Study: Cases Of Uncommon Liver Disease More Prevalent Around Toxic Waste Sites In New York City
According to a new study, exposure to toxins from hazardous waste sites may be a significant risk factor for developing primary biliary cirrhosis (PBC), a disease that slowly destroys the bile ducts in the liver.
Published in the March 2006 issue of Hepatology, researchers found significant clusters of the disease near Superfund toxic waste sites (SFS) and that the majority of patients in New York City who need liver transplants because of PBC, reside near state-designated Superfund sites. Hepatology is published on behalf of the American Association for the Study of Liver Diseases by John Wiley & Sons Inc.
PBC is an uncommon liver disease of unknown cause, though it reportedly appears in geographic clusters. Researchers, led by Aftab Ala, MD, of Mount Sinai School of Medicine in New York City, examined the prevalence and potential clustering of PBC near New York City's most toxic waste sites, which are state-designated Superfund sites.
The researchers collected zip code data on 172 patients in New York City in need of orthotopic liver transplant (OLT) between 1995 and 2003 due to either PBC or primary sclerosing cholangitis (PSC), a disease in which the bile ducts inside and outside the liver become inflamed and scarred. They compared the patients' zip codes to zip codes of known SFS in the city. Of the city's 174 zip codes, 89 included or bordered Superfund sites and 85 did not.
The researchers then calculated the expected prevalence of PBC-OLT and PSC-OLT, adjusting for demographic characteristics. They compared the mean standardized prevalence ratios in zip codes containing or adjacent to a SFS to the remaining zip codes. Lastly, they used SaTScanTM, a statistical software package, to detect specific clusters.
"The prevalence ratio of PBC-OLT, not PSC-OLT, was significantly higher in zip codes containing or adjacent to (Superfund sites)," the authors report. The standardized prevalence ratio of PBC-OLT cases near SFS was statistically significantly higher than in zip codes that did not have, nor border with, a toxic site. Meanwhile, the standardized prevalence ratio of PSC-OLT cases near SFS was not statistically different from zip codes without a toxic site nearby. The density of SFS and the prevalence ratio of PBC-OLT were both highest in the borough of Staten Island, while Manhattan had the lowest values for both.
The cluster-detection software uncovered five clusters of PBC-OLT. One was on Staten Island, two were in Brooklyn and two in Queens. Superfund sites near these clusters were contaminated by volatile organic compounds, like benzene and toluene, and chlorinated hydrocarbons, like trichloroethylene and tetrachloroethylene. The cluster on Staten Island was statistically significant, and located near a Superfund site contaminated with volatile aromatic hydrocarbons and trichloroethylene.
"This is the first epidemiological study to show a statistically significant clustering of PBC patients near known sources of environmental toxins and one of relatively few studies linking proximity to SFS to a specific disease," the authors write.
Though the exact mechanism by which proximity to toxins may increase PBC patient exposure is not clear, the authors suggest inhalation is the likely method. Still, confounding factors may play a role, such as socioeconomics that influence where people live, the researchers said.
"Our observations further support the hypothesis that environmental toxin exposure is a risk factor for PBC," the authors conclude. They urge researchers in other locations to further investigate the association.
Additional information on the research, as published in Hepatology, is available online at http://www.interscience.wiley.com/journal/hepatology (Increased prevalence of primary biliary cirrhosis near superfund toxic waste sites).
Additional information on primary biliary cirrhosis can be found at http://digestive.niddk.nih.gov/ddiseases/pubs/primarybiliarycirrhosis/index.htm.
Additional information on primary sclerosing cholangitis can be found at http://digestive.niddk.nih.gov/ddiseases/pubs/primarysclerosingcholangitis/index.htm.
This article originally appeared in the 03/01/2006 issue of Environmental Protection.