Organic contaminant speciation and bioavailability in the terrestrial environment

Organic contaminants are ubiquitous in the terrestrial environment. Many of the compounds considered environmental pollutants are both persistent and exhibit toxic, carcinogenic, mutagenic and teratogenic potential. Over the past 10 years they have received increased scientific and legislative attention worldwide as the risk they may pose to ecosystems, including plants and humans, has been recognized. Legislation and guidance determining management and acceptable levels for organic contaminants in soil is often based on total soil concentration. Sometimes this guidance encompasses whole compound groups, such as total polycyclic aromatic hydrocarbons (PAHs), rather than individual species (NEPM, 1999). It has become increasingly clear that the environmental abundance, distribution, bioavailability and ecotoxicity of organic pollutants can be better understood in terms of individual chemical species. The toxicity, environmental behaviour and bioavailability of organic compounds is known to be strongly dependent on compound structure and associated physical and chemical properties. Therefore, total soil concentration (in particular for a group of compounds) may not represent the portion of compound/component compound that may be posing a risk in terms of mobility or availability to plants, microorganisms and higher organisms (Alexander, 2000). Although the role of chemical species in metal behaviour and bioavailability has been well recognized for many years and extensively researched (Naidu et al., 2003; Sauve, 2003) this has not been the case for organic pollutants. Species specific assessment is critical to the prediction of actual risk posed by organic pollutants to environmental systems. This is limited by our understanding of individual organic chemical species present in soil, factors affecting their abundance in soil and differences between their environmental fate, behaviour and bioavailability (Chapter 2).