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Radioactive fall-out from the Chernobyl nuclear power plant accident in 1986 and cancer rates in Sweden, a 25-year follow up
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för medicinska vetenskaper, Arbets- och miljömedicin.ORCID-id: 0000-0002-9455-0753
2019 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Aim: The current research aimed to study the association between exposure to low-dose radiation fallout after the Chernobyl accident in 1986 and the incidence of cancer in Sweden.

Methods: A nationwide study population, selecting information from nine counties out of 21 in Sweden for the period from 1980 – 2010.

In the first study, an ecological design was defined for two closed cohorts from 1980 and 1986. A possible exposure response pattern between the exposure to 137Cs on the ground and the cancer incidence after the Chernobyl nuclear power plant accident was investigated in the nine northernmost counties of Sweden (n=2.2 million). The activity of 137Cs at the county, municipality and parish level in 1986 was retrieved from the Swedish Radiation Safety Authority (SSI) and used as a proxy for received dose of ionizing radiation. Information about diagnoses of cancer (ICD-7 code 140-209) from 1958 – 2009 were received from the Swedish Cancer Registry, National Board of Health and Welfare (368,244 cases were reported for the period 1958 to 2009). The incidence rate ratios were calculated by using Poisson Regression for pre-Chernobyl (1980 – 1986) and post-Chernobyl (1986 – 2009) using average deposition of 137Cs at three geographical levels: county (n=9), municipality (n=95), and parish level (n=612). Also, a time trend analysis with age standardized cancer incidence in the study population and in the general Swedish population was drawn from 1980 – 2009.

In the second study, a closed cohort was defined as all individuals living in the three most contaminated counties in mid-Sweden in 1986. Fallout of 137Cs was retrieved as a digital map from the Geological Survey of Sweden, demographic data from Statistics Sweden, and cancer diagnosis from the Swedish Cancer Registry, National Board of Health and Welfare. Individuals were assigned an annual 137Cs exposure based on their place of residence (1986 through 1990), from which 5-year cumulative 137Cs exposures were calculated, accounting for the physical decay of 137Cs and changing residencies. Hazard ratios for having cancer during the follow-up period, adjusted for age, sex, rural/non-rural residence, and pre-Chernobyl total cancer incidence, were calculated.

Results: No obvious exposure-response pattern in the age-standardized total cancer incidence rate ratios could be seen in the first study. However, a spurious association between the fallout and cancer incidence was present, where areas with the lowest incidence of cancer before the accident coincidentally had the lowest fallout of cesium-137. Increasing the geographical resolution of exposure from the average values of nine counties to the average values of 612 parishes resulted in two to three times higher degree of variance explanation by regression model. There was a secular trend, with an increase in age standardized incidence of cancer from 1980 – 2009. This trend was stronger in the general Swedish population compared to the nine counties of the present study.

In the second study, 734,537 people identified were divided into three exposure categories: the first quartile was low exposure (0.0 to 45.4 kBq/m2), the second and third quartiles were intermediate exposure (45.41 to 118.8 kBq/m2), and the fourth quartile was highest exposure (118.81 to 564.71 kBq/m2). Between 1991 and 2010, 82,495 cancer cases were registered in the three counties. Adjusted HRs (95% CI) were 1.03 (1.01 to 1.05) for intermediate exposure, and 1.05 (1.03 to 1.07) for the highest exposure, when comparing to the reference exposure.

Conclusion: Using the ecological data, there was no exposure response trend; however, after refining the data to the individual level of exposure, there was an overall exposure response pattern. Nonetheless, due to the time dependency, these results were restricted to the age group of 25 – 49 among males. Using register-based data only, for determining the association between low-dose exposure to radiation and the risk of developing cancer, is difficult since we cannot control for other significant factors that are associated with cancer.

Ort, förlag, år, upplaga, sidor
Uppsala: Uppsala University, 2019. , s. 112
Nationell ämneskategori
Annan medicinsk grundvetenskap
Forskningsämne
Arbets- och miljömedicin
Identifikatorer
URN: urn:nbn:se:uu:diva-380570OAI: oai:DiVA.org:uu-380570DiVA, id: diva2:1300568
Presentation
2019-05-10, Akademiska sjukhuset (Arbets- och miljömedicin), Dag Hammarskjölds Väg 60, Uppsala, 09:00 (Svenska)
Opponent
Handledare
Tillgänglig från: 2019-04-12 Skapad: 2019-03-28 Senast uppdaterad: 2019-05-16Bibliografiskt granskad
Delarbeten
1. Cancer incidence in northern Sweden before and after the Chernobyl nuclear power plant accident
Öppna denna publikation i ny flik eller fönster >>Cancer incidence in northern Sweden before and after the Chernobyl nuclear power plant accident
2014 (Engelska)Ingår i: Radiation and Environmental Biophysics, ISSN 0301-634X, E-ISSN 1432-2099, Vol. 53, nr 3, s. 495-504Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Sweden received about 5 % of the total release of Cs-137 from the Chernobyl nuclear power plant accident in 1986. The distribution of the fallout mainly affected northern Sweden, where some parts of the population could have received an estimated annual effective dose of 1-2 mSv per year. It is disputed whether an increased incidence of cancer can be detected in epidemiological studies after the Chernobyl nuclear power plant accident outside the former Union of Soviet Socialist Republics. In the present paper, a possible exposure-response pattern between deposition of Cs-137 and cancer incidence after the Chernobyl nuclear power plant accident was investigated in the nine northernmost counties of Sweden (2.2 million inhabitants in 1986). The activity of Cs-137 from the fallout maps at 1986 was used as a proxy for the received dose of ionizing radiation. Diagnoses of cancer (ICD-7 code 140-209) from 1980 to 2009 were received from the Swedish Cancer Registry (273,222 cases). Age-adjusted incidence rate ratios, stratified by gender, were calculated with Poisson regression in two closed cohorts of the population in the nine counties 1980 and 1986, respectively. The follow-up periods were 1980-1985 and 1986-2009, respectively. The average surface-weighted deposition of Cs-137 at three geographical levels; county (n = 9), municipality (n = 95) and parish level (n = 612) was applied for the two cohorts to study the pre- and the post-Chernobyl periods separately. To analyze time trends, the age-standardized total cancer incidence was calculated for the general Swedish population and the population in the nine counties. Joinpoint regression was used to compare the average annual percent change in the general population and the study population within each gender. No obvious exposure-response pattern was seen in the age-adjusted total cancer incidence rate ratios. A spurious association between fallout and cancer incidence was present, where areas with the lowest incidence of cancer before the accident coincidentally had the lowest fallout of Cs-137. Increasing the geographical resolution of exposure from nine county averages to 612 parish averages resulted in a two to three times higher value of variance in the regression model. There was a secular trend with an increase in age-standardized incidence of cancer in both genders from 1980 to 2009, but significant only in females. This trend was stronger and statistically significant for both genders in the general Swedish population compared to the nine counties. In conclusion, using both high quality cancer registry data and high resolution exposure maps of Cs-137 deposition, it was not possible to distinguish an effect of Cs-137 on cancer incidence after the Chernobyl nuclear power plant accident in Sweden.

Nyckelord
Cancer, Cesium-137, Chernobyl, Ecological study, Environment, Epidemiology, Ionizing radiation, Nuclear accident, Radiation, Sweden
Nationell ämneskategori
Arbetsmedicin och miljömedicin
Identifikatorer
urn:nbn:se:uu:diva-231289 (URN)10.1007/s00411-014-0545-6 (DOI)000339898300003 ()24811728 (PubMedID)
Tillgänglig från: 2014-09-08 Skapad: 2014-09-07 Senast uppdaterad: 2019-03-28Bibliografiskt granskad
2. Total cancer incidence in relation to 137Cs fallout in the most contaminated counties in Sweden after the Chernobyl nuclear power plant accident: a register-based study
Öppna denna publikation i ny flik eller fönster >>Total cancer incidence in relation to 137Cs fallout in the most contaminated counties in Sweden after the Chernobyl nuclear power plant accident: a register-based study
2016 (Engelska)Ingår i: BMJ Open, ISSN 2044-6055, E-ISSN 2044-6055, Vol. 6, nr 12, artikel-id e011924Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

OBJECTIVES: To determine the total cancer incidence in relation to a 5-year exposure to caesium-137 ((137)Cs) from the 1986 Chernobyl nuclear power plant accident.

METHODS: A closed cohort was defined as all individuals living in the three most contaminated counties in mid-Sweden in 1986. Fallout of (137)Cs was retrieved as a digital map from the Geological Survey of Sweden, demographic data from Statistics Sweden, and cancer diagnosis from the National Board of Health and Welfare. Individuals were assigned an annual (137)Cs exposure based on their place of residence (1986-1990), from which 5-year cumulative (137)Cs exposures were calculated, accounting for the physical decay of (137)Cs and changing residencies. HRs were adjusted for age, sex, rural/non-rural residence and pre-Chernobyl total cancer incidence.

RESULTS: The 734 537 people identified were categorised by exposure: the first quartile was low exposure (0.0-45.4 kBq/m(2)), the second and third quartiles were intermediate exposure (45.41-118.8 kBq/m(2)), and the fourth quartile was the highest exposure (118.81-564.71 kBq/m(2)). Between 1991 and 2010, 82 495 cancer cases were registered in the 3 counties. Adjusted HRs (95% CI) were 1.03 (1.01 to 1.05) for intermediate exposure and 1.05 (1.03 to 1.07) for the highest exposure compared to the reference exposure.

CONCLUSIONS: We found a small overall exposure-response pattern of the total cancer incidence related to (137)Cs after adjustment for age, sex, rural residence and pre-Chernobyl cancer incidence.

Nationell ämneskategori
Arbetsmedicin och miljömedicin
Identifikatorer
urn:nbn:se:uu:diva-311895 (URN)10.1136/bmjopen-2016-011924 (DOI)000391303600003 ()27998898 (PubMedID)
Tillgänglig från: 2017-01-03 Skapad: 2017-01-03 Senast uppdaterad: 2019-03-28Bibliografiskt granskad

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