November 2, 1999
by Edmund Tsang
After a two-year-long campaign by Mobile Bay Watch, an environmental advocacy group, a task force associated with Envision Mobile/Baldwin was officially organized in August to evaluate the air quality of Mobile County. The results of the study, however, may not provide the definitive answer to the nagging questions of some Mobilians who suspect that the tons of pollutants emitted into the air and water by heavy industries located in Mobile County may be responsible for the higher-than-average incidence of cancer in the county.
Two recent health studies point out the difficult tasks of tracing cancer occurrences in Mobile County to their sources. Nonetheless, both studies sustain the suspicion that there might be a correlation between the emitted industrial pollutants that are known to be carcinogenic and the high cancer rates in Mobile County.
In January 1999, air samples were taken for three consecutive days in Prichard by the Environmental Protection Agency (EPA) to assess the concentration of Volatile Organic Compounds (VOCs). According to the report, "[T]he samples taken during this study indicate the wide-ranging presence of air pollutants in and around east Prichard, Alabama and area locations. Especially noteworthy is the presence of chlorinated hydrocarbons and aromatic hydrocarbons in all samples, including the control location. In addition to these compounds, aliphatic hydrocarbons, aldehydes and a few other miscellaneous compounds (isopropanol, carbon disulfide) were also detected." The report also stated that "In addition to the sampling results and analyses presented above, it is also important to note that the Cumulative Exposure Project data for areas in and around the City of Prichard indicate that chemicals other than VOCs may be present at levels of potential concern."
To assess health impact, the detected pollutants are compared to a benchmark called Risk-Based Concentration (RBC). Kenneth L. Mitchell, Ph.D., the EPA scientist who carried out the analysis of the Prichard air study, stated in the report that there are several obstacles to drawing a concrete connection between health hazard and the detected pollutants. "There are a number of detected chemicals for which the RBC table does not provide a health-based screening benchmark. This is usually due to the lack of toxicity information for these chemicals....Not assessing such detected chemicals...will tend to underestimate the potential public health threat presented by airborne pollutants." Another "caveat" to drawing definitive correlation is that "[T]he RBC health-based screening benchmarks for non-carcinogenic effects have traditionally been derived for adult-only exposures, rather than for children."
Furthermore, the report stated that "[A]cute exposure levels have been developed by several different organizations. However, there are no inhalation exposure values that were derived using a consistent basis to protect the general public from planned industrial emissions. Values designed for protection of the general public exist, but they are intended to address accidental releases and use methodologies that are often not reproducible."
Stephen W. Schaffer, Ph.D., professor of pharmacology at the University of South Alabama who teaches toxicology to medical students, said "chronic" exposure to low-level toxic pollutants is difficult to detect even though it may be just as serious as "acute" exposure. "Let's take the pesticides as an example," Schaffer said. "You have extremely toxic pesticides, such as some of the rodenticides. Because they are so toxic, there is little question what the cause of the toxicity is. On the other hand, the fungicides are not very toxic; they are designed to show low toxicity to plants and humans. Nonetheless, there is some evidence that some of them may cause birth defects and cancers."
"Another major source of toxicity in the area is heavy metal toxicity," Schaffer said. "While very high doses of some heavy metals can be lethal, lower doses have been linked to damage to the kidney, lungs, brain, heart and liver. These forms of toxicity are often slow developing and are difficult to distinguish from other causes."
While physicians receive training in recognizing toxicity, "usually they deal with acute toxicity. To recognize a chronic form of toxicity is not very easy."
Regarding air-borne pollutants, Schaffer said, "the frequency of respiratory cancer is very high along the Gulf Coast." While air pollution is capable of causing cancer, "it is difficult to quantify its contribution towards the high cancer rate," Schaffer added. "The reason for this is that the vast majority of respiratory cancers are caused by cigarette smoking."
To eliminate such lifestyle factors in assessing whether some localities in Mobile County experience higher than usual cancer mortality, Mark A. Moberg, Ph.D., professor of sociology and anthropology at the University of South Alabama, compared the recorded mortality rates by zip codes within Mobile County against statewide rather than U.S. averages. "The comparison of Mobile County cancer deaths with state averages may help to control for lifestyle factors," Moberg said, "for it is unlikely that behavioral contributors to cancer such as diet or smoking differ significantly between Mobile County and the rest of the state." Moberg, who received a grant from the National Science Foundation's cultural anthropology program in 1997 to study grassroots environmental justice and social movements in southern Alabama, said he was motivated to carry out the study because "residents of some neighborhoods expressed the belief that their localities experienced unusually high rates of cancer mortality. Community activists have speculated that many of these cancer deaths may have resulted from exposure to industrial pollution in some residential areas, especially those of north Mobile County."
Moberg used a procedure outlined by the epidemiologist Jay Gould, requesting data from the Alabama Department of Public Health on the number of deaths annually attributed to cancer for each of the zip codes in Mobile County between 1988 and 1996. "One of the limitations of the study is that the Department of Public Health classified all cancer deaths together, although some cancers are much more likely than others to have arisen from exposure to pollution," Moberg said. "Given the tendency of cancers to metastasize, the cancer recorded on a death certificate may not have been the malignancy that gave rise to it. Nor are death certificates an optimal source of data on cancer rates prevailing within a particular area. Obviously, residents seeking treatment or those whose cancer is in remission are omitted from these calculations."
Moberg noted that in Alabama as throughout the U.S., cancer death rates are typically higher for African Americans than for whites, are higher for males than females, and increase with age. "While the data control for ethnicity, age, and sex," Moberg said of his study, " they cannot completely eliminate the interplay of socioeconomic and behavioral variables, both of which influence cancer rates and mortality."
The Prichard Air Quality Study stated: "Many of the compounds that exceed a conservative health-based screening benchmark were also reported as released to air in 1996 by TRI (Toxic Release Inventory) facilities within 5 miles of Prichard (1996 date are the most recent from the TRI that are available)."
According to report, "[W]ith regard to those chemicals that exceeded a human health- based screening benchmark, all (with the exception of acetaldehyde), are either chlorinated hydrocarbons or aromatic or aliphatic hydrocarbons. The following is specifically noted:
1. Chloromethane, chloroform, carbon tetrachloride, benzene, 1,4-dichlorobenzene, and acetaldehyde all exceed a carcinogenic risk of 1x10-6 in at least one sample. Chloroform exceeded a carcinogenic risk of 1x10-6 in two samples (grab at Prichard City Hall and grab at Mobile County School).
2. Toluene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, naphthalene, and bexane all exceeded a hazard quotient of 0.1 in at least one sample. 1,2,4-trimethylbenzene exceeded a hazard quotient of 0.1 in two samples (Vigor High School and Prichard City Hall)."
The report added that "If the concentrations found in this study are representative of ambient air and long-term exposures to such air occurs, adverse health outcomes such as cancer and non-cancer effects may be possible."
The Prichard Air Study report concluded that "[G]iven the frequency at which these chemicals were observed and that concentrations often exceed conservative health-based screening benchmarks, this limited sample event provides sufficient evidence that additional study of the area's air quality may be warranted. Specifically, the scope of the current study is insufficient to fully evaluate the impact of Prichard air quality on public health; nonetheless, the study does provide adequate evidence that a potential threat to public health may exist."
Moberg said his review of Alabama Department of Public Health data shows that there were 7,203 recorded deaths between 1988-1996 in Mobile, compared with 7,002 expected deaths. Moberg said the distribution of cancer deaths tend to be quite uneven, with recorded deaths in some zip codes falling well below state averages -- see Table.
"Yet this analysis bears out the claim that cancer death rates are much higher than state averages in some residential areas located near industrial zones," Moberg added. "In the zip codes of Axis, 36505, and an adjacent area of north Mobile County, 36521, eighty cancer deaths were recorded between 1988 and 1996 from a combined population of 1,358. This mortality rate is nearly four times higher than what would have been expected given the demographic composition of the area. Although the population of the Axis zip code itself is quite small, just 127 in 1990, sixteen deaths from cancer were recorded there over the nine-year period covered by the study. This is five times greater than the mortality that would be expected for the zip code's population."
While there are limitations of the study, Moberg said "the data demonstrate that cancer mortality in the most heavily industrialized area of Mobile County is substantially higher than state averages, suggesting a public-health concern that urgently demands further investigation."
In an interview published in the August, 1999 issue of Mobile Bay Monthly, Mobile Bay Watch Board Member Michael Meshad, M.D., told the magazine that he sees "more young patients with cancers than most other places in the country," including breast cancer, colon cancer, lymphoma, and sarcoma.
Recognizing the inherent difficulty of pinpointing the causes of higher cancer rates in Mobile County, Dr. Meshad said the state has started a statewide tumor registry that is now two years old. Previously, individual hospitals compiled their own data. "If we're waiting to prove that these [industrial] emissions are contributing to a rise in malignant disease, that will never happen to everyone's satisfaction," Dr. Meshad told Mobile Bay Monthly. "I don't have any hopes that combining the data will turn up anything to convince anybody that we have a problem. But look at the EPA statistics and see how Mobile ranks. We're the worst in the U.S. in a lot of categories. And we seem to have a large number of young people with cancer."
|Zip Code||1990 Population||Expected Deaths||Recorded Deaths|
|Total (all zip codes)||7,002.1||7,203|
Source: Dr. Mark Moberg, based on data provided by Alabama Department of Public Health