Development of criteria for the minimization of the impacts of underestimated pathways of human exposure to atmospheric pollutants

Air pollution is still the cause of several diseases, among which cancer is often associated to excessive or anomalous exposure to air pollutants. In addition to well-known sources of emission of air pollutants, several activities are still unregulated or not adequately controlled by conventional removal technologies; furthermore, the presence of local criticalities may elude the conventional monitoring approach. This thesis aims at providing new options to detect anomalous situations of exposure and to minimize the impacts of air pollutants by acting on two different levels: the prevention of excessive intakes and the prevention of emissions into the atmosphere. Carcinogenic organic air pollutants will receive special attention in this thesis. After a short introduction to the topic, in the second chapter of this thesis, potential critical situations of exposure are presented, with a special focus on two of the most potent carcinogenic air pollutants: dioxin and benzene. Open issues regarding both the lack of regulations for some activities and the inadequacy of some conventional monitoring approaches are described. Proposals for integrative monitoring techniques and methodologies for exposure assessment are then briefly presented. Four of them were developed during this doctoral research and are described in more details in the third chapter of this thesis; the purpose of these methodologies is to offer additional tools to detect anomalous situations of exposure to air pollutants, in both rural and urban contexts, and to estimate the dominant source of exposure to specific compounds in an area. The fourth chapter is dedicated to presenting a proposal for a limit value of dioxin deposition to soil. Dioxin are able to accumulate in the food chain; therefore, this chapter presents the development of a reverse food-chain model, starting from the Tolerable Daily Intake proposed by the World Health Organization, running through the food chain backwards on the basis of the diet of a population and determining a safe value to preserve fields and pastures. Such method represents an attempt to overcome the current absence of a regulatory limit value for atmospheric deposition of dioxin to soil. This approach aims at reducing the potential exposure to dioxin by preventing excessive intake. In the fifth chapter, a critical analysis on biofilters is carried out. Biofilters are a specific kind of air pollution control technology, widely used to treat air streams with low concentrations of volatile organic compounds (VOCs). Biofilters may be inefficient under unsteady conditions of inlet loading rate; in addition, when treating high flow rates, biofilters cannot guarantee a proper dilution of the plume in the atmosphere, due to intrinsic design reasons. Biotrickling filters (BTFs) are here presented in a review as a more efficient alternative; the improvements in air quality obtained when replacing a biofilter with BTFs are also highlighted through dispersion simulations. This chapter aims at proposing an alternative to reduce exposure directly at the emission level, rather than at the receptor level. The same aim is pursued in the final part of this thesis, in which an innovative VOC removal technology is studied: non-thermal plasma (NTP). Two laboratory activities are presented: initially, NTP is applied to treat two mixtures of air and VOCs, chosen to represent typical emissions from real industrial activities; the positive results in terms of VOC removal and the partial formation of more soluble byproducts led to a second exper-imental activity in which NTP was applied as a pre-treatment to a biofilter. NTP revealed to be a promising option to manage peaks of inlet loading rate, which biofilters are often subject to in real cases.