Groups of Critical Organs of Organism. Berganie’s Law

The law of French scientist Berganie runs: radiosensitivity of a cell is directly proportional to its reproductive ability and inversely proportional to degree of its differentiation. Thus, the more intensive the processes of cell division in tissues or organs are, and the less differentiated the tissue is, the more sensitive a cell to radiation is.

 

According to this law all organs are subdivided into 3 groups of critical organs:

· the whole body, gonads, organs of blood formation (red bone marrow);

· all other organs and tissues;

· skin, bones, thyroid gland.

Hygienic Standards of Radiation. Maximum Permissible Dose (MPD) of Ionizing Radiation

To protect the working people and population against radiation the following norms are established:

according to effect on 1 group of critical organs the maximaum permissible doses (MPD) of radiation at external irradiation are established:

Ø Category A-persons professionally contacting radiation –MPD - 2 ber/year (0.2 Sv/year) or 40 miliber/week.

Ø Category B-people who are in premises adjacent to sources of radiation – MPD – 0.2 ber (0.02 Sv/year).

Ø Category C - all the other population - MPD – 0.1 ber (0.01 Sv/year).

Principles of Radiation Safety at Work with Closed Sources of Radiation

A closed source emits into the environment only electromagnetic radiation - x-ray or gamma radiation.The basis of protective measures is laws of transmission of radiation:

· The dose of external radiation is proportional to intensity and time of action;

· The intensity of radiation is inversely proportional to distance;

· The intensity of radiation decreases depending on thickness of screens.

Hence there are 4 principles of protection from radiation:

· protection by amount of dose (MPD),

· protection by distance,

· protection by time,

· protection by screens.

There are 5 kinds of screens for protection from radiation:

· protective containers for storage of radioisotopes;

· protective screens for equipment;

· mobile protective screens;

· protective screens in building constructions (walls, ceilings, doors, floors);

· screens of individual means of protection - lead gloves, aprons, etc.

Principles of Radiation Safety at Work with Open Sources of Radiation

An open source emits into the environment not only x-ray and gamma radiation, but also flows of radioactive particles (alpha-, beta-particles and neutrons).

The main principles of protection are the following:

· Use of principles of protection at work with closed sources;

· Hermetic sealing, automatization of equipment, isolating clothing, special boxes and drafting devices for work with isotopes;

· Special nonabsorbing coverings of surfaces, frequent cleaning of surfaces from radioactive pollution;

· Special ventilation equipment (exhaust ventilation is equipped with filters), water drains (in special sediment chambers), sufficient water supply;

· Special lay-out of premises with the protective screens; a lay-out of site of radiological department – a remote location of radiological laboratories from residential buildings, other hospital departments depending on their class (there are 4 classes of radiological laboratories according to annual amount of used radioactive substances);

· Careful radiation and medical control of personnel;

· Observance of personal hygiene and requirements to overalls.

 

Problems of Radiation Ecology

Concept of Natural Radiation Background (NRB)

Natural radiating background is a natural level of radioactivity in the given area, basically dependent on natural factors. On average it makes up about 100 miliber/year, but it can have significant fluctuations in view of natural and anthropogenic reasons. In the Crimea it makes up 6-30 miliroentgen/hour (it may be higher in the mountainous part of the Crimea due to radioactivity of granite masses containing uranium).

Structure of NRB

· Space radiation (25-40 %) – (2 protection screens against it – EMF of the Earth and ozone layer) - it varies in connection with fluctuations of solar activity and interplanetary EMF; due to it a person on Earth gets 28 mber/year on average;

· Natural radioactivity of ground (granite - uranium), air, water;

· Foodstuffs - about 25 % of NRB.

Thus, in NRB the external radiation makes up 75 %, the internal one (more dangerous) -25 %.

Additional anthropogenic sources of NRB increase for populationinclude the following:

· Regions of the atomic power stations and effects of their accidents and nuclear explosions;

· Diagnostic x-ray procedures (on roentgenoscopy the patient gets 1 ber at once); it is expedient to exclude unnecessary diagnostic x-ray procedures.

· Television – while watching color TV 4 hours a day a person gets 50 mrem per year. It should be taken into consideration in respect to children.

Dynamics of NRB

It has been investigated since the 50s of the last century. The increase of NRB took place in the 50s of the last century caused by mass tests of the nuclear weapon, than the decrease was observed in the 70s connected with convention on interdiction of nuclear tests in three environments: air, water, underground (now only underground explosions are permissible); the growth of NRB since 70s is explained by the development of atomic power stations.

Recommendations for Practical Classes on the Theme

Key Questions

Concept of radioactivity, hygienic characteristics of the basic types of ionizing radiation.

Basic values and units of ionizing radiation.

Effect of ionizing radiation on organism. The threshold and stochastic (nonthreshold) effects.

Estimation of doses of external and internal radiation.

Groups of critical organs. MPD of radiation.

Principles of protection at work with closed and open sources of radiation.

Natural radiation background: components, levels, dynamics.

Sources of radioactive pollution of biosphere.

Ecologic and hygienic effects of Chernobyl accident.

Methods of neutralization of radioactive wastes.

Hygienic requirements to x-ray and radiological departments.

Learning Objectives

Characteristics of types of radiation. Ionizing ability. Particle track in the air and tissues. Screens.

Biological effect of radiation. The basic kinds of radiation damage. Conditions of their occurrence.

Concept of closed and open sources of radiation. Principles and ways of protection.

Natural radiation background: levels, sources, dynamics. Its evaluation with the help of Geiger counter.

Hygienic requirements to hospitals using sources of radioactive radiation. Structure of x-ray and radiological departments.

Self Test

1. To create the radiation safety of the medical personnel of an X-ray room the protective means like screens are used including lead glass on the screen, large and small mobile protective screens, curtain and protective mittens made of lead rubber. What other means of shielding are necessary?

*A. an apron from lead material

B. boots from lead rubber

C. limitation of a working day duration

D. remote control of x-ray device

E. no other measures are necessary

 

2. In radiological department for intracavitary therapy a gamma-device, source of cobalt isotope, is used which is in a steel ampoule. Which of the following methods of personnel protection from radiation effect should be used primarily in view of a source type?

*A. shielding of the source and workplace

B. hermetic sealing of device

C. measures of a lay-out character (zoning of premise)

D. effective ventilation of premises

E. use of means of individual protection and sanitary processing of personnel

 

3. At graduation examinations a student said to the examiner that the greatest penetration into a human organism has alpha-radiation. A correct answer to the question is

*A. gamma-radiation

B. neutron radiation

C. alpha-radiation

D. proton radiation

E. beta-radiation

Problem Solving

1. At work with radioactive isotopes a radiation dose made up 100 mrem/hour at a 30-hour working week. Give your estimation of working conditions in the laboratory.

2. A radiation dose of the doctor-radiologist made up 110 mrem/week, or 6 rem per year. What protective measures are necessary in this case?

Standard Answers:

1. The working conditions do not meet the hygienic requirements, as a week dose of radiation makes up 100 mrem/hour х 30 hours = 3000 mrem, at MPD = 40 mrem/week. It is necessary to find out the reasons of MPD excess and eliminate them; if impossible - to strengthen all kinds of radiation protection at work with open sources of radiation.

2. The dose of radiation exceeds MPD at external irradiation (40 mrem per week and 2 rem per year) that can result in chronic radiation illness and occurrence of remote harmful effects (mutagenic, cancerogenic). The radiologist works with open sources of radiation (emission of radiation and flows of radioactive particles). The protection by dose, time, distance, screens and complex of measures on prevention of radionuclide entry into organism are necessary.

 

 

Appendix

Devices of Dosimetric Control

Depending on type of detector and methods of radiation registration the dosimetric devices are subdivided into:

· ionizational (with ionization chamber, Geiger counters)

· scintillational

· luminescent (thermoluminescent)

· photographic

· chemical

· semi-conductor

· calorimetric

Table 38

Characteristics of Dosimetric Devices

Name	Type	Registered radiation	Range of measurements	Weight, kg
Dosimeter	СРП-68-01	gamma	1-3000 µR/h	3.6
	ДРГ-05 М	gamma, roentgen	1-10000 mR/sec	2.0
	ДКС-04	gamma, beta, neutrons	0,1-1000 mR/h	0.25
	ДБГ-06 Т	gamma	0.01-99,9 mR/h 0.01-1000 µSv/h	0.25
	ДРГ-01 Т	gamma	0.01-99.9 mR/h	0.25
Radiometer- dosimeter	МКС-01Р-01	alpha, beta, gamma, neutrons	1-30000 particles/min/ сm2 1-100000 particles/min/сm2 0.01-10000 µSv/h µR/sec	18.0
Individual dosimeter	КДТ-02ДТУ-01КИД-08 C	gamma	5-1,000,000 mR	41.4
Individual dosimeter	КИД-2	gamma, roentgen	0.005-1.0 R	4.0 0.04
Individual. dosimeter	ИФК-2,3ИФКУ	beta, gamma, neutron	0.01-3 rad, rem	a film

 

 

Theme No 20.

Industrial Toxicology.

Toxicology of Agrochemicals and Hygiene of Their Application

Concept of Toxicology and Industrial Toxicology

Toxicology is a science studying mechanism of action of various toxins (poisons) on organism.Toxicology is divided into military, household and industrial.

Industrial toxicology is a section of toxicology studying mechanism of action on organism of industrial poisons, i.e. chemical substances which a person come in contact with in industry and which can cause the development of occupational poisonings.

Basic Parameters of Toxicity of Industrial Poisons

For the toxic and hygienic characteristics of industrial poisonings it is necessary to know the basic parameters of their toxicity, i.e. parameters ofdependence "dose - effect" (toxicodynamics) and parameters ofdependence "time - effect" (toxicokinetics).

All these parameters are determined in experiments on laboratory animals and then approximated to a person taking into account FSS - factor of specific sensitivity - differences in toxicological parameters for different kinds of warm-blooded animals (white mice, rats, rabbits).

Key Parameters of Level of Poison Toxicity

Parameters of toxicodynamics are the following (See Table 39):

v Acute toxicity (at a single effect):

Ø Lethal doses (concentrations) – LD0, LD100, LD50 (amount of animals died at effect of this dose).

Ø Threshold of acute effect - Lim ac.— a minimum effective dose for common toxic effects, Lim ac. sp.— for specific effects (for example, irritating effect).

Ø Zone of acute effect - Z ac. = LD50/Lim ac.— the less the dose is, the more dangerous the substance is in respect of probable acute poisonings.

v Subacute toxicity is studied in experiments on animals for 30-45 days.

It is determined coefficient of cumulation (C. cum.) = LD50 at a single action/LD50 totally during 30 days.

v Chronic toxicity (at prolonged effect – within months or years) - is the most important parameter as it represents the real conditions of effect of industrial poisons on person:

Lim ch (threshold of chronic effect by common toxic and specific and remote effects).

Abroad LOAEL (low observable adverse effect level) and NOAEL (non-observable adverse effect level) correspond to the concepts of threshold and subthreshold dose.

The zone of chronic action - Z ch = Lim ac/Lim ch - the larger it is, the higher the risk of occurrence of chronic poisonings.