A review of cancer statistics in four New Orleans-area zip codes where vermiculite was produced shows little, if any, increased rates for cancers associated with this exposure. Overall cancer incidence rates in these areas were found to be similar to statewide cancer rates. The review was conducted by the Louisiana Department of Health using data provided by the Louisiana Tumor Registry.
The review studied cancer incidence rates (the occurrence of cancer, not cancer related deaths) from 1991 to 2000. Data was compiled for four demographic groups (white and black females and white and black males) in the following zip codes: 70084, 70117, 70121 and 70126.
How the review was conducted
The review used what is known as Standardized Incidence Ratios (SIRs) to compare actual cancer cases to expected cancer cases. The number of expected cases for any given zip code is a number that is based on cancer incidence rates for the entire state. SIR is the ratio of the actual cases to the expected cases. SIRs greater than one mean there are more cancers than would be expected. For example, if 10 cases are discovered, but only five cases are expected, the SIR would be 10/5 = 2 (or twice the expected rate).
What does this mean?
Researchers also point out that drawing conclusions when there are only a few actual cancer cases is difficult at best. In these situations, a high or low SIR might be due more to chance than to factors that influence disease.
Dr. Raoult Ratard, state epidemiologist with DHH’s Office of Public Health, explained that mesothelioma is the cancer most associated with exposure to asbestos in vermiculite.
“For asbestos, mesothelioma is the most important cancer to study,” Ratard said. “Rates for it are lower than expected in all zip codes combined, but we found higher rates of mesothelioma in one of the zip codes. This is the only higher-than-expected rate we detected.”
Dr. Ratard explained that these instances of mesothelioma represent only four cases. “It’s difficult to determine if this is significant since these individuals could have worked in jobs with asbestos exposure,” he added.
Ratard said lung cancer rates are also important, but that for all areas studied only white males have higher rates, and these elevated rates are not consistent across all zip codes.
“For lung cancer, the effect of asbestos as a risk factor is difficult to separate from the other known risk factor, smoking,” he added.
White males and females in the 70084, 70117, 70121 and 70126 zip codes combined had significantly higher SIRs for stomach cancer. White males in this category had significantly lower SIRs for mesothelioma.
In zip code 70084, white females had significantly higher SIRs for digestive tract cancers , and black females and black males had statistically higher incidence for lung and bronchus cancer. White females had lower rates of respiratory cancer.
In zip code 70117, white males had significantly higher incidence ratios for digestive tract cancer, respiratory cancer, lung and bronchus cancer, and stomach cancer when compared to the state of Louisiana.
In zip code 70121, black females had a statistically higher incidence for mesothelioma, and black males had lower rates of digestive tract cancer.
In zip code 70126, black males had lower rates of respiratory and lung and bronchus cancer.
The incidence of cancer overall in each of these zip codes is as expected when compared to the state of Louisiana.
The review was done because the Environmental Protection Agency (EPA) determined that some exfoliation plants in Orleans, Jefferson and St. John the Baptist Parishes received vermiculite contaminated with asbestos fibers. The vermiculite originated from the W.R. Grace mine in Libby, Mont.
A health statistics review was funded by the Agency for Toxic Substances and Disease Registry (ATSDR). It was conducted to evaluate whether the populations residing in zip codes 70084 (St. John the Baptist Parish), 70117 and 70126 (Orleans Parish), and 70121 (Jefferson Parish), zip codes in which W.R. Grace operated, had elevated cancer incidence for cancer sites associated with exposures to asbestos.
The Tumor Registry provided the Department of Health – Office of Public Health with 10 years of cancer data, focusing on the four zip codes. The data were used to compare the observed number of cases to the expected number of cases based on incidence rates for the state of Louisiana as a whole.
According to Sharon Howard, assistant secretary for DHH’s Office of Public Health, the next step is to meet with federal health officials.
“Our review was funded by the ATSDR as part of a nationwide review, so our first step will be to determine how this information fits into the national project, as well as learn the overall conclusions of the federal government,” Howard explained.
LDH will provide residents living in these communities with follow-up education on the findings, and will meet with the Louisiana Department of Environmental Quality to discuss other possible actions.