The feasibility of epidemiologic studies of waterborne arsenic: a mortality study in Millard County, Utah.
In 1976, a U.S. maximum contaminant level (MCL) standard for arsenic in drinking water was set at 50 micrograms/liter ([[micro]gram]/L or ppb) by the National Interim Primary Drinking Water Regulation (1). Before 1976, the state of Utah's public water supply program, like the programs of many other U.S. states, was using the 1962 U.S. Public Health Service drinking-water standard of 50 [[micro]gram]/L. The U.S. Public Health Service drinking-water standards first mentioned arsenic in the 1942 edition, which also set the MCL at 50 [[micro]gram]/L. The World Health Organization (WHO) has set a recommended drinking-water arsenic standard of 25 [[micro]gram]/L (2). There is considerable debate about whether the U.S. MCL for drinking water arsenic should be lowered. The current U.S. standard is based on an analysis of cross-sectional Taiwanese data in which the health outcomes of blackfoot disease and skin cancer were assessed simultaneously with arsenic exposure (3-5). Arsenic exposure was assigned to large groups of the population according to average concentrations of arsenic in village wells, and determination of exposure was not further refined. Because the health outcomes and other contributing factors (e.g., diet) experienced in the Taiwanese population are dramatically different from those of the U.S. population, lowering the U.S. standard on the basis of the Taiwanese data is controversial (6). Recent work suggests that consideration of alternative models of health effect thresholds may be more appropriate than the current dose-response curve (7). In addition, reports of noncarcinogenic effects call into question whether cancer is the most sensitive end point (8-10).
Previous workshops on arsenic in drinking water have emphasized the importance of studying populations that are similar to U.S. populations, but have stopped short of advocating the study of a U.S. population (American Water Works Association Research Foundation, Ellicott City workshop, 1994). Andelman and Barnett analyzed the feasibility of relating arsenic in drinking water to skin cancer in U.S. populations (11). Characteristics cited for a successful study include a sufficiently high and well-documented exposure to arsenic in drinking water, persistent exposure over a time period sufficient to entail a large-enough total arsenic dose, a latency period sufficient for development of disease, no substantial arsenic exposure from other sources, and a population large enough to provide the statistical power to distinguish differences in disease rates among exposed and unexposed populations. Andelman and Barnett concluded that researchers were unlikely to find a U.S. population that provided sufficient statistical power for an epidemiologic study Other types of study designs and noncarcinogenic end points, however, were not considered (11).
This paper introduces a retrospective cohort mortality study currently under way in several remote communities in Utah (12). The purpose of the study is to evaluate associations with arsenic in drinking water. A wealth of knowledge about the area's drinking-water history, various water delivery systems, and population characteristics has been accumulated. This paper also discusses previous difficulties in determining the feasibility of studying the health effects of arsenic in drinking water. Evidence is presented to suggest that such studies are possible in U.S. populations.
In the late 1970s, a Utah cohort of western Millard County residents was assembled for the purpose of conducting a health effect study of waterborne arsenic (13). Cohort members resided in one of several towns, including Hinckley, Deseret, and Delta. Data on cohort members from Oasis and Abraham were subsequently added. Historic church records dating from 1900 through 1962 from the towns were abstracted for demographic and vital information and duration of residence. The historic records contained information on family structure, such as birth, marriage, and death dates.
Andelman and Barnett suggest that a prospective study design is the most feasible for a study of this nature; however, tracing individuals over time for their resi-dence history and health information would be impossible (11). Because of the historical nature of this cohort, residence history is already established by the historical church records, and many of the deaths for cohort members have already oc-curred and are recorded in the historical records. Death certificates were collected for those who were noted as deceased in the historical records, and cause of death was coded according to the ICD-9 coding rubric (14).
To date, the cohort has 4,058 members: 1,551 (38.2%) alive, 2,203 (54.3%) deceased, and 304 (7.5%) with unknown vital status (Table 1). Most of these individuals have residence histories in the study area that exceed 20 years. A standardized mortality ratio (SMR) analysis is planned. The observed deaths in the study population will be evaluated against the expected number of deaths for each cause-of-death category, as calculated from death rates in the Utah general population. Also planned is an analysis using Cox proportional hazards models to assess time-related variables such as length of cohort membership or duration of exposure and survival.
Another characteristic desirable for a successful study is a well-characterized, persistent exposure to arsenic with a sufficient latency period. The residence information forms the foundation of the study population and provides data necessary for determining the length of exposure to drinking-water [TABULAR DATA FOR TABLE 1 OMITTED] arsenic. While the latency period for nonmelanoma skin cancer is 10 to 18 years, the residence history for many in the cohort easily exceeds that length of time. The time that has passed provides sufficient latency for the disease to develop.
In the current study, arsenic exposure for the cohort members was originally assigned according to town of residence, as indicated in the historic church record. This practice, however, is not optimal, as it assumes that exposure is associated with a source that is not precisely defined. Drinking-water arsenic measurements for individual wells were made available through the Utah Department of Environmental Quality, Division of Drinking Water. Concentrations of arsenic in drinking water were measured between 1960 and 1991 in Delta, Hinckley, Abraham, Deseret, and Oasis. Additional drinking water arsenic concentrations were documented at selected sites during a separate study of drinking water arsenic metabolism in 1997, but are not presented.
To strengthen the arsenic exposure assessment, geologists, environ-mental specialists, and water supply workers were contacted and interviewed. This research provided a history of the drinking-water sources and records of when individual wells rather than municipal drinking-water systems were used. In addition to arsenic measurements from wells in the study area, supplementary data and information that were collected included geologic and hydrologic history of the study area, water supply history, well depths, and locations of wells in the study area (15). This information was reviewed, and arsenic exposure was assigned after the precise demographic location of a well was linked with the community that it served. The type of well (municipal versus private) was also specified. Information on test dates provides an indication of arsenic concentrations in drinking water in the area over time. For the cohort, a basic demographic assessment of age, gender, and exposure level by vital status was made with SAS statistical software (16).
Geologic and Hydrologic History
Consultation with a Utah state geologist revealed information on naturally occurring geologic formations associated with arsenic and identified formations that could come into contact with the groundwater. In Utah, the formation of arsenic is associated with volcanic processes. Extinct volcanoes in the Delta and Hinckley area are no more than 12 miles away from both towns (see photo). These volcanoes date back to the quaternary geologic period, or about 10,000 to 800,000 years ago (17). It is suspected that when the volcanoes were active, arsenic-contaminated ash and dust fell on the area. Today, both ground and surface water flow toward Delta and Hinckley via the Sevier River from northeast to southwest [ILLUSTRATION FOR FIGURE 1 OMITTED]. Eventually surface water flows toward the Sevier Lake, which is dry most of the year.
Water Supply History
In Delta, the municipal water system was phased in over a number of years [ILLUSTRATION FOR PHOTO OMITTED]. According to the City of Delta public works director, all residents used their own well sources for drinking water before the 1930s. Around 1929 or 1930, a factory in town ceased operation, and the two wells it had drilled were ceded to the town for potable water. The two wells functioned well into the late 1940s, when one of them no longer had the needed pumping capacity and was capped. In 1953, a new second well was drilled and brought on line. A third and fourth well were added in the 1970s and 1980s, respectively. These four wells are currently in use, as they meet all current federal regulations and have arsenic measures below 50 [[micro]gram]/L.
Before 1963, all homes in Hinckley were supplied by individual wells. In 1963, the Hinckley town well was drilled, and it had enough capacity to serve all of the homes. It was discovered, however, that arsenic levels frequently were above 120 [[micro]gram]/L and peaked as high as 285 [[micro]gram]/L. The well was capped in December 1981, and an alternative source approximately 2.5 miles to the south and east of town was located and put into service. This new source is shared by the towns of Hinckley, Deseret, and Oasis. Surface water was never used as a drinking-water source in the study area of Delta, Hinckley, Deseret, Oasis, and Abraham.
Table 2 outlines the supplementary geologic data that are available from various resources in Utah for the improvement of arsenic exposure estimates at the individual level. On the basis of previous arsenic measurements and of the geologic and water supply information, arsenic levels were grouped by town and by type of well (municipal versus private) (Table 3, also Table 2, Item 1). For all public and private wells in the current study area - Delta, Hinckley, Deseret, and Oasis - arsenic levels ranged widely from near zero to 580 [[micro]gram]/L. More definitive well locations were sought to clearly distinguish between areas with historically high and low levels of arsenic in drinking water. Because private wells tended to be drilled at shallower depths and to have higher arsenic levels, the private-versus-municipal classification was maintained (15).
In addition to the historic arsenic measurements presented in Table 3, the state of Utah maintains a computerized database of water rights. The water rights database has the added advantage of providing a precise location for the wells on a coordinate system. All wells listed in Table 3 were checked in the water rights database to assign coordinates and town locations. Compared with the unconfirmed well locations in Table 3, the confirmed and more precise results presented in Table 4 reflect a decreased range of arsenic values that are all less than 50 [[micro]gram]/L. Hinckley's [TABULAR DATA FOR TABLE 3 OMITTED] [TABULAR DATA FOR TABLE 4 OMITTED] [TABULAR DATA FOR TABLE 5 OMITTED] measurements were mostly above 50 [[micro]gram]/L; only two were less than 50 [[micro]gram]/L. Arsenic measurements in the Deseret and Oasis area remained the same for the public supply (all below 50 [[micro]gram]/L). Measurements from private wells rose to above 50 [[micro]gram]/L. In Table 3, data from 99 wells for the immediate study area (Delta, Hinckley, Deseret, and Oasis) are presented. The improved location information in Table 4 resulted in usable data for 92 wells.
The exposure analysis plan will use the arsenic exposures presented in Tables 3 and 4 and in Item 1 of Table 2 to indicate relative levels of arsenic in the two main study communities: Hinckley and environs (high arsenic) and Delta (low arsenic). With additional information from Table 2 to be collected, however, it may be possible to link a cohort member's exposure with a well to provide an estimate of the number of years an individual was exposed to a certain arsenic level (Table 2, Item 2). The water quality database from Table 2, Item 3, will be checked (as will compliance data in Table 2, Item 4) for arsenic levels to gauge the stability of arsenic over time. The Central Utah District Health Department data may provide data on arsenic concentrations in private wells in the area (Table 2, Item 5). The additional information will be used and summarized to estimate as complete an exposure scenario at the individual level as possible. An example of the exposure matrix is given in Table 5. Once exposed and unexposed status is known, number of residence years will be factored in, and an average concentration of arsenic exposure will be calculated. The final exposure variable for drinking-water arsenic will be unique to each individual in the cohort.
The completeness of this cohort and the data available about drinking-water arsenic for the study area support the idea that a health outcome study of drinking-water arsenic is feasible in the United States. This study can be accomplished in a reasonable amount of time, and a sufficient sample size can be achieved without the study having to be carried out at a multitude of locations.
The geologic information indicates that arsenic was pervasive in the area long before settlement in modern times. Because the study area was settled in the late 1800s, it is reasonable to assume that cohort members incurred exposures in excess of the current MCL in Hinckley, Deseret, and Oasis. As enrollment of this cohort continues, more detailed information on residence history for all cohort members will be collected in an effort to refine determination of the exposure. The goal is to obtain the number of person-years of drinking-water arsenic exposure for each individual, based on years of residence history at the time of the arsenic measurement.
Although arsenic measurements were made over a span of 21 years, the majority of samples were collected in 1974 or later, when sampling procedures and specimen preservation were optimal. Because the water-sampling period overlaps the latter part of the cohort enrollment period, we are certain that part of the exposure of the cohort members was at levels we are reporting. Historical records show that for a given location in the valley, the water quality has not changed considerably over time since the area is served 100 percent by groundwater supplies. The supplemental data described in this paper will allow a review of historic arsenic concentrations and testing methods in Utah so that we can gauge arsenic concentration stability in these communities over time.
Individual components of exposure collected in the epidemiologic study, such as length of residence and location of residence, along with the supplemental information described in this paper, have been used to greatly improve exposure assessment. The gross categorization of exposure on the basis of town of residence is replaced with individual exposure assessments. The refined determination of exposure by location becomes more important for smaller locations, such as those in our study, as the precise identification of the drinking water source improves the precision with which individual exposures of participants are determined. It is clear from the map that the complex distribution of arsenic in the groundwater must be considered in such a study. This reduces possible bias from exposure misclassification and therefore will improve the planned mortality analysis.
Acknowledgements: The authors thank Becky Hylland, geologist at the Utah Department of Environmental Quality, Salt Lake City, Utah; Wes Petersen, of Hinckley, Utah; Rawlin Dalley, of Public Works in Hinckley, Utah; Neil Forster, Public Works Director, Delta, Utah; Roger Anderson, Curator, Great Basin Museum, Delta, Utah; and Stuart Vandiviere, Senior Environmental Employment Program, U.S. EPA.
The views expressed in this article are those of the individual authors and do not necessarily reflect the views and policies of the U.S. Environmental Protection Agency. The research described in this article has been supported by the United States Environmental Protection Agency through Contract 68-D2-0187. It has been subject to the agency's peer and administrative review, and it has been approved for publication. Mention of organizations, trade names, or commercial products does not constitute endorsement or recommendation for use.
Supplementary Data Available for the Improvement of Arsenic Exposure Assessment
Item 1(*) Historic arsenic measures for private wells, irrigation wells, and public supply (Delta).These data indicate relative levels (i.e., high versus low) of drinking-water arsenic in Delta, Hinckley, and environs on selected dates.
Item 2(*) Utah Division of Water Rights, computerized database of water rights. The data identify the use of some wells in Phase I, (i.e.,for domestic consumption or livestock use). One can rule out well sources used for livestock to refine human exposure. The data contain coordinates of wells for location and well depth, which may be helpful in interpreting arsenic levels from other data sources. Year of water right and person or family name are also included. This information can provide a time period of reference for when the arsenic measurements may have applied to individual exposure.
Item 3 State of Utah water quality database. Water quality data are available for the entire state from the present back to 1978. This information can provide supplementary arsenic readings that can help researchers to gauge the stability of arsenic measures over time.
Item 4 Source location information database for public water supplies. As with the water quality database, this information can be used to assess arsenic levels in source water used for public supplies back to 1978.
Item 5 Central Utah District Health Department. The department may have additional information on private wells in the area. Inorganic chemical analysis reports may be available and may include an arsenic determination.
* Item used in current exposure assessment.
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13. Southwick, J.W., MM. Beck, R. Isaacs, A.E. Western, and J. Whitley (1981), Community Health Associated with Arsenic in Drinking Water in Millard County, Utah, Springfield, Va: National Technical Information Service, Publication Number 82-108374.
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15. Unchis, D. (1996), "Drinking Water, Arsenic and Cancer: An Evaluation of Exposure Data in Millard County, Utah," Master's thesis, Washington, D.C.: George Washington University
16. SAS Version 6.11 (1996), Cary, N.C.: SAS Institute, Inc.
17. Department of Geology, Brigham Young University (1975, reprinted 1992), Geological Highway Map of Utah, Provo, Utah: Brigham Young University Geology Studies, Special Publication 3.
18. Allen, D.V., and J.I. Steiger (1995), Ground-Water Conditions in Utah, Spring of 1995, Cooperative Investigations Report Number 35, Salt Lake City, Utah: Utah Department of Natural Resources, Division of Water Resources.
Corresponding Author: Denise Riedel Lewis, U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Human Studies Division, Research Triangle Park, NC 27711.
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|Author:||Calderon, Rebecca L.|
|Publication:||Journal of Environmental Health|
|Date:||May 1, 1998|
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