Our immediate environment – the atmosphere, soils, surface water and groundwater – is host to a vast number of chemical reactions, even leaving aside the biochemical reactions of living organisms. Environmental chemists aim to define and quantify these reactions, make analytical determinations of reactants and products, construct predictive models, and relate their findings to the functioning of ecosystems. A major part of the research effort is to take account of natural organic matter and mineral particulates, because these abundant, poorly defined, components exert a powerful and ubiquitous chemical influence on the environment. This book focuses on the most chemically significant fraction of natural organic matter, humic substances.

Humic substances are complex, acidic organic molecules formed by the decomposition of plant, animal and microbial material. They are abundant and persistent in the biosphere and immediate subsurface, being present in particulate and dissolved forms in soils, waters and sediments. They interact with a variety of solutes, adsorb at surfaces, and are photochemically active. Humic substances first came to prominence in agriculture, because of their positive influence on the structure, water retention properties, and nutrient status of soils. More negatively, they pose problems to the water supply industry, requiring removal to minimise water colour, and giving rise to potentially mutagenic by-products as a result of chlorination. There is interest in using humic substances to recover metals from wastewaters and from seawater. Schnitzer (1991) lists a variety of uses of humic matter, in agriculture, industry, environmental engineering, and medicine.