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Based on its review of numerous air quality studies, the Agency for Toxic Substances and Disease Registry (ATSDR) concludes that releases of air contaminants from the Eastern Michaud Flats (EMF) Superfund site near Pocatello, Idaho, poses a public health hazard. This hazard has existed since at least 1975 and will continue to exist in the future unless emissions from the two phosphate processing plants on the site--FMC Corporation and J.R. Simplot Company-- and from other sources are reduced. Important information on the nature and extent of this public health hazard follows:

  • What pollutants have reached hazardous levels? Many agencies and researchers have measured the levels of air pollution in the area near the EMF Superfund site. These studies have measured air concentrations of the pollutants that FMC and Simplot emit in the greatest quantities. Of these pollutants, only airborne particulate matter--or particles and aerosols in the air--and sulfates have reached levels that are known to be associated with adverse health effects among exposed populations. Whether considering total suspended particulates (TSP), fine and coarse particulates combined (PM10), or fine particulates (PM2.5), air concentrations of particulate matter near the site have reached, and continue to reach, elevated and potentially unhealthy levels, as described below; and short-term levels of sulfates have periodically reached concentrations of health concern. Emissions from FMC and Simplot account for a very large quantity of the airborne particulate matter and sulfates in the area, but other sources undoubtedly contribute to this problem as well.
  • ATSDR thoroughly reviewed the available data for acids, metals, and other pollutants released from FMC and Simplot, but none appear individually to have reached levels of health concern; however, there is uncertainty in this conclusion. Current science provides little evidence as to whether the mix of these air contaminants may increase or decrease their toxicological effects because of cumulative exposures. However, the epidemiological evidence does indicate that PM, a measure of a mix of contaminants present in air, including many of the acids and metals detected in the EMF study area, is a good surrogate measure for estimating the short-term and long-term adverse cardiopulmonary health effects from exposure. From this standpoint, ATSDR evaluated and made definitive public health statements regarding the cumulative health effects of the exposure to the mix of acid aerosols and particulate metal contaminants present in the EMF study area as measured by PM. To confirm the above finding for acids and metals, ATSDR recommends ongoing air sampling for these pollutants.

    Phosphine may have reached levels of health concern at the FMC fenceline. However, these levels of health concerns were obtained using unreliable methods. ATSDR recommends that more monitoring be performed to confirm these data.

  • How are airborne particulate matter and sulfates harmful? High levels of airborne particulate matter and sulfates, like those observed near the EMF site, are known to be associated with various health problems, such as asthma attacks, upper respiratory illnesses, and chronic bronchitis. Certain people are known to suffer from these pollution-related respiratory problems more so than others. These people include children, the elderly, smokers, people with heart disease, and people with asthma or other forms of lung disease.
  • It is impossible to predict, however, exactly how many people will develop these problems after being exposed to airborne particulate matter, because people are exposed to many respiratory irritants every day, such as cigarette smoke and indoor air contaminants. Though it is difficult to prove that air pollution is the main cause of any one health problem, ATSDR notes that the elevated incidence of certain respiratory problems among residents living in the EMF study area is reasonably consistent with exposures to unhealthy levels of airborne particulate matter and sulfates.

    Though exposure to particulate matter has not been shown conclusively to cause cancer, individual components of particulate matter may be carcinogenic. Based on a review of the limited data available on these components, ATSDR concludes that exposure to potentially carcinogenic heavy metals found in particulate matter in the EMF study area are not likely to result in an appreciable increased risk of carcinogenic health effects in the exposed population. However, this conclusion is limited by the fact that data on annual average concentrations for metals are not available for time periods before 1994, when levels of PM, and hence heavy metals, were notably higher. For some metals, the paucity of toxicological data and the lack of data on the exact chemical species found in the ambient air prevents a complete assessment of the public health implications of exposure.

  • Is air quality in the area generally getting better or worse? There is no single measurement that characterizes overall "air quality" for a region. A relevant indicator of air quality for the EMF study area, however, is levels of airborne particulate matter, the main contaminant of concern for this site. Based on a review of nearly 25 years of air sampling data in the Pocatello area, ATSDR has found that levels of particulate matter since 1994 (when averaged over the long term) are more than 30% lower than levels measured prior to that time. This decrease is most likely the effect of emissions controls that have been implemented on a wide range of sources throughout the EMF study area. Though this trend is certainly encouraging and suggests improving air quality, ATSDR also notes that potentially unhealthy levels of particulate matter continue to be frequently observed in some parts of the Fort Hall Indian Reservation and periodically observed in the cities of Chubbuck and Pocatello. The next two questions address this topic further. Note, the available sampling data are insufficient to determine whether levels of metals and inorganic aerosols in the area are increasing or decreasing.

  • In what parts of the Fort Hall Indian Reservation are air pollution levels hazardous? Air monitors have been operated on the Fort Hall Indian Reservation at locations directly across from the FMC facility for the last 3 years. These monitors consistently measure the highest concentrations of particulate matter in the entire area surrounding the EMF site--a trend suggesting that potentially hazardous levels of air pollution frequently occur on the Fort Hall Indian Reservation at locations between FMC and Interstate 86. Because levels of particulate matter are known to vary over short distances in this area, however, ATSDR is not certain whether unhealthy levels of air pollution occur at locations north of Interstate 86. ATSDR believes this is a critical data gap for this site and highly recommends that air monitors be placed at additional locations on the Fort Hall Indian Reservation, and near where people live, to determine the areas where unhealthy levels of air pollution occur.

  • In what parts of Chubbuck and Pocatello are air pollution levels hazardous? The air quality data indicate that episodes of potentially unhealthy air pollution have affected the entire cities of Chubbuck and Pocatello. These episodes are infrequent and are typically associated with inversions or stagnation conditions, which trap air pollution in the lowest levels of the atmosphere. The fact that the two cities are located in or at the mouth of a valley makes this situation worse, since the mountains prevent pollutants from dispersing. During past pollution episodes, which most often occur in the winter, airborne particulate matter has been measured at potentially unhealthy levels throughout the entire Portneuf Valley--from Idaho State University to Chubbuck School. Though no pollution episodes occurred between 1994 and 1998, the recent and severe episode in December 1999 shows that unhealthy levels of air pollution can still occur throughout Chubbuck and Pocatello. ATSDR believes these episodes will continue to occur in the future unless emissions sources of particulate matter at FMC and Simplot and elsewhere in the area are reduced.
  • Moreover, the ambient air monitoring data indicate that long-term average levels of particulate matter in much of Chubbuck and Pocatello reached potentially unhealthy levels between 1975 and 1993. These long-term levels were highest in areas closest to FMC and Simplot, and decreased with distance from the facilities.

  • What is being done about the air pollution in the area? State and federal environmental agencies, the Shoshone-Bannock Tribes, the Cities of Chubbuck and Pocatello, FMC, and Simplot have all made efforts to improve air quality near the EMF site and have plans to continue to improve air quality in the future. Most noteworthy are the efforts to control or eliminate the known sources of pollution, thus helping to prevent air quality problems from occurring in the first place. Additionally, state environmental officials have implemented a program that warns residents of potentially unhealthy levels of air pollution before they occur. ATSDR encourages residents to heed these warnings, which are typically broadcast by the media and recommend residents, especially persons with respiratory conditions, to remain indoors and to avoid moderate levels of exercise as much as possible when air quality is expected to be poor.

The remainder of this health consultation clarifies, defends, and expands upon, the general findings listed above. Moreover, the health consultation presents additional information (e.g., site descriptions, a list of community concerns, a review of air pollution studies) that ATSDR considered when evaluating health concerns for this site. As noted throughout this document, this health consultation does not consider potential exposures to airborne radionuclides--a topic that will be addressed in a future ATSDR health consultation. ATSDR also plans to conduct other public health actions at the EMF site. These actions include: evaluating cancer incidence; preparing a comprehensive public health assessment; continuing to implement health education and outreach activities, as needed; and, evaluating the feasibility of conducting an additional health study in the EMF study area.


The Agency for Toxic Substances and Disease Registry (ATSDR) prepared this health consultation to address community concerns regarding inhalation exposures to potentially unhealthy levels of air pollution near the Eastern Michaud Flats Contamination (EMF) National Priorities List (NPL) site. ATSDR previously evaluated potential exposures to site-related contaminants in its 1990 Preliminary Public Health Assessment (ATSDR 1990). Since then, a Remedial Investigation (RI) was conducted at the site, during which a large volume of environmental monitoring data was generated (Bechtel 1996). In 1997, ATSDR prepared a Site Review and Update, in which the Agency committed to reviewing the data released during the RI. This health consultation, therefore, presents ATSDR's re-evaluation of the inhalation exposure pathway, considering the most recent information available.

In preparing this health consultation, ATSDR is also responding to concerns that members of the Shoshone-Bannock Tribes have raised regarding the impacts of releases from the EMF site on air quality at the Fort Hall Indian Reservation. Among these concerns, the Shoshone-Bannock Tribes have specifically requested that ATSDR enhance the 1995 Fort Hall Air Emissions Study to determine the health effects of radionuclide emissions and to consider a broader geographic area than had been considered in the 1995 study (Sho-Ban 1996). In response to this request, ATSDR indicated that the air exposure pathways and the populations-at-risk need to be better defined in order to address the concerns of the tribe (ATSDR 1996). This health consultation begins the process of addressing the concerns of the Shoshone-Bannock Tribes by attempting to better define the past, current, and future air exposure pathways for nearby communities.

The Shoshone-Bannock Tribes have also expressed concerns regarding air exposures to workers at FMC, Simplot, an adjacent railroad area, and other contract workers at and near these facilities. ATSDR's official mandate, however, under the 1980 Superfund law, and as amended in 1986, focuses primarily on health issues related to the uncontrolled release of hazardous substances into the environment as it relates to community exposures. Except for very limited authority to examine health issues of workers who perform remediation tasks, ATSDR's mandate does not include the health of workers--an issue that is mainly the responsibility of the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH). These agencies can evaluate in much greater detail worker health issues at the EMF site (e.g., see sidebar).

This health consultation is one of many documents that ATSDR has prepared, or has committed to prepare, for the EMF site. In October, 1998, ATSDR released health consultations that addressed the potential for past, present, and future human exposures to site-related contaminants in the groundwater, surface water and sediment, and surface soil (ATSDR 1998a; 1998b; 1998c). This health consultation supplements the previous documents by focusing strictly on site-related contaminants in ambient air. ATSDR currently plans to address the inhalation exposure pathway in two separate health consultations: the first health consultation (i.e., this health consultation) addresses all site-related contaminants other than radionuclides, and a later health consultation will address only radionuclides. ATSDR also plans to evaluate the incidence of cancer in the Pocatello area and in Fort Hall in a later health consultation. Combined, the 1998 health consultations, this health consultation, and the future health consultations on radionuclides and cancer incidence, will provide the basis for a comprehensive assessment of public health issues associated with the EMF site.

Overall, therefore, the purpose of this health consultation is to obtain and review existing data relevant to air quality issues for the EMF site and to comment on the public health implications of these data. Moreover, the health consultation recommends specific actions that need to be taken to fill notable data gaps and also provides a description of the public health actions taken or planned in relation to the site.


Before reading ATSDR's analyses of public health issues for the EMF site, it is important to understand the specific health concerns raised by community members, the operating histories of the FMC and Simplot phosphate processing plants, and the land use and demographics in the EMF study area. The following discussion reviews these topics.

A. Statement of Issues

The FMC Corporation (FMC) and J.R. Simplot Company (Simplot) operate phosphate processing plants that are located on what the U.S. Environmental Protection Agency (EPA) has designated the EMF NPL site. Members of the Shoshone-Bannock Tribes and residents of Chubbuck and Pocatello have expressed concern regarding the occurrence of asthma and upper respiratory infections in their communities. Some community members believe these health effects are related to exposure to air pollutants emanating from FMC and Simplot. The Shoshone-Bannock Tribes have expressed additional health concerns, including concerns regarding congenital heart problems, heart problems among the elderly, and cancer.

To investigate concerns related to the number of respiratory and renal disorders being treated in a local clinic, ATSDR conducted a health study in 1995 of persons living on the Fort Hall Indian Reservation (ATSDR 1995). This study concluded that the prevalence of pneumonia and chronic bronchitis was statistically significantly elevated among participants living on the Fort Hall Indian Reservation, as compared to participants living at another reservation in a remote part of Nevada. Results of pulmonary function tests showed that participants living on the Fort Hall Indian Reservation had decreased pulmonary function when compared to participants in the control group, but the difference was not statistically significant. Biological monitoring found that levels of cadmium, chromium, and fluoride in the urine samples of all participants were within normally defined values, and no statistically significant difference between the two reservations was observed. The study recognized, however, that this type of biological monitoring would neither identify historically exposed persons nor quantify the exact extent of their past exposures. As indicated in the 1995 ATSDR health study, a major limitation of the study was the uncertainty in attributing exposure to site-related contaminants (i.e., emissions from the two phosphate processing plants) (ATSDR 1995).

It should be noted, however, that attributing exposures to individual sources is often an extremely difficult task, especially in areas with many different sources of environmental contaminants, like the EMF study area. Although it has been well established that FMC and Simplot have historically been major sources of emissions of various air contaminants, many other sources of air pollution are found on the Fort Hall Indian Reservation and in the cities of Chubbuck and Pocatello. These sources include, but are not limited to, other industries, wood stoves, residential fireplaces, automobiles, and agricultural operations. Due to the uncertainty in determining the extent to which each individual source contributes to inhalation exposures, this health consultation does not provide quantitative estimates of each source's impact on levels of air pollution. Rather, this health consultation attempts to delineate areas where persons have been, and are being, exposed to various contaminants at levels that might be associated with adverse health effects.

B. Site Description

As noted above, phosphorous processing facilities owned and operated by FMC and Simplot are located on the EMF NPL site. The nearest major population areas--the cities of Pocatello and Chubbuck, Idaho--are located east-southeast and east-northeast, respectively, of the FMC and Simplot facilities (see Figure 1). The facilities are about 2.5 miles from populated areas of these cities, but some residences are located closer to the facilities. No residences were observed within approximately 0.5 miles of either facility. As Figure 1 shows, the nearest populated area on the Fort Hall Indian Reservation--the Fort Hall Agency--is located about 8 miles north-northeast of the facilities. ATSDR notes, however, that the majority of the population on the Fort Hall Indian Reservation lives in rural areas, including some in proximity to FMC and Simplot.

The FMC phosphorous production facility covers an estimated 1,189 acres, almost all of which lie within the Fort Hall Indian Reservation. The Simplot facility (described below) is located directly east of the FMC facility. The FMC facility has produced phosphorous since 1949; some of the facility's processes have changed little since then. FMC has always produced phosphorous from phosphorous-bearing shale, which is shipped to the facility via rail car during the summer months and stored on site in large stockpiles. After passing through several mechanical processes (e.g., crushing), the phosphate rock is fed to calciners, which remove moisture from the feed. A mixture of this intermediate product, coke, and silica are then further processed in one of the facility's four electric arc furnaces. Outputs from the furnaces include gaseous elemental phosphorus, various gaseous by-products (some of which contain radiological components), and solid wastes called "slag" and "ferrophos" (Bechtel 1993). The elemental phosphorus is subsequently condensed and eventually shipped off site, and the solid wastes are disposed of at various on-site and off-site locations. Though effluents from the calciners and electric arc furnaces pass through air pollution control devices, these operations emit a wide range of air pollutants, as do numerous other sources throughout the facility. Section IV.C of this health consultation describes these emissions in greater detail.

The Simplot Don Plant covers about 745 acres, none of which are on reservation property. As noted above, the Simplot facility adjoins the eastern property boundary of the FMC facility (Bechtel 1996). Since 1944, the Simplot facility has produced various phosphorous-containing products; currently, the facility produces 12 principal products, including phosphoric acid, five grades of solid fertilizers, and four grades of liquid fertilizers (Bechtel 1996). Phosphate ore is one of the principal feeds to Simplot's processes. Prior to September, 1991, the Simplot facility received its ore from mines via rail car. Since then, however, the facility has received its ore through a slurry pipeline. The incoming slurry then passes through various processes, depending on the product being made. Many of the products also use sulfuric acid as a feed, which Simplot manufactures on site. Like the processes at FMC, the processes at Simplot emit contaminants to the air and generate many forms of solid and liquid waste. Air pollution control devices at the Simplot facility help minimize adverse impacts on local air quality, but the facility has emitted, and continues to emit, a wide range of contaminants to the air. Section IV.C revisits this issue.

C. Land Use and Demographics

According to the RI (Bechtel 1996), the EMF NPL site (referred to in this document as "the EMF study area") includes land belonging to the Fort Hall Indian Reservation, the Bureau of Land Management (BLM), Bannock and Power Counties, and portions of the cities of Pocatello and Chubbuck. Land use on the Fort Hall Indian Reservation in the EMF study area is mainly agricultural with scattered residences. BLM land is designated as multiple use. Unincorporated land in Bannock and Power Counties is mostly agricultural, also with scattered residences, and land within the cities of Pocatello and Chubbuck in the EMF study area is primarily zoned for residential use.

In addition to owning the land on which the facilities operate, FMC and Simplot also own all land (with the exception of road rights-of-way) between the facilities and Interstate 86, as well as substantial property located immediately north of Interstate 86 and east of the facilities. Other land uses in the area include a dragstrip located across the access road from FMC, which has recently closed, and a softball field across the street from Simplot. Until March 12, 1995, the Bannock Paving Company (BAPCO) operated a paving and aggregate handling facility on land leased from, and adjacent to, the FMC facility. BAPCO periodically conducted many industrial operations at this site, such as processing asphalt, drying coke, and crushing slag and ferrophos (Bechtel 1996). The land owned by FMC to the north of the facility is reportedly deed restricted, prohibiting current or potential future residential use; however, access to much of this land is not restricted. The number of people who access the land immediately north of FMC is believed to be limited, but passers by and off-site workers clearly use the area.

The area within a 1-mile radius of the FMC and Simplot facilities is sparsely populated, as is typical of areas with primarily agricultural and industrial land uses. However, the area within a 5-mile radius of the facilities includes much of the cities of Chubbuck and Pocatello, as well as a larger portion of the Fort Hall Indian Reservation. As a result, the area within 5 miles of the facilities is considerably more populated than the area within just 1 mile of the facilities. The "Public Health Implications" section of this health consultation describes the demographics of the potentially exposed population in greater detail.

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