Probabilistic Approach to Deriving Risk-Based Exposure Guidelines: Application to Extremely Low Frequency Magnetic Fields

Abstract

Guidelines for environmental and occupational exposures are based upon risk estimates that consider many variables, each typically defined as a single point value. This paper recommends that probabilistic methods, which characterise uncertainty in the form of distributions, be used instead. The advantages of a probabilistic approach include the maximal use of existing data; identification of the likelihood of effects at various exposure levels; improved accuracy and confidence in risk estimates; avoidance of inflated risk estimates produced by compounding the average or 'worst case' values; increased ability to separate risk analysis from risk management judgements; and improved risk communication and research focus. As an example, the rationale and justification for deriving magnetic field guidelines using the probabilistic approach are described. Existing occupational guidelines for exposures to extremely-low-frequency (ELF) fields are designed to prevent short-term effects of induced electric fields and currents on excitable tissues, e.g., the heart and nervous system. However, existing ELF guidelines are based on limited and selected data which are summarised only as single point estimates. Another source of uncertainty in the guidelines derives from the assumption that induced currents of 10 mA.m -2 are without effect. The degree of protection afforded by these guidelines is therefore not known. Finally, standard reference dose methods for deriving acceptable exposure levels from experimentally determined NOAEL thresholds have not been followed. The use of probabilistic methods to update these guidelines would address these issues and greatly improve the scientific basis for these guidelines.