Surface Water Photochemistry

The idea behind the creation of this volume was to give substance to the Photochemistry part of the Comprehensive Series in Photochemical and Photobiological Sciences. For this reason, the book provides a thorough description of photochemical processes in surface waters, including direct and indirect photolysis reactions. The main objective is to give insight into both the functioning of ecosystems and the behavior of emerging pollutants in those ecosystems. Experienced and well-known authors have contributed their knowledge and expertise to the individual chapters. The different book chapters will in fact document the latest researches concerning the photochemical fate of organic pollutants in surface waters and topics such as the environmental formation and reactivity of transient species, as well as a chemometric approach to the study of environmental photochemistry. Particular attention will be given to the role of natural organic matter in photochemical reactions and to recently developed tools, analytical techniques and strategies for the determination of primary compounds and transformation intermediates in the aqueous environment. The book is divided into 14 chapters, each with a distinct focus. The first chapter gives a general overview of the topic and introduces the contents that will be expanded in the following chapters. Chapter 2 deals with the chemical and biological processes that affect the chemical composition of surface waters, including the seasonal and the long-term trends. This is important because water chemistry is closely related to direct and most notably indirect photochemical reactions. Chapter 3 gives insight into the penetration of sunlight into the water column of natural water bodies. Photochemical processes are strongly affected by sunlight irradiance, the penetration of which in the water column depends on several components including the dissolved organic matter. Chapter 4 provides examples of how pollutants can be directly transformed upon absorption of sunlight. Particular attention is given to reaction classes that are common to a wide variety of substrates and that can take place in the presence of particular molecular structures. Chapter 5 gives insight into the photoreactivity of organic matter, including its capacity to both produce and scavenge reactive species, with particular attention to the reactivity of its different size fractions. Chapter 6 provides insight into the use of fluorescence techniques (with particular focus on the excitation-emission matrix) for the characterization of organic matter in surface waters and the identification of photoactive material, most notably humic substances. In Chapter 7, an overview is given of the main processes involved in the generation of ·OH radicals (photochemical formation upon irradiation of natural organic matter, nitrate and nitrite) and in their scavenging in natural waters. The results of current approaches aimed at the prediction of ·OH reactivity toward organic compounds is also presented. Chapter 8 describes the role played by singlet oxygen in surface waters. It is produced in aqueous solution by photoexcited organic matter, it has a microheterogeneous distribution in the bulk phase and in the hydrophobic cores of humic substances, and it may have important implications for the degradation of hydrophilic and hydrophobic contaminants. Chapter 9 gives insight into the transformation processes of organic compounds in the presence of iron species under irradiation, including the photochemistry of iron complexes. Particular attention is devoted to the speciation of iron under conditions that are relevant to surface waters. Chapter 10 provides a model approach to quantitatively assess radiation absorption in multicomponent systems and the associated generation of transient species, by irradiation of photosensitizers such as natural organic matter, nitrate and nitrite. By this approach, one derives important implications for the modeling of pollutant phototransformation kinetics. Chapter 11 describes the crucial role played by chemometric methods, based on the design of experiments and surface response methodology, in the understanding of the statistically significant variables that affect the photoinduced processes. Chapter 12 presents the more recent approaches used in environmental analysis. Particular attention is given to the description of targeted/untargeted strategy and to the choice of suitable instrumentation for monitoring micropollutants in surface waters. Chapter 13 gives insight into the techniques that can be used to assess the transformation (including the phototransformation) of pollutants in environmental waters. These techniques can also be used in laboratory experiments, to simulate the abiotic transformation of pollutants occurring in the euphotic zone and leading to potentially harmful transformation products. Chapter 14 provides a case study, namely the photodegradation of a pollutant (the herbicide Irgarol) by Fenton and photo-Fenton reactions in river water. The focus on modeling and on transformation intermediates should make the book appealing not only to academics but also to people working in chemical manufacturing industries and dealing with the assessment of the environmental persistence of chemicals. Companies involved in nanomaterials or pharmaceuticals production should be interested in the understanding of the environmental transformations to which their products are subjected once discharged. For this reason, this book aims at being helpful in different ways to analysts, environmental chemists, toxicologists, hydrologists, environment scientists and technologists, risk assessors, and water treatment consultants. In addition to professionals, anyone with a deep interest in the covered fields as well as teachers and students at the undergraduate and postgraduate level, would be able to use some of the materials presented here to get insight into the photochemistry of surface waters. We would like to take this opportunity to express gratitude to Dr. Massimo Trotta and prof. Giulio Nori for giving us the occasion to edit this book, the Royal Society of Chemistry team and in particular Ms Antonia Pass for her collaboration and patience during the production of this volume. We would also like to thank all colleagues who accepted to be involved in this project, for their excellent contributions to this book.