Fourth, the magnitude of the effect, for most environmental exposure levels, may be relatively small but extremely significant for public health.
For the most part, exposure levels less than 1000 mg/kg/day did not affect food consumption except during short intervals at the beginning of treatment (Hatakenaka, 1995; Wood, 1996) or post-dosing (Hatakenaka, 1995).
In addition, the actual exposures of most workers were not measured on most days, thus exposure levels were described in terms of relatively broad ranges; short-term peak exposures were rarely identified.
For example, as described in epidemiological studies below, most workers' exposures were not measured on most days and exposure levels were generally described in terms of relatively broad ranges.
Although it is of interest to know about sources of variation or uncertainty in general, the critical need in epidemiologic studies is to identify those variables that are most important in determining exposure levels and most amenable to capture within populations.
It is most likely that exposure levels as well as the components of the solvent mixtures have changed throughout the working life of the workers.
Concentration-dependent elimination behavior for TCDD has been observed at high exposure levels, most obviously at serum lipid concentrations > 1,000 ppt (Aylward et al. 2005).
In most cases, however, when exposure levels are lower or much lower, genetic susceptibility can play a role in modulating individual risk.
Almost all individual studies on magnetic fields and childhood leukaemia have found increased risks associated with the top percentiles of exposure levels; most of them, however, have involved a small number of exposed cases at the top percentiles.
Moreover, AC and PC HIF-1α levels remained elevated after 24 h for most exposures, whereas expression levels in EC cell line had already returned to baseline.
