What chemicals are we exposed to on a daily basis? That is the central question of ‘non-targeted analysis’ or NTA, an emerging field of analytical science that aims to identify all chemicals around us. A daunting task, because how can you be sure to detect everything if you don’t know exactly what you’re looking for? In a paper in Environmental Science and Technology, researchers at the Universities of Amsterdam (UvA, the Netherlands) and Queensland (UQ, Australia) assess this problem. In a meta-analysis of NTA results published over the past six years, they estimate that less than 2% of all chemicals have been identified.

According to Viktoriia Turkina who performed the research as a PhD student with Dr Saer Samanipour  at the UvA’s Van ‘t Hoff Institute for Molecular Sciences, this limitation underscores the urgent need for a more proactive approach to chemical monitoring and management. “We need to incorporate more data-driven strategies into our studies to be able to effectively protect the human and environmental health”, she says.

Samanipour explains that current monitoring of chemicals is rather limited since it’s expensive, time consuming, and requires specialized experts. “As an example, in the Netherlands we have one of the most sophisticated monitoring programs for chemicals known to be of concern to human health. Yet we target less than 1000 chemicals. There are far more chemicals out there that we don’t know about.”

A vast chemical space

To deal with those chemicals, some 15 to 20 years ago the concept of non-targeted analysis was introduced to look at possible exposure in an unbiased manner. The idea is to take a sample from the environment (air, water, soil, sewer sludge) or the human body (hair, blood, etc ) and analyse it using well-established analytical techniques such as chromatography coupled with high resolution mass spectroscopy. The challenge then is to trace the obtained signal back to the structures of chemicals that may be present in the sample. This will include already known  chemicals, but also chemicals of which the potential presence in the environment is yet unknown.

In theory, this ‘chemical space’ includes as many as 10⁶⁰ compounds, an incomprehensible number that exceeds the number of stars in the universe by far. On the other hand, the number of organic and inorganic substances published in the scientific literature and public databases is estimated at around 180 million. To make their research even more manageable, Turkina, Samanipour and co-workers focused on a subset of 60.000 well-described compounds from the NORMAN database. Turkina: “This served as the reference to establish what is covered in NTA studies, and more importantly, to develop an idea about what is being overlooked.”

The vast ‘exposome’ of chemicals that humans are exposed to on a daily basis is a sign of our times, according to Samanipour. “These days we are soaking in a giant ocean of chemicals. The chemical industry is part of that, but also nature is running all a whole bunch of reactions that result in exposure. And we expose ourselves to chemicals by the stuff we use – think for instance of the problem of microplastics. To solve all this we have to be able to go beyond pointing fingers. With our research, we hope to contribute to finding a solution together. Because we all are in the same boat.”

Much room for improvement

The meta analysis, which included 57 NTA papers, revealed that only around 2% of the estimated chemical space was covered. This can indicate that the actual exposure to chemicals is indeed quite low, however, it can also point to shortcomings in the applied analyses. According to Turkina and Samanipour, the latter is indeed the case. They focused on NTA studies applying liquid chromatography coupled with high resolution mass spectrometry (LC-HRMS) -one of the most comprehensive methods for the analysis of complex environmental and biological samples.

It turned out that there was much room for improvement. For instance in sample preparation, they observed a bias towards specific compounds rather than capturing a more diverse set of chemicals. They also observed poor selection and inconsistent reporting of LC-HRMS parameters and data acquisition methods. “In general”, Samanipour says, “the chemical analysis community is to a great extent driven by the available technology that vendors have developed for specific analysis purposes. Thus the instrumental set-up and data processing methods are rather limited when it comes to non-targeted analysis.”

To Samanipour, the NTA approach is definitely worth pursuing. “But we need to develop it further and push it forward. Together with vendors we can develop new powerful and more versatile analytical technologies, as well as effective data analysis protocols.” He also advocates a data-driven approach were the theoretical chemical space is ‘back calculated’  towards a subset of chemicals that are highly likely to be present in our environment. “Basically we have to better understand what is the true chemical space of exposure. And once those boundaries are defined, then it becomes a lot easier to assess that number of 2% we have determined.”

Jupiter’s moon Europa is one of a handful of worlds in our solar system that could potentially harbor conditions suitable for life. Previous research has shown that beneath its water-ice crust lies a salty ocean of liquid water with a rocky seafloor. However, planetary scientists had not confirmed if that ocean contained the chemicals needed for life, particularly carbon.

Astronomers using data from NASA’s James Webb Space Telescope have identified carbon dioxide in a specific region on the icy surface of Europa. Analysis indicates that this carbon likely originated in the subsurface ocean and was not delivered by meteorites or other external sources. Moreover, it was deposited on a geologically recent timescale. This discovery has important implications for the potential habitability of Europa’s ocean.

“On Earth, life likes chemical diversity – the more diversity, the better. We’re carbon-based life. Understanding the chemistry of Europa’s ocean will help us determine whether it’s hostile to life as we know it, or if it might be a good place for life,” said Geronimo Villanueva of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, lead author of one of two independent papers describing the findings.

“We now think that we have observational evidence that the carbon we see on Europa’s surface came from the ocean. That’s not a trivial thing. Carbon is a biologically essential element,” added Samantha Trumbo of Cornell University in Ithaca, New York, lead author of the second paper analyzing these data.

NASA plans to launch its Europa Clipper spacecraft, which will perform dozens of close flybys of Europa to further investigate whether it could have conditions suitable for life, in October 2024.

A Surface-Ocean Connection

Webb finds that on Europa’s surface, carbon dioxide is most abundant in a region called Tara Regio – a geologically young area of generally resurfaced terrain known as “chaos terrain.” The surface ice has been disrupted, and there likely has been an exchange of material between the subsurface ocean and the icy surface.

“Previous observations from the Hubble Space Telescope show evidence for ocean-derived salt in Tara Regio,” explained Trumbo. “Now we’re seeing that carbon dioxide is heavily concentrated there as well. We think this implies that the carbon probably has its ultimate origin in the internal ocean.”

“Scientists are debating how much Europa’s ocean connects to its surface. I think that question has been a big driver of Europa exploration,” said Villanueva. “This suggests that we may be able to learn some basic things about the ocean’s composition even before we drill through the ice to get the full picture.”

Both teams identified the carbon dioxide using data from the integral field unit of Webb’s Near-Infrared Spectrograph (NIRSpec). This instrument mode provides spectra with a resolution of 200 x 200 miles (320 x 320 kilometers) on the surface of Europa, which has a diameter of 1,944 miles, allowing astronomers to determine where specific chemicals are located.

Carbon dioxide isn’t stable on Europa’s surface. Therefore, the scientists say it’s likely that it was supplied on a geologically recent timescale – a conclusion bolstered by its concentration in a region of young terrain.

“These observations only took a few minutes of the observatory’s time,” said Heidi Hammel of the Association of Universities for Research in Astronomy, a Webb interdisciplinary scientist leading Webb’s Cycle 1 Guaranteed Time Observations of the solar system. “Even with this short period of time, we were able to do really big science. This work gives a first hint of all the amazing solar system science we’ll be able to do with Webb.”

Searching for a Plume

Villanueva’s team also looked for evidence of a plume of water vapor erupting from Europa’s surface. Researchers using NASA’s Hubble Space Telescope reported tentative detections of plumes in 2013, 2016, and 2017. However, finding definitive proof has been difficult.

The new Webb data shows no evidence of plume activity, which allowed Villanueva’s team to set a strict upper limit on the rate of material potentially being ejected. The team stressed, however, that their non-detection does not rule out a plume.

“There is always a possibility that these plumes are variable and that you can only see them at certain times. All we can say with 100% confidence is that we did not detect a plume at Europa when we made these observations with Webb,” said Hammel.

These findings may help inform NASA’s Europa Clipper mission, as well as ESA’s (European Space Agency’s) upcoming Jupiter Icy Moons Explorer (JUICE).

The two papers will be published in Science on Sept. 21.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.