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Daniel Hryhorczuk,^1,2,3 Victoria Persky,² Julie Piorkowski,² Jennifer Davis,⁴ C. Michael Moomey,⁴ Anne Krantz,^1,2,3 Ken D. Runkle,⁴ Tiffanie Saxer,⁴ Thomas Baughman,⁴ and Ken McCann⁴

¹Great Lakes Center for Children's Environmental Health, John H. Stroger Jr. Hospital of Cook County, Chicago, Illinois, USA; ²University of Illinois-Chicago School of Public Health, Chicago, Illinois, USA; ³Toxikon Consortium, Chicago, Illinois, USA; ⁴Division of Environmental Health, Illinois Department of Public Health, Springfield, Illinois, USA

Abstract
Many older homes are equipped with mercury-containing gas regulators that reduce the pressure of natural gas in the mains to the low pressure used in home gas piping. Removal of these regulators can result in elemental mercury spills inside the home. In the summer of 2000, mercury spills were discovered in the basements of several Chicago-area homes after removal of gas regulators by gas company contractors. Subsequent inspections of approximately 361,000 homes by two northern Illinois gas companies showed that 1,363 homes had residential mercury contamination. Urine mercury screening was offered to concerned residents, and results of urine bioassays and indoor mercury air measurements were available for 171 homes. Six of these 171 homes (3.5%) had a cumulative total of nine residents with a urine mercury ≥ 10 µg/L. The highest urine mercury concentration observed in a resident was 26 µg/L. Positive bioassays were most strongly associated with mercury air concentrations > 10 µg/m³ on the first floor [odds ratio (OR) = 21.4 ; 95% confidence interval (CI) , 3.6-125.9] rather than in the basement (OR = 3.0 ; 95% CI, 0.3-26) , and first-floor air samples were more predictive of positive bioassays than were basement samples. Overall, the risk of residential mercury contamination after gas regulator removal ranged from 0.9/1,000 to 4.3/1,000 homes, depending on the gas company, although the risk was considerably higher (20 of 120 homes, 16.7%) for one of the contractors performing removal work for one of the gas companies. Gas companies, their contractors, and residents should be aware of these risks and should take appropriate actions to prevent these spills from occurring and remediate them if they occur. Key words: elemental mercury, environmental, gas regulator, public health, residential, screening, surveillance. Environ Health Perspect 114:848-852 (2006) . doi:10.1289/ehp.8401 available via http://dx.doi.org/ [Online 27 February 2006]

Address correspondence to D. Hryhorczuk, Great Lakes Center for Children's Environmental Health, John H. Stroger Jr. Hospital of Cook County, 1900 W. Polk St., Room 500, Chicago, IL 60612 USA. Telephone: (312) 864-5520. Fax: (312) 413-7369. E-mail: dhryhorc@uic.edu

We acknowledge the public health contributions of the members of the Chicago Mercury Task Force partners, led by the Office of the Illinois Attorney General, and including the Illinois Department of Public Health, Illinois Environmental Protection Agency, U.S. Environmental Protection Agency (EPA) , the Agency for Toxic Substances and Disease Registry (ATSDR) , the Cook County Health Department, the Chicago Department of Environment, the Illinois Commerce Commission, and the Illinois Poison Center. We also thank the National Center for Environmental Health for its advice and consultation.

This work was funded in part by the Association of Occupational and Environmental Clinics through cooperative agreements U50/ATU300014 and U50/ATU374312 with the ATSDR to fund pediatric environmental health specialty units. The cooperative agreements include funds from the U.S. EPA.

The authors declare they have no competing financial interests.

Received 13 June 2005 ; accepted 27 February 2006.