Analysis of biological effects and limits of exposure to weak magnetic fields

Adverse biological outcomes due to thermal effects of exposure to high power magnetic fields are well understood and are the basis for standards for limiting human exposure to such fields. Over the past few decades a controversy has arisen over possible adverse biological effects due to exposure to weak, low frequency magnetic fields. This paper involves a critical analysis of the voluminous literature with a view to a theoretical investigation and comparison of the most prominent limits of exposure to weak magnetic fields and geomagnetic field to elucidate the main points of contention. Most of the weak magnetic fields that have been used in these experiments are below international exposure limits and quite a few fields are below Adair's minimum theoretical exposure limit. There is a large variation in the response of biological systems for various AC magnetic field strength to frequency ratio with no clear correlation. These results demonstrate that characterizing the biological effects by AC magnetic field strength to frequency ratio does not appear to be a reliable technique.