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Within-day variability of magnetic fields among electric utility workers: consequences for measurement strategies

Artikel i vetenskaplig tidskrift
Författare M. P. van der Woord
H. Kromhout
Lars Barregård
P. Jonsson
Publicerad i Aihaj
Volym 61
Nummer/häfte 1
Sidor 31-8
Publiceringsår 2000
Publicerad vid Institutionen för invärtesmedicin
Institutionen för samhällsmedicin
Sidor 31-8
Språk en
Länkar www.ncbi.nlm.nih.gov/entrez/query.f...
Ämnesord *Electromagnetic Fields, *Environmental Monitoring, Human, *Occupational Exposure, Power Plants, Risk Assessment/standards, Sweden, Time Factors
Ämneskategorier Yrkesmedicin

Sammanfattning

Occupational exposure to 50-Hz magnetic fields was surveyed among electric utility workers to investigate (1) components of exposure variability, (2) patterns of autocorrelation between short-term measurements, and (3) imprecision and misclassification due to short-term measurements. Spot measurements every 10 seconds during 81 working days were analyzed for 42 electric utility workers from 10 occupational subgroups and during 8 working days for 4 office workers from the same company. For the 8-hour time-weighted average (TWA) magnetic fields, the variability was partitioned into its components: within workers, between workers, and between groups. For spot measurements of magnetic fields, the within-day variance component also was examined. Autocorrelation functions were determined and numbers of short-term measurements necessary for reliable estimates of 8-hour TWA magnetic fields were assessed. Spot measurements of magnetic fields, as well as 8-hour TWA magnetic fields, were approximately lognormally distributed among workers. The mean exposure to magnetic fields was 0.47 microT (n = 81 days) in electric utility workers and 0.12 microT (n = 8 days) in office workers. A large fraction, 76% of the spot measurements total variance, could be attributed to variability within days. For the 8-hour TWA magnetic fields, between-group variability was small and of the same magnitude as between-worker variability. Significant autocorrelations between short-term averages of 7.5, 15, and 30 minutes were present, when taken within periods of 30 minutes. One-hour averages showed no autocorrelation. Simulations showed that, due to high within-day variability and autocorrelation, a limited number of short-term measurements of magnetic fields in electric utility workers are likely to result in imprecise estimates of 8-hour TWA magnetic fields. Measurement strategies relying on short-term (spot) measurements are therefore likely to result in misclassification of exposure and consequently absent or spurious exposure-response relations.

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