The world’s high background natural

radiation areasBy

Pakpong Roongruangsree 5480978

HBNRAs

• High Background Natural Radiation Areas• The paper reviews issues • Dosimetric : measurement of absorbed dose• Epidemiological : causes of diseases• Radiological : emission of energy in waves

• Failures to report any increase in cancer incidence• Validity of linear no-threshold hypotheses

Background radiation

• 80% of annual effective dose comes from background natural radiation• Radon produce large proportion of radiation in man’s environment• HBNRAs residents receive more radiation than Normal background

radiation areas (NBRAs) • Inhabitants’ annual effective dose (He) : tissue weighted sum of health

effects of low levels of radiation in body • Low: He = 5 mSv per year medium: He = 5-10 mSv per year• high He = 20-50 mSv per year very high: He > 50 mSv per year

Linear no-threshold (LNT)

• Epidemiological studies fails to report the increase in cancer in HBNRAs• LNT is a model assuming that biological damage is proportional to effective dose of radiation in long term

Yangjiang (China)

• Yangjiang, Guangdong province with 5 generations of people• Natural external radiation : Monazite containing Th-232, U-238,K-4• He = 4.27 mSv per year• Health survey spans 20 years• Thyroid nodularity in 50-56 years old female • Cumulative dose 2 fold higher than NBRAs

• Thyroid incidence is higher in HBNRA but may be from low iodine consumption

Yangjiang (China)

• Radiation may cause chromosomal diseases• Dicentric and ring chromosomal aberrations • But no significant increase in frequency

• Cancer-related mortality• Leukemia, breast cancer, lung cancer : not higher than NBRAs• Non-leukemia cancer : 14.6 % lower than NBRAs• Adaptive response for lymphocyte • High incidence of Down’s syndrome : may be from age of maternity

Kerala, Tamil and Orissa coasts (India)• Monazite and heavy minerals : ilmenite, rutile, zircon, garnet• Orissa He = 0.78-3.86 mSv per year• Kerala He = 0.5-15 mSv per year• No significant difference in fertility index, sex ratio, infant mortality• High incidence of mental retardation• But no difference in chromosomal aberration in newborns in cord blood

samples• Negative correlation between Telomere length and age

• Radiation has no effects on telomere length• No relation to malignant tumor

Poços de Caldas, Arax’a, Tapira (Brazil)• Volcanic alkaline, monazite sand abundant • High radium concentration in coastal lagoon in Rio de Janeiro• He = 3.5-10 mSv per year• Cancer mortality in 10 years is lower than expected (Arax’a)• With confounders ( not relate to radiation)

• Guarapari beach sand Ra activity: 200 times higher than Organization for Economic Co-operation and development (OECD) limits• Increase in chromosomal aberration in HBNRA

Ramsar (Iran)

• Hot springs brings up Ra-226 and its decay products (9 as spas)• Bedrock contains Uranium, decay to Ra• He = 0.6-131 mSv per year (mean = 6 mSv)• Ra-226 substitutes for Ca, RaCO3

(used as building materials)• External and Internal He = 3.0-202 mSv per year • In 50 years He = 10.1 Sv ( 10 folds 50 years limit of 1 Sv for workers)• Chromosomal aberration in cells show significant positive results • Tumor biomarkers in blood in Ramsar : significant correlations between

chronic exposure and tumor markers

• Higher cancer mortality in females who remains indoor compare to NBRA• Later studies : Adaptive response also presents as well

• Reduce frequency of chromosomal aberration in HBNRA residents• Resistance to high radiation doses• No significant difference in males

• Negative correlation in lung cancer • Continuous exposure may trigger anti oxidant and repair enzyme

production• Ramsar has much less residents than Yangjiang and Kerala

• Small study cases• Difficult to collect observation

Ramsar (Iran)

Discussion

• Most of the studies conclude with no links between exposure and cancer mortality• Confounders also interfere in methodology such as maternal age etc.

• Robust statistic is needed • Resistant against errors• Deviation from assumptions

• Chromosomal aberration is a reliable biodosimetric tool• Yet it shows no evidence for correlation with effective dose

• Validity of Linear no-threshold (LNT) is questioned • Beneficial effect of exposure to radiation is shown by adaptive effect

Discussion

• High concentration of Ra gas • Lung cancer could be from the indoor radon gas rather than outdoor• Lack of evidence yet again

• Radon barrier : the most effective way too reduce it effect• Plastic and rubber damp proof sheets(polyethylene)

References

• Abubakar, S. A.; Ahmad, T. R. The world’s high background netural radiation areas (HBNRAs) revisited: A broad overview of the dosimetric, epidemiological and radiobiological issues. Radiat. Meas. 2015, 73, 51-59.• Princeton University.

http://web.princeton.edu/sites/ehs/osradtraining/biologicaleffects/Risk.htm/ (accessed March 18, 2015).• Visqueen Radon Membrane CE Mark to EN 13967 ; Visqueen building

product : London, 2014; Visqueen Radon Membrane EN 13967 Type A.