title: Human health risk assessment of air emissions from development of unconventional natural gas resources.
abstract: BACKGROUND
  Technological advances (e.g. directional drilling, hydraulic fracturing), have led to increases in unconventional natural gas development (NGD), raising questions about health impacts.
  
  
  OBJECTIVE
  We estimated health risks for exposures to air emissions from a NGD project in Garfield County, Colorado with the objective of supporting risk prevention recommendations in a health impact assessment (HIA).
  
  
  METHODS
  We used EPA guidance to estimate chronic and subchronic non-cancer hazard indices and cancer risks from exposure to hydrocarbons for two populations: (1) residents living >½ mile from wells and (2) residents living ≤ ½ mile from wells.
  
  
  RESULTS
  Residents living ≤ ½ mile from wells are at greater risk for health effects from NGD than are residents living >½ mile from wells. Subchronic exposures to air pollutants during well completion activities present the greatest potential for health effects. The subchronic non-cancer hazard index (HI) of 5 for residents ≤ ½ mile from wells was driven primarily by exposure to trimethylbenzenes, xylenes, and aliphatic hydrocarbons. Chronic HIs were 1 and 0.4. for residents ≤ ½ mile from wells and >½ mile from wells, respectively. Cumulative cancer risks were 10 in a million and 6 in a million for residents living ≤ ½ mile and >½ mile from wells, respectively, with benzene as the major contributor to the risk.
  
  
  CONCLUSIONS
  Risk assessment can be used in HIAs to direct health risk prevention strategies. Risk management approaches should focus on reducing exposures to emissions during well completions. These preliminary results indicate that health effects resulting from air emissions during unconventional NGD warrant further study. Prospective studies should focus on health effects associated with air pollution.
authors.affiliation: Colorado School of Public Health, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045, USA. lisa.mckenzie@ucdenver.edu
authors.forename: Lisa M
authors.initials: LM
authors.lastname: McKenzie
authors.forename: Roxana Z
authors.initials: RZ
authors.lastname: Witter
authors.forename: Lee S
authors.initials: LS
authors.lastname: Newman
authors.forename: John L
authors.initials: JL
authors.lastname: Adgate
mesh_terms: D000393:Air Pollutants / Q000032:analysis / Q000633:toxicity*; D000397:Air Pollution / Q000009:adverse effects* / Q000032:analysis / Q000517:prevention & control*; D003120:Colorado / Q000453:epidemiology; D004781:Environmental Exposure; D004784:Environmental Monitoring; D062665:Epidemiological Monitoring; D006801:Humans; D006838:Hydrocarbons / Q000032:analysis / Q000633:toxicity*; D059206:Natural Gas / Q000032:analysis / Q000633:toxicity*; D009369:Neoplasms / Q000139:chemically induced / Q000453:epidemiology*; D011634:Public Health; D018570:Risk Assessment
chemical_list: D000393:Air Pollutants; D006838:Hydrocarbons; D059206:Natural Gas