Candidate sites of action for microdosimetry associated with exposure to extremely-low-frequency magnetic fields, electric fields and contact currents.

Recent advances enable one to apply numerical techniques to anatomically-correct human models to compute current densities and electric fields in tissue due to exposure to electric fields, magnetic fields, or contact currents. These methods have proved to be informative in estimating exceedance of basic restrictions prescribed by exposure guideline organizations. To date, the analyses have been conducted with a resolution on the order of millimeters. However, these techniques have future roles to play at higher levels of resolution at those sites in target tissues suspected of transducing local electric fields into biological responses. Two specific cases in which high resolution "microdosimetry" would yield value involve (a) residential settings and childhood leukemia and (b) worker exposure and cardiovascular disease. Recent research suggests that residential contact currents on the order of microamperes can produce biologically significant dose (expressed as the local electric field) to the bone marrow of a child. Microdosimetry would focus on pluripotent progenitor cells resident in the marrow compartment, as well as anatomic features that distinguish a child's from an adult's marrow. Laboratory and epidemiologic research has suggested that magnetic field exposure may affect heart rate variability, a measure reflective of autonomic nervous system control of cardiac activity. Given the physical attributes of the central nervous system and the sites that could serve as substrates for field interactions, future microdosimetry addressing heart rate variability effects may be well-advised to focus on the electrically excitable dendritic arborizations of neurons. In both cases, microdosimetry will help shed light on primary interactions in tissue.