LIVER CANCER LINKED TO VINYL CHLORIDE CONTAMINATION AT NPL SITES IN MARYLAND AND DELAWARE

Of the 38 “final” National Priority List (NPL) sites in Maryland (MD) and Delaware (DE), 18 have vinyl chloride monomer (VCM) as a contaminant of concern, 13 in MD and 5 in DE¹. This contamination was from disposal of solvents and sludge containing VCM and other chlorinated hydrocarbons that degrade into VCM. These wastes were placed in permeable soils ca. 30 years ago, initiating leachate infiltration into regional aquifers.

VCM is ranked as a Category “A” carcinogen from epidemiological evidence gathered from polyvinyl chloride plastics plant studies, and supported by animal testing². The liver is the target organ. Chronic exposure to VCM (in drinking water) at concentrations of 0.24 to 0.48 micrograms per liter (ug/L) produces an excess cancer risk of one incident in 100 thousand residents. This concentration is significantly below the maximum contaminant level (MCL) for VCM (2 ug/L).

In this study using 2003-2007 data, the number of NPL sites having VCM contamination in each of these counties¹ was compared with the annual incidence of liver cancer per 100 thousand inhabitants³. In MD, Cecil County had the greatest number of sites (4) and the highest incidence of liver cancer, at 8.2 (per 10⁵ pop.). The state average was only 5.3 and the U.S. national average was 6.0. In DE, New Castle County had the greatest number of these sites (3) and had the highest yearly incidence of liver cancer at 6.1, with a state average of 5.5. Only Calvert County MD had an above average incidence of liver cancer (8.0), yet had no NPL sites. Data on VCM contamination in Calvert County is currently unknown.

Data plots of these comparisons using NPL sites from both states show a strong linear correlation (R = 0.8877). The NPL/VCM comparisons support the USEPA toxicological evidence linking VCM (toxicant) to liver cancer (adverse health effect). Although other contaminants (e.g., arsenic) and non-environmental factors can also cause liver cancer, this study underscores the potential danger of long-term ingestion of water from aquifers in areas that have VCM concentrations even at levels that meet drinking-water standards.

1/ USEPA, Region III, Mid-Atlantic Superfund, 2010; 2/ USEPA Integrated Risk Information System; 3/ Centers for Disease Control and Prevention, 95% confidence interval, age adjusted.