An Evaluation of Chemical Persistence Screening Approaches

A chemical's ability to persist in the environment is an important criterion in determining whether concern is warranted. Screening is commonly conducted based on the maximum degradation half-life of the chemical in any given medium (air, water, soil and sediment), or in terms of model-based estimates of the chemical's overall persistence (half-life or residence time) in the environment. In practice, however, both approaches are hindered by the limited availability of degradation data. Straightforward guidelines are therefore proposed in this paper to help predetermine which half-lives are likely to be pertinent, irrespective of the screening approach adopted. The guidelines are based on partitioning coefficients (Henry's Law constant and the octanol-water partitioning coefficient). The values selected for use in the guidelines result in a quantifiable trade-off between data acquisition requirements and uncertainty. Initial screening can be performed with whatever data is readily available. Overall persistence predictions will be conservative. False negatives are not generated. The guideline values can then be adjusted iteratively to facilitate step-wise or tiered screening. Using this iterative approach in national and international screening initiatives will result in significant time and money savings.