Pharmaceuticals in the Waterways and a Little Bit of OrganicChemistry

By Elisa Dallo, Clean Water Institute Intern, Summer 2022

Stormwater is water from the rain or snowstorm that rushes over impermeable
surfaces like pavements, parking lots, and roofs. Stormwater systems are specifically
termed as Municipal Separate Storm Sewer Systems or otherwise known as MS4. The
“separate” term is due to the system not being part of the sanitary sewer system where
wastes from drains like toilets are destined for treatment plants for filtration. To reduce
flooding, storm drains are established so stormwater is diverted off of paved surfaces
and into watersheds like streams, creeks, and rivers. As more landscapes–like parking
lots, sidewalks, and streets–develop, more stormwater gets sent directly to watersheds.
This elicits a reasonable call of concern as many pollutants flow with stormwaters and
eventually destroy aquatic life when they reach streams.

Surprisingly, a good example of a not-so-obvious contaminant is pharmaceutical
drugs. We may not realize it as we dump used needles on pavements or flush unused
medications down the toilet. Even if the sanitary sewer system is separate from MS4,
drugs can go through sewage-treatment plants undetected and reach the MS4 instead.
As a result, drugs can act as contaminants and end up in waterways. Although the
concentration of pharmaceutical compounds is lower in rivers than the usually
prescribed dose and therefore hardly affects human health, the compounds can
drastically affect aquatic wildlife like fish. Some pharmaceutical drugs contain endocrine
disruptors which alter internal biological processes like hormone regulation. Endocrine
disruptors are usually estrogen found in birth control pills. One study observed that
fish–bass–in the Potomac River are found to be especially vulnerable to these
disruptors as they underwent secondary sexual characteristic changes. Therefore, it
could lead to reproductive failure and population decline. The study is yet to account for
key mutations that cause the intersex phenomenon, but the trends suggested
endocrine-disrupting compounds are responsible. Whether drug compounds affect
aquatic wildlife more than human health remains a serious concern and worthy of
research. It is important to conduct further studies in relation to stormwaters,
mismanaged trash, and proper disposal of medications in order to generate more
aggressive long-term solutions and regulations such as upgrading treatment
infrastructure–which is especially important when considering that most treatment plants
are not currently designed to filter drug compounds in water.

Some of the ways to reduce pharmaceutical waste are already in place. One of
the most obvious examples is to be educated about proper disposal and practice it by
not dumping unused/used medications on pavements and into storm drains. The same
goes with flushing drugs down the toilet. Instead, participate in drug take-back programs
where consumers like us have a safe way to properly and legally dispose of unused
drugs to the right authorities. Another simple solution is to limit bulk purchases to
minimize pharmaceutical footprints in the water. Environmental groups are already
appealing to drug manufacturers to design environment-friendly drugs where
compounds break down upon excretion or are thoroughly metabolized by the body.
​
A good example of eco-friendly drugs is the ones that react through
“organocatalysis”. Catalysts are molecules or substances that increase the rate of
reactions. Usually, metals are used for catalyzing reactions but metal catalysts are
expensive, rare, and harmful to the environment. Thanks to Nobel Prize winners David
MacMillan and Benjamin List for the development of asymmetric organocatalysis, we
are now able to use organic carbon-based catalysts that are easily handled in
large-scale reactions. In addition, this discovery prevents the use of large amounts of
solvents and can therefore minimize waste. The term “asymmetric” comes from the fact
that only one analog of the two mirror images of the molecule exists. Organic molecules
exhibit a special characteristic called chirality. When the two molecules face each other,
they are a mirror of each other but when laid on top of the other, they do not match. This
pair of molecules is always produced during certain reactions. For example, the
s-limonene is the molecule responsible for the lemon scent whereas its analog,
r-limonene is responsible for the orange scent. A left-handed molecule can only be
pharmaceutically useful but its right-handed partner could cause health issues.
Asymmetric organocatalysis is very efficient as it only produces the desired analog.

Now that there are many ways and simple innovations in place to help minimize
pollution in watersheds, we still have a long way to go. Further research is necessary to
assess whether pharmaceuticals in streams have adverse effects on human health.
More efforts on source control are needed as well in order to strengthen long-term
solutions. But while we are waiting for more long-term solutions, it is no doubt helpful
that we continue to practice basic measures that reduce pharmaceutical pollution in our
water.