Drugs in drinking water

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  • Published: Apr 7, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: Drugs in drinking water

Breakdown of beta blockers: new metabolites found

The human body often does not fully metabolise drugs and, after use, pharmaceuticals can end up in soil, rivers, lakes and even drinking water. In these environments, they may have harmful effects on wildlife and humans.

The human body often does not fully metabolise drugs and, after use, pharmaceuticals can end up in soil, rivers, lakes and even drinking water. In these environments, they may have harmful effects on wildlife and humans. A number of these compounds are ‘endocrine disrupting’. This means they interfere with the hormonal systems of organisms, affecting development and reproduction, and notably causing the ‘feminisation’ of male fish.

As well as the drug itself, its metabolites are also important, as these are often the form that reaches the environment. They may have similar effects to the drug and in some cases more adverse effects. Identifying degradation products is therefore important in order to understand the long-term effects of a drug in the environment.

In a study newly published in the Journal of Mass Spectrometry, Swedish researchers investigated the presence of pharmaceutical metabolites in wetlands. Wetlands, such as swamps and peat bogs, are natural purifiers and are increasingly being artificially built to treat wastewater. Constructed wetlands have been shown to successfully remove contaminants (including pharmaceuticals) from wastewater, but understanding of exactly how they break drugs down is limited.

Compounds never before identified

To shed new light on this, this study focused on beta blockers – widely prescribed to treat angina, high blood pressure and anxiety – in wetlands. The researchers looked specifically at metoprolol and propranolol, both of which are found on the WHO List of Essential Medicines, and atenolol, a beta blocker similar to propranolol but with fewer of its nasty nervous system side effects, such as insomnia and hallucinations. Although attempts have been made to study how these drugs are broken down in wetlands, efforts have so far been limited to already known transformation products. This study went one step further to look for unknown degradation products.

The researchers took samples from wetlands in California representing different designs, including an open-water wetland (divided into two sections to mimic day and night-time conditions) plus a ‘cattail’ wetland (containing cattail plants, also known as bulrush) ,which contained less oxygen. These different conditions affect the type and function of the microbes in the wetland, and therefore how compounds are broken down.

The wetland samples were incubated with the drugs and the degradation products characterised using high-resolution mass spectrometry. Each compound was broken down differently. Atenolol for example was very rapidly degraded to form metoprolol acid, a known metabolite. The scientists also identified a tropylium cation – a transformation product never before described in any biological or environmental system.

Metroprolol, which is known to form two metabolites in wetlands, showed the greatest metabolic diversity of all the beta blockers, although it was broken down more slowly. The researchers again identified metoprolol acid plus five other compounds, including one transformation product with an unknown structure.

Finally, they looked at propranolol, a common beta blocker but for which no major degradation products had been identified in wetlands. Two major peaks were observed for 1-napthol: a known transformation product and human metabolite. The scientists also identified a sulfate of the drug, which has previously only been synthesised.

Unpredictable pathways

The drugs were rapidly broken down by most wetlands, but there were significant differences between them. The lit open-water wetland ,for example, contained 10 times more propranolol sulfate than those kept in the dark, and this compound was not found at all in the cattail wetlands.

This study breaks new ground by identifying several compounds in wetlands that have never before been identified as transformation products. “Our study shows the diversity of transformation products forming from contaminants in the environment, which is important to be aware of when working with emerging contaminants,” explains author of the study Dr Curt Pettersson, Head of Analytical Pharmaceutical Chemistry at Uppsala University.

Indeed, there were major differences in how the compounds were broken down, despite their very similar structures. This suggests that predicting how drugs break down in wetlands may be difficult, and thus that further experimental work is necessary. Fortunately, we are equipped with the tools necessary. “The study also shows that we have the ability to identify these compounds, even when they occur in complex matrices and at low concentrations,” Pettersson concludes.

Related Links

J. Mass Spectrom, 2016, 8, 154–163, John et al.. Identification of transformation products from β-blocking agents formed in wetland microcosms using LC-Q-ToF.

Pharmaceuticals in the environment

WHO List of Essential Medicines: April 2015

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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