Bioavailability is increasingly recognised as the key issue linking increased levels of toxicants with actually occurring adverse effects in ecosystems, whilst taking the modifying effects of the abiotic components of the environment into account. Various factors may affect bioavailability in the field, and often these factors are time- and space-dependent. This is one of the main reasons why legislators have been reluctant in implementing bioavailability in risk assessment procedures. Over the last few years, however, considerable scientific progress has been made with regard to better understanding of chemical and ecological mechanisms responsible for rendering chemicals available for uptake and toxicity. As a consequence, legislators face the challenge to anticipate the scientific progress and to implement bioavailability in legislation. This paper discusses the possibilities of implementing various methodologies within a maximum period of time of three years.