Perchlorate is a primary ingredient in solid rocket propellant and has been used for decades by DOD, NASA, and the defense industry in the manufacturing, testing, and firing of rockets and missiles. On the basis of 1998 manufacturer data, EPA estimated that 90 percent of the perchlorate produced in the United States is manufactured for use by the military and NASA. Total typical production quantities average several million pounds per year. Private industry has used perchlorate to manufacture products such as fireworks, flares, automobile airbags, and commercial explosives. Perchlorate is a salt, both manufactured and naturally occurring, and is easily dissolved and transported in water. It has been found in drinking water, groundwater, surface water, and soil across the country. There is no national primary drinking water regulation for perchlorate. In 1992 and again in 1995, EPA established a provisional reference dose range for perchlorate of 0.0001 to 0.0005 milligrams per kilogram of body weight per day. This converts to a drinking water concentration of between 4 and 18 parts per billion. On the basis of the drinking water conversion, EPA identified a corresponding provisional cleanup level for perchlorate of between 4 and 18 parts per billion. Perchlorate was initially identified as a contaminant of concern by EPA in 1985, when it was found in wells at hazardous waste sites in California. Perchlorate became a chemical of regulatory concern in 1997 after California found perchlorate in the groundwater near Aerojet, a rocket manufacturer in Rancho Cordova. At the time, perchlorate could not reliably be detected below 400 parts per billion in water. In April 1997, a new analytical method capable of detecting perchlorate in drinking water at concentrations of 4 parts per billion became available. This development prompted several states to test drinking water, as well as groundwater and surface water, for perchlorate. Within 2 years, perchlorate had been detected in drinking water in 3 western states and groundwater and surface water in 11 states across the United States. Perchlorate in drinking water is considered a more immediate concern. In light of emerging concerns about perchlorate, EPA published in 1998 its first draft risk assessment on the environmental risks of perchlorate exposure. In February 1999, an external panel of independent scientists reviewed EPA’s draft risk assessment and recommended additional studies and analyses to provide more data on perchlorate and its health effects. DOD and industry researchers conducted laboratory and field studies of the health effects of perchlorate and submitted them to EPA. On the basis of an analysis of these studies, EPA revised its draft perchlorate risk assessment and released it for peer review and public comment in January 2002. The revised draft risk assessment included a proposed reference dose equivalent to a concentration of 1 part per billion in drinking water, if it is assumed all exposure comes only from drinking water. After a second panel peer review, and some disagreement about the proposed reference dose, EPA, DOD, NASA, and the Department of Energy asked NAS, in 2003, to review EPA’s perchlorate risk assessment and key studies of the health effects of perchlorate. These and other recent health studies have shown that the consumption of perchlorate affects the human thyroid by decreasing the amount of iodine absorbed. Iodine deficiency can result in developmental delays if it occurs during pregnancy and early infancy and can result in hypothyroidism if it occurs during adulthood. The purpose of the NAS study was, in part, to assess the extent to which studies have shown negative health effects from perchlorate. In January 2005, NAS reported that existing studies did not support a clear link between perchlorate exposure and developmental effects, and NAS recommended additional research on perchlorate exposure and its effect on children and pregnant women. NAS also recommended a safe exposure level, or reference dose, for perchlorate of 0.0007 milligrams per kilogram of body weight per day. (For comparison, EPA’s draft reference dose for perchlorate in its 2002 draft risk assessment, which equated to a drinking water concentration of 1 part per billion, was based on a daily dose of 0.00003 milligrams per kilogram of body weight per day.) According to NAS, the reference dose is conservative and includes safeguards to protect the most sensitive population, the fetus of the nearly iodine-deficient pregnant woman. In February 2005, EPA established a new reference dose for perchlorate on the basis of the NAS recommendation. The new reference dose is equivalent to 24.5 parts per billion in drinking water, assuming that an adult weighing 70 kilograms (or 154 pounds) consumes 2 liters of drinking water per day, and that all perchlorate ingested comes from drinking water. If EPA establishes a drinking water standard for perchlorate, however, it may be less than 24.5 parts per billion because humans may consume perchlorate from other sources, such as produce and milk. In addition to studies of perchlorate and health effects, other federal agencies, research groups, and universities have conducted or are conducting studies of perchlorate found in food and the environment. For example, the U.S. Geological Survey collected soil samples from California and New Mexico to test for the presence of perchlorate in natural minerals and materials. In 2003, an environmental research group reported that it sampled lettuce purchased in northern California and found perchlorate above 30 parts per billion in 4 of 22 samples. In September 2003, researchers from Texas Tech University sampled 8 bottles of milk and 1 can of evaporated milk and found perchlorate concentrations up to 6 parts per billion in seven of the milk samples and more than 1 part per billion in the evaporated milk sample. In 2004, the Food and Drug Administration sampled the following items for perchlorate: lettuce, bottled water, milk, tomatoes, carrots, cantaloupe, and spinach. Produce samples were taken from areas where officials said they believed irrigation water contained perchlorate. These data are currently being evaluated, but preliminary results show perchlorate was found in some samples. Method 314.0 is the EPA-approved method for analyzing perchlorate in drinking water under the Safe Drinking Water Act. Method 314.0 can detect perchlorate concentrations of 1 part per billion in finished (treated) drinking water but has a minimum reporting limit of 4 parts per billion. Both EPA and DOD officials have expressed concerns about using Method 314.0 to test for perchlorate in media other than drinking water, such as groundwater, surface water, and soil (where researchers mix soil with a liquid to extract the sample). According to EPA, sediment and dissolved ions commonly found in groundwater and surface water can yield false positive results if the method is not used properly. Analysis methods other than Method 314.0 are available, and EPA has approved their use to analyze specific sites for perchlorate. Further, two new methods have been developed for the analysis of perchlorate in drinking water, and another is expected to be available in the spring of 2005. These three methods have minimum reporting limits ranging from 0.02 to 0.1 parts per billion. However, Method 314.0 has been the principal method used to test and report on the presence of perchlorate in all media, including soil, sediment, groundwater, and surface water. Various treatment technologies to remove perchlorate from groundwater and surface water are in use or under review. Biological treatment and ion exchange systems are among the technologies currently in use. Biological treatment uses microbes to destroy perchlorate by converting the perchlorate ion to nontoxic ions, oxygen, and chloride. Ion exchange systems replace the perchlorate ion with chloride, which is an ion found in table salt. Several federal environmental laws provide EPA, and states authorized by EPA, with broad authorities to respond to actual or threatened releases of substances that may endanger public health or the environment. For example, the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), as amended, authorizes EPA to investigate the release of any hazardous substance, pollutant, or contaminant. The Resource Conservation and Recovery Act of 1976 (RCRA) gives EPA authority to order a cleanup of hazardous waste when there is an imminent and substantial endangerment to public health or the environment, and one federal court has ruled that perchlorate is a hazardous waste under RCRA. The Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) provisions authorize EPA, which may, in turn, authorize states, to regulate the discharge of pollutants into waters of the United States. These pollutants may include contaminants such as perchlorate. The Safe Drinking Water Act authorizes EPA to respond to actual or threatened releases of contaminants into public water systems or underground sources of drinking water, regardless of whether the contaminant is regulated or unregulated, where there is an imminent and substantial endangerment to health and the appropriate state and local governments have not taken appropriate actions. Under certain environmental laws such as RCRA, EPA can authorize states to implement the requirements as long as the state programs are at least equivalent to the federal program and provide for adequate enforcement. A detailed summary of these and other laws and regulations is presented in appendix IV. In addition, some states have their own environmental and water quality laws that provide state and local agencies with the authority to monitor, sample, and require cleanup of various hazardous substances, both regulated and unregulated, that pose an imminent and substantial danger to public health. For example, the California Water Code authorizes Regional Water Control Boards to require sampling of waste discharges and to direct cleanup and abatement, if necessary, of any threat to water, which may include the release of a contaminant such as perchlorate. DOD’s September 2003 interim policy on perchlorate sampling states that the military services shall sample for perchlorate where service officials suspect the presence of perchlorate on the basis of prior or current DOD activities, and where a complete human exposure pathway is likely to exist. The policy also states that the services shall sample for perchlorate (1) as required by the Safe Drinking Water Act’s Unregulated Contaminant Monitoring Regulation and the Clean Water Act’s NPDES program and (2) as part of cleanup conducted under DOD’s Environmental Restoration Program. While DOD’s policy requires it to sample where the two conditions of release and exposure are met, it does not specify whether the services may sample for perchlorate when requested by state agencies or EPA, apart from requirements under environmental laws and regulations. Further, except for at a few sites,DOD has not independently directed the services to clean up perchlorate. We previously reported that DOD has cleaned up perchlorate when directed to do so by EPA or a state environmental agency under various environmental laws, or when perchlorate is found on closed ranges. Various federal and state agencies have reported finding perchlorate at almost 400 sites in 35 states, the District of Columbia, and 2 commonwealths of the United States in drinking water, surface water, groundwater, and soil. Perchlorate was found at a variety of sites including public water systems, private wells, military installations, commercial manufacturers, and residential areas. The concentration levels reported ranged from 4 parts per billion to more than 3.7 million parts per billion in groundwater at 1 site, yet roughly two-thirds of sites had concentration levels at or below 18 parts per billion, the upper limit of EPA’s provisional cleanup guidance for perchlorate. Federal and state agencies are not required to routinely report perchlorate findings to EPA, and EPA does not currently have a formal process to centrally track or monitor perchlorate detections or the status of a cleanup. As a result, a greater number of sites may exist in the United States than is presented in this report. Through discussions with federal and state environmental agency officials and a review of perchlorate sampling reports, we identified 395 sites in the United States and its commonwealths where perchlorate was found in drinking water, groundwater, surface water, sediment, or soil. A table of reported perchlorate detections in the United States and its commonwealths as of January 2005 is presented in appendix II. Most of the sites and the highest levels of perchlorate were found in a small number of states. More than one-half of all sites, or 224, was found in Texas and California, where both states have conducted broad investigations to determine the extent of perchlorate. The highest perchlorate concentrations were found in 5 states—Arkansas, California, Nevada, Texas, and Utah—where 11 sites had concentrations exceeding 500,000 parts per billion. However, the majority of the 395 sites had lower levels of perchlorate. We found 249 sites where the highest concentration was equal to or less than 18 parts per billion, the upper limit of EPA’s provisional cleanup level, and 271 sites where the highest concentration was less than 24.5 parts per billion, the drinking water concentration equivalent calculated on the basis of EPA’s newly established reference dose (see fig. 1). According to EPA and state agency officials, perchlorate found at 110 of the sites was due to activities related to defense and aerospace, such as propellant manufacturing, rocket motor research and test firing, or explosives disposal. At 58 sites, officials said the source of the perchlorate found was manufacturing and handling, agriculture, and a variety of commercial activities such as fireworks and flare manufacturing (see fig. 2). At the remaining 227 sites, EPA and state agency officials said the source of the perchlorate found was either undetermined or naturally occurring. Further, all 105 sites with naturally occurring perchlorate are located in the Texas high plains region where perchlorate concentrations range from 4 to 59 parts per billion. and 2003 under the Safe Drinking Water Act’s Unregulated Contaminant Monitoring Regulation, 3,722 public drinking water systems had sampled drinking water and reported the results to EPA. Of these public drinking water systems, 153, or about 4 percent, reported finding perchlorate. Located across 26 states and 2 commonwealths, these 153 sites accounted for more than one-third of the sites we identified, where perchlorate concentrations reported ranged from 4 parts per billion to 420 parts per billion and averaged less than 10 parts per billion. Only 14 of the 153 public drinking water systems had concentration levels above 24.5 parts per billion, the drinking water equivalent calculated on the basis of EPA’s revised perchlorate reference dose. California had the most public water systems with perchlorate, where 58 systems reported finding perchlorate in drinking water. The highest drinking water perchlorate concentration of 420 parts per billion was found in Puerto Rico in 2002. Subsequent sampling in Puerto Rico did not find any perchlorate, and officials said the source of the initial finding was undetermined. Because of the proximity of these 153 public water systems to populated areas, an EPA official estimated that about 10 million people may have been exposed to perchlorate through their drinking water. EPA officials told us that they do not know the source of most of the perchlorate found in public water systems, but that perchlorate found in 32 water systems in Arizona, California, and Nevada was likely due to previous perchlorate manufacturing in Nevada. Regional EPA and state officials told us they did not plan to clean up perchlorate found at public drinking water sites pending a decision to establish a drinking water standard for perchlorate. In some cases, officials did not plan to clean up because subsequent sampling was unable to confirm that perchlorate was present. EPA officials said the agency does not centrally track or monitor perchlorate detections, or the status of cleanup activities, other than under the Safe Drinking Water Act where EPA collected data from public water systems for 1 year. As a result, it is difficult to determine the extent of perchlorate in the United States. EPA maintains a listing of sites known to EPA where cleanup or other response actions are under way, but the list does not include all sites because some sites have not been reported to EPA. As a result, EPA officials said they did not always know whether other federal and state agencies found perchlorate because, as is generally the case with unregulated contaminants, there is no requirement for states or other federal agencies to routinely report perchlorate findings to EPA. For example, except as required under specific environmental programs, DOD is not required to report to EPA when perchlorate is found on active installations and facilities. Consequently, EPA region officials in California said they did not know that the Department of the Navy found perchlorate at the Naval Air Weapons Station at China Lake. Further, even where EPA has authorized states to implement the RCRA program, states are not required to routinely notify EPA about perchlorate found under the program. For example, EPA region officials in California said the Nevada state agency did not tell them perchlorate was found at Rocketdyne, an aerospace facility in Reno, or that it was being cleaned up. EPA only learned about the perchlorate finding when the facility’s RCRA permit was renewed. We also found that communication and data sharing between EPA and state agency officials varied. Because states are not required to routinely notify EPA about perchlorate, some EPA region officials told us they contacted state agencies to ask whether new sites had been found. Some EPA region and state officials told us they participated in monthly or quarterly meetings to discuss perchlorate, and most EPA and state officials told us they had good working relationships and shared information about perchlorate. Yet a few EPA region officials told us they did not always know whether states found perchlorate, at what levels, or what actions were taken. For example, an EPA region official told us he did not know what actions were taken at three RCRA sites in Utah where perchlorate was found. Although there is no federal standard for perchlorate in drinking water or a federal cleanup standard, EPA and state environmental agencies authorized by EPA have investigated suspected sites; collected samples and analyzed for perchlorate; and, when perchlorate is found, cleaned up or limited perchlorate releases under broad authorities found in various federal environmental laws and regulations. Further, both EPA and authorized states have required responsible parties to sample and clean up perchlorate under other state laws. Most responsible parties sampled and cleaned up when required by regulation or directed by EPA or states. DOD sampled and cleaned up on the basis of its interpretation of federal and state legal requirements and its own policy. Of the 395 sites where perchlorate has been found, EPA or state environmental officials told us cleanup is under way or planned at 51 of them. We found EPA and state environmental agencies have investigated, sampled, and cleaned up perchlorate, or have required sampling and cleanup, pursuant to general authorities contained in various federal and state environmental laws and regulations. According to EPA and state agency officials, state agencies have also established levels for sampling and cleanup, and some state environmental laws provide that other authorities are to respond to contaminant releases, including perchlorate. Both EPA and state environmental agencies have used federal environmental laws, such as CERCLA, RCRA, and the NPDES provisions of the Clean Water Act, as authority to respond to releases of substances that may endanger public health or the environment, including perchlorate. EPA and the states have used such authority to sample and clean up as well as require the sampling and cleanup of perchlorate. For example: As part of a CERCLA review, EPA sampled groundwater near former government-owned grain storage facilities in Iowa and found perchlorate in residential and commercial drinking water wells at three sites. During subsequent sampling, EPA did not find perchlorate at two of the sites but confirmed perchlorate at the third site. EPA is providing bottled drinking water to certain persons until an uncontaminated drinking water supply becomes available. During sampling required as part of a RCRA permit, ATK Thiokol, a Utah explosives and rocket fuel manufacturer, found perchlorate. Under authority provided by RCRA, Utah required the manufacturer to install a monitoring well to determine the extent of perchlorate and take steps to prevent additional perchlorate releases. Under the NPDES program, Texas required the Navy to reduce perchlorate levels in wastewater discharges at the McGregor Naval Weapons Industrial Reserve Plant to 4 parts per billion, the lowest level at which perchlorate could be detected. According to EPA and state officials, EPA and state environmental agencies have investigated and sampled groundwater and surface water areas for perchlorate, or requested that responsible parties or others do so, pursuant to agency oversight responsibilities to protect water quality and human health. For example: EPA plans to sample five waste disposal sites in Niagara Falls, New York, to determine whether the groundwater contains perchlorate from manufacturing that took place in the area between 1908 and 1975. EPA asked Patrick Air Force Base and the Cape Canaveral Air Force Station, Florida, to sample groundwater for perchlorate near rocket launch sites. Previously, both installations inventoried areas where perchlorate was suspected and conducted limited sampling. DOD officials did not find perchlorate at Patrick Air Force Base, and, according to an EPA official, the Department of the Air Force said it would not conduct additional sampling at either installation until there is a federal standard for perchlorate. Between 1998 and 2002, Utah sampled public drinking water systems considered at risk for the presence of perchlorate because of nearby perchlorate use and found perchlorate concentrations at more than 42 parts per billion in three wells at two sites. Texas contracted with Texas Tech University to sample drinking water wells for perchlorate in 54 counties after perchlorate was found in five public water systems in the high plains region of the state. The university study found perchlorate in some drinking water wells and concluded that the most likely source was natural occurrence. When perchlorate was found, according to state and EPA officials, state agencies have taken steps to minimize human exposure or perform cleanup, or required responsible parties to do so, pursuant to the same general authorities contained in federal environmental laws and regulations. For example: Nevada is requiring Pepcon, a former perchlorate manufacturing site, to install a cleanup system to remove perchlorate from groundwater. Massachusetts closed a public well and provided bottled drinking water to students at a nearby school when perchlorate was found in a city public water system. At the request of California, United Technologies, a large rocket testing facility in Santa Clara County, stopped releasing perchlorate and cleaned up perchlorate found in the groundwater. Without a federal standard for perchlorate, according to EPA and state officials, at least nine states have established nonregulatory action levels or advisories for perchlorate ranging from under 1 part per billion to 18 parts per billion. States that have sampled, or required responsible parties to sample, report, and clean up, have used these advisories as the levels at which action must be taken. For example: Oregon initiates in-depth site studies to determine the cause and extent of perchlorate when concentrations of 18 parts per billion or greater are found. Nevada required the Kerr-McGee Chemical site in Henderson to treat groundwater and reduce perchlorate concentration releases to 18 parts per billion, which is Nevada’s action level for perchlorate. According to Utah officials, Utah does not have a written action level for perchlorate, but, if perchlorate concentrations exceed 18 parts per billion, the state may require the responsible party to clean up. Finally, in addition to state laws enacted to allow states to assume responsibility for enforcing federal environmental laws, other state environmental laws provide authority to respond to contaminant releases, including perchlorate. For example, EPA and state officials told us that both California and Nevada state agencies have required cleanup at some sites under state water quality laws. According to EPA and state officials, private industry and public water suppliers have generally complied with regulations requiring sampling, such as those under (1) the RCRA and NPDES permit programs, where responsible parties have been required to sample and report hazardous releases to state environmental agencies, or (2) the Safe Drinking Water Act’s Unregulated Contaminant Monitoring Regulation, which required sampling for unregulated contaminants, such as perchlorate, between 2001 and 2003. Further, according to EPA and state officials, private industry has generally responded by reducing perchlorate and cleaning up when required by regulation or directed by EPA or state agencies. DOD’s perchlorate sampling policy requires the military services to sample where the particular installation must do so, under laws or regulations such as the Clean Water Act’s NPDES permit program, or where a reasonable basis exists to suspect that a perchlorate release has occurred as a result of DOD activities and that a complete human exposure pathway is likely to exist. However, DOD’s policy on perchlorate sampling does not address cleanup. We found DOD has sampled for perchlorate on closed installations when requested by EPA or a state agency and cleaned up on active and closed installations when required by a specific environmental law, regulation, or program, such as the environmental restoration program at formerly used defense sites. For example, at EPA’s request, the U.S. Army Corps of Engineers (Corps) installed monitoring wells and is sampling for perchlorate at Camp Bonneville, a closed installation near Vancouver, Washington. Utah state officials told us DOD is removing soil containing perchlorate at the former Wendover Air Force Base in Utah, where the Corps found perchlorate in 2004. According to EPA and state officials, DOD has been reluctant to (1) sample on or near active installations because there is no specific federal regulatory standard for perchlorate or (2) sample where DOD determined the criteria to sample were not met as outlined in its policy. Except where there is a legal requirement to sample at a particular installation, DOD’s perchlorate policy does not require sampling unless the two conditions of release and exposure are met. Utah state officials told us the agency asked the Department of the Army to sample for perchlorate at two active installations, Dugway Proving Grounds and Deseret Chemical Depot. Previously, in 1998, the Army reported that perchlorate had been used at Dugway for more than 20 years. According to state agency officials, the Army said there was not a clear potential for human exposure to perchlorate at these sites, and it would not sample unless a higher Army level approved the sampling. In February 2005, Utah officials told us Dugway Proving Grounds had not requested permission from Army headquarters to sample, and they did not know whether Deseret requested permission to sample. In fiscal years 2004 and 2005, several provisions to federal law were enacted that encourage DOD to conduct health studies and evaluate perchlorate found at military sites. For example, the Ronald W. Reagan National Defense Authorization Act for Fiscal Year 2005 states that the Secretary of Defense should develop a plan for cleaning up perchlorate resulting from DOD activities, when the perchlorate poses a health hazard, and continue evaluating identified sites. In October 2004, DOD and California agreed to a procedure for prioritizing perchlorate sampling at DOD facilities in California. The procedure includes steps to identify and prioritize the investigation of areas on active installations and military sites (1) where the presence of perchlorate is likely based on previous and current defense-related activities and (2) near drinking water sources where perchlorate was found. Although DOD has been urged by Congress to evaluate sites where the presence of perchlorate is suspected, DOD’s September 2003 perchlorate policy continues to require sampling on active installations only where there is a suspected release due to DOD activities and a likely human exposure pathway, or where required under specific laws, such as the Clean Water Act. EPA, state agencies, and responsible parties are cleaning or planning to clean up at 51 of the 395 sites we identified. At 23 sites, EPA, states, and responsible parties are cleaning up or working to reduce perchlorate releases. For example, EPA required several defense, petroleum, and other companies to clean up perchlorate in Baldwin Park, California, a CERCLA site. The cleanup involves extracting and treating up to 26 million gallons of water per day, after which the water is distributed to several nearby communities. Texas required Longhorn Army Ammunition Plant, a closed DOD facility, to clean up by limiting perchlorate releases to a daily average concentration of 4 parts per billion (and a maximum of 13 parts per billion per day) under the NPDES program. Kerr-McGee Chemical, a former perchlorate manufacturer in Nevada, is cleaning up using an ion exchange system. According to officials, Nevada required the facility to clean up perchlorate under a state water law after perchlorate concentrations up to 3.7 million parts per billion were found in the groundwater. At 28 sites, EPA and state agency officials told us that federal and state governments and private parties are evaluating the extent of perchlorate and potential cleanup methodologies. Unidynamics, an Arizona propellant manufacturer located at a CERCLA site, responded to EPA’s concern about perchlorate at the site and is investigating perchlorate treatment methods. According to officials, after Kansas asked Slurry Explosives to clean up perchlorate under a state environmental law, the manufacturer began investigating a biological method to clean up. The remaining 344 sites are not being cleaned up for a variety of reasons. The reason most often cited by EPA and state officials was that they were waiting for a federal requirement to do so. In some instances, officials said they would not clean up sites where perchlorate was naturally occurring or where subsequent sampling was unable to find perchlorate. Since 1998, EPA and DOD have sponsored a number of studies of the health risks of perchlorate using experimental, field study, and data analysis methods. We reviewed 90 of these studies and found that 44 offered conclusions or observations on whether perchlorate had a health effect. Of these, 26 studies found that perchlorate had an adverse effect. However, in some of these studies, it was unknown whether the observed adverse effects would be reversible over time. In January 2005, NAS issued its report on EPA’s draft health assessment and the potential health effects of perchlorate. The NAS report considered many of the same health risk studies that we reviewed and concluded that an exposure level higher than initially recommended by EPA may not adversely affect a healthy adult, but recommended more study of the effects of perchlorate on pregnant women and children. DOD, industry, and EPA sponsored the majority of the 90 health studies we reviewed; the remaining studies were conducted by academic researchers and other federal agencies. Of these 90 studies, 49 used an experimental design methodology to determine the effects of perchlorate on humans, mammals, fish, and/or amphibians by exposing these groups to differing dose amounts of perchlorate over varied periods of time and comparing the results with other groups that were not exposed. Twelve were field studies that compared humans, mammals, fish, and/or amphibians in areas known to be contaminated with the same groups in areas known to be uncontaminated. Both methodologies have limitations; that is, the experimental studies were generally short in duration, and the field studies were generally limited by the researchers’ inability to control whether, how much, or how long the population in the contaminated areas was exposed. Finally, 29 studies used a data analysis methodology where researchers reviewed several publicly available human and animal studies and used data derived from these studies to determine the process by which perchlorate affects the human thyroid and the highest exposure levels that did not adversely affect humans. The 3 remaining studies used another or unknown methodology. Appendix III provides data on these studies, including who sponsored them; what methodologies were used; and, where presented, the author’s conclusions or findings on the effects of perchlorate. Many of the studies we reviewed contained only research findings, not conclusions or observations, on the health effects of perchlorate. Only 44 studies had conclusions on whether perchlorate had an adverse effect. Of these, 29 studies evaluated the effect of perchlorate on development, and 18 found adverse effects resulting from maternal exposure to perchlorate. Adverse effects of perchlorate on the adult thyroid are difficult to evaluate because they may happen over longer time periods than can be observed in a research study. However, the adverse effects of perchlorate on development can be more easily studied and measured within study time frames. Moreover, we found different studies used the same perchlorate dose amount but observed different effects. The different effects were attributed to variables such as the study design type or age of the subjects, but the precise cause of the difference is unresolved. Such unresolved questions are one of the bases for the differing conclusions in EPA, DOD, and academic studies on perchlorate dose amounts and effects. According to EPA officials, the most sensitive population for perchlorate exposure is the fetus of a pregnant woman who is also nearly iodine-deficient. However, none of the 90 studies we reviewed considered this population. Some studies reviewed pregnant rat populations and the effect on the thyroid, but we did not find any studies that considered perchlorate’s effect on nearly iodine-deficient pregnant populations and the thyroid. In January 2005, NAS issued its report on EPA’s draft health assessment and the potential health effects of perchlorate. NAS reported that although perchlorate affects thyroid functioning, there was not enough evidence to show that perchlorate causes adverse effects at the levels found in most environmental samples. Most of the studies NAS reviewed were field studies, the report said, which are limited because they cannot control whether, how much, or how long a population in a contaminated area is exposed. NAS concluded that the studies did not support a clear link between perchlorate exposure and changes in the thyroid function in newborns and hypothyroidism or thyroid cancer in adults. In its report, NAS noted that only 1 study examined the relationship between perchlorate exposure and adverse effects on children, and that no studies investigated the relationship between perchlorate exposure and adverse effects on vulnerable groups, such as low-birth-weight infants. NAS concluded that an exposure level higher than initially recommended by EPA may not adversely affect a healthy adult. The report did not recommend a drinking water standard; however, it did recommend that additional research be conducted on perchlorate exposure and its effect on children and pregnant women. Perchlorate has been found in the groundwater, surface water, drinking water, or soil in 35 states, the District of Columbia, and 2 commonwealths of the United States where concentrations reported ranged from 4 parts per billion to millions of parts per billion. According to EPA and state environmental agency officials, a leading known cause of the perchlorate found was defense-related activities. In addition, EPA and state officials attributed the cause of the perchlorate found at more than one-half of sites to natural occurrence or undetermined sources. State and other federal agencies do not always report perchlorate detections to EPA, however, because EPA, other federal agencies, and the states do not have a standardized approach for reporting perchlorate data nationwide. As a result, a greater number of sites with perchlorate may already exist. Further, EPA does not track the status of cleanup at sites where perchlorate has been found. Without a formal system to track and monitor perchlorate findings and cleanup activities, EPA and the states do not have the most current and complete accounting of perchlorate as an emerging contaminant of concern, including the extent of perchlorate found and the extent or effectiveness of cleanup projects. In order to ensure that EPA has reliable information on perchlorate and the status of cleanup efforts, and to better coordinate lessons learned between federal agencies and states on investigating and cleaning up perchlorate, we recommend that, in coordination with states and other federal agencies, EPA use existing authorities or seek additional authority, if necessary, to establish a formal structure to centrally track and monitor perchlorate detections and the status of cleanup efforts across the federal government and state agencies. In its April 26, 2005, letter (see app. V), EPA agreed with our findings and conclusions on the extent of perchlorate in the United States and that defense-related activities have been found to be associated with perchlorate detections. However, EPA did not agree with our recommendation that it establish a formal structure to centrally track and monitor perchlorate detections and the status of cleanup efforts across the federal government and state agencies. In its letter, EPA stated that it already had significant information and data on perchlorate concentrations in various environmental media, where much of the information was provided by other federal and state agencies as well as private parties. EPA also asserted that the development and maintenance of a new tracking system would require additional resources or the redirection of resources from other activities. To justify a tracking system, EPA would have to analyze its associated costs and benefits. As our report explains, however, state and other federal agencies do not always report perchlorate detections to EPA. Further, without a formal system to track and monitor perchlorate findings and cleanup activities, EPA does not have the most current and complete accounting of perchlorate as an emerging contaminant of concern. To underscore our point, in commenting on a draft of this report, DOD provided a listing of four sites where it found perchlorate between 2000 and 2004. These sites were not in EPA’s database. (We added these sites to our listing in app. II.) With regard to the cost benefit aspect of EPA’s comments, we believe that EPA is misconstruing the extent of work necessary to implement a more formalized and structured system to track perchlorate. We are not proposing an elaborate new system but, instead, believe that EPA needs to work toward a more structured process than what is currently in place to track and monitor perchlorate routinely. Currently, EPA’s regions are spending time and effort contacting their counterparts in other federal agencies and states on an ad hoc basis to obtain more current information about perchlorate. However, this is being done without any structure or consistency related to how and when contacts are made, how frequently they are made, or what specific information is collected. As a result, we found that EPA does not have complete, current, or accurate information to track the occurrence of perchlorate—the type of information that would be needed when making a determination about the need for regulation. We continue to believe that such information is necessary and that it can be obtained without an elaborate or costly undertaking. In contrast to EPA’s view of our report’s accuracy, DOD said in its April 26, 2005, letter (see app. VI), that our report did not provide an accurate assessment of perchlorate issues and activities. DOD asserted that our report mischaracterized DOD’s response to perchlorate and cited examples of where DOD has sampled and invested in cleanup technologies, even though perchlorate is currently unregulated. We disagree with DOD’s position. Our report credits DOD with actions it has taken but also points out where DOD has not acted. For example, our report acknowledges that DOD is sampling for perchlorate as required under various environmental laws, or when certain criteria exist as specified in DOD’s sampling policy; that is, where the presence of perchlorate is suspected based on prior or current DOD activities and a complete exposure pathway to humans is likely to exist. While DOD states that it has a policy that establishes an affirmative obligation to sample and not a limitation, that view is not shared by some regulators. As we point out in our report, there have been a number of instances where EPA or state agencies asked the services to sample but service officials declined because they did not believe the conditions met with DOD’s sampling policy. As such, DOD has used its policy to limit testing for perchlorate that environmental regulators believed was necessary. With regard to DOD’s point that perchlorate is unregulated, we are well aware that many other contaminants, like perchlorate, are not specifically regulated, yet are being addressed and cleaned up as hazards under various environmental laws. DOD also stated that we did not accurately summarize the findings of the NAS study and other scientific and technical data. We believe our report accurately summarizes key information from both NAS as well as 90 other studies of the potential health risks of perchlorate, as specified by the requester of this report. Finally, DOD disagreed with our recommendation that EPA establish a more formal structure to centrally track and monitor perchlorate because it was not clear that such a system will provide added value. DOD stated that it will continue to share its information on perchlorate. As previously noted, in commenting on this report, DOD provided information on four locations where perchlorate has been found, in one case as long as 5 years ago, and which do not appear on EPA’s list of perchlorate detection sites. Whether this omission occurred as a result of a DOD or an EPA oversight is unknown, but it underscores the need for a more structured and formalized system. Both EPA and DOD provided technical comments as enclosures to their letters, which we incorporated in our report as appropriate. As agreed with your office, unless you publicly announce the contents of this report earlier, we plan no further distribution until 30 days from the report date. At that time, we will send copies of this report to the appropriate congressional committees; the Administrator, Environmental Protection Agency; the Secretary of Defense; and other interested parties. We will also provide copies to others upon request. In addition, the report will be available, at no charge, on the GAO Web site at http://www.gao.gov. If you or your staff have any questions, please call me or Edward Zadjura at (202) 512-3841. Contributors to this report are listed in appendix VII. We identified (1) the estimated extent of perchlorate nationwide; (2) what actions the federal government, state governments, and responsible parties have taken to clean up or eliminate the source of perchlorate found; and (3) what studies of the potential health risks from perchlorate have been conducted and, where presented, the author’s conclusions or findings on the health effects of perchlorate. To provide an estimate of the extent of perchlorate in the United States, we compiled and analyzed data on perchlorate detections from the Environmental Protection Agency (EPA), the Department of Defense (DOD), the U.S. Geological Survey, and state agencies. For each site, our review shows the highest perchlorate concentration reported for all media sampled as of January 2005, although officials may have sampled the site more than once, in varying locations and media, and found differing levels of perchlorate. We also interviewed officials from EPA headquarters and regional offices, DOD, and selected state agencies to determine the accuracy and completeness of our compiled list of perchlorate detections. To identify what actions the government and private sector have taken to address perchlorate and the extent to which responsible parties have taken action to clean up and eliminate the source of perchlorate, we reviewed federal and state laws, regulations, and policies on water quality and environmental cleanup and interviewed EPA and state agency officials on their roles, responsibilities, and authorities to monitor and respond to instances of perchlorate found. We interviewed officials from EPA headquarters and each of its 10 regions. We also interviewed officials from state environmental agencies in California, Oregon, Texas, and Utah. We selected these states because they (1) had higher estimated numbers of sites where perchlorate was found and higher perchlorate concentration levels and/or (2) had taken steps to investigate and respond to perchlorate. During interviews with state agency officials, we discussed whether parties responsible for perchlorate had taken action to clean up and whether federal or local governments required that they stop activities causing the release of perchlorate. Finally, we reviewed and analyzed data from federal and state agencies to determine the status and extent of cleanup efforts. To identify studies of the potential health risks from perchlorate, we conducted a literature search for studies of perchlorate health risks published since 1998. We also interviewed DOD and EPA officials to obtain a list of the studies they considered important in assessing perchlorate health risks. We examined the references for each study so that we could include any other key studies that we had not obtained through the literature search and DOD and EPA interviews. We identified 125 studies of perchlorate and the thyroid but did not review 35 of these studies because they were not directly related to the effects of perchlorate on the thyroid. Our review of 90 studies included the title; the author and publication information; the sponsor or recipient; a description of the study subjects; the type of research design and controls; and, where presented, the author’s conclusions or findings about the adverse effects of perchlorate on health. We conducted our work from June 2004 to March 2005 in accordance with generally accepted government auditing standards, including an assessment of data reliability and internal controls. Anniston Army Depot, Calhoun County Atmore Utility Board, Escambia County Daphne Utilities Board, Baldwin County Fort McClellan, City of Anniston Mobile County Water and Fire Protection Authority, Mobile County Montgomery Water Works, Montgomery County Redstone Army Arsenal (NASA Marshall Space Flight Center) Amount (ppb) Amount (ppb) Amount (ppb) Royal Palm Beach Utilities, Palm Beach County Sebring Water and Sewer System, Highlands County Three Worlds Camp Resort, Polk County City of Watkinsville, Oconee County Feagin Mill, Houston County Iowa Army Ammunition Plant, Middletown Chanute Air Force Base, Rantoul City of Joliet, Will and Kendall Counties City of Rock Island, Rock Island County Sangamo Electric Dump/Crab Orchard National Wildlife Refuge, City of Carterville (Department of the Interior) Amount (ppb) City of Hagerstown, Washington County Fort George Meade, City of Odenton Naval Surface Warfare Center, Indian Head White Oak Federal Research Center (Naval Surface Warfare Center) City of Deming, Luna County Fort Wingate Depot, Gallup Holloman Air Force Base, Alamogordo Kirtland Air Force Base, Albuquerque Los Alamos National Laboratory, City of Los Alamos (Department of Energy) Melrose Air Force Bombing Range, City of Clovis Mountain View Albuquerque, City of South Valley New Mexico American Water Company, City of Clovis Sandia National Labs, City of Albuquerque (Department of Energy) Amount (ppb) Amount (ppb) Amount (ppb) Maple Water Service Company, Bailey County McClain private well, Midland County McGregor Naval Weapons Industrial Reserve Plant, McLennan County McMurries private well, Martin County Minnix private well, Midland County Mobile Home Park, Lubbock County Nelms private well, Midland County Nobels private well, Midland County North State Highway 115, Winkler County North University Estates, Lubbock County North West Yoakum, Yoakum County O'Brien private well, Dawson County Offield private well, Midland County Pantex Plant, City of Amarillo, Carson County (Department of Energy) Amount (ppb) Purdue Farms, Incorporated, Accomack County Camp Bonneville, City of Vancouver City of Puyallup, Pierce County Firgrove Mutual, Incorporated, Pierce County Lacey Water Department, Thurston County Lakewood Water District, Pierce County Allegheny Ballistics Lab, City of Rocket Center Parts per billion (ppb). Author’s findings/ conclusions about the adverse effects of perchlorate on health New diagnostic Not identified/ criteria (see Unknown. original study for experimental controls) Established incidence probabilities (see original study for experimental controls) Adverse effects indicated. New diagnostic Adverse effects criteria for indicated. reviewing data (see original study for experimental controls) Revised Analysis Crofton of the Thyroid Hormone Data from the Mouse Immunotoxicology Study (from Keil et al., 1999) Nonadverse effects indicated. No information available on adverse effects. Nonadverse effects indicated. Adverse effects to development indicated. Keil, et al. Dose, duration, Nonadverse age, sex, and weight (dose levels independently verified) effects indicated. Information on adverse effects is incomplete. Keil, et al. Dose, duration, Nonadverse age, sex, strain, effects indicated. and weight No adverse (dose levels effects indicated. independently verified) ManTech Environmental Technology, Inc. Dose, duration, Nonadverse and sex, and weight adverse effects indicated. ManTech Environmental Technology, Inc. Nonadverse effects and adverse developmental effects indicated. Author’s findings/ conclusions about the adverse effects of perchlorate on health Nonadverse effects and adverse developmental effects indicated. Bekkedal, et Department of Animal al. Defense developmental effects indicated. Adverse effects to development indicated. Protection Agency/ Original study: Perchlorate Study Group development indicated. Dose, duration, Adverse effects to and age development indicated. Adverse effects to development indicated. Adverse effects to development indicated. Effects not studied. Dose, duration, Adverse effects to and sex development indicated. No adverse developmental effects indicated. Nonadverse and adverse effects indicated. Nonadverse and adverse effects indicated. Nonadverse effects indicated. No information available on adverse effects. Nonadverse effects indicated. No information available on adverse effects. Nonadverse effects indicated. No information adverse effects. Analysis of Dose- Marcus Response Functions for Effects of Perchlorate on Serum Hormone from Data of Greer et al. (2000, 2002) and Merrill (2001a) Nonadverse effects indicated. No information available on adverse effects. Nonadverse effects indicated. Potential adverse developmental effects indicated. Anion Selectivity by Van Sande, Ministere de Cells the Sodium Iodide et al. Symporter la Politique Scientifique, and Fonds effects indicated. No information available on adverse effects. Not identified/ Not identified/ Review/ Unknown Unknown effects indicated. No information available on adverse effects. Effects not studied. Nonadverse effects indicated. No information available on adverse developmental effects. Effects not studied (model developed). Effects not studied (model developed). Effects not studied. Effects not studied (model developed). Effects not studied (model developed). Carr, et al. Nonadverse effects indicated. No adverse developmental effects indicated. Carr, et al. Adverse developmental effects indicated. Carr, et al. Adverse developmental effects indicated. Carr, et al. Adverse developmental effects indicated. Effects not studied (reference dose developed). Sharma, et Perchlorate al. Dose, repeated No adverse study, bacteria strain, and sex effects indicated. Dose, duration, Nonadverse and switched exposed/control No information litters with exposed/ control dams effects indicated. available on adverse developmental effects. Dose, duration, Nonadverse and switched exposed/ control litters with exposed/ control dams effects indicated. No information available on adverse developmental effects. Not identified/ Unknown. Nonadverse and adverse effects indicated. Findings not used--design limitations too great. No adverse effects indicated. Tsui, et al. Effects not studied. No nonadverse or adverse effects indicated. Author’s findings/ conclusions about the adverse effects of perchlorate on health Nonadverse effects indicated. No information available on adverse developmental effects. Nonadverse effects indicated. No information available on adverse developmental effects. No adverse effects indicated. York, et al. Nonadverse effects indicated. Adverse effects to development indicated. Author’s findings/ conclusions about the adverse effects of perchlorate on health Adverse effects indicated. Clewell, et al. Nonadverse effects indicated. No information available on adverse effects. Duration, dose, Nonadverse and and recovery adverse effects period indicated. York, et al. Nonadverse effects indicated. Adverse developmental effects indicated. York, et al. Nonadverse effects indicated. No adverse developmental effects indicated. York, et al. Nonadverse effects indicated. No adverse developmental effects indicated. No adverse developmental effects indicated. No adverse effects indicated. Effects not studied. Nonadverse effects indicated. No adverse effects indicated. Not identified/ No effects Unknown indicated. Baseline tests Nonadverse performed to ensure subjects No information had no prior available of thyroid adverse effects. problems effects indicated. Not identified/ Unknown. Clewell, et al. Dose, duration, Effects not and model controls studied (model developed). Clewell, et al. Dose, duration, Effects not and model controls studied (model developed). Dose, duration, Effects not and model controls studied (model developed). Dose, duration, Effects not and model controls studied (model developed). Yu, et al. Dose, duration, Nonadverse and model controls effects indicated. No information available on adverse effects. Effects not studied (reference dose developed). In Vitro Mammalian San and Cell Gene Mutation Clarke Test (L5178Y/TK Mouse Lymphoma Assay) No adverse effect indicated. Adverse effect on development indicated. Consultative Letter: Channel Kinetic Data for Iodide Uptake Inhibition in the Thyroid by Perchlorate (2- Week Drinking Water Study) No effects indicated. Effects not studied (model developed). Nonadverese effects indicated. Adverse effects to development indicated. Effects not studied (bechmark dose developed). Incidence rates, No adverse age, sex, race/ethnicity, population size, and demographic features effects indicated. Effects not studied. Adverse effects to development indicated. Dose and breeding pairs (analysis with paired groups and individual pups) Nonadverse effects indicated. Adverse effects to development indicated. Iodide Transport in Harrison, et Howard Xenopus Laevis al. Effects not studied. Nonadverse effects indicated. No information available on adverse developmental effects. The Resource Conservation and Recovery Act (RCRA) was enacted as an amendment to the Solid Waste Disposal Act to create a framework for the management of hazardous and nonhazardous solid waste. It authorizes EPA to control hazardous waste from the point where waste is generated through its transportation, treatment, storage, and disposal. EPA regulations define hazardous waste to include waste specifically listed in the regulation as well as those defined as “characteristic waste.” Characteristic hazardous waste is defined as waste that is ignitable, corrosive, reactive, or toxic. A federal district court in California ruled, in part, that perchlorate is a hazardous waste under RCRA because it is ignitable, under certain conditions. RCRA requires owners and operators of facilities that treat, store, and dispose of hazardous waste, including federal agencies, to obtain permits specifying how they will safely manage waste. Under RCRA’s corrective action provisions, facilities seeking or holding RCRA permits can be required to clean up their hazardous waste contamination. Under RCRA, EPA has the authority to order a cleanup of hazardous waste when there is an imminent and substantial endangerment to public health or the environment. EPA may authorize states to administer their own programs in lieu of the federal program, as long as these programs are equivalent to and consistent with the federal program and provide for adequate enforcement. Under RCRA, state agencies have required RCRA permit holders to sample for and report on perchlorate detections and prevent additional releases. The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund, governs the cleanup of releases or threatened releases of hazardous substances, pollutants, or contaminants. CERCLA’s definition of a hazardous substance includes substances regulated under various other environmental laws, including RCRA, the Clean Air Act, the Clean Water Act, and the Toxic Substances Control Act. Under section 120 of CERCLA, the federal government is subject to and must comply with CERCLA’s requirements to the same extent as any nongovernmental entity. CERCLA provides broad authority to EPA to respond to releases or threatened releases of hazardous substances or pollutants or contaminants that may endanger public health or the environment. Under these provisions, DOD has responded to perchlorate found on military installations and facilities. CERCLA establishes prohibitions and requirements for contaminated sites; provides for the liability for hazardous substances at these sites; and provides for the use of the Hazardous Substances Superfund, a trust fund to provide for cleanup, for example, when a responsible party cannot be identified. The law authorizes short-term removal—where actions may be taken to address releases or threatened releases requiring prompt response—and long-term response—where actions may be taken to permanently reduce the danger associated with a release. EPA identifies the most hazardous sites, those requiring long-term action, by listing them on the National Priorities List. The Clean Water Act authorizes EPA to regulate the discharge of pollutants into waters of the United States. EPA may authorize states to carry out a state program in lieu of the federal program if the state program meets the requirements of the Clean Water Act, including providing for adequate enforcement. The act defines a pollutant to include virtually all waste material. The act provides for the establishment of national discharge limitations, water quality standards, and a permit program and has provisions for addressing oil and toxic substance spills. Covered private parties as well as federal facilities must comply with the requirements of the act. According to EPA, since pollutants are defined broadly in the act to include most waste material, perchlorate would likely fall within this definition. Under the Clean Water Act’s National Pollution Discharge Elimination System (NPDES) program, facilities discharging pollutants into waters of the United States from point sources are required to obtain an NPDES permit from EPA or authorized states. NPDES permits include specific limits on the quantity of pollutants that may be discharged and require monitoring of those discharges to ensure compliance. Industrial, municipal, and other facilities must obtain permits to discharge specific pollutants if their discharges go directly to waters of the United States. Sites with NPDES permits are required to routinely sample and report to state regulatory agencies on the release of specified pollutants, which may include contaminants such as perchlorate. Under section 107 of the Federal Facility Compliance Act of 1992, EPA was required, in consultation with DOD and the states, to issue a rule identifying when military munitions become hazardous waste under RCRA and to provide for protective storage and transportation of that waste. Under the rule issued by EPA, used or fired military munitions become waste subject to RCRA regulation if, among other things, (1) they are transported off-range for waste management purposes or (2) they or their constituents are recovered, collected, and then disposed of by burial on or off a range. Unexploded, used, and fired military munitions are known sources of perchlorate. Under RCRA, as amended by the Federal Facility Compliance Act, EPA maintains that DOD installations may be required to sample and monitor off-range for perchlorate as well as other contaminants associated with military munitions where EPA has evidence that the contaminants are creating an imminent and substantial endangerment to health or the environment. The Safe Drinking Water Act authorizes EPA to issue national primary drinking water regulations setting maximum contaminant-level goals and maximum contaminant levels for drinking water that must be met by public water systems. EPA may authorize states to carry out primary enforcement authority for implementing the Safe Drinking Water Act if, among other things, the states adopt drinking water regulations that are no less stringent than the national primary drinking water regulations. EPA has set standards for approximately 90 contaminants in drinking water; however, most of the more than 200 chemical contaminants associated with munitions use, including perchlorate, are currently unregulated under the Safe Drinking Water Act. The 1996 amendments to the Safe Drinking Water Act required EPA to (1) establish criteria for a monitoring program for unregulated contaminants, where a maximum contamination level has not been established, and (2) publish a list of contaminants chosen from those not currently monitored by public water systems. EPA’s regulation, referred to as the Unregulated Contaminant Monitoring Regulation, was issued in 1999 and supplemented in 2000 and 2001. The purpose of the regulation was to determine whether a contaminant occurs at a frequency and in concentrations that warrant further analysis and research on its potential effects, and to possibly establish future drinking water regulations. The first step in the most recent program required public water systems serving more than 10,000 customers—and a sample of 800 small public water systems serving 10,000 or fewer customers—to monitor drinking water for perchlorate and 11 other unregulated contaminants over a consecutive 12-month period during 2001 and 2003 and to report the results to EPA. According to EPA, large public water systems provide drinking water to about 80 percent of the U.S. population served by public water systems. In addition to the individuals named above, John Delicath, Christine Frye, Alan Kasdan, Karen Keegan, Roderick Moore, Edith Ngwa, James Rose, and Rebecca Shea made key contributions to this report.

Summary: Perchlorate, a primary ingredient in propellant, has been used for decades in the manufacture and firing of rockets and missiles. Other uses include fireworks, flares, and explosives. Perchlorate has been found in drinking water, groundwater, surface water, and soil in the United States. The National Academy of Sciences (NAS) reviewed studies of perchlorate's health effects and reported in January 2005 that certain levels of exposure may not adversely affect healthy adults but recommended more studies be conducted on the effects of perchlorate exposure in children and pregnant women. GAO determined (1) the estimated extent of perchlorate in the United States, (2) what actions have been taken to address perchlorate, and (3) what studies of perchlorate's health risks have reported. Perchlorate contamination has been found in water and soil at almost 400 sites in the United States where concentration levels ranged from a minimum reporting level of 4 parts per billion to millions of parts per billion. More than one-half of all sites were in California and Texas, and sites in Arkansas, California, Texas, Nevada, and Utah had some of the highest concentration levels. Yet, most sites had lower levels of contamination; roughly two-thirds of sites had concentration levels at or below the Environmental Protection Agency's (EPA) provisional cleanup standard of 18 parts per billion. Federal and state agencies are not required to routinely report perchlorate findings to EPA, and EPA does not centrally track or monitor perchlorate detections or the status of cleanup. As a result, a greater number of contaminated sites than we reported may already exist. Although there is no specific federal requirement to clean up perchlorate, EPA and state agencies have used broad authorities under various environmental laws and regulations, as well as state laws and action levels, to sample and clean up and/or require the sampling and cleanup of perchlorate by responsible parties. Further, under certain federal and state environmental laws, private industry may be required to sample for contaminants, such as perchlorate. According to EPA and state officials, private industry and public water suppliers have generally complied with regulations requiring sampling and agency requests to sample. The Department of Defense (DOD) has sampled and cleaned up perchlorate in some locations when required by laws and regulations, but the department has been reluctant to sample on or near active installations under other circumstances. Except where there is a specific legal requirement, DOD's perchlorate sampling policy requires the services to sample only under certain conditions. Cleanup is planned or under way at 51 of the almost 400 perchlorate-contaminated sites identified to date. Since 1998, EPA and DOD have sponsored a number of perchlorate health risk studies using varying study methodologies. We reviewed 90 of these studies that generally examined whether and how perchlorate affected the thyroid. About one-quarter concluded that perchlorate had an adverse effect. In January 2005, NAS reported on the potential health effects of perchlorate and concluded that a total exposure level from all sources, higher than that initially recommended by EPA (a dose equivalent to 1 part per billion in drinking water, assuming that all exposure came from drinking water) may not adversely affect a healthy adult. On the basis of NAS' report, EPA revised its reference dose to a level that is equivalent to 24.5 parts per billion in drinking water (if it is assumed that all exposure comes only from drinking water). The reference dose is not a drinking water standard; it is a scientific estimate of the total daily exposure level from all sources that is not expected to cause adverse effects in humans, including the most sensitive populations.