INTRODUCTION 0F ENVIRONMENTAL CHEMISTRY :
It is probably true to say that the term environmental chemistry has no precise definition. It means different things to different people. We are not about to offer a new definition. It is clear that environmental chemists are playing their part in the big environmental issues —stratospheric ozone (O3) depletion, global warming and the like.
Similarly, the role of environmental chemistry in regional-scale and local problems —for example, the effects of acid rain or contamination of water resources —is well established. This brief discussion illustrates the clear link in our minds between environmental chemistry and human beings. For many people, ‘environmental chemistry’ is implicitly linked to ‘pollution’. We hope this book demonstrates that such a view is limited and shows that environmental chemistry’ has a much wider scope.
Terms like contamination and pollution have little meaning without a frame of reference for comparison. How can we hope to understand the behaviour and impacts of chemical contaminants without understanding how natural chemical systems work? For many years a relatively small group of scientists has been steadily unravelling how the chemical systems of the Earth work, both today and in the geological past.
The discussions in this book draw on a small fraction of this material. Our aim is to demonstrate the various scales, rates and types of natural chemical processes that occur on Earth. We also attempt to show the
actual or possible effects that humans may have on natural chemical systems. The importance of human influences is usually most clear when direct comparison with the unperturbed, natural systems is possible.
Hydrogen and helium are the most abundant elements in the universe, relics of the earliest moments in element production. However, it is the stellar production process that led to the characteristic cosmic abundance of the elements Lithium (Li), beryllium (Be) and boron (B) are not very stable in stellar interiors, hence the low abundance of these light elements in the universe.
Carbon (C), nitrogen (N) and oxygen (O) are formed in an efficient cyclic process in stars that leads to their relatively high abundance. Silicon (Si) is rather resistant to photodissociation (destruction by light) in stars, so it is also abundant and dominates the rocky world we see about us.