NATURAL RADIATION RELATED TO THE HUMAN HEALTH ON THE WORLD AND IN SOME VIETNAMESE URBAN AREAS

LA THANH LONG¹, NGUYỄN NGỌC CHÂN²,
NGUYỄN BÁ NGẠN², NGUYỄN QUANG MIÊN³

¹Division of Geophysics; ²Geophysical Society of Việt Nam; ³Institute of Archeology of Việt Nam

Abstract: Up to present time, the problem of high-dose radiation has been well studied on many sides, from the permitted maximum dose limit, threshold values causing harms, and preventing measures when it contacting. For protecting the health and life of persons contacting with radio-activity (radio-active materials or ionized radiations) during their work, each nation has books for referring and guiding the realization of above regulations, or in a higher level, technical regulations on radioactive hygiene-safety, conforming to the level of techno-scientific and socio-economic development level and politico-economic interests of each country. However, the radiation of low-dose still is the problem of discussion of many scientists.

In fact, up to now there still is not work on harms caused by low-dose radiation. Therefore, when human body suffers such maladies as: white blood, lung cancer, liver cancer, ... leading to the death, not many persons can concretely speak on the cause of them, but only vaguely on different factors of the living environment, among them, the impact of low-dose radiation (natural and man-made). This expresses the complicated character of the radiation domain in the recognition of the impact of low-dose radiation which is mainly from natural one. Therefore, we must pay special attention to negative influences of the natural radiation to human health and life.

However, the study on the harm of environmental radiation for the human health in our country still does not attract the public attention, even some urgent matters, such as background of environmental natural radiation, significant minimum dose value, negative influence of low-dose radiation. In this paper, the authors touch upon 4 problems needing to be paid attention, namely: nature of environmental natural radiation, impact of ionic radiation to the human body, some pathologic manifestations of the body after the impact of radiation, and some study works investigating on the natural radiation background of the environment aiming to protect the public health on the world and in the country.

I. NATURE OF THE ENVIRONMENTAL NATURAL RADIATION

The environmental radiation is related to ionized radiation (low-dose radiation), including all different forms of radiation, from those existing in the nature belonging to the living environment of the mankind and those (including fission fragments and particles) created by human (called as man-made radiation).

The natural radiations include: spatial ones, radiations from natural radioactive elements lying in rocks of the Earth surface, radioactive nuclides existing in water (including surface water, groundwater, sea water, ...), radioactive nuclides existing in the atmospheric bed existing near the Earth surface (including radioactive dusts and gasiform radioactive isotopes, mainly radon).

Our world contains many radioactive matters that existed since the creation of the Earth. There are over 60 radioactive elements found in the nature, the origin of them can be divided into 3 main types: 1) Radioactive elements existing since the creation of the Earth, called as primitive radioactive elements; 2) Radioactive elements formed by the interaction between spatial rays and Earth's materials; 3) Radioactive elements created by human.

Radioactive elements of the two first types are called as natural ones, while those of the third type are called as man-made radioactive elements. During their disintegration, radioactive elements create superfluous energy in the form of electro-magnetic waves and molecule flow that are called as radiation. Together with spatial radiation coming from the space, the radiation originated from natural radioactive elements forms the natural radiation background. The radioactive elements having a long life in the nature usually exist in the form of dirty substances in petrified fuels. In the Earth's entrails, such substances do not make any person radiated, but when they are fired and escape to the atmosphere, then diffused in soil, they increase the radiation background.

The most common cause of the radiation background increase is radon, a gas occurring by the disintegration of radium. Other radioactive elements are formed during the disintegration process and exist in-situ in the earth’s entrails. As for radon, it flies upwards from the earth surface, and if it pervades and is scattered, it does not cause any harm, but if it is concentrated in a house built upon the place where there is radon below, it will cause injury to the health of housemasters. In comparison with the quantity of natural radiation, that of man-made radiation is very small. However, a part of this is disseminated in the environment of our world. Therefore, we can find natural and man-made radioactive elements every- where in our living environment, in soil, water and air.

All radioactive elements existing in the nature penetrate the human body with a fixed radiation dose. They disseminate ionized radiation, and if they are in the outside of human body they will cause an outside projection dose; they can also penetrate the human body through the respiratory and digestive lines, causing an inside projection dose. Contributing most greatly in the projection dose there are radon and its descendants. In 2000, the UN Scientific Committee on the Effects of Atomic Radiation made the statistics and showed that the contribution of radon in the radioactive projection dose up to 50%. Just because of that, radon can be considered as a source of natural radiation having greatest influence to the human health.

Man-made radiation is composed of ionized radiations, radioactive isotopes, radioactive sources used in medical services, in industry, agriculture, construction, and defense techniques, fission fragments and particles created by nuclear weapon tests and nuclear incidents, …

II. IMPACT OF RADIATION TO HUMAN BODY

The essence nature of impact of every radiation to the matter in general, and human body in particular, consists of the ionizing process. Different forms of radiation have different ionizing abilities, which are characterized by the ion ratio, also called as ion density. This is the ion couple number created on a unit of their path. The experimental results have been showing that the ionization density of alpha (α) radiation is very great, of beta (b) radiation is very smaller than the above one. The average ionization density of b radiation in the air reaches only tens ion couples on 1 cm of movement. The ionization ability of gamma (γ) ray is much smaller, equal only some ion couples on 1 cm of movement in the air.

The harmful influence of radiations to the human body is their impact process to its organs. When penetrated by radiations, the body organs become feebler, because these radiations yield the energy to the environment for stimulating and ionizing atoms and molecules in these organs of the body. We know that in the human body, the water quantity occupies 70-75%, therefore, when radiations go through the body, the water is separated as follows: H₂O → OH^- + H⁺

The result of this reaction forms hydro peroxide and the hydroxide radicle. Compounds having this peroxide are typical strong oxidizing matters. Thus, the presence of H₂O in body organs will have the action of changing the structure of albumin molecule. Radiations can make many living enzymes become important, and many glands in the body and cellules destroyed. However, harmful impacts of radiations to human body still depend on different factors, such as impact position, impact dosage, state of body, … Through experiments and in practice, one suggest remarks on factors of harmful impact of radiation to human body as follows:

1. Harm level of outside projection radiation to human body and the infiltration of radioactive matters into the body

As for radioactive sources situated outside the body, the harmful impact depends on their infiltrating ability. It is clear that the γ radiation has very strong infiltrating ability, and great harm efficiency. The α and b radiations have feeble infiltration ability; the air and human skin can completely stop them, therefore, in fact they cause little harm. In the contrary, radioactive matters existing in the atmosphere, drinking water, aliments and living personal items infiltrate into the body through respiratory and digestive paths, and wounds, so radiations having feeble infiltration ability will cause very great harms.

In the other side, when penetrating into human body radioactive matters continue to impact to the time when they will be all disintegrated, because of that, the isotope having long cycle of half-disintegration will cause longest harm. A fact worth to pay attention is the penetration of radiation through the respiratory path is much more harmful than through digestive path, because the respiratory system has the larger contact area with radioactive matters and absorbs them faster than organs of the digestive system.

2. Harm of ion radiations depending on their dose

The human has been observing that a same radiation dose, if projects with more low dose (with the projecting time more long), its harm is more little. For example, if it projects with a dose of 600 R through a screen blocking soft rays for medicine aims, it will cause burns; but, if each day it projects with a dose of 200 R the skin will be burnt when it receives a dose up to 1500-2000 R. A detailed observation allow to recognize that the injury of the previous day still exists and increases the harm of the next day. From this, we can conclude that the harm caused by ion radiation has the accumulating character. In the daily life, human body receives only a little radiation dose (low-dose radiation), but day by day, month by month, this impact prolongs, making the radiation dose accumulated that becomes very high to the level possible of causing great harm. Therefore, one has been regulating that in a lifetime the human body is permitted to receive a radiation dose of below 200 R.

3. Harm level depending on the body area impacted by radiations

The experiment lets see that the withstanding level of each part of human body is different when impacted by the same radiation dose. Some parts of body can withstand a very great radiation dose, even greater than that all the body can withstand. For example, small knots on human body can withstand a dose up to 10.000 R and can also withstand 400 R on an area of 400 cm². But, in fact, if a dose of 400 R is projected to human body in a time, this person can get disease, and if a dose of 600 R is projected, it can lead to the death. Because of this, scientists have been determining crucial parts on human body that, when suffer the impact of ion radiations or of radioactive matters, will be more heavily wound than others.

4. Body ability of suffering the impact of ion radiations depending on the human age

The investigation results let see that young men suffer the impact of ion radiations weaker than older ones. Therefore, the hygiene of radioactive security stipulates that persons younger than 18 years may not contact radioactive matters (not received for working in special organs having contact with radioactive matters); persons of below 30 years may not receive a dose of greater than 50 R (for workmen and employees working with the contact with radioactive matters). The cause is that, in younger age the sexual organs are vulnerable with the harm caused by ion radiations.

5. Ability of causing harm of radiations and radioactive isotopes depending on their properties

As above said, different radiation forms have different abilities of infiltration and ionization, therefore cause different harms to human body. In the other side, the same radiation form, but with different energy, causes different harm level. Besides, the radioactive isotope having the more long half-disintegration cycle, causes the more great and long-time harm, when it penetrates into the body. For example, the isotope natri-24 (Na²⁴) projects the β radiation with the energy of up to 1.4 MeV and the γ quantum with the energy of up to 2.8 MeV, but when penetrating into the body causes not great harm, because its half-disintegration cycle is only 14.8 hours. At the same time, the isotope calci-45 (Ca⁴⁵) projects the β radiation with very little energy, only of 0.25 MeV, but having the half-disintegration cycle of up to 180 days, therefore when penetrating into the body it causes very great harm.

Annually, each of us receives in average a natural radiation dose of about 2 mSv. According to studies of ICRP, this dose can cause 80 death cases by cancer among 1,000,000 cases (Declaration 60 of ICRP, 1990). Although radon contributes up to 50% in the projection dose of radiation to human, but if we have appropriate protection measures, we can significantly decrease this projection dose.

Disadvantageous effects for the health from radon are caused by alpha particles projected from this gas and its descendants. These particles will destroy cellules of human body when they are projected from the inner of our body (in the case when we respire, eat or drink radon components). The danger is just a high radon projection dose, which is possible to cause the pulmonary cancer. According to the evaluation of epidemiology, if we live in the environment having the radon concentration of 20 Bq/m³, it is possible that 3 among 1000 persons will caught by pulmonary cancer caused by radon. And this probability increases 10 times if this is combined with tobacco smoke.

The greatest contribution in the radon projection dose is the radon concentration within the house (occupying 95%). Apart from radon, the radiation dose caused by components of the uranium, thorium families, and the change of ⁴⁰K element in accordance to different geographic situation, types of construction materials, types of house architecture, etc.; this projection dose can be controlled by portable equipments measuring radiation doses or dosimeter for environmental radiations. The measurement of radon concentration within houses and in the air can be realized by 2 methods: the most widespread method is measuring immediately by initiative measurement equipments, and the second is measuring accumulatively by passive measurement equipments.

III. PATHOLOGIC MANIFESTATIONS OF THE BODY WHEN IT SUFFERS THE RADIATION IMPACT

When human suffers the impact of ion radiations of low dose, its harm cannot be immediately recognized, because the ability of its body is very great, therefore only after a time, the disease is manifested. But, if a very great dose surpassing the permitted maximum limit is projected into the body, just after 7 to 10 days, disease clearly occurs. And so, if we do not observe hygienic principles on regulated dose, the following disease symptoms will occur:

1. The skin is dry, possible peeled; fingernails are dry, broken, and knots appear;

2. The blood can be changed in composition among this the leukaemia is most dangerous, because it is difficult to be early found out and to be treated;

3. The eyes are easy to be inflamed;

4. The genitals can lose the ability of activity, or can lead to give birth to monster, and these phenomena can be transmitted to further generations;

5. The impact of low-dose ion radiations (lower than permitted dose limit) to human body in long time has the harmful influence level depending on many sides, such as: projection conditions, projection mode, impacted situation, and body state.

The evolution of the body caused by harmful influences during the process of impact of radiations usually consists of exhaustion manifestations, prolonged headache, lack of appetite, sleepy feeling, diminution of memory, etc., at this time, the blood can have some changes, but very little, to the level that examination cannot discover. It is especial that above diseases are not fixed, have not clear and strong manifestations, but sometimes disappear in a long time, giving the normal working possibility.

To further stage, the above symptoms have stronger manifestations, sometimes leading to heavy insupportableness. The work ability diminishes to the level that easy work can cause fatigue. At that time, symptoms from the blood clearly change, the blood pressure is lowered and heart rhythms increase, the pain in the left of the chest occurs. Pathologic manifestations in endocrines, digestive organs, genitals appear, sometimes there is haemorrhage in tooth roots.

To the final stage, diseases become grave, the patient must always rest in bed. At that time, microbes in the blood are excited for development and disease increase. The blood is strongly changed, the forms of nutriment exchange are destroyed. The nervous changes, such as indifference, hot temper, occur. The patient can be dead in this stage, however, in no little cases the disease prolongs in many years but it does not increase.

The greatest danger for persons continually contacting with ion radiations is that tumours are easy to be broken out. They usually occur in body parts suffering most radioactive projection, or in organs most sensitive with radiations, such as blood, genitals. As for when human inspires radon, thoron and their disintegrated products, he will have tumours in the lungs. In the case when radioactive matters penetrate human body, they will form tumours in the place where they are mostly concentrated. Therefore, for warding off diseases caused by ion radiations to persons continually contacting directly with radioactive matters, it is necessary to seriously observe hygienic principles on doses and regulations on radioactive security. First of all, it is necessary to fully understand principles opposing influence of radiations and checking up the dose of radioactive contamination for early having surmounting measures.

IV. SOME WORKS STUDYING ON THE NATURAL RADIATION BACKGROUND OF ENVIRONMENT AIMING TO PROTECT THE COMMUNITY HEALTH OF THE WORLD AND VIỆT NAM

The influence of natural radiation to human health plays a very important role. The knowledge and control of this influence to the quality of the life is necessary. Developing countries, such as USA, Soviet Union (previous), United Kingdom, etc., have been carrying out the study on the determination of the natural radiation background, as well as the determination of the annual total projection dose that began since the 80 decade of the XX century. In 1981, USA [6] published materials evaluating the annual total projection dose of the natural radiation background to human body in the whole country (Table I).

Table I. Annual total projection dose of the natural radiation background in USA

Source of radiations	Rate of projection dose (mSv/person)
- Radiation of cosmic ray	0.45
- Radiation on the earth's surface
+ External projection	0.6
+ Internal projection	0.25
Total	1.30

In 1987, USA published the detailed investigation materials on the evaluation of the annual average efficacious projection dose of the natural radiation background to members of the com-munity on the whole country (Table 2).

Table 2. Annual average efficacious projection dose of the natural radiation background in USA

Source of radiations	Annual average efficacious dose
	µSv	mrem
- Respiration (radon and disintegration products)	2,000	200
- Radioactive nuclides accumulated within body (^40K, ^210Po)	390	39
- Radiations on the earth's surface	280	28
- Cosmic radiations	270	27
- Radiations in the atmosphere (^14C)	10	1
Total	3,000 = 3 mSv	300

In 1987, the Soviet Union (previous) [5] published documents on the annual equivalent values of efficacious dose rate from the natural radiation background in areas having normal background (Table 3).

Table 3. Annual equivalent values of efficacious dose rate
from the natural radiation background in Soviet Union (previous) [5]

Source of radiations	Annual equivalent efficacious dose (mSv)		Total dose
Cosmic radiations
Ionizing composition	0.280		0.280
Electronic composition	0.021		0.021
Cosmic nuclides		0.015	0.015
Natural radioactive nuclides:
- ^40K	0.120	0.180	0.300
- ^87Rb		0.006	0.006
Uranium row	0.09		1.037
- ^238U → ^234U		0.010 ^238U → ^234U
- ^230Th → ^226Ra		0.007 ^230Th
- ^222Rn → ^214Po		0.800 ^222Rn → ^214Ra
- ^210Pb → ^210Po		0.130 ^210Pb → ^210Po
Thorium row	0.14		0.326
- ^232Th; ^228Ra → ^224Ra		0.003 ^232Th
- ^220Rn → ^208Tl		0.013 ^228Ra → ^224Ra 0.170 ^220Rn → ^208Tl
Total	0.651	1.334	1.985

In 1988, the International Association of Energy (IAEA) [2] published the annual average efficacious dose rate for the world from natural radiation sources (Table 4).

Table 4. Annual average efficacious dose rate for the world from natural radiation sources [2]

Source of radiations	External projection (mSv)	Internal projection (mSv)	Total of projec-tion dose (mSv)
Cosmic rays	0.410		0.41
Radioactive nuclides in the cosmos		0.015	0.015
Natural sources:
- ^40K	0.150	0.18	0.330
- Row ^238U	0.100	1.239	1.339
- Row ^232Th	0.160	0.176	0.336
Total	0.820	1.616	2.436

Since 1993, North European countries including Denmark, Finland, Norway, Ireland and Sweden [9] published the results of investigation on the annual average efficacious dose rate of the natural radiation background projecting to the community (Table 5).

Table 5. Results of investigation on the annual average efficacious dose rate of the natural radiation background projecting to the community in some North European countries [9].

Source types	Finland	Sweden	Denmark	Norway	Ireland
Gamma radiation from soil and construction material (mSv)	0.5	0.5	0.3	0.5	0.2
Radon content in houses and working places (mSv)	2.0	1.9	1.0	1.7	0.2
Radioactive elements in human body (mSv)	0.3	0.3	0.3	0.35	0.3
Cosmic radiations (mSv)	0.3	0.3	0.3	0.3	0.3
Total (mSv)	3.1	3.0	1.9	2.85	1.0

In 2005, the European Committee published the annual average efficacious dose rate on the world (materials of investigation in 2000) caused by natural and artificial radiations (Table 6).

Parallel with methods of determining external projection dose caused by gamma radiation, radon measurement method has been deployed by equipments of initiative and accumulating measurement by passive measuring equipments. Results of radon measurement have been contributing in the determination of internal projection dose through respiratory line.

Table 6. Annual average efficacious dose rate on the world caused by natural and artificial radiations (materials of investigation in 2000)

Source of radiations	Dose rate (mSv)	%
Natural background (total of all source types)	2.4	46.07
Respiration (mainly radon)	1.2	23.04
Surface gamma ray	0.5	9.60
Cosmic ray	0.4	7.68
Digestion	0.3	5.76
Medical diagnosis	0.4	7.68
Nuclear test in the atmosphere	0.005	0.10
Chernobyl event	0.002	0.04
Electro-atomic plant	0.002	0.04
Total of dose ration/year	5.209	100

Table 7. Results of measurement of radon in the air and within houses in some urban areas in Việt Nam [7]

No.	Cities and townlets	Radon in the air (Bq/m^3)	Radon within houses (Bq/m^3)	Number of points	Notes
1	Hà Nội			98	1 area surpassing 148 Bq/m^3
2	Đà Nẵng - Hội An			121	2 vị trí
3	Điện Biên			59	2 areas surpassing 148 Bq/m^3
4	Huế			68	2 areas surpassing 148 Bq/m^3
5	Đồng Hới			39	3 areas surpassing 148 Bq/m^3
6	Vinh			50
7	Sầm Sơn - Thanh Hoá			60	3 areas surpassing 148 Bq/m^3
8	Cao Bằng			90
9	Thái Nguyên			20
10	Hà Giang			82
11	Sơn La			50
12	Hà Đông			24

In the Table 7, the results of measurement of Rn concentration in the air and within houses of 12 cities and townlets are presented. The total of investigated points is 761; the radon concentration in the air oscillates from 1.0 to 37.9 Bq/m³ (except for positions situated near radioactive anomalies), while the radon concentration within houses – from 5 to 406 Bq/m³, among them 13 houses have the Rn concentration surpassing the limit level of 148 Bq/m³. These are house type having the non-airy architecture, built by granite on a geological background having high radioactive intensity, such as on magmatic rock basement, on coastal placer anomalies: ilmenite, titanium, …, on tectonic faults, or built by construction materials (brick, tile) baked by coal having high radioactive activity.

Together with the development of the task of industrialization and moderni-zation of the country, the people life becomes gradually ameliorated, but at the same time this leads to negative impacts, making the environment deteriorated, that causes harm to human life. For garanteeing the sustainable development, during recent years the Government has been paying attention to the protection of environment. However, there still are many remaining problems in the radiation to environment, because, for developing the industry, it is necessary to strengthen the work of mineral prospecting, exploration, exploitation, and processing. If we want to reach the norm on electric energy, we must develop the industry of atomic electricity. In the medicine, for modernizing the diagnosis and treatment of diseases, it is necessary to develop the radioactive medicine, etc..

So, the necessity and urgency for us are investigation and evaluation of the natural radiation background in the environment with the following aims:

1. Evaluating the natural radiation background, determining the annual average value of the total equivalent dose projected to the people community;

2. Evaluating the natural radiation background, determining the annual average dose of radioactive medicine as well as radiations in industry, agriculture and defense.

The results of the investigation on environmental radiations have the following significances:

1. Controlling the environmental contamination in the radiation side, aiming to suggest measures of in time processing;

2. Creating the scientific basis for the development of economy, radioactive medicine, industry of atomic electricity, planning of land use, trade and tourism, etc..

At present, the task of environment protection aiming to limit the harmful impact including the environmental radiations is the common task of each country and each nation. In Việt Nam, the survey on environmental radiations has great significance not only in the health protection, raising the life quality of people, but also has strong effect on the task of industrialization and modernization of the country.

REFERENCES

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3. IAEA, 2000. Environmental radiation. IAEA.

4. IAEA, 2003. Guidelines for radioelement mapping using gamma ray spectrometry data. IAEA.

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