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Тopic № 2
methods of DETERMINATION of intensity and preventive dose OF the ultraviolet radiATiON
1. Learning objective
1.1. Become familiar with physical and biological characteristics of ultraviolet radiation (UVR).
1.2. Master the methods of measuring the ultraviolet radiation intensity.
1.3. Master the measures of the ultraviolet radiation intensity and the calculations of the exposure to it using the different measuring methods.
2.1. You should know:
2.1.1. Nature, physical characteristics and spectral distribution of the solar radiation.
2.1.2. Physical characteristics, spectral distribution and biological effect of the ultraviolet radiation (UVR).
2.1.3. Dosimetric units and measuring methods of the UVR.
2.2. :You should have the following skills:
2.2.1. Working with ultravioletmeter (uphymeter) according to its instruction.
2.2.2. Determination of the reagent titre and substance concentration by volumetric titrimerty methods.
2.2.3. Using the mathematical methods of the UVR intensity and dose assessment.
3. Self-training questions
3.1. The nature of the solar radiation, basic constituent elements of corpuscular and electromagnetic portions of the solar radiation.
3.2. Spectral distribution of the ultraviolet diapason of the solar radiation at the edge of the atmosphere and earth surface (regions А, В, С). The ozone layer and its hygienic significance.
3.3 Artificial ultraviolet radiation sources, their physical and hygienic characteristics.
3.4. Main effects (biogenic and non-biogenic) of the UVR and their particularities for each of the UVR region separately.
3.5. Measuring methods of the UVR intensity – physical, photochemical, biological, mathematical (calculation).
3.6. Ultraviolet intensity measures used with these methods and their interrelation.
3.7. Erythemal, physiologic and preventive ultraviolet radiation doses.
4. Self-training assignments
4.1. Forearm skin was locally exposed to the LE-30 lamp during 5 (five) minutes. Barely perceptible reddening (erythema) appeared under the second window of Gorbachov’s biodosimeter after 20 hours. Calculate the UVR intensity in biological, photochemical, physical measures. What are physiological and preventive doses in these measures?
4.2. Erythemal ultraviolet dose is reached by the exposure to the LE-30 lamp during 4 minutes at a distance of 2 m from the source. Calculate the exposure time required to receive the preventive dose at a distance of 4 meters from the source?
5. Structure of the lesson
This is a laboratory lesson. At the beginning of the lesson students will have their knowledge of basics checked. After that, according to the instruction manuals (see appendix), students will perform the measuring of the UVR intensity at the indicated distance from the LE-30 lamp or the direct MQL (mercury-quartz lamp) using three methods – physical, photochemical, biological.
Students will only perform the first phase of the biological method measuring during this lesson. They will irradiate the forearm skin of each other using the Gorbachov’s biodosimeter and indicate numbers of windows or the exposure time on the skin. Students will be able to determine the erythemal dose after 18-20 hours. Then they should write it down in the protocol, and prepare the calculations of the physiological and preventive doses for themselves for the next lesson.
6.1.1. Загальна гігієна. Пропедевтика гігієни. /Є.Г.Гончарук, Ю.І.Кундієв, В.Г.Бардов та ін./ За ред. Є.Г. Гончарука. – К.: Вища школа, 1995. – С. 207-239.
6.1.2. Общая гигиена. Пропедевтика гигиены. /Е.И.Гончарук, Ю.И.Кундиев, В.Г.Бардов и др. – К.: Вища школа, 2000 – С. 254-289.
6.1.3. Габович Р.Д., Познанский С.С., Шахбазян Г.Х. Гигиена. – К.: 1983 – С. 31-36.
6.1.4. Загальна гігієна. Посібник до практичних занять. /І.І.Даценко, О.Б.Денисюк, С.Л.Долошицький та ін. /За ред І.І.Даценко – Львів.: “Світ”, 1992 – С. 48-50; 2-ге вид. – Львів: «Світ», 2001. – С. 78-84.
6.1.5. Lecture materials.
6.2.1. Минх А.А. Методы гигиенических исследований. – М.: Медицина, 1971 – С. 42-48.
6.2.2. Загальна гігієна та екологія людини (Навчальний посібник). – За ред. В.Г. Бардова та І.В. Сергети. – Вінниця; «Нова книга»; 2002.. – С. 15—22.
7. Equipment required for the lesson
1. The ultravioletmeter (uphymeter) DAU-81 or another type.
2. Gorbachov’s biodosimeter.
3. Tape-line or tape-measure.
4. Artificial UVR sources: direct mercury-quartz lamp (MQL), mercury-arc lamp (MAL), erythemal lamp (LE-30), bactericidal lamp (LB-30).
5. Reagents: 0.1 n. oxalic acid solution (6.3 g per liter of distilled water);
0.1 n. solution of the oxalic acid and nitrate uranil 5.02 g/l;
0.1 n. solution of potassium permanganate KMnO4 (3.16 g per liter of distilled water);
6% solution of sulphuric acid (60 ml of concentrated acid per liter of distilled water).
6. Quartz test-tubes covered by black paper with a window of 3 – 4 cm2 area – 2.
The solar radiation, its physical characteristics
and spectral distribution.
The solar radiation is an integral corpuscular flow (consisting of protons, alfa-elements, electrons, neutrons, neutrinos) and electromagnetic (photon) radiation.
Electromagnetic portion of the solar radiation
(according to R.F.Donnelly, O.R.White, 1980)
The solar ultraviolet radiation wave lenght less then 290 nm is completely absorbed by oxygen and ozone of the upper atmosphere. Atmospheric pollution by factory waste helps the ozone layer destruction resulting in appearance of “ozone holes”. The shortest and the most harmful UV waves reach the earth surface through these “ozone holes”.
Artificial UVR sources:
The solar and artificial UVR band consists of three regions:
Spectral distribution and the main characteristics of the ultraviolet radiation are shown in figure 2.1.
Fig. 2.1. Spectral distribution and the main characteristics
of the ultraviolet radiation (UVR)
Biological effects of the ultraviolet radiation may be biogenic (general-stimulatory, vitamin D formation, chromogenic) and non-biogenic (bactericidal, carcinogenic, etc.).
1. General-stimulatory (erythemal) effect of the ultraviolet radiation is typical for the wave length of 250-320 nm, reaching the maximum at 250 and 297 nm (double peak) and the minimum at 280 nm. This effect results in the photolysis of skin proteins (the UV rays may penetrate the skin as deep as 3-4 mm). The following toxic products of photolysis are generated during this process: histamine, choline, adenosine, pyrimidine etc. These substances are absorbed by blood, they can stimulate metabolism, reticuloendothelial system (RES), marrow, rise the levels of haemoglobin, erythrocytes and leucocytes, increase enzyme activity and liver function, stimulate the activity of the nervous system etc.
The UVR general-stimulatory effect is emphasized by its erythemal effect, which consists in reflex dilation of capillary vessels, particularly when exposed to the intensive infrared radiation. The erythemal effect may result in the skin burn if exposed to the extensive radiation.
2. Vitamin D forming (аntirachitic) effect of the UVR is typical for the 315-207 nm wave length (region B), reaching the maximum at 280-297 nm. This effect consists in the decomposition of calciferols: ergosterin (7,8-dehydrochplecterol) of the skin fat (in sebaceous glands) turns into the vitamines D2 (ergocholecalciferol), D3 (cholecalciferol), and the provitamin 2,2-dehydroergosterin – into the vitamin D4 under the UVR influence due to the decomposition of the benzene ring.
3. Chromogenic (tanning) effect of the UVR is typical for regions A, B with wave lenght of 280-340 nm, reaching the maximum at 320-330 nm and 240-260 nm. Transformation of tyrosine (amino acid), dioxyphenilalanine and the products of adrenaline decay helps to generate the black pigment melanin under the influence of the UVR and the enzyme tyrosinase. This pigment protects the skin and the whole body from the ultraviolet, optical and infrared radiation surplus.
4. Bactericidal (non-biogenic) effect of the UVR is typical for regions C and B with wave lenght from 300 to 180 nm, reaching maximum at 254 nm (according to some other sources – 253.7-267.5 nm). First, the irritation of bacteria under the influence of the UVR activates their metabolism, then a dose increase provokes the bacteriostatic effect and further - photodecomposition, protein denaturation and microorganisms death.
5. Photo-ophthalmic effect of the UVR (the inflammation of the eye mucous membrane) may be observed high in the mountains (“snow disease” among the alpinists), and also among the electric welders and physiotherapists that don’t follow the security rules during the work with the artificial UVR sources.
6. Cancerogenic effect of the UVR is more evident in hot tropical climate conditions and during an exposure to high levels and long-term action of the UVR technical sources (electric welding etc.).
Measuring methods of the ultraviolet radiation intensity
1. An integral (total) flow of the solar radiation is measured by pyranometer (e.g. Yanishevskiy’s pyranometer). The measure units are . The solar constant is 2 at the upper atmosphere and 1 near the earth surface.
2. Biological method – an erythemal dose determination using the Gorbachov’s biodosimeter (fig. 2.2). A minimal erythemal dose (MED) or biodose is the shortest exposure time to the UVR (minutes), which causes the barely perceptible reddening (erythema) on non-tanned skin 15-20 hours after the exposure (for children - 1-3 hours).
Gorbachov’s biodosimeter is 6-window (1.5×1.0 сm) plane-table with the sliding cover, that may close all or some of the windows. This device (biodosimeter) is fixed on the non-tanned skin (the internal surface of the forearm) to determine the biodose. It is useful to mark the window numbers and locations on the skin. After warming up of the lamp (10-15 minutes), a student is exposed to an artificial source of the UVR at the distance of 0.5 m. Then the window #1 is opened, and after that we open a new window every minute. This way, the window #1 is irradiated for 6 minutes, #2 – 5 minutes, #3 – 4 minutes, #4 – 3 minutes, #5 – 2 minutes, #6 – 1 minute. The exposure time and distance may be different depending on a power of the UVR source and other conditions.
The skin is checked for the reddening 18-20 hours after. An erythemal dose is the exposure time of a window with the smallest erythema.
A physiological dose is 1/2 - 1/4, and a preventive dose is 1/8 of erythemal dose.
A preventive dose for the exposure distance, required for the patient can be calculated using the following formula:
where В is a distance from the lamp to the patient in meters;
С – a standard distance for the determination of a preventive dose in meters, (0.5 m);
А – an erythemal dose at a standard exposure distance in minutes.
Comment: As it’s above mentioned, students will only perform the first phase of the biological method measuring during this lesson. They will irradiate the forearm skin of each other using the Gorbachov’s biodosimeter and indicate numbers of windows on the skin. Students will be able to determine the erythemal dose after 18-20 hours. Then they should write it down in the protocol and prepare the calculations of the physiological and preventive doses for themselves for the next lesson.
Fig. 2.2. Gorbachov’s biodosimeter.
3. Photochemical (Oxalic Acid) method was elaborated by Z.N. Kylichkova. It is based on the oxalic acid decomposition being in proportion with the intensity and duration of the UV irradiation in the presence of nitrate uranil.
Measuring result is the mass (in milligrams) of the decomposed oxalic acid per 1 cm2 of the solution surface. An erythemal dose is 3.7 – 4.1 mg/cm2 of the decomposed oxalic acid, a physiological dose is 1 mg/cm2, a preventive dose is 0.5 mg/cm2.
Intensity of the ultraviolet radiation can be determined using this method as the mass (in milligrams) of the decomposed oxalic acid per 1 cm2 of the solution surface per certain amount of time (day, hour).
Reagents: 0.1 n. oxalic acid solution (6.3 g per liter of distilled water); effecting 0.1 n. solution of potassium permanganate (3.16 g КМnО4 per liter of distilled water): effecting 0,1 n. solution of the oxalic acid and nitrate uranil (6.3 g of oxalic acid and 5.02 g of nitrate uranil per liter of distilled water); 6 % solution of sulphuric acid (60 ml of concentrated acid per liter of distilled water).
Order of testing:
A closed test-tube is exposed to the sun for a day (to determine the intensity of the Sun or the sky UVR) or to an artificial source of the UVR for an hour (LE-30 lamp, MQ etc). The test-tube is kept in a light-tight case after this exposure.
Comment: Student are provided with pre-made solution to speed up the work.
Intensity of the UVR is determined as the mass (in mg) of the decomposed oxalic acid per 1 cm2 of the surface of solution during the exposure time (hour).
Intensity of the UVR may be calculated by this formula:
Х = ,
Т – a titer 0.1 n. solution of КМnО4 determined by oxalic acid;
V1 and V2 – volumes of КМnО4, used for titration of oxalic acid with nitrate uranil, before and after an exposure of the UVR, in ml;
6.3 (mg) – the mass of oxalic acid per 1 ml of 0.1 n. solution;
S – a light-window area of quartz test-tube, cm2;
t – the time of a test-tube exposure to the source of the UVR, in hours (to the sun) or minutes (to the artificial source of the UVR).
Comment. The result of the UVR measuring is determined as a mass (in mg) of decomposed oxalic acid per 1 cm2 per minute (from artificial source) or per hour (from the sun).
Conclusion (example). The intensity of the solar UVR, determined by this method is 1.3 of decomposed oxalic acid. This is 0.3 of an erythemal dose. A man needs to receive at least 1/8 of an erythemal dose every day, for this he is required to spend 24 minutes each day outdoors.
4. Physical (photoelectrical) method measures the intensity of the UVR with the ultravioletmeter (short form is uphymeter). Uphymeter is a device containing the magnium (for length range of 220-290 nm) or stibium-caesium (290-340 nm) photoelement. Results of the measuring are represented in mW/cm2 or mcW/cm2.
Due to the erythemal effect being different at various wave length, and being maximal one when =297 nm, a special unit – microer is introduced. 1 mcer =1 mcW/cm2 when = 297 nm. The results in mcW/cm2 have to be multiplied by the relative biological effectiveness (RBE) (tabl.1) if the wave length is different.
E.g., the intensity of the UVR, measured by an uphymeter, is 6 mcW/cm2, of which 4 mcW/cm2 at =297 nm, and 2 mcW/sm2 at =310 nm. Radiation dose is: 41+20,03=4,06 mcer. It has been determined, that 1 MЕD=700-1000 mcer; and 1 preventive dose – 100 mcer.
Relative biological effectiveness of the UVR different bands
Similarly to the above mentioned, the bactericidal effect is maximal at the wavelength of 254 nm and decreases if the wave lenght is different, so microbact has been introduced.
1 microbact = 1 mcW/cm2 at =254 nm. A result in mcW/cm2 is to be multiplied by the relative bactericidal effectiveness (RBcE) coefficient (tabl. 2) if the wave lenght is different from 254 nm.
Relative bactericidal effectiveness
There are several types of uphymeter. The instructions on using the automatic UVR dosimeter ДАУ-81 (DAU-81) for measuring the intensity of the UVR and radiation dose are given below.
A dosimeter measures an energy (band to 500 W/m2) and dose (band from 10 J/m2 to 15 MJ/m2) of radiation at the exposure angles between +80 and - 80 from the artificial sources: bacteridcidal diapason UVR-DB from 0.22 to 0.28 mcm (region C); lamps LUV-40, LUV-80 with band from 0.32 to 0.40 mcm (optical region).
A dosimeter ДАУ-81 (DAU-81) consists of a measuring block and converters – primary (UV-C) with F-29 photoelement for wave length 0.22 – 0.28 nm (region C); primary (UV-A) with F-26 photoelement and UV and C2C23 color filters for wave length 0.32 – 0.40 mcm (region A); primary (FAR) with F-25 photoelement and C3C25 and ZC4 color filters for wave length 0.38 – 0.71mcm (optical region).
Dosimeter setup. Connect the primary converter for the selected region (C, A or optical region) to the measuring block and a cable of radiation source (UV lamp) to a control system.
Plug the device into the electrical supply network. Press the “Power” button. The device is ready when the pointer is not at 0 immediately after that.
Order of testing. Press “Power” and switch on the dosimeter.
Press the radiation wave band of energetic illumination switch button (“10”) (the primary converter is closed), after that press the “Уст. 0” (Set 0) button to set the microampermeter pointer to zero.
Press the “500” button. Take the deck off the primary converter. Check the data of the ampermeter. Select a more sensitive mode if the pointer shows less than 1/5 of the scale.
Set necessary dose of irradiation according to the sensor.
Press the “Reset” button. The counter has to show zero.
A chime will make a sound and the radiation source (UV lamp) will be switched off when the necessary dose has been reached.
Write down the data, and press “Reset”. The counter has to show zero.
Dosimeter is ready again after a necessary dose of radiation is set according to the sensor.
2.5. Calculation methods of determination of the UV radiation intensity.
2.5.1. The following formula is used for the calculation of erythemal flow from a movable source of the UVR
ℱsource of radiation = 5.4 S H/t,
ℱ is the general (integral) flow of irradiation device, ;
5.4 – safety factor;
S – area of the room, m2;
t – the duration of the irradiation source work, min;
H – dose of the preventive UV irradiation, .
Values of H: - if 1 MЕD = 800 mcer (mcW/cm2 ) = 5000 ;
- if 1/2 MЕD = 400 mcer (mcW/cm2 )=2500 ;
- if 1/4 MЕD = 200 mcer (mcW/cm2 ) = 1250 ;
- if 1/8 MЕD = 100 mcer (mcW/cm2 ) = 625 .
Comment: The calculation of the preventive UVR dose during the exposure to the sun or the open air with the tables is shown in the topic #3 - “Usage of the UV radiation for disease prevention and air sanation”.
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