A cartoon of three houses with wastewater heading into the sewer below, with title text "Secrets in Sewers" within the pipe
Written by: Challie Facemire
Illustrated by: Claire Murphy

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Alzheimer's disease: a disease characterized by a decline of mental abilities and loss of function of some brain cells....more

Genetic predisposition: when someone has an increase in the chance of disease or other condition because of their genes...more

Microplastic: very small pieces of plastic that have been formed by other plastic products breaking down into smaller pieces.

Nanoplastic: tiny particles of plastic so small that they can pass into the cells of organisms.

Wastewater (effluent): treated water that is released from a city's Wastewater Treatment Plant... more

Waterway: a flow of water that is able to be travelled by boat; these include rivers, canals, and more...more

An anatomy drawing showing veins in the face

The veins in your body hold information about the chemicals you eat and drink. In the same way, a sewer holds some of the same types of information about the local community. Image by Elisa Schorn from Heidelberg University-HeidICON via Wikimedia Commons.

If you want to know how healthy you are, you might visit the doctor for a blood test. But what do you do if you want to know how healthy your neighborhood is? Or how healthy your city is? The best source of information may be right under your home or your street.

There, you may find a series of pipes crisscrossing your neighborhood and city. Sliding and flowing through the sewers is everything you flush down a city toilet. Like the veins in your body, the veins of the sewer contain a lot of information about the people in an area. It is that smelly source that gives researchers like Rolf Halden clues about the health of a community.

For over 15 years, Halden has been using wastewater that runs through our sewers as an information source. Halden gathers information on what people eat, what toxins are present, and what medications and drugs people use. Then he determines how these things affect the health of a community.

City Disease Tracking

Information about certain diseases we are susceptible to can be found in our DNA. For example, people can have a genetic predisposition for diseases like Alzheimer’s. But it is not just DNA that determines if a person will get sick and what will cause their illness; the environment plays a role too.

A picture of a hamburger on a plate with a side of fries at a restaurant

What you eat, how much exercise you get, and what certain things you may be exposed to (like chemicals or too much sunlight) can affect how likely you are to develop certain diseases. Image by Robin Stickel via Wikimedia Commons.

What a person is eating, doing, and being exposed to can trigger a disease that they might be more likely to have. In his research, Halden looks for those disease triggers and how they impact a neighborhood of people. Then he works to figure out how we can use that knowledge to stop people from being exposed so they can avoid developing those diseases.

Halden and his research group are working with the city of Tempe, Arizona in the USA on two very important projects. They are looking at wastewater in Tempe to track viruses and to prevent diseases, from COVID-19 to the common flu. They are also tracking the use of everyday chemicals, like medicines and drugs. They are doing this to better understand how and why people are using them, and how to help them to not use drugs and get better. If the city knows where people are using drugs, they know where clinics are most needed for drug users to get help.

Tracking Toxins and Human Health in Sewers

The sewers don’t just contain our body waste and the medications we take. They also contain toxins that we put down our drains. Heavy metals, like mercury and the flame retardants that are used in some toys and other products, are an example of these toxins.

A young person's hand reaching toward a faucet that has water coming out of it.

There are many ways for unsafe chemicals to end up in our water. Image by musiking via Pixabay.

Halden researches how chemicals get into our wastewater systems. He looks at the types and the amount of toxins. Then he tracks these to see where they are coming from. These toxins can end up in recycled wastewater, which can be used to water grass, flush toilets, fill manmade lakes, and more. If the toxins aren't removed before this, they can seep into the groundwater, and groundwater is used for us to drink. This is a big problem because toxins in our drinking water can make us sick.

Halden uses this information to help make technologies that can remove the toxins from our systems. Sometimes this means the U.S. Food and Drug Administration takes a chemical out of circulation nationwide with the help of data produced by Halden’s research team.

Teeny Tiny Plastic

You wake up in the morning, brush your teeth, then wash your face. As you scrub your face, you may feel little plastic beads against your skin that get formulated into some personal care products. More tiny plastic particles may be present in your salt, drinking water, and the food you consume. Today, plastics are everywhere and their impact on human health is still not well understood.

A young man washing his face with a scrubber

Plastics are added to or form many of the things you use every day. Plastic microbeads used to be added to some face washes until they were banned in 2015. Image by Marco Duarte via Pixabay.

To learn more about whether these chemicals make it into our bodies, Halden and his team are looking at wastewater for signs that people have had plastic go through their bodies. His team can even determine if plastic components have traveled through the human body. They do this by looking at slight changes in the chemical’s structure that reveal past exposure of humans.

We use so much plastic in our every-day lives, and that plastic breaks down, but never really goes away. People put a lot of plastic down drains, from laundry that releases plastic fibers to disposable contact lenses. Over time small plastics break down into smaller and smaller pieces—these are called microplastics. If they become even smaller, to where they can’t be seen with normal microscopes, they are called nanoplastics.

From what people put into drains, to what is in landfills, a lot of microplastics wash into rivers and waterways and then end up in tap water and bottled water. In these ways the plastic comes back and can do harm to us. One thing we all can do is to use fewer plastics to reduce the source of these microplastics that are around and within us.


Secrets in Sewers was created in collaboration with The Biodesign Institute at ASU.

Water splash image by Dirk Wohlrabe via Pixabay.

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Bibliographic details:

  • Article: Secrets in Sewers
  • Author(s): Challie Facemire
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: January 25, 2022
  • Date accessed: September 29, 2022
  • Link: https://askabiologist.asu.edu/explore/secrets-sewers

APA Style

Challie Facemire. (2022, January 25). Secrets in Sewers. ASU - Ask A Biologist. Retrieved September 29, 2022 from https://askabiologist.asu.edu/explore/secrets-sewers

American Psychological Association. For more info, see http://owl.english.purdue.edu/owl/resource/560/10/

Chicago Manual of Style

Challie Facemire. "Secrets in Sewers". ASU - Ask A Biologist. 25 January, 2022. https://askabiologist.asu.edu/explore/secrets-sewers

MLA 2017 Style

Challie Facemire. "Secrets in Sewers". ASU - Ask A Biologist. 25 Jan 2022. ASU - Ask A Biologist, Web. 29 Sep 2022. https://askabiologist.asu.edu/explore/secrets-sewers

Modern Language Association, 7th Ed. For more info, see http://owl.english.purdue.edu/owl/resource/747/08/
A splash of water with a yellow green reflection
What secrets can be found in the water that we flush down the toilet or wash down the sink?

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