The prevalent groundwater toxin in areas around Palo Alto's Stanford Research Park and Mountain View's northern region received new recognition as a health hazard by federal officials. On Nov. 3, the U.S. Department of Health and Human Services announced it is adding trichloroethylene (TCE) to a list of known carcinogens in the department's biannual report on cancer-causing hazards.
The news comes as no big surprise. Federal health officials, for about 15 years, have warned that TCE could reasonably be linked to various forms of cancer. Since then about 20 epidemiological studies have shown a connection between TCE and various forms of cancer in mice, including kidney cancer and lymphoma, leading medical authorities to now reclassify it as a known carcinogen, said Dr. Linda Birnbaum, director of the National Institute of Environmental Health Sciences, which helps compile the carcinogen report.
"There's been concern about TCE and other solvents for a long time," Birnbaum said. "It takes a lot of analysis and a lot of review of the literature to compile this report."
The substance, an industrial solvent and degreaser, was heavily used on U.S. military bases and during the heyday of Silicon Valley's semiconductor industry. Tens of thousands of gallons of TCE were dumped into the ground and made their way into the groundwater in Santa Clara County before the chemical's hazards to public health were fully acknowledged.
Based on the new classification, a number of new regulations could be coming down the pipeline for TCE management, Birnbaum said. The White House is looking into further Environmental Protection Agency (EPA) limitations on TCE use in industrial degreasing and in dry-cleaning businesses. Data sheets for employee safety in handling toxic materials could also be updated, she said.
While the connection between TCE and cancer is now considered firm, the chemical's connection to other diseases remains less clear. Asked about a potential link between TCE and neurological degenerative diseases such as ALS, Birnbaum pointed to a 2014 study of the U.S. Marine Corps base Camp Lejeune in North Carolina, believed to have the largest TCE contamination in the country. The study tracked about 9,000 deaths at the base and found a higher hazard rate for ALS, but it was considered nonsignificant since it was based on small numbers, making it impossible to pin down separate effects, Birnbaum said. The link between TCE and various forms of cancer was far more evident.
TCE is among the most prevalent hazardous substances in the U.S., and it is found in at least 1,045 of the nation's Superfund sites, according to the Agency for Toxic Substances and Disease Registry. TCE is considered carcinogenic to humans by all routes of exposure, according to the EPA's 2011 health assessment report.