Environ. Sci. Technol. 2007, 41, 2505-2509
Trichloroethylene Uptake into Fruits and Vegetables: Three-Year Field Monitoring Study W I L L I A M J . D O U C E T T E , * ,† JULIE K. CHARD,† HEIDI FABRIZIUS,† COREEN CROUCH,† MICHAEL R. PETERSEN,† TERRY E. CARLSEN,† BRANDON K. CHARD,† AND KYLE GORDER‡ Utah State University, Utah Water Research Laboratory, 8200 Old Main Hill, Logan, Utah 84322-8200, and Environmental Management Division, Hill Air Force Base, Utah
Trichloroethylene (TCE) contaminated groundwater migrating into communities surrounding Hill Air Force Base (HAFB) in northern Utah prompted a multiyear monitoring program (2001-2003) to examine the extent of TCE uptake and transfer into edible fruits. During the initial sampling in fall 2001, TCE was detected in a small fraction of the 167 fruit and tree core samples collected from 17 private residences. Samples were analyzed using headspace gas chromatography (GC) with electron capture detection (ECD) with limited confirmation by mass spectrometry (MS) in selected ion monitoring mode. In fall 2002, over 300 samples were collected from the same general locations sampled in 2001. No TCE was found in any of the fruit or vegetable samples above the method detection limit (MDL) for the headspace GC/MS method (approximately 0.1 µg/ kg fresh weight, depending on sample size), but TCE was again detected in several fruit tree trunk core samples. The detection of TCE in fruit in 2001, but not in 2002, may have been due to improvements in the analytical procedure or changes in the environmental conditions impacting transfer to fruit. The 2003 monitoring focused on repeated sampling over several months at five locations that were selected to represent the range of exposure scenarios evaluated during the previous years. No TCE was identified in any of the fruit above the MDL during 2003, however TCE was again found in tree core samples as observed in 2001 and 2002.
Introduction Trichloroethylene (TCE) is one of the most frequently identified groundwater contaminants in the United States. TCE is also the most common contaminant found in the shallow groundwater aquifers in and around Hill Air Force Base (HAFB) in northern Utah. Previous field studies conducted at HAFB (1, 2) and other sites (e.g., 3-6) have identified TCE in trees growing over contaminated groundwater. TCE concentrations in tree trunk cores are presumed to be a function of factors such as the TCE concentration in * Corresponding author phone: (435) 797-3178; fax: (435) 7973663; e-mail:
[email protected]. † Utah State University. ‡ Hill Air Force Base. 10.1021/es0621804 CCC: $37.00 Published on Web 02/23/2007
2007 American Chemical Society
the groundwater, the depth to groundwater, the age and type of tree, the amount and frequency of rainfall or irrigation (2), and the location on the tree where the sample is collected (6). The detection of TCE in on-base trees, together with the migration of shallow groundwater plumes into residential areas containing numerous fruit trees, prompted concerns that TCE could be taken up and transferred into edible fruit. While the uptake of TCE into trees such as hybrid poplars and willows has been well documented, much less is known about the uptake of TCE by fruit trees and the potential transfer into edible plant tissue. The general lack of quantitative data describing the transfer of organic contaminants into fruits combined with the concerns of base officials and local residents prompted a multiyear field monitoring survey in 2001-2003. The main concern and focus of the sampling effort was directed toward fruit trees since they are longer-lived and deeper-rooted than garden vegetables. However, vegetables such as tomatoes and carrots were also sampled during fall 2002 since the only previous uptake data for TCE was generated in laboratory studies (7, 8). Prior to sampling in fall 2002, the headspace method used specifically for apples, peaches, tomatoes, and carrots was validated following an EPA protocol to increase the reliability of the results. A 2-year laboratory uptake study was also conducted concurrently with the final 2 years of the field survey (9).
Materials and Methods Hill Air Force Base, Utah. Hill Air Force Base, Utah is located in northern Utah about 40 km north of Salt Lake City and about 8 km south of Ogden. The Great Salt Lake is approximately 19 km to the west of HAFB and the Wasatch Mountain Range is about 6.5 km to the east. The surface elevation ranges from approximately 1400 to 1525 meters above sea level (National Geodetic Vertical Datum of 1929). The climate in the vicinity of HAFB is temperate and semiarid. The frost-free growing season is generally from May through September. The average annual precipitation recorded during the period 1978 to 1990 at a gauge located 1 km northeast of the base was 50 cm (19.8 in.). The majority of precipitation falls from October though May. May is usually the wettest month, and June and July are the driest months. Potential average annual evaporation is approximately 114 cm (45 in.) of water per year. The inappropriate disposal of chlorinated degreasing solvents, mainly TCE, during the period of 1967 to 1975 resulted in the contamination of shallow aquifers (not used as a drinking water source) at several sites in and around HAFB. Historically, groundwater concentrations of TCE within the plumes have ranged from 0.005 to 10 mg/L. Sampling Locations. Samples were collected during August, September, and October 2001 and 2002 and June through October 2003 at private properties around HAFB mainly associated with Operable Units (OU) 4, 5, 6, and 12 (Figure 1). In 2001, the locations and types of plant tissue sampled were selected mainly on specific requests from landowners, although some attempt was made to include locations thought to be within and outside the historical plume boundaries. One hundred and sixty seven samples, mainly from apple, peach, cherry, and pear trees, were collected from 17 private residences. Of the 167 samples, 64 were tree trunk cores. Cores were collected from only large diameter trees so that any perceived impact on fruit trees could be minimized. VOL. 41, NO. 7, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Sampling locations associated with TCE groundwater contamination at Hill Air Force Base, Utah. TCE plumes are shown as shaded areas, with plume boundaries defined by the Maximum Contaminant Level (MCL) for TCE of 5 µg/L. In 2002, an expanded number of residential orchards and gardens were selected based on the willingness of residents to participate, participation in the previous year’s sampling, TCE groundwater concentration, depth to groundwater, and availability of selected plant types. To minimize concerns regarding the suitability of the analytical method to a wide variety of sample matrices, sampling focused on four representative fruits and vegetables (apples, peaches, carrots, and tomatoes) and a small number of fruit trees (apple, peach, walnut, cherry, and apricot). Prior to the 2002 sampling, a headspace GC/MS method was validated following U.S. EPA guidelines (http://www.epa.gov/SW-846/pdfs/methdev.pdf) for use on apples, peaches, carrots, and tomatoes. “Clean” fruit and vegetable specimens from a comparable reference or control area were also sampled and analyzed. Over 300 samples (including replicates) were collected in the fall of 2002, including 150 apple samples, 107 peach samples, 76 tomato samples, and 35 carrot samples, from 31 private residences in six communities surrounding HAFB (Clinton, Layton, Riverdale, Roy, South Weber, and Sunset). In addition to the edible plant samples, 58 tree trunk core samples (apple, peach, walnut, cherry, and apricot) were also collected and analyzed. In 2003, five locations were selected for repeated sampling during June through October to represent the following range of relative site characteristics: (1) presence of at least one fruit tree large enough for repeated sampling; (2) shallow groundwater (
