Gaining an Understanding of Nanoparticles in the Environment Using Atomic Spectroscopy: Denise M. Mitrano, the 2022 winner of the Emerging Leader in Atomic Spectroscopy Award

Denise M. Mitrano is an Assistant Professor of Environmental Chemistry of Anthropogenic Materials at ETH Zurich in the Department of Environmental Systems Science. Her research is directed to understanding the impact and interaction of nanoparticles in the environment using atomic spectroscopy techniques, such as inductively coupled plasma–mass spectrometry (ICP-MS) and single-particle ICP-MS (sp-ICP-MS). She is the winner of the 2022 Emerging Leader in Atomic Spectroscopy Award. Chosen by an independent committee, the Emerging Leader in Atomic Spectroscopy Award recognizes the achievements and aspirations of a talented young atomic spectroscopist who has made strides early in his or her career toward the advancement of atomic spectroscopy techniques and applications. We recently interviewed Mitrano about her work.

You and your colleagues have published a paper describing the release of microplastic fibers from textiles from abrasion, which can contribute towards the concentration of microplastics in the environment (1). What was most surprising to you about this finding?

Microplastics can enter the environment from a variety of different sources: either as the breakdown of macroplastic litter, such as plastic bottles and mismanaged waste, or from daily use of everyday items, such as textiles. Polyester textiles make up a large proportion of the clothes we wear, and thus can represent an important source of microplastic fibers when they are washed or worn. How the textile is processed, finished, and washed throughout its lifecycle can dictate the amount of microplastic fibers that are shed over time—and so the material choice, manufacturing, and use can all impact microplastic fiber release. Because of this, I am often asked if consumers should choose to purchase garments made of certain materials to be more environmentally friendly, but there is no easy answer. Synthetic textiles can shed microplastic fibers that may negatively impact the environment, but growing cotton consumes a lot of water, and with other natural fibers, such as wool, one must consider animal welfare. When it comes to clothing in particular, my advice is always simply to consume less and use the garments you do own for longer—this is certainly the best way to reduce environmental impacts on many levels when it comes to the fashion industry.

The recently published book Biogeochemistry of Anthropogenic Particles, which you, Praetorius, Lespes, and Slaveykova edited (2), is a collection of articles on the biogeochemical cycle of human-produced particles in the environment, emphasizing the distribution of nano- and micro-scale sizes. What motivated you to publish this book and how much coverage do you give to analytical methods in it?

As scientists long working in the field of nanoparticle analysis, we were interested in how different methods and concepts of the fate, transport, and biological interactions of nanomaterials could be translated across different areas of research, especially considering that anthropogenic particles (engineered nanomaterials, microplastics, incidental nanomaterials) have been receiving increased attention compared to natural colloids. It was interesting to note that researchers across the collection emphasized the importance of good measurement and analytical practices, and continue to develop and use methods that were initially developed in the context of environmental health and safety of engineered nanomaterials in new ways. What was once considered a specialist technique, such as sp-ICP-MS, which I helped to develop during my PhD, is becoming increasingly commonplace and standardized. Collectively, the boundaries continue to be pushed to measure smaller, more diverse particles in complex matrices with greater ease—so it is exciting to imagine what will be possible in the near future.

One of your most highly cited papers involves analysis of silver nanoparticles (AgNPs) using sp-ICP-MS (3). What is unique or special about using ICP-MS, operated in a single-particle counting mode (sp-ICP-MS), for nanoparticle characterization? How did you arrive at this approach?

While I always had an interest in analytical chemistry, as new student in the area of nanometrology I certainly owe a significant amount of gratitude to my PhD supervisor, Jim Ranville, for seeing the promise of this technique, how it could be utilized in environmental contexts, and for suggesting that I further develop this methodology early on in my career! Single-particle ICP-MS is a technique that is capable of counting and sizing individual inorganic nanoparticles at trace concentrations. This method paved the way for being able to understand the behavior of nanoparticles at more environmentally and biologically relevant concentrations. Even when I first began to present this method at scientific conferences, it garnered a considerable amount of attention as a promising technique in the field of environmental chemistry, and other researchers were keen to implement it in their laboratory. This was eventually facilitated both by the standardization of the technique (as an ISO method) as well as by instrumentation and software developments specifically dedicated to process data in single-particle mode. In recent years, the method has continued to mature with additional development in how to capture and process data as well as in the diversity of materials that can be studied (including multi-element particle analysis when using an ICP-TOF-MS instrument instead of a quadrupole ICP-MS system).

In another of your papers, you described the application of sp-ICP-MS and asymmetrical flow field flow fractionation ICP-MS (AF4-ICP-MS) for characterizing silver engineered nanoparticles in the environment (4). Which of these techniques is preferred for characterizing silver engineered nanoparticles ?

Both sp-ICP-MS and AF4-ICP-MS can be used for many inorganic nanoparticles, not only Ag, and thus are suitable to be used for a wide range of applications and study systems. The two techniques also provide different but potentially complementary data. However, as with any analytical method, there are pros and cons of each technique, and each has its limitations, depending on the research question. SP-ICP-MS can count and size individual nanoparticles at very low concentrations, but one is not able to assess the aggregation state, for example, if a nanoparticle is aggregated to an organic particle (which wouldn’t be detected in single-particle mode with a quadrupole ICP-MS used in this approach); or, if many small nanoparticles were homoaggregated, the signal would register as one, larger particle. Conversely, AF4-ICP-MS is able to provide more information as to the size of a more complex, particle agglomerate (in addition to measuring the size of individual particles), but finding the “best” operational conditions in this chromatography-like technique is often much less straightforward compared to sp-ICP-MS, and the detection limits are higher. Knowing the strengths and limitations of each of the techniques will allow the researcher to select the best method for the objective at hand, or potentially design a series of tests utilizing both methods to have a more complete understanding of the particles in their system.

While your initial field of research was focused on the characterization of engineered nanomaterials, more recently you have been focused on nanoplastics and microplastics research. How were you able to bridge this gap and how did the analytical tools you use to approach these two different fields change?

I was very interested in applying the skills and process understanding I gained in studying engineered nanomaterials to different particulate materials of emerging concern, including plastics. However, analytically, measuring plastics can be very different and more challenging than measuring inorganic (nano)particles. Therefore, I developed a new approach to synthesize nano- and microplastics doped with a trace metal to more easily, and quickly, quantify them in complex matrices using techniques that are more standardized in metals analysis, including ICP-MS and sp-ICP-MS. By using the metal as a proxy for the plastics, we could spike them into a variety of laboratory- and pilot-scale facilities, which allowed us to investigate the fate and transport of plastics in environmental systems (waterways, porous media) and in wastewater and drinking water treatment plants, and to study biological uptake and interactions of plastics. This approach has opened up a completely new avenue for those studying plastic pollution and has provided many new opportunities to utilize atomic spectroscopy in a field where that would not have been possible otherwise.

What do you find most interesting about being an analytical chemist working in the field of environmental chemistry?

The thing I like most about being an analytical chemist is that other researchers are able to use our methods and take them even further. In a way, this amplifies my contributions across the field of environmental science to provide others with the tools to answer their most interesting questions. Being an expert in nanometrology has allowed me to collaborate across many different research fields with colleagues whose expertise is very different from mine, and so I’m constantly able to learn about new areas of science.

What is it about science that motivates you? Would you share some of your work and organizational habits that have helped you be productive and successful professionally?

On a day-to-day basis, to me science, and especially analytical method development, is about problem solving and the excitement when you have finally accomplished a difficult puzzle (sometimes after much trial and error!). But the implications of our work go beyond the laboratory. The natural environment is experiencing ever-increasing pressures from anthropogenic stressors. Understanding how human activities influence physical, chemical, and biological cycles is a central component of modern geosciences and I find it very rewarding to contribute knowledge that can lead toward the protection of our waterways and soils. Additionally, mentoring students to become independent scientists, and more generally independent thinkers, is a key motivator—we get to have a lot of fun with science.

Perhaps the two things that have helped my professional success the most are to keep an open mind and to ask many questions. This has opened the door for a lot of new ideas and collaborations that wouldn’t have come about if I were solely focused on my day-to-day work. Naturally, learning to balance the demands of organizing multiple projects on different topical subjects simultaneously took time, but in the end I feel that I am gaining an increasingly holistic view of my field, which helps me to better identify key research gaps and develop better research objectives.

What is your next area of interest for your research?

In the field of environmental health and safety of engineered nanomaterials, I saw first-hand how important it was to develop standardized methods for particle analysis. Therefore, beyond developing novel techniques to measure nano- and microplastics, I am also keen to work toward standardization of promising methodologies together with others so that as a community we can have more trustworthy and comparable results when assessing plastics concentration in the environment.

In recent years, we have laid the foundation for using the metal-doped plastics we synthesized to assess plastic fate and transport in a variety of systems. However, there are still many other aspects to explore to understand the risks of plastics in the environment and therefore the time is ripe to expand upon this foundation to investigate particle fluxes in other key environmental and biological systems where plastics are known to be in high concentrations.

Do you have any words of advice for young people desiring a career in science?

Be brave and think outside the box! As a young scientist, you have the opportunity to focus on a new field and develop innovative methods that are not yet established. This may entail risks, but in the best-case scenario, you can become a pioneer in your own field.

References

(1) Y. Cai, D.M. Mitrano, R. Hufenus, and B. Nowack, Formation of Fiber Fragments during Abrasion of Polyester Textiles, Environ. Sci. Technol. 55(12), 8001–8009 (2021).

(2) D.M. Mitrano, A. Praetorius, G. Lespes, and V.I. Slaveykova, eds., Biogeochemistry of Anthropogenic Particles (Frontiers Media SA., 2021).

https://books.google.com/books?hl=en&lr=&id=chAvEAAAQBAJ&oi=fnd&pg=PP1&ots=KoKGXq9Plf&sig=kILs9mkanNGjhPjpWybbvIT2BSs#v=onepage&q&f=false

(3) D.M. Mitrano, E.K. Lesher, A. Bednar, J. Monserud, C.P. Higgins, and J.F. Ranville, Detecting nanoparticulate silver using single‐particle inductively coupled plasma–mass spectrometry, Environ. Toxicol. Chem. 31(1), 115–121 (2012).

(4) D.M. Mitrano, A. Barber, A. Bednar, P. Westerhoff, C.P. Higgins, and J.F. Ranville, Silver nanoparticle characterization using single particle ICP-MS (SP-ICP-MS) and asymmetrical flow field flow fractionation ICP-MS (AF4-ICP-MS), J. Anal. At. Spectrom. 27(7), 1131–1142 (2012).

Denise M. Mitrano, the 2022 winner of the Emerging Leader in Atomic Spectroscopy Award, is an Assistant Professor of Environmental Chemistry of Anthropogenic Materials at ETH Zurich in the Department of Environmental Systems Science. Mitrano earned her BS degree (cum laude) in chemistry from Salve Regina University in Newport, Rhode Island, in 2008, and received her PhD in 2012 in geochemistry from the Colorado School of Mines, with advisement from Professor James F. Ranville. Her thesis title was, “Development of ICP-MS Based Nanometrology Techniques for Characterization of Nanoparticles in Environmental Systems.” She has become a leader in the area of nanometrology, including the detection and transformation of particles in consumer products and in the environment. She is particularly interested in developing new analytical tools to systematically understand the mechanisms and processes driving the fate, transport, and biological interactions of particles, including engineered nanomaterials and nano- and microplastics. Her interest in a “safer by design” approach for both nanomaterials and plastics is exemplified by her work on the boundaries of environmental science, materials science, and policy to promote sustainability and environmental health and safety of new materials. She has recently been awarded the SNSF Marie Heim Vögtlin Prize for Outstanding Young Woman Researcher of the Year in Switzerland (2022) and the 2022 James J. Morgan Early Career Award from ES&T and the ACS Division of Environmental Chemistry.