CHAPTER 1 PRINCIPLES AND CONCEPTS IN ECOLOGICAL RISK ASSESSMENT 11 CHAPTER 1 PRINCIPLES AND CONCEPTS IN ECOLOGICAL RISK ASSESSMENT Jensen J., Mesman M., Bierkens J. and Rutgers M. 1.1 Scope and content Numerous decisions have to be made before, during and after conducting an ecolog- ical risk assessment. This book is an attempt to guide risk assessors and stakeholders in the decision making process. Its main objectives are to: 1. Present and describe the basic structure of a decision support system (DSS) for as- sessing site specific risk from contaminated land to ecosystems. 2. List, review and provide further references for useful tools for site specific risk as- sessment with special attention to bioavailability. 3. Present a basic flow chart for assisting in the selection of risk assessment tools. 4. Present and recommend ways to weight, scale and use the results of the tests in a DSS. This book represents the final outcome of the EU project Liberation (Development of a decision support system for sustainable management of contaminated land by linking bioavailability, ecological risk and ground water pollution of organic pollut- ants, EVK1-CT-2001-00105). Although special attention was given to organic pollut- ants, most of the conclusions, the choice of bioassays, scaling of results etc. can also be used in the case of heavy metal contaminated sites provided adjusted tools for estimating bioavailability of heavy metals are applied. Useful and more detailed in- formation about heavy metals and possibilities to assess their bioavailability can be found in e.g. Peijnenburg et al. (1997), Plette et al. (1999), Zhang et al. (2001), Ehlers and Luthy (2003) and Van Straalen et al. (2005). This DSS is not a comprehensive “all-you-need-to-have” document for managing risk of contaminated land, as it focuses primarily on supporting decisions made when assessing risk to the terrestrial environment. It addresses only indirectly the risk to ground water and associated (connected) fresh water systems. Nevertheless informa- tion about e.g. reduced bioavailability may be useful when assessing potential risk for leaching of contaminants to ground water or fresh water. Recognising these limi- tations is important in the decision making process. Therefore, risk assessors focus- ing on the ecological impact of a contaminated site need to collaborate closely with risk assessors concerned about the risk to humans and ground water. Moreover, all risk assessors need to have close contact with the relevant stakeholders and other parties involved in the management and the current and future use of the site. This book is organised as follows: after a brief introduction to the overall principles and concepts in ecological risk assessment and decision support systems in Chapter