polybrominated diphenyl ethers (PBDEs) are additive flame retardants that have been -widely used globally for the last 30-40 years. In their functional operation, PBDEs are released from parent products when exposed to heat and light in order to retard combustion reactions. The physiochemical properties of PBDEs coupled with widespread use and production has led to ubiquitous environmental contamination by these compounds. In recent years PBDEs have become increasingly well studied and evidence of their toxicity to biota and occurrence in remote and pristine environments has led to the - implementation of legislation to control their use and production. A great many studies have been published on PBDEs, and key concepts are introduced in Chapter 1. However, comparatively little data exists for the UK. Data is lacking on both marine and terrestrial birds of prey; this is disconcerting, given the potential toxicity of PBDEs, as predatory birds have been susceptible to the adverse effects of anthropogenic organic contaminants in the past. Utilising the eggs and livers of two predatory bird sentinel species, the northern gannet (Morus bassanus) and the sparrowhawk (Accipiter nisus), collected as pati of the activities of the Predatory Bird Monitoring Scheme (PBMS), this work aimed to detennine detailed long-term temporal and spatial trends of PBDEs in UK marine and terrestrial systems. In addition, stable isotope residues of carbon and nitrogen were used to identify if changes in the diets of these birds could influence the trends in contaminant residues in their eggs. Furthermore, other potentially confounding factors such as age, sex and body condition were assessed using sparrowhawk livers - a matrix which allowed for the PBDE contamination in male sparrowhawks to be characterised. The findings of the studies conducted as part of this thesis are presented in Papers IIV and discussed collectively in Chapter 2. Methodologies are provided in Papers I-IV and supplemented by Appendix 2. Other POPs, for which data is presented in Paper 4, are discussed in Chapter 1 and Appendix 3. Contributions to relevant studies regarding PBDE toxicity and trends in UK air are presented in Appendices 4 and 5. Key conclusions and recommendations for further work are given in Chapters 3 and 4.