Children’s Environmental Health in Michigan
Childhood Cancer: Solvents: Benzene and TCE
A variety of solvents, including benzene, carbon tetrachloride, methylene chloride, styrene, toluene, trichloroethylene (TCE), tetrachloroethylene (PCE), and xylene, have been linked to various types of cancer (Clapp et al. 2005). Occupational exposures to benzene, carbon tetrachloride, and TCE have been linked with an increased risk of cancer (Glass et al. 2003; Wilcosky et al. 1984; Scott and Chiu 2006). Of these chemicals, the strongest causal association between exposure and cancer development is for benzene, where relatively low levels of exposure have been linked to cancer (Smith et al. 2007; Mehlman 2006). A strong associated has also been established between parental occupational exposure to these solvents and an increased risk of childhood leukemia in their children. Limited data also exists that suggests a link between paternal exposure to solvents such as well paints and/or inks and an increased risk for central nervous system (CNS) or brain cancer among their children (Feychtinget al. 2001; Colt and Blair, 1995).
Direct exposure to organic solvents such as benzene, TCE, PCE, and styrene during childhood has also been associated with an increased risk for the development of cancer, specifically Non-Hodgkin’s Lymphoma (NHL). Numerous case-control studies have associated increased prevalence of NHL among children who live near railways, oil refineries, and petrochemical plants with an increased exposure to solvents, primarily benzene (Clapp et al. 2005; Fagliano et al. 2003). Furthermore, case control studies have demonstrated increased risks of NHL among children whose fathers had occupational exposures to solvents, indicating that germline cell (in this case, sperm) DNA mutations from solvent exposure may have the potential to cause cancer in one’s offspring (Clapp et al. 2005).
For childhood cancers, the solvents benzene and trichloroethylene are of particular concern, due to the increased risk of carcinogenesis they pose, their prevalence in industry, and their ability to persist in the environment (IARC 1987, IARC 1995, ATSDR 2003). The International Agency for Research on Cancer (IARC) has classified benzene as a Group 1 carcinogen (known human carcinogen) and TCE is classified as a Group 2A carcinogen (probable human carcinogen); the EPA has also classified benzene as a known human carcinogen (EPA 2008a) and acknowledges the evidence of TCE as a potential human carcinogen, although it has made no formal carcinogen classification of the latter (IARC 1995, EPA 2008b).
This section provides background information on the presence and potential health effects of these solvents and reviews existing Michigan policies related to regulating these solvents. Best policy practices from other states are highlighted and recommendations are provided to further protect Michigan’s children from exposure to these solvents.
Sources and Routes of Exposure
Solvents are a class of liquid organic chemicals that are generally used to dissolve or dilute materials that are otherwise insoluble in water. There are many different types of solvents, but most solvents are derived from petroleum. Solvents are widely used in industry and in households in paints, varnishes, lacquers, inks, aerosols, dyes, adhesives, fuels, and fuel additives (Bruckner, Warren 2001). Although most daily human exposure to solvents involves exposure to a complex mixture of chemicals, this section will focus on only two of the many common solvents for which we have the strongest data on possible links to cancer in childhood: benzene and 1,1,2-trichloroethylene (TCE).
Benzene, an aromatic hydrocarbon, was historically used as a general purpose solvent, but it is currently used primarily in the production of plastics, resins, and some synthetic and nylon fibers (Bruckner, Warren 2001; Clapp et al. 2005). Benzene is also used in the production of some types of rubbers, lubricants, dyes, detergents, drugs and pesticides (Clapp et al. 2005).
Benzene is found in crude oil and can be released during incomplete combustion of fossil fuels (Belsonet al. 2007; Clapp et al. 2005). In addition, benzene is added to gasoline to reduce knocking, and accounts for roughly 1-2% by volume of gasoline (Bruckner, Warren 2001). These sources (gasoline vapor and transportation exhaust) account for a large proportion of the benzene component of outdoor air contamination, and the majority of benzene exposure among nonsmokers (Bruckner and Warren 2001; EPA 2007; Wallace 1996). Benzene is found in cigarette smoke, and environmental tobacco smoke is a major source of indoor benzene exposure in places where indoor smoking occurs (Wallace 1996). Benzene is also added to some paints and hobby glues, which can also serve as important points of exposure. (Belson et al. 2007).
Like most solvents, the primary exposure route for benzene is via inhalation of contaminated air or vapors. Other possible exposure routes include dermal absorption after direct contact with substances containing benzene or ingestion of drinking water contaminated with benzene (Bruckner and Warren 2001).
Acute effects of high levels of benzene exposure, either through inhalation or consumption, can include dizziness, drowsiness, increased heart rate, confusion, headaches, and unconsciousness; rapid exposure to very high levels of benzene can result in death (Agency for Toxic Substances and Disease Registry, 2011; EPA 2000). Benzene has a well-documented association with cancer, and is classified as a Group A human carcinogen by the EPA (EPA 2000). Non-cancer chronic health effects of benzene exposure, which will not be discussed further in this section, may include blood disorders, impaired fertility in women, and low birth weight (EPA 2000).
Leaking underground storage tanks (USTs) may be a potential source
Relatively few epidemiologic studies concerning the association between leaking underground storage tanks and cancer have been conducted. Notably, researchers found an increased risk of leukemia in the affected area of a gasoline spill from a UST in Pennsylvania. This association suggests a possible association between long-term exposures to benzene in gasoline vapors from UST spills and the development of leukemia (Talbott et al. 2011).
Follow this link for a map of leaking underground storage tanks in Michigan: (http://circleofblue.org/LUST.html).