| Abstrakt: |
Small area statistics on health (SMASH) -system is a GIS application used for rapid investigations of cancer near geographically defined exposure sources in Finland. In the River Kymijoki, the environmental levels of dioxins and furans, deriving from the production of a chlorophenol product called Ky-5 from 1939 to 1984, are among the highest in the world (i.e., between 0.5 and 350 ng g-1 (I-TEQ)). This study investigates the risk of total cancer and selected cancer subtypes in farmers living near the River Kymijoki, presuming that highest dioxin exposures occur closest to the river. The SMASH -system holds, in squares of size 0.5 km x 0.5 km, register-data from the Central Population Register, the Finnish Cancer Register and the Statistics Finland. Exposure assessment was based on the distance of residence to the River Kymijoki in 1980. SMASH was used to create datasets of three cohorts of farmers (living closer than 1 km, 1 to 4 km, or 5 to 19 km from the river) and their incident cancers between 1981 and 2000. Expected numbers were counted based on incidence rates in all farmers in Finland. Estimates of relative risk (RR) were obtained from Poisson-regression models using observed and expected numbers of cancer and adjusting for sex, age and calendar period. The RRs for total cancer in farmers were 1.00, 0.97, and 1.21 by decreasing distance to the river; the respective numbers of observed cases (and 95% confidence intervals, CI) were 388 (reference), 134 (0.80-1.18) and 100 (0.97-1.51). For farmers living closest to the river, the RRs were statistically significantly increased during 1981-90 (RR = 1.40) but not during (1.09). Likewise, the RRs were statistically significantly increased for farmers aged less than 45 years (RR = 1.81) in 1980, but not for those aged 45 to 59 years (1.09), or those aged 60 years or more (1.04). Increased (but statistically non-significant) RRs were observed for cancers of the testis, nervous system (significant), breast, pancreas, bladder, liver, ovary, thyroid, prostate, and rectum, and for soft tissue sarcoma, malignant non-melanoma of the skin, Hodgkin's disease and leukaemia. The results are suggestive of increased cancer risk in farmers living close to the River Kymijoki. However, GIS can only give first approximations of risk and the results need to be confirmed in individual-level studies. The fact that the risk was increased during 1981-1990 but not during 1991-2000 suggests that any increase in risk may already be fading away. [ABSTRACT FROM AUTHOR] |
