Critical Reviews in Environmental Science and Technology, 33(1):1–29(2003)
Worldwide Occurrence and Fate of
Chlorofluorocarbons in Groundwater
Patrick Höhener ,* David Werner, Christian Balsiger, and Gabriele
Pasteris
Swiss Federal Institute of Technology (EPFL), ENAC, ISTE-LPE, CH-1015 Lausanne,
Switzerland
*
Corresponding author. Phone 0041 21 693 57 50, Fax 0041 21 693 28 59 E-Mail [email protected]
ABSTRACT: Chlorofluorocarbons (CFCs) are synthetic halogenated volatile organic compounds
that have been manufactured since 1930 and can be detected analytically in water in pg L–1 concentrations. The use as tracers for age dating of pristine groundwater has been summarized by previous
review articles, where occasional failure of the CFC age-dating technique caused by local CFC
contamination in excess of the equilibrium with modern air was reported. This article summarizes the
worldwide occurrence of CFCs in groundwater with a focus on contaminated aquifers. CFC data from
24 aquifers and two regions on four continents are compiled. In 10 aquifers, contamination in more
than 20% of samples with either CFC-11, CFC-12, or CFC-113 is reported. Pathways of CFC input
to groundwater such as local atmospheric pollution, river water infiltration, landfills, and industrial
solvent spills are discussed. The aerobic and anaerobic biotransformation reactions and natural
attenuation processes of CFCs in aquifers are also reviewed. Microbially catalyzed reductive dechlorination of CFCs occurs in anaerobic aquifers. Little is known about the presence of other CFCs and
degradation products of CFCs, among which some are known to be toxic (HCFC-21) or carcinogenic
(HCFC-31). Risk assessment for groundwater resources should include HCFC measurements to
better identify transformation reactions.
KEY WORDS: freons, refrigerants, pollution, aquifer vulnerability, age dating.
I. INTRODUCTION
A. Nomenclature and Characteristics of CFCs
Chlorofluorocarbons (CFCs) are synthetic organic chemicals fully substituted
with chlorine and fluorine atoms. They have been manufactured since the 1930s
(Siegemund et al., 1988) and were used world-wide as aerosol propellants, refrigerants, foam blowing agents, solvents, and intermediates for the synthesis of fluorinated polymers (Table 1). CFCs were produced by several manufacturers and sold
under many different trade names such as Freon, Flugene, or Frigen. They are also
called refrigerant, followed by a number (e.g., R-113, Siegemund et al., 1988). The
three figures indicate the number of carbon atoms minus one (for methane deriva1064-3389/03/$.50
© 2003 by CRC Press LLC
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tives, the figure 0 is omitted); the number of hydrogen atoms plus one, and the
number of fluorine atoms. All other bonds are saturated with chlorine. Letters are
used in addition to discriminate between isomers. In this article, the term CFC
followed by the number will be used as compound name (Table 1). HFCs and HCFCs
contain at least one hydrogen atom in the molecule and are numbered similarly. The
chemical characteristics of the important compounds on the world market reveal low
boiling points, high vapor pressures, and moderate to low water solubilities (Table 1).
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The estimated atmospheric lifetimes of CFCs are tens or hundreds of years, those of
HFCs and HCFCs are in the order of some years (Table 1).
B. World Production of CFC and HCFCs
Records of production (Figure 1), sales, and atmospheric releases have been
published by the Alternative Fluorocarbons Environmental Acceptability Study
(AFEAS), an organization grouping the 11 world-leading manufacturers of volatile
fluorinated compounds. Production of CFC-12 preceded those of CFC-11 and
CFC-113 by ~ 10 and 30 years, respectively (Busenberg and Plummer, 1992; Cook
and Solomon, 1995). Total world production of CFCs and HCFCs peaked in 1986
with ~ 106 metric tons per year (Key et al., 1997). CFC-11 and CFC-12 made up
to 77 % of total global production of CFCs until 1994 (Key et al., 1997). Due to
the release into the environment, the volatility and excellent chemical stability,
CFCs accumulated in the atmosphere (Montzka et al., 1999) and were proven to
be involved in the depletion of the stratospheric ozone (Molina and Rowland,
1974) and in global warming (Watson et al., 1990). Many governments thus signed
the Montreal protocol on substances that deplete the ozone layer (UNEP, 1987)
and decreased the production of CFCs in the 1990s coming to a ban in 1996. Only
some medical applications are still allowed. It is predicted that CFC concentrations
in the atmosphere will be significant for at least the next century because of the
long atmospheric lifetimes and continuing emissions by long-lived applications
such as in closed-cell insulation foams (Watson et al., 1990). As replacement
products, HFCs and HCFCs are currently used, until they are phased out toward
2020 and 2030 (AFEAS). A steep increase in production of HCFCs and HFC-134a
has been observed since 1990 (Figure 1).
C. Volatile Organic Compounds in Groundwater
The preservation of groundwater resources from pollution by chemicals of
anthropogenic origin is a challenging task for environmental scientists,
hydrogeologists, and policy makers. Volatile organic compounds have been found
to be a threat for groundwater because of the mobility in the unsaturated zone as
gas or liquid and sometimes elevated toxicity (Pankow et al., 1997; Baehr et al.,
1999; Squillace et al., 1999). Much work has been done to understand the transport
and fate of regulated volatile organic compounds such as petroleum hydrocarbons,
chlorinated hydrocarbons, or MTBE in the subsurface (for reviews see Pankow and
Cherry, 1996; Washington, 1996; Wiedemeier et al., 1999). CFCs have received
much less attention because these are not toxic and therefore not regulated in the
subsurface.
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FIGURE 1. Worldwide evolution of the main sales of (hydro)chlorofluorocarbons published
by the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS).
D. Use of CFCs as Age-Dating Tool
CFCs provide hydrogeological tracers and dating tools for young groundwater on a time-scale of 50 years, as reviewed by Plummer et al. (1993); Oster et
al. (1996); Cook and Solomon, (1997); Plummer and Busenberg, (1999). A brief
summary of CFC age-dating technique is given here in order to understand why
CFCs have been measured in many aquifers. Measurements of atmospheric
concentrations of CFCs have been made since 1976 at stations throughout the
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world by the National Oceanic and Atmospheric Administration NOAA (Elkins
et al., 1993) and as part of the atmospheric lifetime experiment (Cunnold et al.,
1994). Atmospheric concentrations show little spatial variation. Only 10% variation was observed between average concentrations in Ireland, Oregon, Barbados,
Samoa and Tasmania (Cunnold et al., 1994). For the period before 1976, atmospheric concentrations have been reconstructed based on manufacturer’s data
and rates of photolysis in the stratosphere (Busenberg and Plummer, 1992;
Walker et al., 2000). Since the mid-1970s, the CFCs have been used routinely for
dating and tracing water masses in oceanographic studies (e.g., Bullister and
Weiss, 1983). In the late 1970s hydrogeologists started to use CFCs (Randall and
Schultz, 1976; Thompson and Hayes, 1979). Using gas chromatographs and
electron capture detectors, analytical methods for CFCs in water with detection
limits for CFC-11, CFC-12, and CFC-113 of 2-5 pg L–1 have been developed
(Thompson and Hayes, 1979; Bullister and Weiss, 1988). Sample contamination
during storage and shipping is avoided by sealing samples into glass ampoules
(Busenberg and Plummer, 1992) or copper tubes (Jean-Baptiste et al., 1994). The
presence of detectable concentrations of CFCs in groundwater indicates recharge
after the late 1940s (Ekwurzel et al., 1994), or mixing of older water with
younger water. Groundwater samples with CFC concentrations between the
analytical detection limit and the equilibrium with atmospheric concentrations at
recharge temperature can potentially be used for age-dating. The solubilities of
CFC-11, CFC-12, and CFC-113 in water and seawater have been determined
(Warner and Weiss, 1985; Bu and Warner, 1995) for the temperature range of 0
to 40˚C and 0 to 40 parts per thousand salinity. Freshwater at 10˚C in equilibrium
with the atmosphere in 1998 (Montzka et al., 1999) contains 780, 350, and 103
pg L–1 of CFC-11, CFC-12, and CFC-113, respectively. The influence of temperature on the concentrations of CFC-11 and CFC-12 at equilibrium with the
atmosphere in selected years is illustrated by Busenberg and Plummer (1992).
The CFC age-dating technique has been reported to give reliable results in a
number of aquifers, but contamination of groundwater with CFCs exceeding
equilibrium with the atmosphere or biotransformation of CFCs has been reported
in other aquifers to exclude them as age-dating tracers (Thompson and Hayes,
1979; Böhlke et al., 1998; Goode, 1998; Hofer and Imboden, 1998; Plummer et
al., 1998b, Plummer and Busenberg, 1999; Bauer et al., 2001).
E. Aims of This Article
This article provides a global overview on the occurrence of CFCs in groundwater and the levels of contamination exceeding equilibrium with modern air.
Furthermore, the article summarizes the processes governing the fate of CFCs in
groundwater. The following specific questions are addressed:
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1. In which concentration ranges do CFCs occur in groundwater, and how frequent is contamination exceeding atmospheric equilibrium?
2. Which sources release CFCs to groundwater?
3. What is the fate of CFCs and the degradation products in groundwater?
4. Do CFCs and the degradation products in groundwater represent a risk to
human health?
The implications for the sustainable preservation of groundwater resources are
discussed.
II. OCCURRENCE OF CFCs IN GROUNDWATER
A. Reporting Limit at Picograms per Liter
For this study, CFC-data measured in the pg L–1 range from the peer-reviewed
literature for age-dating of groundwater are summarized (Table 2), giving an
overview on 24 porous and fractured aquifers on four continents. In addition to the
aquifers reported in Table 2, CFC concentrations have been measured in other
aquifers to calculate CFC-derived water ages, without the complete reporting of
concentration data (Dunkle Shapiro et al., 1998; Happell and Wallace, 1998;
Jacobsen et al., 1999; Delin et al., 2000). In all the studies there were only few
water samples with CFC concentrations below the detection limits of the analytical
techniques. CFC-free samples were obtained from volcanic hot springs (Thompson
and Hayes, 1979), from the Delmarva Peninsula (Dunkle et al., 1993), and from
deep groundwater samples from the Upper Florida aquifer in Georgia (Katz et al.,
1995; Plummer et al., 1998b). Also, a deep artesian well from the Lloyd aquifer on
Long Island (NY, USA, Happell and Wallace, 1998) and a deep Pannonian well
in Hungary (Böhlke et al., 1998) were reported to be free of CFCs. All other
samples had detectable concentrations of CFCs (Table 2). For the aquifers in which
CFC-11 and CFC–12 data are reported, the analyses are plotted in Figure 2. Grey
areas enclose a range in which both concentrations of CFC-11 and CFC-12 are
within 50% in agreement with calculated equilibrium concentrations with respect
to present or past atmospheric concentrations at 10˚C. Because of differing temperatures of groundwater samples or different altitudes, margins of 50% deviation
from equilibrium are allowed for the display of these areas. In only eight aquifers,
all water samples had CFC concentrations at or below expected equilibrium
concentrations with respect to local air (Figure 2, Table 2). These eight completely
uncontaminated aquifers included volcanic hot springs and porous aquifers in rural
areas in Ontario, New Jersey, and Germany, and a fractured aquifer in South
Africa. In only a few aquifers were the CFC-11 and CFC-12 data both lying in the
equilibrium zone (Figure 2a). In a number of samples such as, for example, at
Sturgeon Falls (Ontario), CFC-11 concentrations were lower than expected from
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FIGURE 2. Concentrations of CFC-11 and CFC-12 in (a) aquifers without contamination, (b)
porous aquifers with contaminated samples, (c) porous aquifers, contamination by river water
infiltration, (d) fractured aquifers. Grey areas denote equilibrium with respect to modern air.
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CFC-12 concentrations, and data points are lying left from the equilibrium zone
(Figure 2a). In 16 aquifers (Table 2), 5% or more of the samples contain at least
one CFC in a concentration exceeding significantly the equilibrium with modern
air. The measured concentrations in these aquifers are shown for porous aquifers
(Figure 2b), aquifers influenced by river water (Figure 2c), and fractured aquifers
(Figure 2d). No clear trend is evident whether CFC-11 or CFC-12 excess is more
frequent. Furthermore, there is no obvious correlation between the location of
partially contaminated aquifers and the population density (Figure 3). Contamination can be as high as three orders of magnitude over air equilibrium (Figure 2c and
2d). It should be noted that the analytical techniques used in the studies that were
aimed at age-dating of groundwater are so sensitive that samples with CFC
contamination several orders of magnitude higher than equilibrium with air cannot
been quantified properly. Therefore, reported data tend to underestimate the frequency of samples with very high concentrations. Fractured aquifers (Figure 2d)
are particularly affected by high numbers of contaminated samples. A number of
aquifers showed anomalies in having lower CFC-11 concentrations than expected,
as, for example, the Valdosta aquifer in Georgia (Figure 2d). The low CFC-11
concentrations are explained by degradation (Plummer et al., 1998a,b). In some
samples from the Delmarva Peninsula and also from New Jersey, lower than
expected CFC-12 concentrations were observed (Figure 2b). In a buried-valley
aquifer near Dayton, Ohio, CFC-11- and CFC-12-based water ages did not agree
with 3H-3He based ages because both CFCs were degraded under the anoxic and
methanogenic conditions in the aquifer (Dunkle Shapiro et al., 1998).
B. Reporting Limit at Micrograms per Liter
Squillace and co-workers (1999) collected samples from 2948 wells in the
conterminous U.S. that were considered as not affected by point source contamination. In the untreated ambient groundwater, CFC-11, -12, –113 and 57 other,
nonfluorinated volatile organic compounds were analyzed with techniques having
the detection limit at 0.2 µg L–1. This limit is 2 to 3 orders of magnitude higher than
the equilibrium concentration of the CFCs with modern air. In urban areas having
> 386 people per km2, CFC-11 was found in 3.1%, CFC-12 in 2.8% and CFC-113
in 1.3% of the wells. In rural areas, the frequencies were 0.6%, 0.8%, and 0.1%,
respectively. The most frequently detected VOCs were MTBE, tetra- and
trichloroethene, and trichloromethane (Squillace et al., 1999). In the Glassboro
region of southern New Jersey, the occurrence of 85 different VOCs was studied
in a network of 78 newly installed wells in an area of 930 km2 comprising the
Philadelphia metropolitan region (Baehr et al., 1999). 6% of the wells exceeded 0.1
µg L–1 in CFC-11, 4% of the wells exceeded 0.1 µg L–1 in CFC-12. Data for CFC113 were not reported. In summary, these two studies illustrate that CFCs are
detected at the µg L–1 range in ~ 1 to 6 out of 100 groundwater samples taken in
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FIGURE 3. Frequency of samples contaminated with CFCs over equilibrium with modern
air in (a) North America and (b) Europe, and population density (Tobler et al., 1997) as
persons per square kilometer in 1995.
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urban areas in the U.S. To our knowledge, similar studies for Europe or other
continents are lacking.
C. Occurrence of CFC-113
Data of the CFC-113 concentrations in aquifers have been reported less
frequently than for CFC-11 and CFC-12 (Table 2). In Figure 4, measured concentrations from 12 aquifers are summarized. Only in four aquifers in Germany,
Georgia, Florida, and South Africa were all CFC-113 samples not exceeding the
equilibrium concentration in freshwater. In the other aquifers, some or all samples
exceeded the equilibrium concentration (Figure 4). At the two landfill sites, the
equilibrium was exceeded by 3 to 6 orders of magnitude. At the hazardous landfill
at Gloucester, Canada (Lesage et al., 1990), the CFC-113 was found to be the
organic chemical at greatest concentrations. HCFC-123a and chlorotrifluoroethene
were detected in smaller concentrations in the landfill plume, and laboratory
studies confirmed that those compounds, as well as HCFC-133 and HCFC-133b,
are transformation products from anaerobic biotransformation of CFC-113 (Lesage
et al., 1992; Lesage et al., 1993).
FIGURE 4. Open diamonds: Reported concentrations of CFC-113 in aquifers. Black diamonds: Samples < detection limit. The solid line indicates equilibrium with modern air at
10˚C.
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III. SOURCES FOR CFCs IN GROUNDWATER
A. Local Air Pollution
Although CFCs were found to be almost homogeneously distributed in the
global atmosphere in remote areas (Cunnold et al., 1994), local and temporal
excesses of up to 160% of the CFC concentrations in the atmosphere have been
found in the air at Heidelberg, Germany (Oster et al., 1996), at Taipei City (Wang
et al., 2000; Chang et al., 2001), and also in the New York metropolitan area (Ho
et al., 1998). Maximum CFC-11 and CFC-12 concentrations in soil air in 1990 near
Heidelberg were 700 and 500 pptv, respectively (Oster et al., 1996). The same
authors show that short-term temporal variability of CFCs in air is significantly
damped by molecular diffusion in the vadose zone, and that local excesses in
groundwater therefore are do not exceed 60% (CFC-11) and 100% (CFC-12),
respectively. Anomalous high CFC-11 and CFC-12 concentrations in soil gas from
Gascoyne, North Dakota, were explained by a sorption/desorption mechanism in
soil under varying moisture content (Russell and Thompson, 1983). However,
similar studies on soil gas profiles in the unsaturated zone did not confirm such a
mechanism (Weeks et al., 1982; Cook and Solomon, 1995; Oster et al., 1996).
B. Volcanism
It has been speculated that under high temperatures such as in volcanoes
methane could be halogenated and CFCs could be formed naturally (Gribble,
1994). However, recent analyses of volcano gases in Italy and Japan did not detect
elevated concentrations of CFC-11 and CFC-12 (Jordan et al., 2000), and volcanic
hot springs in Arkansas had CFC-11 concentrations not exceeding the detection
limits of 3 pg L–1 (Thompson and Hayes, 1979). CFC concentrations in gas samples
from the unsaturated zone in boreholes in tertiary volcanic rocks at Yucca Mountain were all below concentrations in modern air (Thorstensson et al., 1998).
Volcanism thus can be excluded as a mechanism leading to elevated CFC concentrations in groundwater.
C. Infiltration of Contaminated River Water and Sewage Water
River water has been clearly identified as a source of CFC input to groundwater (Busenberg and Plummer, 1992; Clark et al., 1995; Böhlke et al., 1998;
Plummer et al., 1998b). A 40-year record of historic CFC contamination in the
Danube river is preserved in the aquifer underlying the little Hungarian Plain
(Böhlke et al., 1998) and could be described using independent 3H and He isotope
techniques for groundwater age dating. Surface waters in Oklahoma had unusual
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by large CFC concentrations especially near Oklahoma City, and treated sewage
as well as industrial runoff discharged into rivers was suspected to be the origin for
CFCs in the aquifer (Schulz et al., 1976; Busenberg and Plummer, 1992). Also, the
Withlacoochee River at Valdosta, Georgia (Plummer et al., 1998a), had elevated
concentrations of CFCs. Travel times from point sources to areas of groundwater
infiltration are too short to allow complete equilibrium with atmospheric concentrations (Böhlke et al., 1998). CFC concentrations in the Hudson estuary in 1991
were found to be greater than atmospheric solubility equilibrium concentrations,
demonstrating that the entire reach was contaminated with CFCs from local
wastewater discharge (Clark et al., 1995).
D. Landfills
Significant amounts of CFCs have been dumped in landfills for municipal and
industrial wastes with spray cans (Laugwitz et al., 1990; Deipser and Stegmann,
1994), insulation foams (Vollrath et al., 1995), and plastics (Haderlein and Pecher,
1988). It has been shown that gaseous emissions from landfills contain significant
CFC concentrations in ranges of 0.1 to 200 mg m–3 for CFC-11 and from 35 to 600
mg m–3 for CFC-12 (Gendebien et al., 1992; Allen et al., 1997). Soil gas surveys
at up to 130 m besides a landfill at Foxhole in Suffolk, UK, revealed elevated
concentrations of CFCs and showed that CFCs can migrate as gaseous pollutants
through the vadose zone (Ward et al., 1996). Groundwater in equilibrium with
typical landfill gas is expected to contain CFCs in the µg L–1 range. Evidence for
CFC contamination in groundwater has been given at a landfill site in North
Norfolk, UK (Bateman, 1998). Groundwater samples from six private wells in the
vicinity of the landfill were orders of magnitude above atmospheric equilibrium.
The maximum CFC-12 concentration found in one well (0.4 µg L–1) was close to
equilibrium with the measured concentration in the landfill gas (1.6 µg L–1 at 10˚C),
and the signature of the relative concentrations of CFC-11, -12, and -113 in the
landfill gas was preserved in the groundwater. This groundwater could be diluted
by 1 part in 4000 and still had a CFC-12 concentration clearly above equilibrium
with modern air (Bateman, 1998). It was concluded that CFC-12 would be a better
tracer for locating the landfill plume than chloride. Furthermore, Busenberg and
Plummer (1999) reported the use of CFCs to map a waste plume at the Idaho
National Engineering and Environmental Laboratory.
E. Solvent Spills
CFC-113 is a dense nonaqueous phase liquid (DNAPL, density 1.58 kg L–1)
with a boiling temperature of 47˚C, which was used as a degreasing solvent in
industry. Similar to trichloroethene, CFC-113 has been dumped as DNAPL solvent
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into the vadose zone, and groundwater plumes with CFC-113 have been reported
at industrial sites and a landfill receiving solvent wastes (Lesage et al., 1990). CFC11 and CFC-12 have boiling temperatures of 23˚C and –30˚C, respectively, and
only CFC-11 has been used occasionally as a solvent. In the Edwards Aquifer in
Texas (Thompson and Hayes, 1979), a 72-km-long anomaly with elevated concentrations of CFC-11 was found in 1979. The origin of the spill is not known. It was
calculated that the total amount of CFC-11 involved to create this plume could be
as small as 21 kg (Thompson and Hayes, 1979).
F. Sampling Artifacts
A few authors report that the origin of CFC-contaminated samples is due to
sampling artifacts. They include sampling equipment such as tubing (Busenberg
and Plummer, 1992; Shapiro, 2001) and well-construction materials such as grout
used to seal the borehole annulus and PVC adhesives (Goode, 1998).
G. Agrochemicals
In the Snake River Plain aquifer underlying rural Idaho, water from irrigated
areas had anomalously high concentrations of CFC-11 and to a lesser extent of
CFC-12 (Figure 2d). Surface water had CFC-11 concentrations up to 6500 pg L–1,
but CFC-12 was in equilibrium with modern air. The potential source of the
supersaturated concentrations in the aquifer was speculatively explained as being
ingredients used in pesticides in the area (Plummer et al., 2000). Fluorinated
pesticides such as trifluralin (Key et al., 1997) may contain traces of CFCs. In the
citrus fruit-growing agricultural area of the Southern San Joaquin valley in California, the age of the groundwater sampled in 5 out of 23 domestic groundwater
wells could not be used for age-dating because at least two of the three CFCs (11,
12, 113) exceeded equilibrium with modern air (Spurlock et al., 2000). CFC-113
was reported to be particularly problematic with anomalous concentrations in 13
wells, but no concentration data are given, and below a field in central Minnesota
CFC-12 concentrations at the water table were reported to by supersaturated by
12%, with respect to uncontaminated air at the time of collection (Delin et al.,
2000).
H. Thermal Heat Pumps
In Switzerland, more than 10,000 pumps were operated in 1992 to extract heat
from the ground for heating buildings. Some of these installations use the geothermal heat gradient in the vadose zone, others are using the heat in groundwater.
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Usually, heat-conducting fluids other than CFCs (e.g., glycols) are pumped through
a closed circuit in the ground, and heat pumps operating with a CFC or HCFC
refrigerant are used in a second circuit above ground. In some installations, the
refrigerant is also circulated directly in the ground. No studies are available
concerning the impact of such heat circuits on groundwater quality. Since 1994,
only HFCs, HCFCs, or other refrigerants are used in new installations in Switzerland.
IV. FATE OF CFCS AND HCFCs IN AQUIFERS
A. Volatilization
In unconfined aquifers, groundwater plumes with CFC concentrations in excess to
equilibrium with soil air are losing CFCs by volatilization. As discussed in Grathwohl et
al. (2000) and Klenk (2000), transfer rates of volatile pollutants through a stagnant
groundwater table are limited by the transverse vertical dispersivity from the groundwater
surface. The resistance for volatilization is thus entirely on the groundwater side and not
on the soil-air side. Once volatile pollutants leave the groundwater, the volatilization from
the unsaturated zone will be fast, if the soil surface is not sealed. Transverse vertical
dispersivities on groundwater are generally in the order of millimeters only (Grathwohl
et al., 2000). From a TCE contaminated aquifer in a tank experiment, the measured
maximum volatilization flux was very small (Klenk, 2000). Observations of the volatilization flux at a field site above a trichloroethene plume with concentrations > 10 µg L–1
yielded a flux of 1.3 mg m–2 d–1 across the soil surface (Smith et al., 1996). Low
volatilization fluxes are consistent with the observation of long contaminant plumes of
volatile recalcitrant compounds such as trichloroethene in aerobic aquifers (Wiedemeier
et al., 1999). However, volatile losses of pollutants increase considerably in case of an
oscillating groundwater table, with peak fluxes during a retreating water table (McCarthy
and Johnson, 1993; Werner and Höhener, 2002). When groundwater is retreating, the airwater interface increases and deeper groundwater layers with higher pollutant concentrations come into contact with the soil air. In a laboratory column experiment, the diffusive
fluxes of CFC-114 from the groundwater through the unsaturated zone to the atmosphere
increased >100-fold when the groundwater table slowly retreated (Werner and Höhener,
2002). However, a complete quantitative understanding of these processes is difficult due
to hysteresis effects and due to entrapped air bubbles in the capillary fringe (McCarthy
and Johnson, 1993).
B. Aerobic Biotransformation
No reports on the aerobic biotransformation of CFCs are available (Sylvestre
et al., 1997), and evidence for the recalcitrance is further given by the consistency
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of concentration profiles of CFCs in aerobic ocean or lake waters compared with
profiles of other tracers (Weiss et al., 1991). HFCs and HCFCs, however, can be
cometabolically transformed by methane- and propane-oxidizing bacteria (De
Flaun et al., 1992; Chang and Criddle, 1995; Oremland et al., 1996; Matheson et
al., 1997; Streger et al., 1999). The order of reactivity was found to be HCFC-22
> HCFC-142b > HFC-134a > HCFC-123 (Chang and Criddle, 1995). Further
compounds reported to be biotransformed by methanotrophs included HCFC-21,
HCFC-141b, and HFC-143, but neither HCFC-124 nor HFC-125 (Streger et al.,
1999). Complete dehalogenation has been found (Streger et al., 1999). Ammoniaoxidizing bacteria have been found to mineralize fluoromethane, HFC-41 (Hyman
et al., 1994).
C. Anaerobic Biotransformation
Before 1989, CFCs have been expected to be resistant to biotransformation
(Rowland and Molina, 1975) because of the chemical stability. Then, however, it
was reported for the first time that CFC-11 and CFC-12 can be dechlorinated in
anaerobic ecosystems such as termite mounds (Khalil and Rasmussen, 1989) and
in rice fields (Khalil and Rasmussen, 1990). Later, CFC-11 dechlorination under
anaerobic conditions has been observed in methanogenic sediment (Lovley and
Woodward, 1992), anoxic aquifer (Semprini et al., 1992), contaminated groundwater (Sonier et al., 1994), anoxic marine water (Shapiro et al., 1997; Lee et al., 1999),
municipal solid waste (Ejlertsson et al., 1996), and in compost and marl (Deipser,
1998b). Abiotic controls did not exhibit dechlorination activity. The CFCs serve
as electron acceptors, as are nitrate, iron(III), sulfate, and CO2 in groundwater. The
degradation of CFC-11, -12, and -13 also occurs in synthetic solutions containing
corrinoids (Krone and Thauer, 1991) or hematin (Lovley and Woodward, 1992)
and in pure culture of Methanosarcina barkeri Fusaro (DSM 804) (Krone and
Thauer, 1992).
The proposed degradation pathway corresponds to a stepwise dehalogenation.
A reaction mechanism involving corrinoids has been proposed (Krone and Thauer,
1991). In various anaerobic environments such as compost, sediments, and pond
water, the rate of CFC-11 disappearance was about 10 times faster that the rate of
CFC-12 disappearance (Oster et al., 1996). In the anoxic Framvaren Fjord, CFC11 was degraded at a first-order rate of 6 to 9 yr–1, but CFC-12 at only a rate of 0.01
to 0.03 yr–1 (Shapiro et al., 1997). The formation of HCFC-21 and HCFC-31 as
products from biotransformation of CFC-11 (Figure 5) and formation of HCFC-22
from CFC-12 was observed in experiments simulating anaerobic conditions in
landfills (Ejlertsson et al., 1996; Deipser, 1998b). HCFC-21, HCFC–22, and
HCFC-31 are trace compounds in landfill gases (Allen et al., 1997). Only HCFC22 has been produced for industrial applications. Neither the toxic HCFC-21 nor
the flammable and carcinogenic HCFC-31 (Figure 6) were produced. HCFC-21
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FIGURE 5. Reductive dechlorination of CFC-11 to HCFC-21, HCFC-31, and HFC-41.
FIGURE 6. Properties and toxicity of fluorinated and chlorinated methanes, adapted from
Svanström (1997). Flammability of vapors restricted the use of compounds as aerosol
propellents.
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and HCFC-31 in landfill gas thus originate from dehalogenation of CFC-11.
Furthermore, HCFC-31 was found to be transformed in anaerobic digesters, but no
analytical technique was available to identify the probable transformation product
fluoromethane (HFC-41) (Deipser, 1998a). In methanogenic landfill leachates
(Lesage et al., 1990; Denovan and Strand, 1992; Lesage et al., 1992) and laboratory
municipal waste digesters (Deipser and Stegmann, 1994; Deipser and Stegmann,
1997; Deipser, 1998a), enzymatic reductive dechlorination of CFC-113 was also
observed leading to the formation of HCFC-123a (1,2-Dichloro-1,1,2trifluoroethane), chlorotrifluoroethene, HCFC-133 and –133b. HCFC-123
(2,2-Dichloro-1,1,1-trifluoroethane) was also reported to be enzymatically dechlorinated under anaerobic conditions in freshwater and salt marsh sediments (Oremland
et al., 1996). In summary, reductive dechlorination of CFCs appears to be a
widespread phenomenon in anaerobic ecosystems, with the order of reactivity
being CFC-11>CFC-113>CFC-12. Once transformed to HCFCs, the reaction rates
of further dechlorination decrease (Deipser, 1998a). Reductive defluorination of
CFCs and HCFCs has not been observed in anaerobic environments at ambient
temperatures because the fluorine-carbon bond is extremely stable (Key et al.,
1997).
D. Abiotic Oxidative Transformation
The chemical reactions of volatile halogenated compounds in the atmosphere
have been studied intensively and are summarized elsewhere (Hayman and Derwent,
1996; Molina et al., 1996). Only HFCs and HCFCs, but not CFCs, are undergoing
photochemical reaction with radicals. As a consequence, CFCs are considered as
recalcitrant in the lower atmosphere as well as in aerobic aquatic environments
(Key et al., 1997). In the atmosphere, trifluoroacetate (TFA) has been found to be
a product of HFC and HCFC reaction with radicals (Jordan and Frank, 1999), but
these concentrations cannot be explained by HFC and HCFC degradation alone
(Jordan and Frank, 1999; Ellis et al., 2001). TFA concentrations of 33 to 220 ng
L–1 have been reported at six Swiss precipitation sampling sites (Berg et al., 2000),
and 140 ng L–1 in major German rivers (Jordan and Frank, 1999), assuming
rainwater as the TFA source. TFA is a compound with virtually no loss mechanism
in the environment (Ellis et al., 2001). In groundwater, the transformation of HFCs
and HCFCs with radicals is assumed to be insignificant (Franklin, 1993).
E. Abiotic Reductive Transformation
Dehalogenation is a potential mechanism for transformation of CFCs and
HCFCs (Sylvestre et al., 1997). CFC-11 has been found to undergo reductive
dechlorination in chemical reaction with zero-valent iron in the absence of molecu-
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lar oxygen (Scheutz et al., 2000), with a half-life time of 22 h at room temperature.
Zero-valent iron has been suggested as a technology to reduce gaseous emissions
of CFCs from old landfills (Scheutz et al., 2000), although the transformation
products of CFC dechlorination by zero-valent iron were not described. The
process could potentially be applied in permeable reactive barriers for groundwater
clean-up (Gillham and O’Hannesin, 1994). Furthermore, a number of other catalysts such as palladium (Juszczyk et al., 1998) or metal carbides (Dhandapani and
Oyama, 1995) have been described to catalyze the dehalogenation of CFCs.
V. RISK OF CFCs AND THE DEGRADATION PRODUCTS IN
GROUNDWATER
Generally, CFCs have a very low toxicity (Downing, 1988). This fact made
these suitable as carrier gas in medical sprays for oral inhalation. Due to the
difficulty of finding equally innocuous gases, mixtures of CFC-11 and CFC-12 are
still used in medical sprays (Rusch, 1991). CFCs in concentrations above the
microgram per liter range in groundwater presumably do not have any adverse
effects toward human health or the functioning of the groundwater ecosystem
(Dekant, 1996). HCFCs and HFCs are generally more toxic than CFCs, due to the
increased reactivity (Berends et al., 1999). These are, to varying extents,
biotransformed in the organism, mainly by cytochrome P450-catalyzed oxidation
of C-H bonds (Dekant, 1996). Studies on HFC or HCFC toxicity focussed on
industrially produced compounds such as, HCFC-123, but not on the isomer
HCFC-123a formed from the dechlorination of CFC-113. The toxicity of fluorinated methanes is better known (Figure 6). As illustrated, the transformation
products of CFC-11 (Figure 5), but not those of CFC-12, are problematic. HCFC21 is toxic, having an exposure limit (MAK-value) of 10 mg m–3 (DFG, 1997).
HCFC-31 is a substance listed as carcinogenic in class III A2, listing substances
shown to be clearly carcinogenic only in animal studies but under conditions
indicative of carcinogenic potential at the workplace (DFG, 1997). For the
chlorofluoroethanes, a similar increase in toxicity during dechlorination is expected, but not well established.
The possible transformation reactions of CFCs and HCFCs have implications
for the risk assessment in groundwater. Because CFCs are found to be degraded in
various anaerobic aquifers (Oster et al., 1996; Böhlke et al., 1998; Dunkle Shapiro
et al., 1998; Kofod and Isenbeck-Schröter, 2000) or marine waters (Shapiro et al.,
1997; Lee et al., 1999), the presence of HCFCs and HFCs is likely, but not reported
due to lack of sensitive analytical techniques. HFCs and HCFCs are difficult to
analyze by gas chromatography due to the lower number of chlorine atoms in the
molecule and the difficulties to obtain standards. Also, the choice of a suited GC
column for complete separation of peaks is not trivial (Sturrock et al., 1993;
Simmonds et al., 1995). However, even the most toxic HCFCs would probably not
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be a health risk at the pg L–1 concentration range. The presence would, however,
be critical in the µg L–1 range near point sources of organofluorine compounds,
such as industrial spill sites. A groundwater plume of CFC-11 in an anaerobic
aquifer is likely to exhibit similar features as a plume of tetrachloroethene
(Wiedemeier et al., 1999): both of these are potentially transformed by reductive
dechlorination to more toxic (HCFC-21, dichloroethenes) and carcinogenic transformation products (HCFC-31, vinylchloride). In anaerobic aquifers, degradation
rates of CFCs are potentially large enough to prevent the migration of CFC plumes
from such point sources. When treating mixed contaminant plumes of chlorinated
solvents and CFCs with dehalogenation techniques such as permeable reactive
subsurface barriers with zero-valent iron (Gillham and O’Hannesin, 1994) or
bioaugmentation (Ellis et al., 2000), great attention has to be paid to the formation
of HCFCs and HFCs as transformation products. These products are equally
mobile, more toxic, and may persist in those anaerobic aquifers. No field studies
can be found at present on the ultimate fate of HCFCs –21, -31, -123a, and –133
and chlorotrifluoroethene in aquifers.
VI. OUTLOOK AND RESEARCH NEEDS
As a result of various regulations regarding the use of CFCs, the production of
CFC-11, CFC-12, and CFC-113 have come almost to a complete end (Figure 1).
However, because of long lifetimes in applications such as foams, CFCs are still
emitted. Modeling results suggest that atmospheric concentrations of CFC-11 and
CFC-12 will reach a maximum around year 2000, and then will slowly decline
(Elkins et al., 1993; Montzka et al., 1999). A similar scenario is likely for CFC113. HFCs and HCFCs as the replacement products for CFCs had sharp increases
in production (AFEAS), and atmospheric concentrations in the 1990s increased
dramatically (Montzka et al., 1999). HFCs and HCFCs will be in use until 2020 or
2030 according to actual outphasing plans.
An interesting question with respect to the presence of CFCs and HCFCs in the
aquatic environment is the time lag between the end of production and the end of
lifetime in use. In a literature study (Pasteris, 2000), CFC and HCFC concentrations in Swiss municipal waste were estimated for the time period from 1930 to
1996. The results (Figure 7) provide an order of magnitude estimate for the CFCcontent of waste disposed in Swiss municipal solid waste landfills. The reduction
of CFC use in aerosols in the late 1970s and the short lifetime of these products
explain the characteristic evolution for this domain. The estimates (Figure 7)
predict a significant contribution of CFCs from rigid foams to present day municipal waste. Solvents have not been included in the figure because these have mainly
been used in industrial applications, and the way of disposal is not evident. For the
period from 1970 to 1985 a mean CFC content of 100 mg CFC per kg waste is
estimated, which corresponded to data measured in a landfill compartment (Baccini
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FIGURE 7. Estimated historic (H) CFC content in municipal waste in Switzerland. From
(Pasteris, 2000). The historic evolution of the (H)CFC sales were multiplied with average
lifetimes and average residual quantities in products (aerosols, 2 yr; residual 4% w/w;
refrigeration, 18 yr, residual 20%; rigid foams, 40 yr, residual 80%).
et al., 1987). This corresponds to approximately 28 mg of fluorine per kg waste.
For 16 mg of this fluorine volatilization from the landfill is likely (aerosol propellant and refrigerant), whereas rapid volatilization is unlikely for 12 mg (foams). A
recent study determined lifetimes of CFCs in closed-cell foams as a function of
particle size of the waste and found half-life times for the diffusive losses of CFCs
in the order of tens to hundred of years (Kjeldsen and Jensen, 2001). Only longterm experimental evidence will tell to what extent old landfills will be continuing
sources of CFCs in the 21st century.
Future research should investigate the distribution and fate of other industrially
produced CFCs and HCFCs than those used for age-dating, namely, those given in
Table 1. It should be noted that a better understanding of the transport pathways
of CFCs to groundwater leads also to a better understanding of the transport of
other VOCs. More work is specifically needed to accurately analyze and better
understand the fate of the HCFCs in groundwater. No studies have looked so far
at the potential anaerobic biotransformation of HFC-134a, HCFC-141b, or -142b
and other HCFCs used as replacement products for CFCs. Furthermore, the fate of
the toxic compounds formed by anaerobic dechlorination of CFCs (HCFC-21, -31,
chlorotrifluoroethene) in groundwater should be investigated in more detail, looking at biotransformation reactions as well as chemical reactions with zero-valent
iron or natural catalysts.
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ACKNOWLEDGMENTS
We thank Walter Giger, Dieter Genske, and Catherine Keller for helpful
comments. Financial support was from Swiss National Science Foundation (Grant
21-57115.99).
REFERENCES
AFEAS, Alternative Fluorocarbons Environmental Acceptability Study. www.afeas.org
Allen, M., Braithwaithe, and A. Hills, C.C., Trace organic compounds in landfill gas at seven U.K.
waste disposal sites. Environ. Sci. Technol. 31: 1054–1061, 1997.
Baccini, P., Henseler, G., Figi, R., and Belevi, H., Water and element balances of municipal solid
waste landfills. Waste Manag. Res. 5: 483–499, 1987.
Baehr, A.L., Stackelberg, P.E., and Baker, R.J., Evaluation of the atmosphere as a source of volatile
organic compounds in shallow groundwater. Water Resour. Res. 35: 127–136, 1999.
Bateman, A., Chlorofluorocarbons in groundwater, Ph D. thesis, University of East Anglia, 1998.
Bauer, S., Fulda, C., and Schäfer, W., A multi-tracer study in a shallow aquifer using dating tracers
H-3, Kr-85, CFC-113 and SF6 — Indication for retarded transport of CFC-113. J. Hydrol. 248:
14–34, 2001.
Berends, A.G., de Rooij, C.G., Shin-ya, S., and Thompson, R.S., Biodegradation and ecotoxicity of
HFCs and HCFCs. Arch. Environ. Con. Tox. 36: 146–151, 1999.
Berg, M., Müller, S., Mühlemann, J., Wiedmer,, and A. Schwarzenbach, R.P., Concentrations and
Mass Fluxes of Chloroacetic Acids and Trifluoroacetic Acid in Rain and Natural Waters in
Switzerland. Environ. Sci. Technol. 34: 2675–2883, 2000.
Beyerle, U., Aeschbach-Hertig, W., Hofer, M., Imboden, D.M., Baur, H., and Kipfer, R., Infiltration
of river water to shallow aquifer investigated with 3H/3He, noble gases and CFCs. J. Hydrol.
220: 169–185, 1999.
Böhlke, J.K., Revesz, K., Busenberg, E., Deak, J., Deseé, E., and Stute, M., Groundwater record of
halocarbon transport by the Danube River. Environ. Sci. Technol. 31: 3293–3299, 1998.
Bu, X. and Warner, M.J., Solubility of chlorofluorocarbon 113 in water and seawater. Deep Sea
Research 42: 1151–1161, 1995.
Bullister, J.L. and Weiss, R.F., Atmospheric chlorofluoromethanes in the Greenland and Norwegian
seas. Science 221: 265–268, 1983.
Bullister, J.L. and Weiss, R.F., Determination of CCl3F and CCl2F2 in seawater and air. Deep-Sea
Res. 35: 839–853, 1988.
Busenberg, E. and and Plummer, L.N., Use of chlorofluorocarbons (CCl3F and CCl2F2) as hydrologic tracers and age-dating tools: The alluvium and terrace system of central Oklahoma.
Water Resour. Res. 28: 2257–2283, 1992.
Busenberg, E. and Plummer, L.N., Dating young groundwater with sulfur hexafluoride: natural and
anthropogenic sources of sulfur hexafluoride. Water Resour. Res. 36: 3011–3030, 2000.
Chang, C.C., Lo, G.G., Tsai, C.H., and Wand, J.L., Concentration variability of halocarbons over an
electronics industrial park and its implication in compliance with the Montreal protocol.
Environ. Sci. Technol. 35: 3273–3279, 2001.
Chang, W.K. and Criddle, C.S., Biotransformation of HCFC-22, HCFC-142b, HCFC-123, and HFC134a by methanotrophic mixed culture MM1. Biodegradation 6: 1–9, 1995.
Clark, J.F., Smethie, W.M., and Simpson, H.J., Chlorofluorocarbons in the Hudson estuary during
summer months. Water Resour. Res. 31: 2553–2560, 1995.
23
130360.pgs
23
1/13/03, 12:50 PM
Cook, P.G. and Solomon, D.K., Transport of atmospheric tracer gases to the water table: Implication
for groundwater dating with chlorofluorocarbons and krypton 85. Water Resour. Res. 31: 263–
270, 1995.
Cook, P.G. and Solomon, D.K., Recent advances in dating young groundwater: chlorofluorocarbons,
3H/3He and 85Kr. J. Hydrol. 191: 245–265, 1997.
Cook, P.G., Solomon, D.K., Plummer, L.N., Busenberg, E., and Schiff, S.L., Chlorofluorocarbons as
tracers of groundwater transport processes in a shallow, silty sand aquifer. Water Resour. Res.
31: 425–434, 1995.
Cook, P.G., Solomon, D.K., Sanford, W.E., Busenberg, E., Plummer, L.N., and Poreda, R.J.,
Inferring shallow groundwater flow in saprolite and fractured rock using environmental
tracers. Water Resour. Res. 32: 1501–1509, 1996.
Cunnold, D.M., Fraser, P.J., Weiss, R.F., Prinn, R.G., Simmonds, P.G., Miller, B.R., Alvea, F.N., and
Crawford, A.J., Global trends and annual releases of CCl3F and CCl2F2 estimated from ALE/GAGE
and other measurements from July 1978 to June 1991. J. Geophys. Res. 99: 1107–1126, 1994.
De Flaun, M.F., Ensley, B.D., and Steffan, R.J., Biological degradation of hydrochlorofluorocarbons
(HCFCs) by a methanotrophic bacterium. Biotechnology 10: 1576–1578, 1992.
Deipser, A., Biodegradation of volatile CFCs, H-CFCs and VC in compost and marl. Waste Manage.
Res.16: 330–341, 1998a.
Deipser, A., Biodegradation of volatile CFCs, H-CFCs and VC in compost and marl. Waste Manage
Res. 16: 330–341, 1998b.
Deipser, A. Stegmann, R., The origin and fate of volatile trace components in municipal solid waste
landfills. Waste Manage. Res. 12: 129–139, 1994.
Deipser, A. and Stegmann, R., Biological degradation of VCCs and CFCs under simulated anaerobic
landfill conditions in laboratory test digesters. Environ. Sci. Pollut. Res. 4: 209–216, 1997.
Dekant, W., Toxicology of chlorofluorocarbon replacements. Environ. Health Perspect 104: 75–83,
1996.
Delin, G.N., Healy, R.W., Landon, M.K., and Bohlke, J.K., Effects of topography and soil
properties on recharge at two sites in an agricultural field. J. Am. Water Res. Assoc. 36:
1401–1416, 2000.
Denovan, B. and Strand, S., Biological degradation of chlorofluorocarbons in anaerobic environments. Chemosphere 24: 935–940, 1992.
DFG, Deutsche Forschungsgemeinschaft, List of MAK and BAT Values 1997. Commission for the
Investigation of Health Hazards of Chemical Compounds in the Work Area, Report No. 33,
WILEY-VCH Verlag GmbH, Weinheim, 1997.
Dhandapani, B. and Oyama, S.T., Novel catalysts for selective dehalogenation of CCl2F2 (CFC-12).
Catalysis letters 35: 353–360, 1995.
Downing, R.C., Fluorocarbon Refrigerants Handbook, Prentice-Hall, Englewood Cliffs, New Jersey, 1988.
Dunkle, S.A., Plummer, L.N., Busenberg, E., Philips, P.J., Denver, J.M., Hamilton, P.A., Michel,
R.L., and Coplen, T.B., Chlorofluorocarbons (CCl3F and CCl2F2) as dating tools and hydrologic tracers in shallow groundwater of the Delmarva Peninsula, Atlantic Coastal Plain, United
States. Water Resour. Res. 29: 3837–3860, 1993.
Dunkle Shapiro, S., Rowe, G., Schlosser, P., Ludin, A., and Stute, M., Tritium-helium 3 dating under
complex conditions in hydraulically stressed areas of a buried-valley aquifer. Water Resour.
Res. 34: 1165–1180, 1998.
Ejlertsson, J., Johansson, E., Karlsson, A., Meyerson, U., and Svensson, B.H., Anaerobic degradation
of xenobiotics by organisms from municipal solid waste under landfilling conditions. Antonie
van Leeuwenhoek 69: 67–74, 1996.
Ekwurzel, B., Schlosser, P., Smethie, W.M., Plummer, L.N., Busenberg, E., Michel, R.L., Weppernig,
R., and Stute, M., Dating of shallow groundwater: Comparison of the transient tracers 3H/4H,
chlorofluorocarbons, and 85Kr. Water Resour. Res. 30: 1693–1708, 1994.
24
130360.pgs
24
1/13/03, 12:50 PM
Elkins, J.W., Thompson, T.M., Swanson, T.H., Butler, J.H., Hall, B.D., Cummings, S.O., Fisher,
D.A., and Raffo, A.G., Decrease in the growth rates of atmospheric chlorofluorocarbons 11
and 12. Nature 365: 780–783, 1993.
Ellis, D.A., Mabury, S.A., Martin, J.W., and Muir, D.C.G., Thermolysis of fluoropolymers as a
potential source of halogenated organic acids in the environment. Nature 412: 321–324, 2001.
Ellis, D.E., Lutz, E.J., Odom, J.M., Buchanan, R.J., Bartlett, C.L., Lee, M.D., Harkness, M.R., and
Deweerd, K.A., Bioaugmentation for accelerated in situ anaerobic bioremediation. Environ.
Sci. Technol. 34: 2254–60, 2000.
Franklin, J., The atmospheric degradation and impact of 1,1,1,2–tetrafluoroethane (hydrofluorocarbon
134a). Chemosphere 27: 1565–1601, 1993.
Gendebien, A. et al., Landfill gas: from environment to energy, Commission of the European
Communities, Directorate General Energy, Luxembourg, 1992, 865 pp.
Gillham, R.W. and O’Hannesin, S.F., Enhanced degradation of halogenated aliphatics by zero-valent
iron. Ground Water 32: 958–967, 1994.
Goode, D.J., Ground-water age and atmospheric tracers: Simulation studies and analysis of field data
from the Mirror Lake Site, New Hampshire, Ph.D. Thesis, Princeton University, 1998.
Grathwohl, P., Klenk, I.D., Eberhardt, C., and Maier, U., Steady state plumes: mechanisms of
transverse mixing in aquifers, in: Contaminated Site Remediation: From Source Zones to
Ecosystems, Melbourne, December 4-8, 2000.
Gribble, G.W., The natural production of chlorinated compounds. Environ. Sci. Technol. 28: A310–
A319, 1994.
Haderlein, S. and Pecher, K., Mobility of chlorofluorocarbons in deposits of shredder wastes from
plastic and metal utilizing industries. Water, Air, Soil Pollut. 37: 459–464, 1988.
Happell, J.D. and Wallace, D.W.R., Removal of atmospheric CCl4 under bulk aerobic conditions in
groundwater and soils. Environ. Sci. Technol. 1998: 1244–1252, 1998.
Hayman, G.D. and Derwent, R.G., Atmospheric chemical reactivity and ozone-forming potentials of
potential CFC replacements. Environ. Sci. Technol. 31: 327–336, 1996.
Ho, D.T., Schlosser, P., Smethie, W.M., and Simpson, H.J., Variability in atmospheric chlorofluorocarbons (CCl3F and CCl2F2) near a large urban area: Implications for groundwater dating.
Environ. Sci. Technol. 32: 2377–2382, 1998.
Hofer, M. and Imboden, D., Simultaneous determination of CFC-11, CFC-12, and Ar in water. Anal.
Chem. 70: 724–729, 1998.
Hyman, M.R., Page, C.L., and Arp, D.J., Oxidation of methyl fluoride and dimethyl ether by
ammonia monooxygenase in Nitrosomonas europaea. AEM 60: 3033–35, 1994.
Jacobsen, O.S., Brusch, W., Laier, T., Hansen, S.U., Spliid, N.H. Helweg, A., Transport and dating of
pesticide residues from a 40 year old point source. Hum. Environ. Exp. Xenobiotics 355–362, 1999.
Jean-Baptiste, P., Messias, M.J., Alba, C., Charlou, J.L., and Bougault, H., A simple copper-tube
sampler for collecting and storing seawater for post-cruise CFC measurements. Deep-Sea Res.
41: 1361–1372, 1994.
Johnston, C.T., Cook, P.G., Frape, S.K., Plummer, L.N., Busenberg, E., and Blackport, R.J., Ground
water age and nitrate distribution within a glacial aquifer beneath a thick unsaturated zone.
Ground Water. Jan Feb 36: 171–180, 1998.
Jordan, A. and Frank, H., Trifluoroacetate in the environment. Evidence for sources other than HFC/
HCFCs. Environ. Sci. Technol. 33: 522–527, 1999.
Jordan, A., Harnsich, J., Borchers, R., LeGuern, F., and Shinoharta, H., Volcanogenic hydrocarbons.
Environ. Sci. Technol. 34: 1122–1124, 2000.
Juszczyk, W., Malinowski, A., and Karpinski, Z., Hydrodechlorination of CCl2F2 (CFC-12) over gammaalumina supported palladium catalysts. Applied catalysis A -General 166: 311–319, 1998.
Katz, B., Lee, T.M., Plummer, L.N., and Busenberg, E., Chemical evolution of groundwater near a
sinkhole lake, northern Florida 1. Flow patterns, age of groundwater, and influence of lake
water leakage. Water Resour. Res. 31: 1549–1564, 1995.
25
130360.pgs
25
1/13/03, 12:50 PM
Katz, B.G., Böhlke, J.K., and Hornsby, H.D., Timescales for nitrate contamination of spring waters,
northern Florida, USA. Chem. Geol. 179: 167–186, 2001.
Key, B.D., Howell, R.D., and Criddle, C.S., Fluorinated organics in the biosphere. Environ. Sci.
Technol. 31: 2245–2254, 1997.
Khalil, M.A.K. and Rasmussen, R.A., The potential of soils as a sink of chlorofluorocarbons and
other man-made chlorocarbons. Geophys. Res. Lett. 16: 679–682, 1989.
Khalil, M.A.K. and Rasmussen, R.A., Emissions of trace gases from Chinese rice fields and boigas
generators: CH4, N2O, CO, CO2, chlorocarbons, and hydrocarbons. Chemosphere 20: 207–
226, 1990.
Kjeldsen, P. and Jensen, M.H., Release of CFC-11 from disposal of polyurethane foam waste.
Environ. Sci. Technol. 35: 3055–3063, 2001.
Klenk, I., Transport of volatile organic compounds (VOC’s) from soil-gas to groundwater, Ph.D.
thesis, University of Tuebingen, 2000.
Kofod, M. and Isenbeck-Schröter, M., Degradation of CFC during riverbed infiltration, in: Groundwater 2000, Copenhagen, Denmark, P.L. Bjerg, P. Engesgaard, and T.D. Krom (Eds.), 2000,
263–264.
Krone, U.E. and Thauer, R.K., Reductive formation of carbon monoxide from CCl4 and freons 11,
12 and 13 catalyzed by corrinoids. Biochemistry 30: 2713–2719, 1991.
Krone, U.E. and Thauer, R.K., Dehalogenation of trichlorofluoromethane (CFC-11) by Methanosarcina
barkeri. FEMS Microbiol. Lett. 90: 201, 1992.
Laugwitz, R., Poller, T., and Deipser, A., Der Beitrag von Hausmülldeponien zum Stoffkreislauf der
Fluorchlorkohlenwasserstoffe. (The contribution of domestic waste landfills to the chlorofluorocarbon cycle, in German). Muell Abfall 22: 316–318, 1990.
Lee, B.S., Bullister, J.L., and Whitney, F.A., Chlorofluorocarbon CFC-11 and carbon tetrachloride
removal in Saanich Inlet, an intermittently anoxic basin. Marine Chemistry. Aug 66: 171–185,
1999.
Lesage, S., Brown, S., and Hosler, K.R., Degradation of chlorofluorocarbon-113 under anaerobic
conditions. Chemosphere 24: 1225–1243, 1992.
Lesage, S., Jackson, R.E., Priddle, M.W., and Riemann, P.G., Occurence and fate of organic solvent
residues in anoxic groundwater at the Gloucester landfill, Canada. Environ. Sci. Technol. 24:
559–566, 1990.
Lesage, S., McBride, R.A., Cureton, P.M., and Brown, S., Fate of organic solvents in landfill
leachates under simulated field conditions and in anaerobic microcosms. Waste Manage. Res.
11: 215–226, 1993.
Lovley, D.R. and Woodward, J.C., Consumption of freons CFC-11 and CFC-12 by anaerobic
sediments and soils. Environ. Sci. Technol. 26: 925, 1992.
Matheson, L.J., Jahnke, L.L., and Oremland, R.S., Inhibition of methane oxidation by Methylococcus
capsulatus with hydrochlorofluorocarbons and fluorinated methanes. Applied Environmental
Microbiol. 63: 2952–56, 1997.
McCarthy, K.A. and Johnson, R.L., Transport of volatile organic compounds across the capillary
fringe. Water Resour. Res. 29: 1675–1683, 1993.
Molina, M. and Rowland, F.S., Stratospheric sink for chlorofluoromethanes: Chlorine atom catalyzed
destruction of ozone. Nature 249: 810–812, 1974.
Molina, M.J., Molina, L.T., and Kolb, C.E., Gas-phase and heterogeneous chemical kinetics of the
troposphere and stratosphere. Annual Review Physical Chemsitry 47: 327–367, 1996.
Montzka, S.A., Butler, J.H., Elkins, J.W., Thompson, T.M., Clarke, A.D., and Lock, L.T., Present and
future trends in the atmospheric burden of ozone-depleting halogens. Nature 398: 690–694,
1999.
Nativ, R., Gunay, G., Hotzl, H., Reichert, B., Solomon, D.K., and Tezcan, L., Separation of
groundwater-flow components in a karstified aquifer using environmental tracers. Applied
Geochemistry. 14: 1001–1014, 1999.
26
130360.pgs
26
1/13/03, 12:50 PM
Oremland, R.S., Lonergan, D.J., Culbertson, C.W., and Lovley, D.R., Microbial degradation of
hydrochlorofluoro-carbons CHCl2F and CHCl2CF3 in soils and sediments. Appl. Environ.
Microbiol. 62: 1818–1821, 1996.
Oster, H., Sonntag, C., and Munnich, K.O., Groundwater age dating with chlorofluorocarbons. Water
Resour. Res. 32: 2989–3001, 1996.
Pankow, J.F. and Cherry, J.A. Dense Chlorinated Solvents and Other DNAPLs in Groundwater.
Waterloo Press, Waterloo, Canada, 1996.
Pankow, J.F., Thomson, N.L., Johnson, R.L., Baehr, A., and Zogorski, J.S., The urban atmosphere
as a non-point source for the transport of MTBE and other volatile organic compounds (VOCs)
to shallow groundwater. Environ. Sci. Technol. 31: 2821–2828, 1997.
Pasteris, G., Substances chlorofluorés volatiles dans les décharges suisses, Masters Thesis, EPFL,
2000.
Plummer, L.N. and Busenberg, E., Chlorofluorocarbons: tools for dating and tracing young groundwater, in: Environmental tracers in subsurface hydrogeology, P. Cook A. Herczeg (Eds.),
Kluwer, Boston, Chapter 15, pp 441–478, 1999.
Plummer, L.N., Busenberg, E., Böhlke, J.K., Nelms, D.L., Michel, R.L., and Schlosser, P., Groundwater residence times in Shenandoah National Park, Blue Ridge Mountains, Virginia, U.S.: A
multi-tracer approach. Chem. Geol. 179: 93–111, 2001.
Plummer, L.N., Busenberg, E., McConnell, J.B., Drenkard, S., Schlosser, P., and Michel, R.L., Flow
of river water into a Karstic limestone aquifer. 1. Tracing the young fraction in groundwater
mixtures in the Upper Floridan Aquifer near Valdosta, Georgia. Applied Geochemistry. Nov
13: 995–1015, 1998a.
Plummer, L.N., Busenberg, E., Drenkard, S., Schlosser, P., Ekwurzel, B., Weppernig, R., McConnell,
J.B., and Michel, R.L., Flow of river water into a karstic limestone aquifer - 2. Dating the
young fraction in groundwater mixtures in the Upper Floridan aquifer near Valdosta, Georgia.
Appl. Geochem. 13: 1017–1043, 1998b.
Plummer, L.N., Michel, R.L., Thurman, E.M., and Glynn, P.D., Environmental tracers for age-dating
yound groundwater, in: Regional groundwater quality, W.M. Alley (Ed.), Van Nostrand, New
York, Chapter 11, pp 255–294, 1993.
Plummer, L.N., Rupert, M.G., Busenberg, E., and Schlosser, P., Age of irrigation water in ground
water from the Eastern Snake River Plain Aquifer, south-central Idaho. Ground Water 38:
264–283, 2000.
Randall, J.H.,and Schultz, T.R., Chlorofluorocarbons as hydrologic tracers: a new technology.
Hydrology Water Resources Arizona Southwest 6: 189–195, 1976.
Reilly, T.E., Plummer, L.N., Phillips, P.J., and Busenberg, E., The use of simulation and multiple tracers
to quantify groundwater flow in a shallow aquifer. Water Resour. Res. 30: 421–433, 1994.
Rowland, F.S. and Molina, M.J., J. Rev. Geophys. Space Phys. 13: 1–35, 1975.
Rusch, G.M., Toxicity studies with new refrigerant gases. Toxicologist 11: 102, 1991.
Russell, A.D. and Thompson, G.M., Mechanisms leading to enrichment of the atmospheric fluorocarbons CCl3F and CCl2F2 in groundwater. Water Resour. Res. 19: 57–60, 1983.
Scheutz, C., Winther, K., and Kjeldsen, P., Removal of halogenated organic compounds in landfill
gas by top covers containing zero-valent iron. Environ. Sci. Technol. 34: 2557–2563, 2000.
Schulz, T.R., Randall, J.H., Wilson, J.G., and Davis, S.N., Groundwater 14: 463–470, 1976.
Semprini, L., Hopkins, G.D., McCarty, P.L., and Roberts, P.V., In situ Transformation of Carbon
Tetrachloride and Other Halogenated Compounds Resulting from Biostimulation under Anoxic Conditions. Environ. Sci. Technol. 26: 2454–2461, 1992.
Shapiro, A.M., Effective matrix diffusion in kilometer-scale transport in fractured cristalline rock.
Water Resour. Res. 37: 507–522, 2001.
Shapiro, S.D., Schlosser, P., Smethie, W.M., and Stute, M., The use of H-3 and tritiogenic He-3 to
determine CFC degradation and vertical mixing rates in Framvaren Fjior, Norway. Mar.
Chem. 59: 141–157, 1997.
27
130360.pgs
27
1/13/03, 12:50 PM
Siegemund, G., Schwertfeger, W., Feiring, A., Smart, B., Behr, F., Vogel, H., and McKusick, B.,
Organic fluorine compounds, in: Ullmann’s Encyclopedia of Industrial Chemistry, W. Gerhartz,
Y.S. Yamamoto, B. Evers, and J.F. Rounsaville (Eds.), VCH Verlagsgesellschaft, Weinheim,
349–392, 1988.
Simmonds, P.G., O’Doherty, S.O., Nickless, G., Sturrock, G.A., Swaby, R., Knight, P., Ricketts, J.,
Woffendin, G., and Smith, R., Automated gas chromatograph/mass spectrometer for routine
atmospheric field measurements of the CFC replacement compounds, the hydrofluorocarbons
and hydrochlorofluorocarbons. Anal. Chem. 67: 717–723, 1995.
Smith, J.A., Tisdale, A.K., and Cho, H.J., Quantification of the natural vapor fluxes of trichloroethene
in the unsaturated zone at Picatinny Arsenal, New Jersey. Environ. Sci. Technol. 30: 2243–
2250, 1996.
Sonier, D.N., Duran, N.L., and Smith, G.B., Dechlorination of Trichlorofluoromethane (CFC-11) by
Sulfate-Reducing Bacteria from an Aquifer Contaminated with Halogenated Aliphatic Compounds. Appl. Environ. Microbiol. 60: 4567–4572, 1994.
Spurlock, F., Burow, K., and Dubrovsky, N., Chlorofluorocarbon dating of herbicide-containing well
waters in Fresno and Tulare counties, California. J. Environ. Qual. 29: 474–483, 2000.
Squillace, P., Moran, M.J., Lapham, W.W., Proce, C.V., Clawges, R.M., and Zogorski, J.S., Volatile
organic compounds in untreated ambient groundwater of the United States, 1985–1995.
Environ. Sci. Technol. 33: 4176–4187, 1999.
Streger, S.H., Condee, C.W., Tonga, P., and DeFlaun, M., Degradation of hydrohalocarbons and
brominated compounds by methane- and propane-oxidising bacteria. Environ. Sci. Technol.
33: 4477–4482, 1999.
Sturrock, G.A., Simonds, P.G., Nickless, G., and Zwiep, D., Analysis of chlorofluorocarbon replacement compounds by capillary gas chromatography. Journal of Chromatography 648: 1993.
Svanström, M., Blowing agents in rigid polyurethane foam, Doctoral thesis at the Department of
Chemical Environmental Science, Chalmers University of Technology, Göteborg, Sweden,
1997.
Sylvestre, M., Bertrand, J.L., and Viel, G., Feasibility study for the potential use of biocatalytic
systems to destroy chlorofluorocarbons (CFCs). Crit. Rev. Environ. Sci. Technol. 27: 87–111,
1997.
Szabo, Z., Rice, D.E., Plummer, L.N., Busenberg, E., and Drenkard, S., Age dating of shallow
groundwater with chlorofluorocarbons, tritium/helium 3 and flow path analysis, Southern New
Jersey Coastal Plain. Water Resour. Res. 32: 1023–1038, 1996.
Talma, A.S., Weaver, J.M.C., Plummer, L.N., and Busenberg, E., CFC tracing of groundwater in
fractured rock aided with 14C and 3H to identify water mixing, in Groundwater: Past
Achievements and Future Challenges, O. Sililo (Ed.), Balkema, Rotterdam, 635–639, 2000.
Thompson, G.M. and Hayes, J.M., Trichlorofluoromethane in groundwater — a possible tracer and
indicator of groundwater age. Water Resour. Res. 15: 547–554, 1979.
Thorstensson, D.C., Weeks, E.P., Haas, H., Busenberg, E., Plummer, L.N., and Peters, C.A., Chemistry of unsaturated zone gases sampled in open boreholes at the crest of Yucca Mountain,
Nevada: Data and basic concepts of chemical and physical processes in the mountain. Water
Resour. Res. 34: 1507–1529, 1998.
Tobler, W, Deichmann, U., Gottsegen, J., and Maloy, K., World population in a grid of spherical
quadrilaterals, International Journal of Population Geography, 3: 203–225, 1997.
UNEP, Montreal protocol on substances that deplete the ozone layer, UNEP Service number 87–
6106, 1987.
Vollrath, A., Hohl, C., and Seiler, H.G., Trace analysis of chlorofluorocarbons/partially halogenated
chlorofluorohydrocarbons (CFC/HCFC) in polymeric foams by headspace capillary gas chromatography with electron-capture detection or ion trap detection combined with preconcentration
on cold trap. Fresenius Journal of Analytical Chemistry 351: 251–259, 1995.
28
130360.pgs
28
1/13/03, 12:50 PM
Walker, S.J., Weiss, R.F., and Salameh, P.K., Reconstructed histories of the annual mean atmospheric mole fraction of the halocarbons CFC-11, CFC-12, CFC-113, and carbon tetrachloride.
J. Geophys. Res. Oceans 105: 14285–14296, 2000.
Wang, J.L., Chew, C., Chen, S.W., and Kuo, S.R., Concentration variability of anthropogenic
halocarbons and applications as internal reference in volatile organic compound measurements. Environ. Sci. Technol. 34: 2243–48, 2000.
Ward, R.S., Williams, G.M., and Hills, C.C., Changes in major and trace components of landfill gas
during subsurface migration. Waste Management Research 14: 243–261, 1996.
Warner, J. and Weiss, R.F., Solubilities of chlorofluorocarbons 11 and 12 in water and seawater.
Deep-Sea Res. 32: 1485–1497, 1985.
Washington, J.W., Gas partitioning of dissolved volatile organic compounds in the vadose zone:
Principles, temperature effects and literature review. Ground Water 34: 709–718, 1996.
Watson, R.T., Rodhe, H., Oeschger, H., and Siegenthaler, U., Greenhouse gases and aerosols, in
Climate Change — the IPCC Scientific Assessment, J.T. Houghton, G.J. Jenkins J.J. Ephraums
(Eds.), Cambridge University Press, Cambridge, 4–40, 1990.
Weeks, E.P., Earp, D.E., and Thompson, G.M., Use of atmospheric fluorocarbons F-11 and F-12 to
determine the diffusion parameters of the unsaturated zone in the southern high plains of
Texas. Water Resour. Res. 18: 1365–1378, 1982.
Weiss, R.F., Carmack, E.C., and Koropalov, V.M., Deep-water renewal and biological production in
Lake Baikal. Nature 349: 665–669, 1991.
Werner, D. and Höhener, P., The influence of water table fluctuations on the volatilization of
contaminants from groundwater, In: S.F. Thorton and S.E. Oswald (Eds.). Groundwater
Quality: Natural and Enhanced Restoration of Groundwater Pollution (Proc. Groundwater
Conf. held at Sheffield, UK, June 2001), IAHS Publ. No. 275, 213–218, 2002
Wiedemeier, T.H., Rifai, H.S., Newell, C.J., and Wilson, J.T. Natural Attenuation of Fuels and
Chlorinated Solvents in the Subsurface, Wiley, New York, 617 pp, 1999.
Yaws, C.L. and Yang, H.C., Henry’s law constant for compound in water, in Thermodynamic and
Physical Property Data, C.L. Yaws (Ed.), Gulf Publishing Company, Houston, TX, 181–206,
1992.
29
130360.pgs
29
1/13/03, 12:50 PM