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HEALTH CONSULTATION

NITRATE IN GROUNDWATER AND METHEMOGLOBINEMIA

LABORATORY FOR ENERGY RELATED HEALTH RESEARCH
DAVIS, YOLO COUNTY, CALIFORNIA


BACKGROUND AND STATEMENT OF ISSUES

Purpose and background of document

This health consultation is being written as part of a public health assessment process investigating the potential community impact of environmental contaminants that may have originated from the Laboratory for Energy-Related Health Research (LEHR) facility. This health consultation investigates whether there have been any infants hospitalized for "blue baby syndrome," or methemoglobinemia, in the vicinity of the LEHR site. Methemoglobinemia is a potentially life-threatening condition in which the blood is unable to transport oxygen normally, and may result if infants drink water with elevated nitrate levels. Private drinking water wells near the LEHR site have elevated levels of nitrate.

The LEHR site was placed on the National Priorities List (NPL) in May 1994 by the U.S. Environmental Protection Agency because of the possibility of contaminants in the groundwater ( 1). The California Department of Health Services is assisting the U.S. Agency for Toxic Substances and Disease Registry (ATSDR) in conducting this health assessment.

Site description

The Laboratory for Energy-Related Health Research (LEHR) site comprises about 15 acres in a rural location on the campus of the University of California at Davis (U.C. Davis), approximately 12 miles west of Sacramento and 70 miles northeast of San Francisco, California ( 2). The LEHR site is located in Solano county, and a 1-mile radius from the site extends north into Yolo county ( Figure 1). The UC Davis campus in 1987 had an enrollment of over 19,000 students, with 4,500 non-student employees, and about 2,800 on-campus residents ( 2). The land use category surrounding UC Davis is intensive agriculture, with 76.8 percent of all land used for this purpose. Irrigation is used on 41 percent of the agricultural land. The average population density in the counties surrounding LEHR ranges from 112 to 806 people per square mile ( 2).

The LEHR facility was operated by U.C. Davis for the United States Department of Energy ( 2). LEHR opened in the late 1950s, and for over 30 years was the site of studies to evaluate the biological effects of radiation on laboratory animals ( 1, 2). Areas of the former LEHR facility were used as landfill for radioactive, chemical, and sanitary wastes. Most of the buildings previously part of the LEHR research facility now comprise the UC Davis Institute for Toxicology and Environmental Health ( 1).

Nitrate in the vicinity of the LEHR site

Groundwater samples from private wells near the LEHR site contain nitrate at levels that are of health concern for infants who drink the water ( 3). These levels do not exhibit a site-related geographic pattern and are thought to result from agricultural use of fertilizers in the area ( 1, 3). In 1989 DOE and UC Davis began supplying bottled water to about 15 families ( 3). However, ATSDR scientists believe there may be other families in the area who are affected by nitrate contamination ( 3). Although the Safe Drinking Water Act as amended in 1986 mandates testing of public water systems for nitrate and other contaminants, water systems (including private wells) with fewer than 15 connections are not subject to this requirement ( 4).

Sources of nitrate in the environment

Nitrate and nitrite occur naturally in the environment, and are a normal component of the human diet. Most of adult's daily nitrate intake comes from certain vegetables, and drinking water is only a small percentage of the total ( 4). However, infants can be exposed to nitrate from water used to prepare their formula ( 4).

Higher than typical levels of nitrate and nitrite can occur in the environment in several ways. Fertilizers containing nitrogen can be converted to nitrate in the soil ( 4). Water from irrigation or heavy rainfall, particularly following drought, can create runoff containing chemical fertilizers from nearby farm fields which can then contaminate well water, especially in more shallow wells. Human waste from septic tanks and animal waste from livestock operations also create nitrate and nitrite when ammonia present in the waste is oxidized ( 4).

Maximum contaminant levels for nitrate/nitrite

Nitrate and nitrite are sometimes expressed in different ways, so the unit of measurement requires explanation. The level of nitrate or nitrite in water can be given as milligrams of nitrate per liter of water (mg/L) or parts of nitrate per million parts of water (ppm). Also, another way nitrate or nitrite can be reported is as mg/L (or ppm) of the nitrogen part of nitrate or nitrite. This is referred to as "nitrate (or nitrite) as nitrogen." The current MCL for nitrate in drinking water is 10 mg/L (nitrate as nitrogen) or 45 mg/L (nitrate). Table 1 shows the different ways MCLs are reported.

Table 1:

Different ways of reporting Maximum Contaminant Levels (MCLs) for nitrate and nitrite.
  Nitrate Nitrite
mg/L 45 10
ppm 45 10
as nitrogen (mg/L) 10 1
as nitrogen (ppm) 10 1

Nitrate levels in the vicinity of the LEHR site

Detections of nitrate in private wells sampled in the area have, on average, exceeded the MCL, and the upper end of the range has been about 2-5 times the MCL (Table 2).


Table2:

Levels of Nitrate (as nitrogen) in private drinking water wells sampled in the LEHR vicinity (ML=10).
Date Mean (mg/L) Range (mg/L)
May 1991 n=11 wells (5) 18.5 9.4 - 32.8
Sept. 1991 n=12* (5) 12.03 2.91 - 18.1
June 1994 n=16 (5) 12.19 3.4 - 27
March 1996 n=16 (6) 16.05 3.8 - 51

* 12 measurements from 11 wells

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