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WATER GREMLIN PUBLIC. HEALTH ASSESSMENT: PUSLIC C-QVI TENT DRAFT TCE Toxicity and Risk Assessment Risk assessment is a science -based tool that is used to -evaluate the potential effects of a chemical on human health. Riskassessment uses the best available scientific information, as well as professional judgment and policy, to estimate risks using standardized processes that allow estimates to be understood and compared, and..ultimately to help government agencies and the public mekeInformed- decisions about. preventing and reducing risks. To determine.a.safe-level of exposure to contaminants, scientists -frequently rely on animal.studies. In. these studies,ahlmals.fo. a laboratory (often rodents) are exposed to. large amounts of a chemical of interest. The amounts such anirnals-are. exposed to are converted to human equivalent concentrations; to account forthe differences between humans and animals In terms of size, weight,. and.respgnse.to chemical exposure. Because it is unclear how well short-term, high=exposure tests on animals predlet how people may respond to low levels of exposure over a longer period of time, scientists err on the side of caution. when determining a safe amount for people. This .is generally done by reducing the amounts shown*to cause an effect in study animals-bya.factor of*lato 6p.to3,000 when setting an amount intended to protect.people. Greater reductions are used when there is less certainty. This helps to increase confidence -that health effects wound be.extremely unlikely at the calculated safe amount, including among sensitive individuals such as children and pregnant women. The likelihood of health effects atthe.2018 modeled con centrations.(2=59 ltg/m3) is low: The potential effects of TCE exposure at these-concentration.s are an increased: riskV certain cancers (kidney, and possibly liver and non -Hodgkin's lymphoma), non -cancer effects to the immu ne-system. a.nd kidney, and a risk of Heart defects during fetal development. The risk:assessment basis and eVidericefor these. potential effects are described below.. Non -Cancer Effects In 2011, the'.U.S. -EPA: d eve loped a Safe inhalation value of 2 µg/m3 for a lifetime of exposure,.l�sed.on a review of*a lame number of studlesV animals and. hum ans exposed to TCE (U.S. EPA, 2011). MDH also conducted. a TCE review in.2013 and 201.8 and concurred with EPN9 inhalation value and the conclusions from their 2011 assessment, which -resulted in the M D H HBV of 2 µg/rtA. MDH afSo developeda•short- term HBV of 2*ltg/m3 thait.1s protective ofa24-hour exposure for pregnant -women in their first eight weeks of pregnancy. EPA concluded that at.a sufficient dose and exposure duration, TCE poses a potential human health hazard forloxlcityto the central nervous system, kidney, liver, immune system, male reproductive .system, and deve loping EPA narrowed down the studies to those considered critical effects — those showing effects at the -lowest levels —to develop a safe level that is protective-ofthei most sensitive health effects. The main effects observed at the lowest exposures involved:the.immune system, the developing fetus, and the kidneys. EPA reviewed all published studies available and chose two critical rodent situdles and -one supporting study as the basis for calculaflrio the safe Inhalation value. The selected studies are described below. • One critical study showed.ao-increased risk of.subtle Impattslo:the immune system,-the1hymus (a specialized organ of the. immune system) weighed less than normal and there was an�increase in markers -associated with autolmmune disease :after mice were exposed to TCE in drinking water: ■ Effect level.finding A small risk of immune:system effects may exist for people exposed.to TCE at -200. µg/m3 continuously over a. long time period. 12