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Marin Health Officials Track Illicit Drug Use by Testing Wastewater

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Two hands one holding a vial, the other a dropper, in a lab.
 (Sinhyu/Getty Images)

Public health officials in Marin County are now tracking illicit drugs in local wastewater — everything from nicotine to methamphetamine and fentanyl. Testing sewer water can illustrate exactly what is “hot” and where, offering a more accurate picture of the drug crisis than simply counting overdoses.

“We know now that our clinical data sources just show us the tip of the iceberg of actual overdoses, because if someone doesn’t call 911, or doesn’t present to the emergency department, we might never hear about it,” said Dr. Haylea Hannah, an epidemiologist for Marin County.

In early February, the Marin public health office began testing weekly samples collected at the Central Marin Sanitation Agency in San Rafael. The move followed the county’s success using sewers for COVID-19 surveillance — communities are increasingly relying on wastewater data to track viral levels, because sewers can show the burden of disease much more accurately than clinical testing data, since people are no longer going to the hospital for PCR tests.

Hannah says the county is testing sewer water for a long list of common drugs like heroin and cocaine. They just added xylazine — also known as “Tranq” — an animal tranquilizer, which is increasingly laced with fentanyl; dealers add fentanyl to extend euphoric effects, but it can cause chronic infections. Since December, five people in San Francisco had low levels of xylazine in their systems when they lethally overdosed.

“New instrumentation can find very small quantities of molecules of interest in the dirty soup that is going down the drain and ultimately into the sewers,” said Rolf Halden, professor and director of the Biodesign Center for Environmental Health Engineering at Arizona State University. “We never know who exactly took a drug, but we can determine the consumption rates of different substances in a community on a per-1,000 people level.”

After someone consumes a drug, their body will metabolize it, and scientists can measure the metabolites that are washed down the drain. That means tests can decipher whether the drug was consumed by a person or flushed down the toilet in a raid.


Scientists can monitor an individual pipe or the confluence that merges at a treatment plant.

“Ideally, with an automated sample, that takes a little sip every so often and creates what’s known as a 24-hour composite sample,” said Halden. “In essence, you have a radar screen and you see the identity and the quantity of the substances that are used in the city.”

Technically, wastewater data could also be used to incriminate. For example, it is possible to test the sewer line from a particular house to determine whether drugs are being consumed inside. However, that should never be the objective, Halden says, because the process should follow a moral and ethical code.

“It’s important that you gain the trust of the community,” said Halden. “And it’s not monopolized by some and used in potentially harmful ways.”

Halden says data collected at Arizona State University during the pandemic revealed that drug-use patterns changed in the community. Dealers faced the same supply-chain disruptions that plagued the consumer market, forcing people to switch up what they were consuming based on what was available. Knowing what’s popular can inform education campaigns and help officials target specific prevention strategies to the neighborhoods that need it most.

For example, if an area shows an increase in heroin consumption, then law enforcement in that neighborhood can stock up on naloxone, marketed as Narcan, to reverse overdoses. Or, if wastewater testing reveals an uptick in fentanyl use at a school, that could motivate parents to discuss the potential threat with their children.

Over time, officials could also track whether a health policy is working to lower drug consumption in a particular area.

“We hope other communities who use wastewater testing involve their community members to ensure that the people most affected by this overdose crisis are also included in the solutions that we’re implementing,” said Hannah.

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