In recent years, scientific concern, public debate and media attention has risen about the environmental presence of natural and synthetic compounds due to the observation that environmental concentrations in the low ng.l-1 and ng.g-1 level may affect human and wildlife. The aim of this doctoral thesis was to develop and to evaluate analytical approaches for the detection of estrogens en chlorotriazines, two important groups of endocrine disrupting chemicals (EDCs), in different environmental matrices, e.g. water, sediments, suspended solids and biota. More specifically, the aim was to develop analytical methods for the detection of these compounds in the low ng.l-1 and ng.g-1 level. Environmental concentrations in an estuarine ecosystem like the Scheldt estuary (Belgium-The Netherlands) were established. In chapter I, the issue of endocrine disruption is introduced and the recent developments in environmental chemistry are discussed. This doctoral thesis was carried out within an interdisciplinary research project, Endis-Risks. This 4 year project focussed on the distribution, exposure and effects of endocrine disrupting chemicals in the Scheldt estuary. In this doctoral research, the emphasis is laid on the estrogens and the chlorotriazine herbicides. In order to understand the possible risks of the environmental occurrence of these compounds, their chemistry, their use, their potential for endocrine disruption and their environmental occurrence is described. Also the legislation in relation to their environmental occurrence and their possible abuse in veterinary practice is introduced. In short, the risk assessment procedure is presented. Finally, the conceptual framework and the outline of this doctoral thesis are formulated. In chapter II.1., the development and validation procedure of an analytical method that enables the routine analysis of (estuarine) water samples for estrogens (E1, E2, E3 and EE2) in concentrations in the low ng.l-1 range is described. The method included extraction of water samples ...