Radiation doses from global fallout and cancer incidence among reindeer herders and Sami in Northern Finland.

OBJECTIVES: People in the Arctic regions are one of the most heavily exposed population from the global fallout from atmospheric atomic bomb testing of the 1950s and 1960s due to their diet rich in reindeer meat in which radionuclides accumulate. We estimated the effect of the radioactive fallout and ethnicity on the cancer incidence in Northern Finland. METHODS: A cohort of the Arctic population in Finland (n=34,653) was identified through the Population Register Centre with grouping by reindeer herding status, ethnicity and radiation exposure. Annual average radiation doses, based on (137)Cs whole-body measurements, were assigned by birth year, gender and reindeer herder status. Incident cancer cases of a priori selected cancer types in the study cohort during 1971-2005 were identified from the Finnish Cancer Registry. RESULTS: A total of 2630 cancer cases were observed versus 3073 expected on the basis of incidence rates in Northern Finland (standardised incidence ratio (SIR) was 0.86 with 95% CI of 0.82 to 0.89). For the indigenous Sami people SIR was even lower, 0.60 (95% CI 0.50 to 0.71). None of the cancer sites was significantly associated with the lifetime cumulative radiation dose. The SIR for the combined group of radiation-related cancer sites increased with the cumulative radiation dose received before 15 years of age (p=0.004). CONCLUSION: Despite the low overall cancer incidence in the Arctic population and ethnic Sami people in Finland and lack of association between the lifetime cumulative radiation exposure from global radioactive fallout and cancer incidence, we found some indication of an increased cancer risk associated with radiation exposure received during childhood. Potential underestimation and misclassification of the radiation dose may affect the results and the findings should be interpreted with caution.

Influence of DNA repair gene polymorphisms on the yield of chromosomal aberrations.

We evaluated the influence of several DNA repair gene polymorphisms on the frequency of chromosomal aberrations (CAs) analyzed in peripheral lymphocytes, using the fluorescence in situ hybridization technique. The CA data were obtained from an earlier study of 84 healthy nonsmokers (48 women and 36 men) carefully characterized for indoor radon exposure. The frequency of translocations showed a wide interindividual variability, which was only partly explained by age. To investigate the potential role of DNA repair polymorphisms in this variation, genotypes of DNA repair genes OGG1 (codon 326), XPD (codon 751), XRCC1 (X-ray repair cross-complementing group 1) (codons 194, 280, and 399), and XRCC3 (X-ray repair cross-complementing group 3) (codon 241) were determined from leukocyte DNA using polymerase chain reaction-based methods. Negative binomial regression models were applied to evaluate the effect of the polymorphisms and other factors (age, gender, radon exposure, and medical exposure) on the frequency of CAs. No interactions between genotypes and radon, medical exposure, or gender were found. Carriers of the XRCC1 codon 280His variant allele had a two-fold increase (frequency ratio [FR] = 2.01, 95% confidence interval [CI] = 1.01-3.98; P = 0.046) in unstable exchanges (dicentrics and ring chromosomes). In addition, the XRCC3 codon 241 homozygous variant genotype (Met/Met) was associated with an increase (FR = 1.70, 95% CI = 1.06-2.74; P = 0.028) in two-way translocations when age was taken into account in the analysis. Our data suggest that the XRCC1 280His and XRCC3 241Met alleles affect individual CA levels, most probably via influencing the DNA repair phenotype.

The mean concentration of uranium in drinking water, urine, and hair of the occupationally unexposed Finnish working population.

Uranium concentrations in the household water, urine, and hair of the occupationally unexposed Finnish working population were determined using inductively coupled plasma mass spectrometry (ICP-MS). The age of the randomly selected participants ranged from 18 to 66 y. The mean concentrations of uranium in water, urine, and hair were 1.25 microg L(-1), 0.016 microg L(-1), and 0.216 microg g(-1), respectively. The mean uranium concentration in hair of the Finnish working population was from 3- to 15-fold higher than the values reported in the literature, while the mean uranium concentration in urine was similar to those measured elsewhere in Europe. The observed large variation in the uranium concentrations in hair and urine can be explained by the variation in the uranium concentration in drinking water. Exceptionally high concentrations have been measured in private drilled wells in the granite areas of Southern Finland.

XRCC1 and XRCC3 variants and risk of glioma and meningioma.

Several single nucleotide polymorphisms (SNPs) affecting DNA repair capacity and modifying cancer susceptibility have been described. We evaluated the association of SNPs Arg194Trp, Arg280His, and Arg399Gln in the X-ray cross-complementing group 1 (XRCC1) and Thr241Met in the X-ray cross-complementing group 3 (XRCC3) DNA repair genes with the risk of brain tumors. The Caucasian study population consisted of 701 glioma (including 320 glioblastoma) cases, 524 meningioma cases, and 1,560 controls in a prospective population-based case-control study conducted in Denmark, Finland, Sweden, and the UK. The studied SNPs were not significantly associated with the risk of brain tumors. The highest odds ratios (ORs) for the associations were observed between the homozygous variant genotype XRCC1 Gln399Gln and the risk of glioma (OR = 1.32; 95% confidence interval, CI, 0.97-1.81), glioblastoma (OR = 1.48; 95% CI, 0.98-2.24), and meningioma (OR = 1.34; 95% CI, 0.96-1.86). However, in pair-wise comparisons a few SNP combinations were associated with the risk of brain tumors: Among others, carriers of both homozygous variant genotypes, i.e., XRCC1 Gln399Gln and XRCC3 Met241Met, were associated with a three-fold increased risk of glioma (OR = 3.18; 95% CI, 1.26-8.04) and meningioma (OR = 2.99; 95% CI, 1.16-7.72). In conclusion, no significant association with brain tumors was found for any of the polymorphisms, when examined one by one. Our results indicated possible associations between combinations of XRCC1 and XRCC3 SNPs and the risk of brain tumors.

Population exposure to ultraviolet radiation in Finland 1920-1995: Exposure trends and a time-series analysis of exposure and cutaneous melanoma incidence.

Ultraviolet radiation (UVR) is the principal cause of cutaneous malignant melanoma (CMM). However, the relation between CMM and UVR exposure is not clear. We present the trends of population exposure to UVR and conduct a time-series analysis of the relation between UVR exposure and incidence of CMM. Data on CMM incidence were obtained from the Finnish Cancer Registry. Clothing coverage of the body was scored from archival photographs and the proportion of uncovered skin was used as a measure of solar exposure. Information on the number of sunny resort holidays, duration of annual holidays, and sunscreen sales were obtained from various sources. Exposed skin area doubled from 1920 to 1985. The average duration of annual holidays increased 30-fold. The number of sunny resort holidays and the sales of sunscreens increased rapidly from 1980. CMM was most strongly associated with solar exposure of 5-19 years earlier. There is a considerable decrease in clothing coverage during the 20th century. UVR exposure preceding CMM occurrence 4 years or less does not appear relevant, whereas the period 5-19 years prior to CMM occurrence might be the most relevant period. However, findings of ecological studies may not be applicable at the individual level.

Well water radioactivity and risk of cancers of the urinary organs.

Water from bedrock frequently contains higher concentrations of natural radionuclides than water from other sources. Bladder and kidneys receive a radiation dose when radioactive isotopes are excreted into urine. The subjects for this case-cohort study were selected from all drilled wells users in Finland. The study comprised 61 bladder cancer and 51 kidney cancer cases diagnosed between 1981 and 1995, as well as a random sample of 274 reference persons, stratified by age and sex. The median activity concentrations of radon in drilled wells used by bladder and kidney cancer cases and the reference cohort were 170, 140, and 130 Bq/L, respectively. The radium concentration was 0.01 Bq/L for all groups and the uranium concentrations were 0.08, 0.07, and 0.06 Bq/L, respectively. The bladder cancer risks associated with radon, radium, and uranium activity concentrations in drinking water were 1.02 (0.68-1.54) per log(100 Bq of radon/L), 0.73 (0.21-2.50) per log(0.1 Bq of radium/L), and 0.77 (0.32-1.89) per log(1 Bq of uranium/L). The corresponding figures for kidney cancer were 0.81 (0.47-1.37), 0.12 (0.01-1.10), and 0.92 (0.36-2.35), respectively. In conclusion, even though ingested radionuclides from drilled wells are a source of radiation exposure, they are not associated with a substantially increased risk of bladder or kidney cancers in concentrations occurring in drilled wells.

Radon and other natural radionuclides in drinking water and risk of stomach cancer: a case-cohort study in Finland.

Very high concentrations of naturally occurring radionuclides are encountered in Finnish groundwaters and wells. Radon ingested through drinking water can cause considerable radiation to the stomach. We assessed the effect of natural uranium and other radionuclides in drinking water on the risk of stomach cancer. Subjects (n = 144,627) in the base cohort had lived outside the municipal tap water system during 1967-1980. A subcohort of 4,590 subjects was formed for use as a reference group by random sampling of the base cohort, with stratification by age and sex. Within the subcohort, 371 subjects had used drinking water from drilled wells prior to 1981. Stomach cancer cases within the subcohort were identified through a cancer registry, and cases using water from drilled wells were selected. Activity concentrations of radon, radium-226 and natural uranium in the drinking water were analyzed using radiochemical and alpha spectrometric methods. The median activity concentration of radon in well water was 130 Bq/l for both the 88 stomach cancer cases and the 274 subjects in the subcohort. Median radium concentrations were 0.007 Bq/l for cases and 0.010 Bq/l for the subcohort, with a median uranium concentration of 0.07 Bq/l for both groups. Risk of stomach cancer was not associated with exposure to radon or other radionuclides. The hazard ratio of stomach cancer was 0.68 for radon (95% CI 0.29-1.59 at 100 Bq/l water), 0.69 per Bq/1 for radium-226 (95% CI 0.33-1.47) and 0.76 per Bq/1 for uranium (95% CI 0.48-1.21). Our results do not indicate an increased risk of stomach cancer from ingestion of radon or other natural radionuclides through drinking water at these exposure levels.

Uranium and other natural radionuclides in drinking water and risk of leukemia: a case-cohort study in Finland.

OBJECTIVE: We assessed the effect of natural uranium and other radionuclides in drinking water on risk of leukemia. METHODS: The subjects (n = 144,627) in the base cohort had lived outside the municipal tapwater system during 1967-1980. A subcohort was formed as a stratified random sample of the base cohort and subjects using drinking water from drilled wells prior to 1981 were identified. A case-cohort design was used comparing exposure among cases with leukemia (n = 35) with a stratified random sample (n = 274) from the subcohort. Activity concentrations of uranium, radium-226, and radon in the drinking water were analyzed using radiochemical and alpha-spectrometric methods. RESULTS: The median activity concentration of uranium in well water was 0.08 Bq/L for the leukemia cases and 0.06 Bq/L for the reference group, radon concentrations 80 and 130 Bq/L, respectively, and radium-226 concentrations 0.01 Bq/L for both groups. The hazard ratio of leukemia for uranium was 0.91 (95% confidence interval 0.73-1.13) per Bq/L. for radon 0.79 per Bq/L (95% CI 0.27-2.29), and for radium-226 0.80 (95% CI 0.46-1.39) per Bq/L. CONCLUSIONS: Our results do not indicate an increased risk of leukemia from ingestion of natural uranium or other radionuclides through drinking water at these exposure levels.