SACRAMENTO — Scientists studying 20 dumps in Southern California have concluded that ordinary landfills, intended for household trash but not hazardous waste, are sources of cancer-causing gases and other toxic chemicals, according to a South Coast Air Quality Management District report released Tuesday.
Researchers with the agency said ground inspections at 17 of the dumps turned up significant levels of one or both of two chemicals known to cause cancer in humans: benzene and vinyl chloride.
Vinyl chloride and benzene have long been found at dumps licensed to receive contaminated industrial wastes. The new study, financed under a $70,000 grant from the Environmental Protection Agency, was intended to determine whether similar problems exist at landfills that receive ordinary trash.
Many of the toxic substances found in gases trapped in landfills could have been the result of illegal dumping, the report said.
Required dumping records were variously described in the study as "too general" and as "useless" for tracing the sources of hazardous materials.
Although benzene, a widely used industrial chemical, is found in many common substances, including gasoline, the origin of the vinyl chloride at the sites puzzled the researchers. In their report, they contended that the most likely source is the breakdown of nontoxic materials buried in the landfills.
Margil W. Wadley, laboratory manager for the air quality district and one of the authors of the study, said there is increasing evidence that ordinary soil bacteria may create vinyl chloride and perhaps other toxic chemicals from nonhazardous materials.
Although the landfills have long been thought to be inactive, the new findings indicate that "underneath the surface, they are boiling like a kettle" and producing toxic substances, Wadley said.
"Landfills closed more than 20 years are still emitting vinyl chloride," he said.
Wadley said the results should be viewed cautiously. Exposure to methane, a natural gas found in garbage dumps, poses a more immediate danger to the public than the cancer-causing substances discussed in the report, he said.
The scientists tested for air contamination in residential areas adjoining five of the 20 sites: near the Scholl Canyon landfill in Glendale, Mountaingate in West Los Angeles, the city of Upland landfill, the city of Redlands landfill and the Calabasas landfill in Agoura.
Only the Scholl Canyon landfill produced enough vinyl chloride to be detected at nearby sampling stations. Although the amount was within the safety limit established by the state Air Resources Board in 1979, that standard may be deceptive because it was based not on health risks but on what could reliably be measured at that time.
The scientists who prepared the report pointed out that their samples were taken in the winter and spring, not during the summer, when stagnant air and warm weather would probably produce the highest concentrations of toxic gases.
"For years, the operators of these dumps have claimed that their sites were free of toxic waste," Assemblyman Charles M. Calderon (D-Alhambra) said Tuesday. "This study confirms that municipal landfills contain significant amounts of toxic waste."
A draft of the report, not yet released by the EPA, was made available by Calderon's office. The lawmaker is the author of legislation requiring extensive testing of dumps around the state for hazardous chemicals.