Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 65

Beyea [BEY 06] tried to estimate the exposure of residents around the Santa Susana Field Laboratory (Simi Valley, USA) to help epidemiologists improve the effectiveness of their studies on radiation-induced diseases. This has been extremely complex, particularly from a meteorological point of view as a result of the particular climate of this region. In addition, the information available on radioactivity releases in the 1950s and 1960s is very limited. Exposures were dominated by the inhalation of radioactive iodine and ground deposition of radiocesium, since milk was a relatively minor source at this location. Out of the 20,000 simulations performed by Beyea, the average number of excess cancers was 260 (95% CI 0–1,800). In 25% of simulations, there were eight or fewer excess cancers; in half of the scenarios, the number of cancers was 50 or more, and in 2.5% of them, the number of cancers expected was 1,800 or more.

Nine specific or “radiosensitive” cancers revealed high incidence rates between 1988 and 1995 in people living within 2 miles of the SSFL. Specifically, the standardized incidence rate was greater than 1.6 for cancers of the blood and lymphatic tissues, bladder, thyroid and upper aerodigestive tract. Between 1996 and 2002, the prevalence rate among people living within 2 miles of the STPE was greater than 1.6 for thyroid cancer [MOR 07]. For his part, summarizing the various epidemiological studies of this site, Weitzberg [WEI 14] considers that no evidence of an increase in cancer in the population around Santa Susana has been scientifically demonstrated. It should be noted that the author probably had conflicts of interest with the company responsible for the accident, while the article by Morgenstern et al. (2007) was commissioned by the Agency for Toxic Substances and Disease Registry (ATSDR).

Epidemiological studies on workers at the SSFL site indicate a trend towards an increase in cancer mortality rate associated with an increase in the cumulative radiation dose to workers when this dose was external [RIT 99a, RIT 99b]. When this exposure was internal, Ritz et al. [RIT 00] also observed a trend between cumulative radiation exposure and cancer mortality (all types), mortality due to lymphopoietic cancers and of the upper aerodigestive tract, but not with lung cancer. On the other hand, Boice et al. [BOI 06] did not confirm this significant increase in cancer mortality in general or to a specific cancer among employees who worked at the SSFL site between 1948 and 1999.

Many class actions have been initiated by the population living around the SSFL site. After 7 years of litigation, 100 local residents received a US$30 million settlement following a trial. Information about the verdict and the conclusions found remains elusive, with only the settlement as proof of the conclusion [ROG 12]. In a study on clusters (disease outbreaks), Ingber and Ross [ING 11] consider that the Santa Susana site lacks evidence to be included in a first analysis.