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Radiation Measuremenls
PERGAMON
Radiation Measurements 31 (1999) 355-358
DISTRIBUTION OF INDOOR RADON LEVELS IN MEXICO
G. ESPINOSA*, J.I. GOLZARRI*, J. R/CKARDS*,AND R.B. GAMMAGE.'*
* Instituto de Fisica, UNAM. Apdo. Postal 20-364, 01000 M6xico, D.F.
** Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA.
ABSTRACT
Our laboratory has carried out a systematic monitoring and evaluation of indoor radon
concentration levels in Mexico for ten years. The results of the distribution of indoor
radon levels for practically the entire country are presented, together with information on
geological characteristics, population density, socioeconomic levels of the population, and
architectural styles of housing.
The measurements of the radon levels were made using the passive method of nuclear
tracks in solids with the end-cup system. CR-39 was used as the detector material in
combination with a one-step chenfical etching procedure and an automatic digital- image
counting system. Wherever a high level was measured, a confirming measurement was
made using a dynamic method. The results are important for future health studies,
including the eventual establishment of patterns for indoor radon concentration, as it has
been done in the USA and Europe.
KEYWORDS
Indoor radon; nuclear track methodology; global information.
~TRODUCTION
Radon is the highest contributor to the effective dose equivalent in man (IAEA, 1989) from the
natural sources and has been studied by multiple countries and organizations (Bochicchio
et aL,
1996; Marcionwsky, 1992; Miles, 1998; Starnd, 1992).
Several countries have conducted national programs of indoor radon concentration measurements in
buildings and houses. These programs were motivated by the need to confirm the relationship
between the exposure to radon of the public in general and the lung cancer risk (Chudhry
et al.,
1996;
Cohen, 1998a,b; Lubin, 1998; Nausen and Cohen, 1987; Nazaroff and Nero, 1988; Stidley and
Samet, 1993).
For many nations, the country wide distribution of indoor radon has been established. This
knowledge is important for determining the risk of lung cancer associated with indoor radon.
For about 10 years, the National Autonomous University of Mexico, with the help of international
organizations, has undertaken the task of developing a cost-effective radon measurement method and
then using this methodology to measure indoor radon levels in many parts of Mexico.
In this paper we present the data of indoor radon concentration collected from the measurements of
some locations with more than 100,000 inhabitants in the national territory, excluding the tropical
zones.
1350-4487/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII:
S 1350-4487(99)00171-7
356
G. Espinosa et aL / Radiation Measurements 31 (1999) 355-358
METHODOLOGY
For this large scale radon measuring program, the passive close-end cup system was selected, using
CR-39, 600 Inn thick polycarbonate (Landauer ®) as the detection material. The CR-39 was cut
automatically by a laser beam into chips of size 9 nun x 18 nun.
To develop the alpha track we used a one-step chemical etching in KOH, 6.25M at 60°C + I°C for 16
hours. (Espinosa and Gammage, 1993). The etched tracks were counted by a Digital Image
Automatic System (DIAS) (Gammage and Espinosa, 1997). All the procedures were optimized step-
by-step, and the calibration was carried out at the Oak Ridge National Laboratory facilities.
The characteristics of Dwellings: The dwellings under study were built in general with volcanic rock
and clay bricks, limestone bricks or soil adobe, with a concrete and iron structure. The walls of the
dwellings can be often covered with gypsum, and several of these materials are expected to contribute
significantly to sources of indoor radon. But on the other hand, the architectural style is communly a
central patio with high ventilation characteristics or open windows and sometimes without a frame or
glass.
RESULTS
In Fig. 1, the locations under study are shown. In Table 1 the names of the towns under study, their
population (INEGI, 1995), the number of surveyed houses, and the indoor radon activity in each
location are given.
Figure 1. Towns under study.
We find that out of 39 locations under study, there are only 8 locations with more than 150 Bq m -3,
but less than 179 Bq m -3, 5 locations with values between 100 to 150 Bq m 3, 23 locations between 50
to 100 Bq m -3, and 3 locations under 50 Bq m "3. It is observed that the larger indoor radon
concentrations are fundamentally related with architectonic styles and type of constructions. This
study did not include rustic and semirustic dwellings.
G. Espinosa et al. /Radiation Measurements 31 (1999) 355-358
Table 1. Towns under study with their population and the indoor radon activity m each location
357
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
2O
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
Towns Under Study
clt~
A~uasealientes
Tijuana
Chihuahua
State
Aguasealientes
Baja California
Chihuahua
Population
582,827
991,592
627,662
Number of
Surveyed
Houses
200
250
200
Lower
Activity
(nq .c)
39
62
69
mgher
Act~ff
Ohm-)
154
119
Mean
A~vity
~Bq m-5
79
78
273 169
Ciudad Juarez Chihuahua 1,011,786 280 63 252 159
Saltiilo Coahuila 527,979 200 35 127 79
Torreon Coahuila 508,076 200 61 160 87
Monclova Coahuila 189,738 150 47 110 60
Mexico City
Durango
Tohea
Distrito Federal
Durallgo
Estado de Mexico
Ciudad Netzahualcoyoti "
Ecatepec Estado de M6xico
Estado de Mexico
Nauealpan
Tlalnepantla
Guanajuato
Leon
Estado de M6xico
Estado de M6xico
Guanajuato
Guanajuato
Guanajuato
Ouanajuato
Hidalgo
Hidalgo
Hidalgo
Jalisco
Jalisco
Jalisco
Irapuato
Cela~a
Pachuca
Tulancingo
Tula
Ouadalajara
Zapopan
Tlaquepaque
Morelia Michoacan
Uruapan Michoacan
NuevoLe6n
NuevoLe6n
8,362,670
464,566
564,476
1,457,124
1,233,868
839,723
713,143
128,171
900
200
200
280
Monterrey
Guadalupe
S. Nicolas de los Garza Nuevo Le6n
Oaxaca Oaxaca
Puebla Puebla
Tehuacan Puebla
Queretaro
Queretaro
260
220
200
100
83
33
23
37
15
90
San Luis Potosi
CiudadObregon
Hermosillo
35
57
275
159
215
115
113
200
117
153
San Luis Potosi
Sonora
73
93
59
61
131
55
263 153
1,042,132 280 34 130 85
412,639 150 60 117 73
354,473 150 58 112 60
220,488 120 47 187 137
110,140 100 32 100 48
82,333 100 15 98 63
214 280
Sonora
Tlaxcala Tlaxcala
Zacatecas Zacatecas
Fresnilio Zacatecas
75 1,633,216 179
925,113 250 47 112 73
449,238 180 49 117 75
578,061 200 40 165 80
250,794 150 31 139 73
1,088,143 280 48 295 170
618,933 200 37 120 55
487,924 200 32 97 43
244,827 180 21 93 37
1,222,569 280 62 201 163
190,468 100 73 260 160
559,222 200 39 193 110
625,466 200 33 148 73
345,222 150 30 132 87
559,154 200 27 157 91
63,423 100 15 169 87
118,742 100 70 263 130
71 100 176,885 175 125
CONCLUSIONS
a) Having this National Atlas, with the indoor radon concentration, the radiological risks and lung
cancer cases associated to radon can be analyzed.
b) With this information, the actions to reduce the indoor radon levels in houses and buildings can be
taken.
c) The radiological conditions could be considered for future constructions, houses or apartments.
d) It could be possible to realize multifactorial epidemiology studies of lung cancer if the influence of
the indoor radon is known.
Acknowledgements -- The authors wish to thank to Dr. E. Ley Koo for his usefully comments. This work was
partially supported by Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. lbr
the U.S. Department of Energy under contract number DE-AC05-96OR22464.
358
G. Espinosa et al. /Radiation Measurements 31 (1999) 355-358
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