Humans,
animals and plants have been exposed to natural radiation since the creation
of life. Interestingly, life evolved in a radiation field that was much
more intense than today. The annual effective radiation dose from natural
and man-made sources for the world's population is about 3 mSv, which includes
exposure to alpha radiation from radon and its progeny nuclides. Nearly
80% of this dose (2.4 mSv) comes from natural background radiation, although
levels of natural radiation can vary greatly. Ramsar, a northern coastal
city in Iran, has areas with some of the highest levels of natural radiation
measured to date. The effective dose equivalents in very high background
radiation areas (VHBRAs) of Ramsar in particular in Talesh Mahalleh, are
a few times higher than the ICRP-recommended radiation dose limits for
radiation workers.
Figure 1. High Background Radiation Areas Around
the World. According to UNSCEAR 2000 report, Ramsar, in northern Iran has some inhabited areas with the highest known natural radiation levels in the world. Figure adapted from Health Research Foundation, Kyoto, Japan with permission
Inhabitants
who live in some houses in this area receive annual doses as high as 132
mSv from external terrestrial sources. The radioactivity of the high background
radiation areas (HBRAs) of Ramsar is due to Ra-226 and its decay products,
which have been brought to the surface by the waters of hot springs. There
are more than 9 hot springs with different concentrations of radium in
Ramsar that are used as spas by both tourists and residents.
Figure 2. Hot water containing different
concentrations of Radium flows
through streams.
According
to the results of the surveys performed to date the radioactivity seems
primarily to be due to the radium dissolved in mineral water and secondarily
to travertine deposits having elevated levels of thorium combined with
lesser concentrations of uranium (Sohrabi 1990). Due to extraordinary levels
of natural radiation in these areas, in some cases 55-200 times higher
than normal background areas, some experts have suggested that dwellings
having such high levels of natural radiation need urgent remedial actions
(Sohrabi 1997). In spite of this, many inhabitants still live in their
unaltered paternal dwellings.
Figure 3. A calibrated survey meter
shows the contact dose rate.
The
preliminary results of cytogenetical, immunological and hematological studies
on the residents of high background radiation areas of Ramsar have been
previously reported (Mortazavi et al. 2001, Ghiassi-Nejad et al. 2002 and
Mortazavi et al. in press), suggesting that exposure to high levels of
natural background radiation can induce radioadaptive response in human
cells. Lymphocytes of Ramsar residents when subjected to 1.5 Gy of gamma
rays showed fewer induced chromosome aberrations compared to residents
in a nearby control area whose lymphocytes were subjected to the same radiation
dose. Despite the fact that in in vitro experiments lymphocytes of some individuals show a synergistic effect after pretreatment with a low dose(Mortazavi et al. 2000), none of the residents of high background radiation areas showed such a response.
Figure 4. A scientist is measuring the dose rate around these HOT oranges!
Based
on results obtained in studies on high background radiation areas of Ramsar,
high levels of natural radiation may have some bio-positive effects such
as enhancing radiation-resistance. More research is needed to assess if
these bio-positive effects have any implication in radiation protection
(Mortazavi et al. 2001). The risk from exposure to low-dose radiation has
been highly politicized for a variety of reasons. This has led to a frequently
exaggerated perception of the potential health effects, and to lasting
public controversies.
Figure 5. A group of scientists from Korea, Japan, India and USA are
visiting HBRAs of Ramsar.
Current
radiation protection recommendations are based on the predictions of an
assumption on linear, no-threshold dose-effect relationship (LNT).Beneficial
effects and lack of detriment after irradiation with low levels of ionizing
radiation, including a prolonged exposure to high levels of natural radiation
of the inhabitants of HBRAs, are inconsistent with LNT (Mortazavi et al. 1999).
Our
preliminary results suggest that prolonged exposure to very high levels
of natural radiation could lead to the induction of radiation resistance
among exposed individuals, which has interesting implications for many
aspects of radiation protection policy.
Figure 6. Experts are measuring
dose rates in different points
of an inhabited area.
The
phenomenon of radioresistance in living organisms has long been a matter
of interest for scientists. Experiments on Drosophila nebulosa collected
in the woods of a high background radiation area in Brazil indicated the
addition of some genes caused the radioresistance found in these flies
compared to flies collected from adjacent control woods. In humans it is
also possible that genetic alterations have occurred over the span of many
generations to induce the radioresistance noted in our study. More research
is needed to clarify the mechanisms that make individuals radioresistant.
Figure 7.a. Two survey meters show the
dose rates of 142 and 143 micro Gy/h
on the wall of the bedroom of
one dwelling.
Figure 7.b. The surveymeter shows the
dose rate on the bed.
There
are many other areas with high levels of background radiation around the
world, and epidemiological studies have indicated that natural radiation
in these areas is not harmful for the inhabitants. Results obtained in
our study are consistent with the hypothesis that a threshold possibly
separates the health effects of natural radiation from the harm of large
doses. This threshold seems to be much higher than the greatest level of
natural radiation.
Radon levels in some dwellings of Ramsar are up to 3700 Bq/m3 (over 100 pCi/L). The people and their ancestors exposed to abnormally high radiation levels over many generations. If a radiation dose of a few hundred mSv per year is detrimental to health causing genetic abnormalities or an increased risk of cancer, it should be evident in these people. Ramsar was divided into eight health districts and a health center provided primary health services in each health district. Indoor radon concentration levels were previously measured in each dwelling by the Iranian Nuclear Regulatory Authority experts. The overall cancer mortality, lung cancer mortality and neonatal death rate of different districts in the years from 2000 to 2001 were collected. The radon prone houses were located in a district named Ramak. Our study showed that the highest lung cancer mortality rate was in Galesh Mahaleeh, where the radon levels were normal. On the other hand, the lowest lung cancer mortality rate was in Ramak, where the highest concentrations of radon in the dwellings were found.
Figure 8. The highest lung cancer mortality rate was in Galesh Mahaleeh, where the radon levels were normal. On the other hand, the lowest lung cancer mortality rate was in Ramak, where the highest concentrations of radon in the dwellings were found.
Figure 9. Different tumor markers and their associted cancers
Tumor Markers
Recently, as no excess cancer rate was reported in these areas by epidemiological studies, we studied the tumor markers in the inhabitants of these areas to shed some light on the impact of high levels of background radiation on cancer induction. The level of background gamma radiation as well as indoor radon was determined using RDS-110 and CR dosimeters. Thirty five individuals from a high background radiation area (HBRA) and 35 individuals from a normal background radiation area (NBRA) were randomly selected to participate in the study. Commercial ELISA kits (sandwich type ELISA tests) were used to measure the serum levels of PSA, CA15.3, CA125, Cyfra21-1, CEA, CA19.9, AFP and Tag72 tumor markers. This study showed that among the eight biomarkers investigated, the means of PSA, CA15.3, CA125, CA19.9 and AFP concentrations between the HBRAs and NBRAs were not significantly different. However, Cyfra21, CEA and Tag72 in HBRA group revealed statistically significant increases compared to those of NBRA group (P<0.05). Furthermore, a statistically significant correlation between the external gamma dose as well as indoor radon level and the concentration of CEA (P<0.001), Cyfra-21(P<0.001) and TAG 72 (P<0.001 and 0.01 respectively) biomarkers were observed. We concluded that chronic exposure to high background radiation induces significant alterations in Cyfra21, CEA and Tag72 levels. We believe that studies with other relevant tumor markers might overcome the limitations of epidemiological studies on cancer incidence in high background radiation areas.
Source:
S Taeb, SMJ Mortazavi, A Ghaderi, H Mozdarani, MR Kardan, SAR Mortazavi, A Soleimani, I Nikokar, M Haghani, A Soofi. Alterations of PSA, CA15.3, CA125, Cyfra21-1, CEA, CA19.9, AFP and Tag72 tumor markers in human blood serum due to long term exposure to high levels of natural background radiation in Ramsar, Iran. International Journal of Radiation Research. in press.
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