Titolo della tesi: Investigation of the contribution of emission sources to atmospheric particulate matter concentration (PM) and to its redox properties
In the last few years, various epidemiological studies were conducted to estimate the health effects of particulate matter (PM) on human population, placing at the core the association between exposure to PM and several adverse outcomes, especially on cardiovascular and respiratory systems. PM mass concentration is typically used to estimate population exposure. However, this indicator misestimate the overall impact of PM, since it does not consider the multiple toxicological effects of the different pollutants that constitute and determine the intrinsic properties of PM. In fact, the complexity and variability of PM can lead to different responses in biological systems. The hypothesis of the mechanisms of PM-related diseases include oxidative stress, inflammatory responses, and genotoxicity. All of them can be mediated by PM-related reactive oxygen species (ROS).
To assess the particles’ oxidative capacity, several acellular methods, defined as oxidative potential (OP) assays, have been developed and proposed as relevant and valid metric for addressing biological exposure to PM. There is still no agreement regarding the most representative assay to measure the OP of PM, but methods mostly used on the PM filter extracts are the dithiothreitol (OPDTT), the 2′,7′-dichlorofluorescin (OPDCFH), and the ascorbic acid (OPAA) assays. Each assay gives different results and probably simulates just a small part of the many potential mechanisms of oxidative stress induction. Therefore, the synergic application of the three assays on the same PM samples is strongly recommended to have a complete characterization of their redox properties. The study of PM composition and toxicity represents a particularly interesting field of research, aimed to a better understanding of the existing relationships between the chemical composition and sources of PM and its adverse effects on human health and environment, useful to plan the appropriate mitigation measures. It is also worth considering the heterogeneity of emission sources and the role that they play on PM physical and chemical properties. The analysis of PM coming from different sources could allow associating specific chemical composition, which depends on the pollutant origin, with a given biological response. In fact, the role of each chemical component on PM toxicity is still to be fully defined.
One of the goals of this PhD thesis is to improve the knowledge about the existing relationships between PM chemical composition and sources and, therefore, to attempt to estimate PM adverse effects on health and environment through the investigation of PM redox properties.
To this aim, a multidisciplinary study based on the synergic application of traditional and innovative approaches to PM was carried out in this PhD research.
PM field samples were collected at monitoring sites differently impacted by anthropic activities by using different techniques, such as traditional monitoring equipment, cascade impactors, biomonitoring methods and very-low volume samplers allowing spatially-resolved determination of PM chemical components. Furthermore, widespread components of PM produced by specific emission sources and characterized by very different chemical compositions were used to compare different experimental procedures on PM from defined emission sources.
Chemical characterization of PM samples was obtained by applying advanced and robust analytical procedures for the determination of inorganic ions, water-soluble and insoluble elements, water-soluble organic carbon (WSOC) and levoglucosan (LVG). PM water-soluble and insoluble fraction were separately analyzed through a well-established fractionation procedure to increase the selectivity of elements as source tracers and to estimate the environmental mobility and bio-accessibility of toxic elements.
Much of the PhD experimental research has focused on the investigation of redox properties of PM since in the last few years, the oxidative potential appears to be the central paradigm in the assessment of PM toxicity. However, there are still operative criticisms affecting its relevance as effective realistic metric to quantify the effects of ambient particles on human health, such as the influence of multiple operative conditions on OP obtained results, as well the lack of standardized operative conditions, which make a challenge to representatively compare inter-laboratory data. Therefore, one of the goals of this research was to explore in depth redox equilibria between PM reactive species.
During the PhD research various monitoring campaigns aimed to improve knowledge about the existing relationships between sources of PM and its related chemical composition were conducted under different conditions and in different geographical areas (i.e. during the national lockdown imposed by Italian government to counter the Covid-19 pandemic). Valuable information for PM source apportionment through a chemical/size fractionation procedure and OP measurements were obtained.
Potential effects of PM composition on biological systems were studied by using an in vitro approach based on the cytotoxic, genotoxic, oxidative, and inflammatory response of bronchial epithelial cell line BEAS-2B after the exposure to PM coming from different sources.
In parallel with the described activity, the reliability of PM biomonitoring techniques for the assessment of atmospheric element concentrations was estimated. To this aim, leaf deposition on riparian species (Arundo donax (L.)) and lichen transplants (Evernia prunastri (L.) Ach.) were used. Furthermore, an integrated approach to assess the effects of PM on functional traits of Quercus ilex (L.) in an urban area was carried out comparing results from OP assays when applied on PM deposited on Q. ilex leaves, and on filters (traditional monitoring system).
Another line of research was the analysis of PM samples in indoor environments of private dwellings and University classrooms, to study the concentration, the chemical composition, and the OP of indoor and outdoor PM to obtain information about the main indoor and outdoor PM emission sources and exposure of occupants.
Lastly, another important study included in the PhD research was related to the project Redox-activity and Health-effects of Atmospheric Primary and Secondary aerosol (PRIN 2017-RHAPS project) in which our groups participated with OP measurements and elemental analysis of PM samples. RHAPS aims to identify specific properties of PM from anthropogenic sources that are responsible for toxicological effects and can be used as new metrics for health-related outdoor pollution studies. The main goal of RHAPS project was to provide a new assessment of the sources and nature of PM components responsible for adverse health
effects in real-world conditions. The experimental field monitoring campaigns have been recently completed and data elaboration is still ongoing.
Supplementary research activities were focused on the evaluation of the capability of food waste materials as low-cost adsorbents for the removal of Volatile Organic Compounds (VOC) from wastewater, and on the analytical characterization of biological matrices (i.e. bees and beehive products, olive oil) to evaluate their potential of accumulating toxic elements, allowing the monitoring of this kind of pollutants concentrations in the environment for integrated measurements. In this context, rapid analytical methods for routinely analyzing a significant number of biological samples were developed and validated.