Towards consistent evaluation of the persistence of organic, inorganic and metallic substances

Several criteria, including persistence (P), bioaccumulation (B), its related factor bioavailability, toxicity (T), and potential for long range transport (LRT) are currently applied when assessing the environmental hazard and risk associated with the use of chemicals of commerce. Whereas information on B and T criteria may be obtained by experimental measurement using standard tests or by the use of mass balance models, in the case of P and LRT no such standard tests exist, except for certain degradation rates in single media. Nor can these properties be measured in the environment at large. Here we focus on the criterion of persistence and its evaluation using steady-state multimedia mass balance models. It is concluded that it is possible to assess the persistence of all chemical substances including organics, inorganics, and metals using a common methodology in which mass balance models are applied to describe the substance's behavior in a specified environment or "unit world." This avoids inconsistent evaluation and excessive regulatory fragmentation, which is likely if assessment procedures are specific to classes of chemicals. It is essential that persistence be recognized as only one of several factors influencing hazard and risk. Regulatory actions must also thus reflect other attributes such as toxicity, bioaccumulation, quantities used, and the societal value of the substances.