Photo: Jonathan Martin

Jean gingerly removed the discs, carefully wrapping them in aluminum foil before placing them in resealable plastic bags for transportation to the lab (see video below). “They’re not as dark as I expected,” he noted while examining the discs. “Previous indoor sampling revealed visible particulate matter, but this campaign is just a proof of concept. Next, we’ll use microscopy to determine particle size and distribution.”

Despite the windy conditions, the sun shone brightly, and the temperature was a balmy 15 degrees Celsius—a striking contrast to the wintry weather during the sampler installation in March. The passive samplers had collected particles and gases for six weeks, awaiting laboratory analysis.

During our descent down the stairs, we discussed the air pollutants we had just breathed in, with a particular focus on persistent mobile organic contaminants (PMOCs). The samplers were designed to measure PMOCs as part of the ALARM (Airborne Global Early Warning System for PMOCs) project, which received funding from the Swedish Research Council for Sustainable Development FORMAS last year. Led by Professor Jonathan Martin of the Department of Environmental Science, the international collaboration aims to address the challenges posed by PMOCs in the atmosphere.

Warning system for persistent mobile organic contaminants

These substances, which have been spreading globally since the 1940s, continue to pose toxic threats to both humans and wildlife. Despite this, most chemicals in commerce today have never been tested for persistence, nor have they been monitored in the environment. As a result, new PMOCs are being discovered, leading to widespread contamination of water resources.

According to Professor Martin, the European Commission recognizes the issues surrounding PMOCs as barriers to the implementation of the Zero Pollution Plan. To proactively address these challenges, the ALARM project will establish and validate a global early warning system for both known and unknown PMOCs present in the air. The collaboration involves deploying a few hundred new silicone-foam passive air samplers in strategic locations around the world, including megacities and remote regions in both hemispheres.

“The atmosphere is a significant vector for the rapid long-range transport of hazardous chemicals. The ALARM project’s systematic screening of PMOCs in global air will benefit society by early identification of emerging risks, thereby empowering sustainable chemical policy and regulation before PMOCs distribute globally,” says Professor Martin.

Silicone-based foam is a better alternative

However, before researchers can test the passive air samplers’ performance, we needed to travel to the top of Mariakliniken on a Tuesday evening. Passive samplers collect gaseous chemicals and particles through diffusion and impaction, meaning that the surface area of the sampler, the physical properties of the airborne substances, and size of particles can determine how much air is sampled. The sampler uptake rates, or how much air is sampled per day, is difficult to measure, which is why calibration is necessary.

The technology behind the silicone-foam discs inside the air samplers were developed and tested in-house by Stefano Papazian. The idea was to develop “an ultraclean and stable sampler” to complement traditional polyurethane foam passive sampling discs used in air pollution monitoring for many decades. A preliminary study will involve sending 50 samplers to research partners Tom Harner and Amandeep Saini at Environment and Climate Change Canada to compare them with traditional polyurethane foam samplers. The samplers will be housed in the same devices at the same location and deployed over a year to compare the kinetic rates of uptake for different chemicals and chemical classes.

According to Papazian, the rationale behind exploring substitutes for polyurethane foam was rooted in the fact that polyurethane reacts with ambient ozone, and breaks down over time, thereby complicating current efforts to discover new molecules in air. The complex degradation products of polyurethane foam makes it difficult to distinguish between environmental chemicals and foam residue. In contrast, silicone foam is relatively unreactive towards ozone or hydroxyl radical, and only produces degradation products containing silicone,thereby raising confidence that any carbon-based molecules detected in the sampler come from the air, not the sampler itself.

Silicone foam samplers may offer additional benefits from a toxicological perspective as well, as they allow for the analysis of both the chemistry and toxicity of the air. Polyurethane foam, on the other hand, exposes cells to degradation products, making it challenging to measure the toxicity of air in past studies.

Non-target analysis to detect unknown PMOCs

Once the silicone-foam discs inside the samplers are retrieved, the ALARM project’s non-target mass spectrometry approach is a comprehensive method that aims to detect all chemicals in the air sample, not just the ones that we already know are problematic. Professor Martin notes that this technique utilizes high-resolution mass spectrometers to measure the mass-to-charge ratio (MS1) and structural fingerprints (MS2) of all molecules in the sample, without prior knowledge of what substances may be present. Non-target analysis has gained attention in recent years due to its ability to detect and identify unknown chemicals in various environmental matrices, but most research to date has been on water and biological samples with little focus on the air we breathe.

Together with open science software and FAIR data infrastructure, the ALARM approach will create a living data resource for end-users and stakeholders. The project’s approach to data sharing will promote transparency and accountability, facilitating collaboration among scientists, policymakers, and other stakeholders. As Professor Martin notes, “The aim is to create a comprehensive early warning system for emerging PMOCs, empowering society to take action to mitigate those risks.”

From PMOCs to exposome passports

The silicone foam samplers used in the ALARM project also have potential applications in understanding the chemical exposome. This refers to the sum of all environmental chemicals that humans are exposed to throughout their lives. By collecting high-resolution mass spectra at the MS1 and MS2 level, by the so-called‘DIA approach’, the same silicone foam used to measure air quality may help researchers understand the chemical exposome, including chemicals in our blood.

Understanding the chemical exposome is important for health research, but extremely  challenging as most of the molecules in human blood that we can detect cannot yet be identified. Many of these substances could come from the air that people breathe, making it crucial to analyze the air to understand our internal chemical exposome, including in blood. To achieve that, Professor Martin envisions inexpensive wearable devices containing a simple piece of silicone foam that can sample air and particles around individuals in large-scale studies, particularly in low-income countries where people are exposed to the highest air pollution. ”Wearable devices to simultaneously sample air and particles would be a significant technological development, making it possible to conduct long-term studies on the effects of air pollution on human health,” he stresses.

The data collected by these devices could also be combined with other data types, such as epidemiological data and information on lifestyle, behaviour, and other environmental factors. This would enable researchers to understand how different environments or behaviours affect human exposure to hazardous chemicals, leading to a better understanding of the chemical exposome and how to reduce exposures in the future.

”Incorporating information about an individual’s environmental exposures over time would help us create data-rich exposome passports. The exposome passport could potentially provide valuable information for personalized medicine and disease prevention, as it could help identify past environmental and lifestyle factors that contribute to disease development in the future,” concludes Professor Martin.

As the sampling campaign concludes on the rooftop of Mariakliniken, it signifies the start of a worldwide quest to chart the extent of global exposure to PMOCs, and with any luck, to turn the notion of exposome passports into a concrete reality.