This paper represents 1 of 9 papers generated from a SETAC Pellston Workshop titled “Science-Based Guidance and Framework for the Evaluation and Identification of PBTs and POPs” (January 2008, Florida, USA). The workshop objectives were to develop guidance and recommendations on the evaluation of substances fulfilling PBT and POP criteria, using scientific information such as experimental and monitoring data, as well as computer models.

Characterization of “significant adverse ecotoxicological effects” of persistent organic pollutants (POPs) presents particular challenges. In the various international conventions on POPs and persistent, bioaccumulative, and toxic substances, guidance on classification is not detailed and, in some cases, is unclear. This paper focuses on several key issues in relation to selection of assessment endpoints, use of appropriate effect measures, and uncertainty in the face of limited data. Because POPs are persistent and bioaccumulative, measures of effect should be based not on concentrations in environmental matrices but rather on residues in the body of the organism or in tissues that are causally linked to adverse responses. To obtain these data, currently used toxicity testing methods may need to be modified or substantiated by toxicokinetic information to ensure that substances with POP-like properties are adequately characterized. These data can be more easily matched to environmental monitoring measurements of body or tissue residues for the purposes of assessing whether adverse effects occur in the environment. In the face of persistence and accumulation in the food chain, and considering the extent and suitability of available data, a suitable policy on the use of uncertainty factors may need to be applied when making judgments about toxicity. This paper offers guidance that can be used to identify candidate POPs that have the potential to cause significant adverse effects in the ecosystem.