In this conversation, Christian Nilsen and Brent Pautler reveal how passive sampling can be a cost-effective tool for measuring emerging contaminants like 6PPD-Q, which poses a severe risk to coho salmon and to strategic investments in green stormwater infrastructure.
About the Speakers
Christian Nilsen, PE, is a Project Manager based in Seattle who focuses on tools for analyzing and prioritizing green stormwater infrastructure. His work includes The Nature Conservancy’s machine-learning-powered Stormwater Heatmap and watershed-planning tools for King County and the City of Tacoma. Christian has served on the Puget Sound Partnership’s Toxics in Fish workgroup and the Department of Ecology 6PPD-Q Spatial Technical Advisory Committee.
Brent Pautler, PhD, is the Chemistry Services Manager at SiREM. He is an Environmental Analytical Chemist based in Ontario with expertise in passive sampling, spectroscopy, chromatography, mass spectrometry, and chemistry informatics. Throughout his career, he has worked with scientists, engineers, and consultants to solve unique problems in the laboratory and the field. He manages and advances SiREM’s passive sampling portfolio, analytical testing services, and compound specific isotope analysis (CSIA) services.
Q&A
What’s your background with contaminants such as 6PPD-Q?
Christian Nilsen
I’m a surface water hydrologist working in urban areas focusing on stormwater runoff. Traditionally, this has involved regulated contaminants like bacteria, metals, and nutrients. Recently, a new chemical called 6PPD-Q, which is toxic to coho salmon, has been identified. I find the evolving science around this chemical really interesting.
Brent Pautler
I’m an environmental chemist specializing in chemicals in the environment, both naturally occurring and man-made. I’m interested in their fate and transport, understanding where they reside, whether in the water or solid phase, or if they partition or volatilize into the air.
Accurate measurement and sampling are crucial for making informed decisions. At SiREM, I’ve expanded the passive sampling portfolio, developing tools to measure chemicals in different compartments. For example, my work with Fisheries and Oceans Canada focused on understanding the bioavailability of petroleum hydrocarbons and PFAS from spill events in marine environments. The sheen on the water surface isn’t the biggest risk; it’s the dissolved contaminants in the water that persist and threaten organisms. After the sheen is cleaned up, it’s crucial to understand the bioavailable fraction that remains dissolved in the water and continues to expose organisms.
When I saw how toxic 6PPD-Q is to coho salmon and that its presence is more of a pulse than a steady level, I considered how passive sampling could be appropriate for this chemical.
How does 6PPD-Q differ from other contaminants like PFAS?
Brent Pautler
PFAS compounds are problematic because their strong carbon-fluorine bonds don’t readily break. PFAS can mimic natural compounds and accumulate in the environment. 6PPD-Q is more of a quick, transient contaminant.
Christian Nilsen
6PPD-Q has a very short half-life, lasting from a few hours to a few days. So, it’s not a forever chemical and is not persistent in the environment. In fact, it’s very dynamic. As a breakdown product of another chemical, its formation and degradation are influenced by factors like sunlight, ozone, and temperature.
That’s important because in stormwater, most chemicals we study are relatively persistent in surface water. Not forever, but persistent, meaning it will be around long enough to reliably measure.
However, with 6PPD-Q, like Brent says, its presence pulses. If you measure at a specific time, it’s very hard to have confidence that the measurement is indicative of a long-term trend.
Why is passive sampling a good choice for measuring levels of 6PPD-Q?
Brent Pautler
For 6PPD-Q, some of the science says it needs to be dissolved to be toxic. To measure what is truly dissolved in water without sampling the particulates or the total suspended solids, you use a passive sampler. Passive samplers are placed in the environment for a period of time, providing a time-weighted average from different runoff events and a sense of natural variability.
Christian Nilsen
In my opinion, passive sampling provides a closer measurement to what’s important for aquatic species. Existing methods like grab sampling and automated sampling measure the entire 6PPD-Q fraction. However, most of the current science says that only the aqueous phase is bioavailable to sensitive species. They’re not absorbing some of the 6PPD-Q fraction or some of the chemical that’s on dissolved organic carbon or sediments.
The lethal concentration of 6PPD-Q for coho salmon in a laboratory setting is between 41 and 95 nanograms per liter. This is a low concentration – a tiny amount – comparable to a few grains of sugar in an Olympic-sized swimming pool. A passive sampler can measure very low concentrations, whereas active sampling might lose some of the chemical concentration to tubing material or bottles.
Brent Pautler
Active sampling continuously samples water from a basin, which requires power and can be affected by power outages, mechanical failures, and other issues. A grab sample captures a single time point, which can be biased depending on when it is taken. If you take the grab sample at the wrong time, you might sample at a high point or low point of stormwater or miss an initial pulse altogether, skewing the results of your sampling.
How does the cost of active sampling compare to passive sampling?
Brent Pautler
In the end, the costs are similar. Both methods have the same analytical chemistry expenses. Passive sampling involves additional costs for fabricating and calibrating the sampler and shipping it to the field. However, it provides consistent data and requires less time in the field due to renting equipment and grabbing samples at other locations, unlike active sampling.
Christian Nilsen
As someone who’s managed urban-stormwater-sampling campaigns, it’s challenging to mobilize in time to get these quick runoff peaks. Storms in developed areas can come through very, very fast, and if you’re not there at the peak, you’re going to miss the sampling event. That’s important for chemicals like 6PPD-Q.
Passive sampling eliminates the need to mobilize for multiple sampling events and the risk of only getting data from one of those events. You put it in a passive sampler, set it, leave it, and collect it after the storm.
What data can be obtained during passive sampling that can help municipalities understand 6PPD-Q in their waterways?
Christian Nilsen
Every municipality needs to be very targeted about their infrastructure improvements. No city has an unlimited budget to build green infrastructure, and you can’t retrofit everything.
With passive sampling, you can compare certain receiving waters and target your green stormwater investments to where they’ll be most beneficial. That’s the thing about 6PPD-Q. We know how to clean it up using very simple infiltration and bioretention methods. The question is where you place these stormwater infrastructure improvements—one stream versus another or one location versus another—for the most benefit. Passive sampling is an efficient and cost-effective way to detect and measure levels of 6PPD-Q in stormwater, helping determine the best locations for stormwater-infrastructure improvements.
