Assessment of occupational risks to extremely low frequency magnetic fields: Validation of an empirical non-expert approach

The expert method of exposure assignment involves relying on chemists or hygienists to estimate occupational exposures using information collected on study subjects. Once the estimation method for a particular contaminant has been made available in the literature, it is not known whether a non-expert, briefly trained by an expert remaining available to answer ad hoc questions, can provide reliable exposure estimates. We explored this issue by comparing estimates of exposure to extremely low frequency magnetic fields (ELF-MF) obtained by an expert to those from a non-expert. Using a published exposure matrix, both the expert and non-expert independently calculated a weekly time-weighted average exposure for 208 maternal jobs by considering three main determinants: the work environment, magnetic field sources, and duration of use or exposure to given sources. Agreement between assessors was tested using the Bland-Altman 95% limits of agreement. The overall mean difference in estimates between the expert and non-expert was 0.004 μT (standard deviation 0.104). The 95% limits of agreement were - 0.20 μT and + 0.21 μT. The work environments and exposure sources were almost always similarly identified but there were differences in estimating exposure duration. This occurred mainly when information collected from study subjects was not sufficiently detailed. Our results suggest that following a short training period and the availability of a clearly described method for estimating exposures, a non-expert can cost-efficiently and reliably assign exposure, at least to ELF-MF.