CATEGORY*: IARC probable carcinogen, NTP reasonably anticipated carcinogen
FOUND IN: Computer components, cleaning products, cosmetics, dry cleaning
THE GIST: Solvents used in the computer manufacturing industry (including toluene, methylene chloride and tricholoroethylene) have been shown to cause mammary tumors in laboratory animals and have been linked to breast cancer risk in human studies.
State of the Evidence on Organic Solvents Other Than Benzene
Industrial use of organic solvents has increased over the last several decades, particularly in the manufacture of computer components. Some solvents used in this industry (including toluene, methylene chloride and trichloroethylene) have been shown to cause mammary tumors in laboratory animals (Labreche, 1997). Such solvents are also used in other industries, such as manufacturing of cleaning products and cosmetics (EPA, 1996).
Organic solvents are lipophilic (fat-seeking) and accumulate in the fat tissue of the breast. They are also passed from mother to infant through breast-feeding (Wolff, 1983).
Several epidemiological studies have linked occupational exposures to organic solvents with increases in breast cancer incidence. Two studies showed an increased risk of breast cancer among workers exposed to chlorinated organic solvents in semiconductor plants (Chang, 2003; McElvenney, 2001). A Danish study showed that women ages 20 to 55 employed in solvent-using industries (fabricated metal, lumber, furniture, printing, chemical, textile and clothing) had double the risk of breast cancer of women employed outside these industries (Hansen, 1999). A 1995 U.S. study suggested an increased breast cancer risk associated with occupational exposure to styrene, as well as to several other organic solvents, including carbon tetrachloride and formaldehyde (Cantor, 1995). These results were validated by studies in Finland, Sweden and Italy (Belli, 1992; Walrath, 1985; Weiderpass, 1999; Wennborg, 1999). Occupational exposures of men to volatile organic solvents are also associated with increased incidence of breast cancer (Villineuve, 2010).
A 2014 study looking at the work histories of around 47,000 women whose sisters had breast cancer indicated that timing of exposure to solvents is key. Women in this study who started working with solvents before their first full-term birth had a greater risk for breast cancer (Ekenga, 2014).
Exposure of young (pre-pubertal) laboratory mice to mixtures of organic solvents similar to those found in an industrial setting induced dose-dependent increases in mammary tumors (Wang, 2002). Laboratory studies have shown that organic solvents are direct mutagens and carcinogens—that is, these chemicals and their breakdown products can exert effects on genes and cells, influencing the rates of gene mutation and altering cell processes in ways that increase the risk of cancer (Labreche, 1997).
*For chemicals that have been shown to be carcinogens, we provide classifications from two authoritative bodies: the International Agency for Research on Cancer (IARC, an international body) and the National Toxicology Program (NTP, a division of the U.S. Department of Health and Human Services). We have categorized endocrine-disrupting compounds where the body of peer-reviewed research indicates a strong foundation for doing so.