Impact/Purpose:

The CATS was a cooperative effort between the Chattanooga-Hamilton County Air Pollution Control Bureau (CHCAPCB) and the United States Environmental Protection Agency (USEPA) to evaluate the potential impact of air pollution on the health of Chattanooga area residents. By collecting air samples and applying the principles of risk assessment science, the partners hoped to better understand how exposures to airborne pollutants may be affecting the health of people in the area. CHCAPCB and USEPA worked with interested stakeholders throughout the process to develop supportable estimates of risk as well as attainable risk management goals and strategies.

The data for this project has been collected and stakeholders developed a risk assessment workplan that has estimates of risk as well as a risk management plan to respond to unacceptable risks identified.

Description:

The Chattanooga-Hamilton County Air Pollution Control Bureau (CHCAPCB), the United States Environmental Protection Agency Region 4 (Region 4), and other stakeholders, in a cooperative effort, conducted an air toxics study in the Chattanooga area (city population approximately 285,536). The primary objective of the study was to determine if residents of this area are exposed to airborne concentrations of air pollutants that may pose unacceptable risks to their health. According to the 1997 Toxics Release Inventory, for industrial facilities located in Hamilton County, there were approximately 2.7 million pounds of chemicals were released into the air by stack or fugitive emissions of which 823,000 pounds are known or potential carcinogens. Ambient air quality monitoring data was collected between November 12, 1998 and October 29, 1999. A total of seven monitors were deployed at six locations. Samples were collected each twelfth day, approximately 30 sampling events. The chemicals analyzed included: sixty-four (64) volatile organic chemicals; formaldehyde (which is a volatile organic chemical but is determined with its own analytical method); sixty-three (63) semi-volatile organic chemicals; and twenty (20) inorganic metals associated with airborne (suspended) particles. The results of this study were used to complete an assessment of the risk to the health of the population in the area. The two categories of chronic exposure were assessed in the risk assessment were central tendency exposure and reasonable maximum exposure. Health risk estimates were calculated for both cancer and non-cancer endpoints. Aggregate non-cancer health risk associated with all chemicals detected in air at each monitoring location, a total hazard index (HI) were initially calculated by summing the hazard quotients for each chemical detected. In the chronic non-cancer health risk assessment, the hazard quotient for the three individual chemicals were at or above a value of one at one or more locations based on reasonable maximum exposure (RME) parameters (manganese, formaldehyde, and cobalt). A hazard quotient greater than one indicates that exposure is higher than a presumed safe concentration and that adverse non-cancer health effects may occur. Total hazard indices (HIs), based on RME parameters, and calculated by summing the hazard quotient for individual chemicals at each sampling location, ranged from a value of two (2) to a value of three (3) for an adult and from a value of four (4) to a value of eight (8) for a child resident. In the assessment of incremental lifetime risks of cancer, estimated risks of cancer for the RME scenario were at or above a level of one excess case of cancer in one million people exposed (1 x 10-6) for a number of individual chemicals. Formaldehyde, chromium, chloroform, benzene, carbon tetrachloride, arsenic, chloromethane, and tetrachloroethylene each posed an incremental cancer risk of greater than 1 x 10-6 at each of the six monitoring locations. Further, benzo(a)pyrene, bromodicloromethane, 1,4-dichlorobenzene, trichloroethylene, benzo(b)fluoranthene, nickel, 1,1,2-trichloroethene, and hexachloro-1,3-butadiene each posed and incremental risk of cancer greater than 1 x 10-6 at one or more of the locations. Total RME incremental risks of cancer summed over all chemicals at the six locations ranged from 7 x 10-5 to 1 x 10-4 (for a 30 year exposure). Hazard quotients at or above a value of one (1) and incremental cancer risks at or above a value of 1 x 10-6 at each monitoring location are summarized in the Chattanooga Air Toxics Study Final Risk Assessment Report. To evaluate potential impacts of short-term acute exposure to airborne contaminants, sample data collected from the six monitoring locations were compared to selected acute screening level toxicity data. Of all the detected constituents at all sampling locations, no contaminant concentration exceeded an acute screening level criterion. Also, Region 4, in conjunction with CHCAPCB, and other stakeholders developed a Risk Management Plan (RMP). The RMP describes how stakeholders will respond to risk assessment results and explores alternatives to mitigate unacceptable risks from air toxics. The RMP was implemented by a Stakeholders Advisory Group (SAG) which was composed of representatives from industry, concerned citizens, and government agencies. In 2003, the SAG requested assistance and received from Region 4 a stationary source modeling analysis of possible sources of toxics metals found in the monitoring study. While the modeling results showed that local sources were the major contributors to the risks from air toxics, there was no one source that contributed an unreasonable amount to the concentrations. Since the initial monitoring study, of the four major sources of these toxic metals, one company has converted to low emission technology, one company has gone out of business, another company will have to comply with the Iron Foundries Maximum Achievable Control Technology (MACT), and the CHCAPCB plans on discussions with the final source not covered by the MACT to seek voluntary reductions. The monitoring study showed that mobile sources have the most significant emissions of air toxic pollutants. The SAG recognized and concluded that the mobile source program being implemented by the Environmental Protection Agency will over time reduce the air toxics from vehicles in the Chattanooga to saver levels. The SAG indicated that in the final report, due in the summer of 2004, it may recommend that Region 4 and the CHCAPCB revisit the air toxics issues in two to four years to determine if improvement in the air toxics levels have been made since the original monitoring study in1998-1999.

Record Details: