Summary of Cancer Study and Exposure Assessment Activities related to the Santa Susana Field Laboratory (Rocketdyne) Site
October 10, 1990 – The California Department of Health Services (CDHS) released a preliminary report reviewing cancer among residents living in five census tracts located in Los Angeles County and within 5 miles of Santa Susana Field Laboratory (SSFL) in two five year groupings from 1978 to 1987. Census tract age-adjusted incidence rates were found to be significantly higher than comparable county rates in three comparisons:
Four census tract incidence rates were in the top quartile in both time periods when age-adjusted incidence rates were ranked:
March 27, 1992 - CDHS released a report that examined the incidence of cancer among residents of Los Angeles (1978 to 1988) and Ventura Counties (1988 to 1989). Cancers were divided into three groups of very radiosensitive (thyroid, bone & joints, all leukemia, excluding chronic lymphocytic leukemia), moderately radiosensitive (breast, lung & bronchus), and possibly radiosensitive (esophagus, stomach, liver, brain & other nervous system, urinary bladder, other urinary system, salivary gland and parathyroid, and multiple myeloma). The analyses found that people living near the SSFL were not at increased risk for developing cancers associated with radiation exposure. The analyses suggested that male residents living in Los Angeles County near SSFL may have had an increased rate of bladder cancer relative to residents living elsewhere in the county. There was also an increased proportion of lung cancer among Ventura men.
Epidemiologic Study to Determine Possible Adverse Effects to Rocketdyne/ Atomics International Workers from Exposure to Ionizing Radiation
June 1997 - Release of the University of California, Los Angeles (UCLA) health study of the Rocketdyne workers who were exposed to radiation. In 1990, the legislature requested an investigation of SSFL Rocketdyne workers to be overseen by the CDHS Occupational Health Branch. The Department of Energy provided funds to the California Public Health Foundation to work with CDHS and oversee the study. CDHS convened an Advisory Panel made up of independent scientists, community and government representatives, and a representative of the union to choose a research team (UCLA) and monitor the progress of the study.
The UCLA study included 4, 607 employees who worked at Rocketdyne between 1950 and 1993. This group had been monitored for radiation exposure and was enrolled in the company’s Health Physics Radiation Monitoring Program. The researchers searched death certificates to find out which Rocketdyne workers have died and the causes of death. The study investigators found that among Rocketdyne workers who were monitored for external radiation, those who received higher doses (especially more than 200 mSv) had an increased risk of dying from cancers of the blood and lymph system (such as leukemia and lymphoma), and from lung cancer. As the dose of external radiation among Rocketdyne workers increased, the investigators also found an increased risk of dying from all cancers. They also found that among Rocketdyne workers who were monitored for internal radiation, those who received a relatively higher dose (especially more than 30 mSV) had an increased risk of dying from cancers of the blood and lymph system, and upper aero-digestive tract cancers (mouth, throat, esophagus and stomach).
September 29, 1997 - The Tri-Counties Regional Cancer Registry responded to an inquiry from Ventura County Public Health for cancer incidence in Simi Valley. The registry epidemiologist sent a letter to the health director in which he summarized cancer incidence data from 1988-1995 for 19 census tracts combined. The cancers examined were the same as the CDHS 1992 study except salivary and parathyroid gland cancers were not included in the “possibly radiosensitive.” They found that the residents of the study area appeared to have cancer incidence risk similar to that of the other residents of the Tri-Counties Region, except for leukemia in women which was significantly lower, and cancer of the lung & bronchus which is higher.
Addendum Report - Epidemiologic Study to Determine Possible Adverse Effects to Rocketdyne/Atomics International Workers from Exposure to Selected Chemicals
January 1999 - UCLA released the final report for the second part of the DOE-funded occupational study. The addendum report focused on the chemical exposure portion, and included a cohort based on presumed exposure to hydrazine (6,107 workers with 176,886 person-years) and a cohort with presumed exposure to asbestos (4,563 workers with 118,749 person-years). Employing an internal comparison method described in the 1997 report, this study reported the observed positive association between presumptive exposures to hydrazine and the rates of dying from cancers of the lung.
June 20, 1999 – The California Environmental Protection Agency (Cal/EPA) released an investigation of CDHS’ handling of the health studies at SSFL. The investigation was ordered by Governor Gray Davis in response to Assemblywoman Kuehl’s concerns. Cal/EPA focused its investigation on the three cancer-related documents described above.
Cal/EPA found that the combined evidence from all three studies did not indicate an increased rate of cancer incidence in the regions examined. The extremely modest cancer incidence increases associated with known radiosensitive tumors could be easily explained by uncontrolled confounding or impression in the data. The results do not support the presence of any major environmental hazard. Further Cal/EPA suggested that a population based case study focused on radiosensitive tumors that addresses occupational and environmental exposures to radiation, while controlling for all known risk factors, should be discussed. Alternatively, a study could include socioeconomic data from the census, all types of cancer, all time periods for which data are available, and consistent epidemiologic methods over time, which would improve confidence in the results of the three earlier studies. Further studies should only be embarked upon if the proposed protocol can provide improved exposure assessment and control for confounders, while substantially improving the precision of the estimates.
December 3, 1999 – The Agency for Toxic Substances and Disease Registry (ATSDR) released a Draft Preliminary Site Evaluation in which they found:
Estimated effects of solvents and mineral oils on cancer incidence and mortality in a cohort of aerospace workers, Zhao et al., 2005 and Estimated effects of hydrazine exposure on cancer incidence and mortality in aerospace workers, Ritz et al
2006 - UCLA continued its worker study with additional funding to include 5 more years of follow-up, the collection of cancer incidence data, and refinement of the job-exposure matrix to measure trichloroethylene (TCE), mineral oils, polycyclic aromatic hydrocarbons (PAHs), and benzene. The findings were released in journal articles. Zhao et al. found that TCE exposure was positively associated with the incidence of kidney and bladder cancers and that exposure to mineral oils was associated with the incidence and mortality of several cancers, including lung and melanoma. Ritz et al. found a positive association between hydrazine exposure and the incidence of lung and colorectal cancers.
February 2, 2006 - UCLA’s Center for Environmental Risk Reduction released the final report entitled, “The Potential for Offsite Exposures Associated with Santa Susana Field Laboratory, Ventura County, California”. This report was funded by ATSDR. Its findings and recommendations were:
The researchers made the following recommendations:
October 10, 2006 - The Tri-Counties Regional Cancer Registry responded to an inquiry for cancer incidence in Simi Valley as a result of publication of studies. They concluded that the occurrence of newly diagnosed invasive cancers in the identified census tract did not show any unusual pattern, but rather had decreased between 1988 and 2004.
2006 - The Boeing Company-funded retrospective cohort study of cancer mortality among Rocketdyne workers was released. The results of this study were published in two journal articles—one focusing on radiation workers, and the other focusing on aerospace workers who tested rocket engines. On the basis of their findings, the authors concluded that “radiation exposure has not caused a detectable increase in cancer deaths” in their cohort of radiation workers. Their study differed in several ways from the first study conducted at UCLA:
October 2006 - The SSFL Advisory Panel (2006), funded by the California State Legislature through the Citizens’ Monitoring and Technical Assistance Fund, conducted independent analyses of potential offsite impacts of contamination and accidents at SSFL, in particular the 1959 partial meltdown of a nuclear reactor (the Sodium Reactor Experiment) at the site. The Panel’s consultants estimated that, contrary to previous governmental reports, the partial meltdown could have released appreciable amounts of radioactive cesium and iodine—much more than was released at Three Mile Island in 1979—and they estimated that those radioactive releases produced about 260 excess cancers (95% confidence bounds of 0 to 1,800), of which 5% were thyroid cancers. The Panel also assessed the potential for offsite contamination of perchlorate, which is a component of rocket fuel and is known to disrupt thyroid function in humans.
The independent analyses conducted on behalf of the Advisory Panel are as follows:
March 2007 - The former UCLA researcher involved in the occupational studies (now at the University of Michigan) released the final report entitled Cancer Incidence in the Community Surrounding the Rocketdyne Facility in Southern California. The study was funded by ATSDR.
The investigators of this study explored the rates at which newly diagnosed cases of cancer occurred in Ventura and Los Angeles Counties between 1988 and 2002 in relation to distance from SSFL. The two-county region was divided into three exposure areas (less than 2 miles, 2-5 miles, and greater than 5 miles from SSFL), and the study period was divided into two follow-up periods (1988-1995 and 1996-2002).
The researchers found associations between distance from SSFL and cancer incidence differed by type of cancer outcome. Standardized incidence rate ratios were close to 1, indicating little or no association, for total cancers and radiosensitive cancers among adults; but the incidence rate of chemosensitive cancers was slightly elevated during both follow-up periods in the population living within 2 miles of SSFL. Results for the 9 specific cancers revealed some elevated incidence rates between 1988 and 1995 among persons living within 2 miles of SSFL. Specifically, the standardized incidence rate ratio was greater than 1.6 for cancers of blood and lymph tissue, bladder, thyroid, and upper aero-digestive tract. Between 1996 and 2002, the rate ratio among persons living within 2 miles of SSFL was greater than 1.6 for thyroid cancer. There were too few childhood cancers to yield informative results.
2007 - The California Cancer Registry (CCR) was asked by Senator Sheila Kuehl to review the incidence of retinoblastoma in Los Angeles and Ventura Counties, with a focus on the area around SSFL. There was a community concern that the risk of retinoblastoma (RB) was increased in children as a result of potential cancer-causing contaminants in the vicinity of SSFL. Senator Kuehl asked the CCR to update previous analyses that included cases diagnosed through 2002 and showed no excess incidence of retinoblastoma in this area.
Based on the incidence of retinoblastoma among children under age 5 in California, and the population under age 5 in the SSFL area, the number of cases that would be expected to occur in this area between 1988 and 2005 was calculated to be 7.5. The total number of retinoblastoma cases observed in this area between 1988 and 2005 was 11, with a 99% confidence interval of 4.3-22.8 cases. Since the confidence interval around the observed included the expected number, the incidence of retinoblastoma in the area of interest was not statistically significantly elevated.
The age distribution of the 11 cases was: 5 under age 1, 1 age 1, 3 age 2, 1 age 3, 1 age 4. Five of the cases had bilateral disease and 6 had unilateral disease. Nearly half (5 cases) were Hispanic, the remainder were non-Hispanic white (n=3), non-Hispanic black (n=1), non-Hispanic Asian/Pacific Islander (n=1), and unknown race/ethnicity (n=1). All 11 cases were diagnosed in 1998 or later: 1 in 1998, 1 in 1999, 1 in 2000, 1 in 2001, 2 in 2002, 1 in 2003, 3 in 2004, and 1 in 2005. All cases resided in the three neighborhoods with the largest populations (Canoga Park, Woodland Hills, Simi Valley) but there were too few cases to analyze incidence in individual neighborhoods. This analysis is consistent with the 2005 report that showed no significant increased risk of retinoblastoma between 1972 and 2002.