knows how much contamination there is, nor what its overall effects are, nor who is causing it (USGS).
There are relatively few possible sources of contamination. Pharmaceutical manufacturers may cause some very high contamination peaks, but the question is controversial (NBC). Antibiotics in agriculture are also a major source (WCP). However, it is clear that some of the contamination is coming from ordinary consumers.
How much? I don’t know. Rather than getting involved in a big-picture controversy on which we don’t have enough data, I decided to hone in on a small concrete detail. We, ordinary consumers, are contaminating the sewer system with our medications. Whether the effect is serious, we cannot know yet. But there is one question that we can try to answer. What is the mechanism that causes it? Or, to put it in a more earthy manner:
Is the contamination caused by pissing, or by flushing?
There are two ways to get a drug into the sewer system. A person can eat the pill and later excrete any excess medicine in his urine or feces. Or he may dispose of old medications by flushing them down the toilet.
I want to know whether the flushing is causing most of the overall contamination. This is an eminently practical question at the grassroots level. People will take the medications they need, whatever the environmental effect. But there are steps that can be taken against flushing, like information campaigns, creating better incentives to return the medications, or good take-back systems.
Finland has a strong take-back system. All aged medications can be returned to pharmacies free of charge, no questions asked. (The waste is then disposed of as hazardous waste). But even in Finland, flushing happens anyways.
I am trying to find a single number that would allow consumers to get an intuitive feel of the damage they cause by flushing. I may have found it in the inverse of the excretion rate. I am calling it the flush rate. This needs a little explanation.
Whenever a medicine is taken, a complex process occurs (ADME). Some drugs are broken down almost entirely. Sometimes these byproducts are as harmful as the drug itself, but typically they are much less bioactive. Thus, passing a drug through a human is a good way to clean it up.
However, it is not a perfect way, and some of the drug passes unchanged directly into the urine or feces. If the body breaks up 98% of the drug, the person still urinates 2%. The flush ratio is the inverse of this, or 50. This means that if the person throws just one pill into the toilet, he causes as much contamination as he causes by eating 50 of those pills.
Some typical values for some drugs are shown below. These must be treated skeptically, as variations can be huge and closely related drugs may have completely different excretion rates. Also added is an estimate of the cost per pill, since this information has an effect on how the medication is likely to be treated.
- Paracetamol, Aspirin (painkiller): Less than 2% excreted. Flush ratio is therefore 1/2%, or about 50. Cost is ~1 cent per pill
- Atorvastatin (anti-cholesterol): <2%. Flush ratio ~50, ~50 cnt per pill
- Carbamazepine (epilepsy medication): 2-3%. Flush ratio ~40, ~20 cnt
- Prozac (antidepressant): ~15%. Flush ratio ~6, ~1 EUR
- Oxycodone (strong painkiller): ~19%. Flush ratio ~5, ~4 EUR
- Cetirizin (anti-histamine): 30%. Flush ratio ~3, ~1 EUR
- Antibiotics: Huge variations. 40-80% of some antibiotics (NIH). Flush ratio ~2, ~1 EUR/pill (for penicillin)
- Lisinopril: (hypertension): 100% (Not metabolized at all by the body). Flush ratio ~1, ~30 cnt/pill.
- Birth control pills (COCP): Special case. The metabolites are hormones which have an environmental effect. Flush ratio not known, but probably low. ~1 EUR/pill
The society-level impact of flushing of course requires knowledge of things like the toxicity of the drug, the speed at which it decays, and the number of people taking the drug. However, a list like the one above does give some indication of where to focus.
My hunch (it is no more than that) is that a low-cost high-flush-ratio over-the-counter (OTC) medicine has the highest contamination risk. People can buy as much medication in reserve as they want, and the low price means they do not have much incentive to make sure the medication does not age (it is much easier to just buy new pills). In addition, people buy these painkillers like candy. Large amounts will go to waste.
My hunch that people are careless with aspirin is supported by one study (LHWMP): aspirin contamination was found in 24% of tested streams. Aspirin can be toxic for example to cats (Manning), although the levels found in the water were in practice far below this toxicity level.
Thus, if I were to prioritize things based on these figures alone, I would target aspirin. The amounts may be tiny, but the point it that there is no reason for them to be there in the first place. Without flushing, the concentration would be close to zero. SInce the aspirin is not passed into the urine, people could take all the aspirin they want, as long as they disposed of the rest correctly.
I can also think of practical things that could follow from the priorization. Why not put extra notifications specifically on aspirin packages to encourage users to dispose of them correctly? If such warnings are put indiscriminately on all medications, they may lose their effect. Focus them where the impact is the greatest.
I emphasize that the analysis above has too little data and too few parameters to be reliable. Aspirin may be a problem, but given that antibiotics and hormones have more severe biological effects, they may be much more serious problems. Someone should try to calculate this; I do not really have the competence.
I feel that this kind of analysis has psychological value, if nothing else. Arguments on environmental issues tend to become heated and repetitive. Sometimes it is worthwhile to look at things from a completely different perspective.
