Pollution is a Latin-derived word, tracing back to the term lutum (mud) and, through it, to the Indo-European root *leu- (filth, dirty).¹  It holds in itself the sense of dirtiness and impurity, both in a physical and in a ritual or moral sense. Hence, bishop Ambrose of Milan (339–397 AD) could pray in pathetic words: “…Thou [Lord] smash our Enemy, so our bodies will be not polluted”. There are a couple of interesting ideas, in our opinion, hidden in the short Ambrose passage that fit quite well for introducing the topics covered in the present book:

• Pollution is evil. It treacherously affects the quality of the environment we live in. In a more or less apparent way, it introduces harmful substances into air, water, and soils, which pass into the food chain, and poison and harm animal and vegetal populations. This ultimately results in the reduction of biodiversity, in damage to wildlife environments, forests and oceans, and in the present global warming problems everyone is perfectly aware of.

• Pollution is an enemy. It threatens our lives, affecting life quality and human health, reducing the availability of safe food and water resources, and the salubrity of air, and causing directly or indirectly diseases and pathologies. Thus, large amounts of human and economic resources have to be devoted to repairing the damage that pollution has caused and is causing, to recovering soils and water bodies, and to preventing possible future problems, in an extenuating everlasting war against time, and against human short sight and stupidity, as well. However, fighting against an enemy requires weapons: NMR is a weapon.

This book aims at presenting a general overview of how various NMR techniques can be profitably exploited in monitoring the analytical parameters of waters and soils and in aiding the design of smart solutions for solving environmental problems.

It is important to stress that environmental monitoring and remediation are multifaceted problems, for dealing with which a change of paradigm in scientists’ mind is somehow required, with the transition from a simply reductionist towards a more holistic and multidisciplinary approach.^2–4  Physicists, chemists, biologists, and ecologists have all to co-operate, crossing their own competencies, skills, and knowledge. This is necessary because the environment is a complex entity. As an example, Figure 1.1 reports a simple scheme where four different environmental compartments intersect to form a fifth compartment indicated as soil. The hydrosphere is the environmental compartment referring to all the forms of water present on and in the planet Earth; the lithosphere refers to the environmental compartment containing the rocks; the atmosphere is the term concerning the gas phase (mainly oxygen and nitrogen) held around the planet by gravitational forces; the biosphere comprises all the living carbon-based organisms occupying all the ecological niches on the Earth.

The graph in Figure 1.1 highlights that all the five environmental compartments are related to each other. This means that polluting one of them causes pollution of all the others. Just as a simple example, misuse of any type of agrochemical implies soil pollution. However, due to the direct contact between soil and water, agrochemicals and their residues can translocate from the former towards the latter. Moreover, agrochemical residues can be highly volatile. Therefore, they can also pollute the atmosphere. Finally, once pollutants enter drinking water or any other food system, they are ingested by humans with all the consequences on human health.

According to what has been outlined above, the interrelations among environmental compartments reveal a multi-layered reality, where complex interactions and interdependences occur, even at molecular, cellular, physiological, and ecological levels. At the same time, projecting a preservation or remediation intervention in an environmental context similarly requires a comprehensive evaluation of all the aspects previously mentioned and of how the different counterparts of such a complex system interact.

Figure 1.2 shows a simple scheme summarizing the sequence of operations that must be accounted for before a remediation is applied.

The first three points referring to the “collection of historical data”, “hydrological investigations”, and “chemical and microbiological analyses” answer the first of the few questions that must be satisfied to design a remediation approach: is the environmental site intensely polluted? Indeed, in order to establish the pollution extent, one has to know which kinds of activities have been carried out on the polluted site. Hence, for facilitating the hydrogeological, chemical, and biological investigations applied to assess present pollutants quantitatively/qualitatively, a historical reconstruction of the anthropic actions must be retrieved. The next question is: how urgent site’s remediation is? The answer to the latter question requires an evaluation of the remediation aims. As a matter of fact, the more the pollution affects human life quality, the more urgent the remediation is. For instance, if pollutants affect groundwater quality that is addressed to human feed, remediation is much more urgent than in the case of the achievement of a golf field! Following the scheme in Figure 1.2, the feasibility of a remediation intervention requires a preliminary lab-scale assessment. This involves working on a limited amount of samples (i.e., from a few mg up to a few grams) somehow modelling the real system. Then, engineers must upgrade the lab-scale feasibility to the pilot-scale one. This means working with medium sized amounts of samples (i.e., from kg to quintals) strictly resembling the real environmental system. Ultimately, everything is ready for the real large-scale action. The latter can be accomplished either in situ (i.e., the environmental compartment is de-polluted without moving it from its original place) or ex situ (i.e., the de-pollution is achieved by removing the contaminated system from its original site and carried out in a separate plant), depending on the practical and economical conveniences.^5,6 

Such a titanic task requires the availability of more and more sophisticated, versatile, sensitive, and powerful analytical tools, able to provide quick, accurate and complete qualitative and quantitative information. It is in this context that modern NMR techniques find their placement, providing a set of smart tools for diverse tasks.

Modern NMR is indeed a collection of different techniques, by which various aspects and features of the behaviour of both organic and inorganic matter can be elucidated, going from molecular structure to molecular dynamics, imaging analysis and so on. Moreover, NMR techniques have largely benefitted from the enormous progresses in instrumental technologies that have been continuously developed in the last few decades.^7–12  More and more powerful cryomagnets have been designed and produced, as well as high sensitivity multichannel probes and cryoprobes. This has allowed a large and widespread availability of high-resolution instruments. At the same time, solid-state probes have become increasingly diffused. In parallel, more and more sophisticated pulse sequences have been developed and implemented. Therefore, as long as environmental problems are concerned, NMR can provide diverse useful tools for different tasks.

The main use of 1D and 2D NMR spectroscopy in organic chemistry is undoubtedly constituted by the determination of molecular structure. In combination with mass spectrometry,^13–15  “traditional” NMR represents an essential tool for the structural elucidation of organic contaminants and their metabolites or degradation by-products.¹⁶  From this standpoint, hyphenated techniques such as liquid chromatography (LC) combined with NMR can provide a powerful and versatile analytical tool.^15,17,18  Certainly, the need to detect at the same time several low-concentration substances in complex matrices has stimulated the development of various high-sensitivity techniques, such as SABRE,¹⁹  CIDNP,²⁰  and NUS.²¹  It is important to stress that NMR can be profitably used in both targeted and untargeted methods, i.e., it can be used for both identifying particular marker species or retrieving an entire metabolic or microconstituent fingerprint^22–24  (that can be subjected, in turn, to suitable multivariate analysis²⁵ ). Indeed, chemical fingerprinting is an excellent way to trace back the origin of some contaminations.^26–28  Metabolomics analysis by NMR^29–32  can also provide important information on the fate of contaminant species (in particular under sub-lethal conditions) when interacting with living species, in order to elucidate their toxicity from a biochemical standpoint.³³  Furthermore, NMR also allows the detection and study of heavy metal contaminants.³⁴  Last, but not least, the use of NMR is essential for the characterization of materials devoted to environmental remediation applications such as sorbent polymers^35–38  or biochar.³⁹ 

An important strength point of NMR is its versatility in relation to the nature and the constitution of the sample to be analysed. For long time, it has been kept for granted that NMR spectra could be acquired only from non-viscous liquid systems. However, the magic angle spinning (MAS) technique has enabled the acquisition of good quality spectra⁴⁰  also from solid or semi-solid samples. More recent developments, such as CMP-NMR,⁴¹  have made possible studying even heterogeneous systems.

Beyond chemical characterization, NMR provides useful tools even for a physical characterization of real systems. In particular, relaxometry (i.e., the study of both longitudinal and transversal relaxation of excited nuclei) allows access to very useful information on the dynamics of molecular systems.^42–44  In particular, motions of liquids within porous media can be monitored and studied by the FFC technique,^45–47  which in turn allows retrieval of useful information on the textural features of the porous medium itself.^48,49  Hence, relaxometric techniques have been proven as a valuable tool for the physico-chemical characterization of systems such as soils^50–52  or sorbents,^39,49,53  thereby providing an essential piece of information for their treatment or possible employment. Besides, FFC NMR finds useful applications in the characterization of foods,^54–57  in monitoring degradation processes,⁵⁸  and in studying paramagnetic species.^59–61  As long as environmental problems are concerned, relaxometric techniques have been profitably exploited not only to assess the quality of soils,⁵²  but also to study the presence of contaminants⁶²  or even to verify the quality of marine life.⁶³  Finally, magnetic resonance imaging (MRI) techniques provide a further powerful tool for the study of environmental systems. In particular, the characteristics and the interactions occurring within the rhizosphere can be adequately investigated, even in combination with other techniques.^64,65  Indeed, MRI allows monitoring not only roots and the surrounding water content, but also the possible accumulation of solutes.^66,67 

In the previous sections, the potential uses of NMR techniques for addressing environmental remediation and relevant issues have been briefly summarized. As Simpson et al. have evidenced in a recent seminal paper,⁶⁸  it can be envisaged that NMR will play a more and more important role in future research concerning environmental problems. At present, the main drawbacks to cope with include the lower sensitivity in comparison to mass spectrometry techniques, the cost, portability, and maintenance of instrumentation, as well as the spread of necessary knowledge and skills. Noticeably, the progress in computer science, the development of artificial intelligence, and the increasing capability of miniaturization will increase the powerfulness of NMR in environmental monitoring, enable the ability of NMR to evaluate human diseases in more detail, and enable early diagnoses.

In general, NMR techniques may become central in environmental issues, provided that more and more information is provided at different levels. Indeed, one of the main problems in extending the application of NMR outside the academic community is the lack of professionals which, in contrast, are more abundant when dealing with chromatography. In other words, even because of the costs and/or the needed quantum physics knowledge, NMR techniques are less used than other more widespread and conceptually simpler analytical methods.

It is the authors’ belief that this book will contribute to opening researchers’ minds in envisaging the potential and the challenges NMR offers in this context.