Particles from traffic pollution - the silent killer
It is sunny Monday morning, and I found myself next the busy E4 on the outskirts of Stockholm. How did I end up here? I was asked to write about how analytical chemistry is so much more than just chromatograms in a lab – analytical chemistry is also sampling, testing and putting pieces of a larger puzzle together. So here we are now. In Hallunda, in the southern part of Stockholm. Ioannis Sadiktsis, researcher in analytical chemistry has invited me to see his research and assist him with field sampling. To better understand what is being emitted by on-road traffic and the potential health effects from the emissions, Ioannis will conduct sampling of very small particles close to this heavily trafficked highway over a whole year. This project is funded by FORMAS. Background Air pollution, which include hazardous gases and particles, causes massive economical losses and is the largest environmental health risk factor for disease and pre-mature death, Ioannis explains. Road traffic is a major source of particles, soot and hazardous polycyclic aromatic compounds (PAC), and is thought to be responsible for a substantial portion of the total pre-mature deaths caused by particles, he continues. Very small particles, with an aerodynamic diameter below 2.5 µm, called PM2.5 can travel deep down into the lungs and cause severe damage, as it takes a long time for the body to clear them out. The underlying biological mechanisms and how particles elicit adverse health effects are not fully understood, but a key mechanism is thought to involve oxidative stress – an imbalance between reactive oxygen species and cellular anti-oxidants, resulting in damage to cellular components leading to disease. Sampling The sampling is as far from the lab as one can think. A big silver-grey box with a wind meter on , the metrological data is needed in order to diffrentiate particles coming from the road, and the ones coming from surrounding environment. A filter is placed down-stream an impactor – this time a round grey device that uses aerodynamic forces to separate particles by size. The filter at the bottom will collect the particles with the right size, while the larger particle having the wrong momentum will not be directed towards the filter and are not collected. In this project one is interested in what chemicals are present on the particles. These chemicals may affect human health and needs to be characterized to better understand what they are and how they interact with human lung cells. At the sampling site one collects particle of size PM10 (<10 µm) for chemical characterization and PM2.5 (<2.5 µm) for in vitro testing on human lung cells. In addition, online instrument is placed in a shed next to the road measuring particle size distribution, nitrogen oxide and soot concentration at the sampling site. Analyzing Back in the in the lab, the filters are extracted and analyzed using quantitative and qualitative techniques to get a broad overview in what is hiding in the organic mixture. Here the sample preparation is just as important as the analysis of the samples. As we have a very complex mixture of compounds of interest, with different properties, polarities, charges etc, the extraction process is complicated, time consuming and difficult to evaluate since you don’t know what you are looking for. When the extraction is finished, the samples are analyzed using non-target GC/MS and LC/MS. This is a kind of broad analytical technique used on complex samples, where one can characterize the chemical composition, try and identify unknowns without much prior knowledge of the chemical content of the samples. Targeted techniques using coupled HPLC/GC/MS to obtain quantitative data for several health relevant PACs will be used as well. The complex organic mixtures will also be tested “in vitro”, meaning in a test tube, where one can start to understand the impact on biological systems from traffic-related emissions. Human lung cells in lab setting are exposed to extracts from the collected particles to see how the cells react to the contaminants. The data collected here, will hopefully give us a less biased chemical profile of what is emitted by on-road traffic. Such profile could be used to disentangle traffic emissions from other emission sources. This may, improve future human exposure and dispersion modeling of traffic emissions. Moreover, the in vitro testing may give us a better understanding of risks associated with traffic-related emissions as well as provide a scientific foundation for prioritizing chemicals to be targeted in future monitoring campaigns. Conclusion In order to minimize the negative impact on health from on-road traffic it is important to understand the composition of traffic-related emissions and the health risks associated with those emissions, and thus being able to mitigate those risks. And also, I once again came to realize, analytical chemistry is not all about using the cool instruments and gadgets, it is just as much sampling, and understanding the chemistry behind the compounds of interest.
