Ecological risk assessment is a tool used to support the risk-based, decision making process in environmental issues (Clark et al. 1999). Both ecological risk assessment and ecotoxicology can use endpoints of contaminant effect from all levels of biological organization, ranging from genes to ecosystems. These endpoints provide different and complementary perspectives, though. Effects of contaminants at lower levels of biological organization might provide information on specifi c mechanisms of action and typical effects of certain groups of chemicals, such as acetylcholinesterase (AChE) inhibition by organophosphates (see Chapter 4 for more information). AChE inhibition may be critical to the identifi cation of an important source of pollution if it is detected in the brain of an important fi sh species whose population is in danger, for example. However, sublethal AChE inhibition per se does not tell much about the overall ecological well being of the individuals in this population. Endpoints of effect related to the ability of

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these fi sh to swim, catch their prey, avoid predation and fi nd partners to reproduce are considered more ecologically relevant, although these types of effect alone usually do not allow the identifi cation of a specifi c group of contaminants as the causal factors. Ecological relevance is a rather subjective term, which depends on what risk managers (decision-makers) and risk assessors (ecotoxicologists) agree upon. However, it is generally accepted that contaminant effects at the population level should be avoided, and that the evaluation of evidence of contaminant related effects at this level of biological organization should be the target for fi sh and wildlife contaminant risk assessments (Clark et al. 1999). A less conservative application of the term defi nes as ecologically relevant any effect that would probably decrease the chances of survival or the reproductive fi tness of individuals, a defi nition which would encompass a broader array of endpoints, including those at suborganismic levels.