Physiological effect of electromagnetic fields

Physiological Effect of Electromagnetic Fields

• Basics

- Electromagnetic field: can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by stationary charges and the magnetic field by moving charges (currents). It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction

- Sources

o Natural sources:

​Electromagnetic fields are present everywhere (electromagnetic spectrum as shown in the above fig) in our environment but are invisible to the human eye. Electric fields are produced by the local build-up of electric charges in the atmosphere associated with thunderstorms. The earth's magnetic field causes a compass needle to orient in a North-South direction and is used by birds and fish for navigation.

o Human-made sources:

X-rays sources, electricity that comes out of every power socket has associated low frequency electromagnetic fields. And various kinds of higher frequency radiowaves are used to transmit information – whether via TV antennas, radio stations or mobile phone base stations.

- Interaction of the electromagnetic fields with biological systems:

Fields of different frequencies interact with the body in different ways. The energy quanta of electromagnetic field (photons) is E = h.f = h.c/ h is the Planck constant (6.62 x 10-34 J.s), f is the frequency, c is speed of light in vacuum  is the wavelength

- Ionizing radiations are extremely high frequency electromagnetic waves (X-rays and gamma rays), which have enough photon energy to produce ionization (create positive and negative electrically charged atoms or parts of molecules) by breaking the atomic bonds that hold molecules in cells together.

- Non-ionizing radiations: is that part of the electromagnetic spectrum which has photon energies too weak to break atomic bonds. They include ultraviolet (UV) radiation, visible light, infrared radiation, radiofrequency and microwave fields, extremely low frequency fields, as well as static electric and magnetic fields.

• Physiological effect:

- A biological effect occurs when exposure to electromagnetic waves causes some noticeable or detectable physiological change in a biological system. If this effect is outside the normal range for the body to compensate, and thus leads to some detrimental health condition, and it it is called adverse health effects.

o Non-ionizing radiations: Even high intensity cannot cause ionization in a biological system. It has been shown that it could produce other biological effects, for instance, by heating, altering chemical reactions or inducing electrical currents in tissues and cells.

o ionizing radiations:

- Direct action – absorption of radiation energy, leading directly to changes in important cellular structures. It is the most important action mechanism in cells with low water content.

- Indirect effects are mediated by water radiolysis products, namely by free radicals H* and OH*, which lead to typical molecular products (H2, O2, H2O2) acting on biologically important structures. It is most important in cells with high water content. The free radicals have free unpaired electrons which cause their high chemical reactivity. They attack chemical bonds in biomolecules and degrade their structure.

- Effects on the cell:

In proliferating cells it is found these levels of radiation damage:

- Transient stopping of proliferation

- Reproductive death of cells (vital functions are maintained but proliferation ability is lost)

- Instantaneous death of cells

- Cell sensitivity to ionising radiation (radiosensitivity), or their resistance (radioresistance) depends mainly on the repair ability of the cell.

Typical symptoms of radiation sickness:

1. Non-lethal – damage to the erythropoiesis (bone marrow), effects on gonads

2. Lethal – gastrointestinal syndrome (damaged epithelium), skin burning, damage to suprarenal glands, damaged vision, nerve syndrome (nerve death) Late sequels – cumulative – genetic damage, cancer.

Factors influencing biological effects:

o Physical and chemical: equivalent dose, dose rate, temperature, spatial distribution of absorbed dose, presence of water and oxygen.

o Biological: species, organ or tissue, degree of cell differentiation, physiological state, spontaneous ability of repair, repopulation and regeneration