title: The role of persistence in chemical evaluations.
abstract: The initial stage in the assessment and priority setting of chemicals for their potential to cause harm to humans and the environment is usually a hazard assessment employing metrics for persistence, bioaccumulation, and inherent toxicity. This hazard assessment is followed, when necessary, by the more demanding task of risk assessment. Hazard assessment of data and processes influencing persistence are discussed, leading to a number of suggestions for more effective evaluation. These include 1) an initial focus on accurate data for intensive chemical partitioning and reaction half-life properties that are universally applicable as distinct from extensive properties that can be included later on a location-specific basis; 2) separate treatments of near-field and far-field exposures; 3) a focus on persistence and its effect on levels of exposure, especially for substances for which "time to exposure" is less than "time to degradation" and have been termed "pseudo-persistent." We show that "continuously present" is a better descriptor of this concern. Case studies illustrate and support these suggestions. Data on the intensive properties and on exposure pathways are best combined in evaluative multimedia mass balance models that can provide a clear depiction of the likely chemical fate, exposure routes, and levels. The information generated by the mass balance models can serve to justify and direct a full risk assessment that includes region-specific information on chemical quantities, estimates of exposure, and potential for adverse effects.
authors.affiliation: Canadian Centre for Environmental Modelling and Chemistry, Trent University, Peterborough, Ontario, Canada.
authors.forename: Donald
authors.initials: D
authors.lastname: Mackay
authors.forename: Dianne M
authors.initials: DM
authors.lastname: Hughes
authors.forename: M Luisa
authors.initials: ML
authors.lastname: Romano
authors.forename: Mark
authors.initials: M
authors.lastname: Bonnell
mesh_terms: D000818:Animals; D054750:Ecotoxicology / Q000379:methods*; D004781:Environmental Exposure / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D004785:Environmental Pollutants / Q000032:analysis* / Q000633:toxicity*; D006207:Half-Life; D060106:Lakes / Q000737:chemistry; D008962:Models, Theoretical; D018570:Risk Assessment; D045483:Rivers / Q000737:chemistry
chemical_list: D004785:Environmental Pollutants
keywords: Hazard assessment; Persistence; Pseudo-persistence; Risk assessment