Challenges in Defining Background Levels for Human and Ecological Risk Assessments

A robust approach to defining, understanding, and tracking contaminant levels is crucial to human and ecological risk evaluation and risk management. Whether materials are present in the environment naturally (mercury, radon, nitrogen, phosphorous) and enhanced by human activities or are man-made (DDT and PCBs), the complexity of contaminant distributions and sources requires careful design and implementation of studies to characterize background. Before collection or analyses of data are initiated, an explicit definition of background appropriate to specific risk assessments is needed. Problems associated with determining background levels of contaminants in fish and seafood illustrate some challenges faced by risk assessors. Major differences in estimates of background may result from differences in sampling and analytical methods including selection of sampling locations, approaches to data analysis and synthesis, and tissues selected for analysis. Different approaches may yield background exposure or risk estimates that differ by 50% or more. Methodological transparency is essential in data collection and analysis to establish background and to ensure that data are used appropriately in both human and ecological risk assessments.