Due to the unique properties of fluorine, millions of tonnes of fluorinated
compounds have been synthesized and serve as key components in various domestic,
industrial and commercial products. In terms of ecological and human risk, one
group of these compounds, the polyfluorinated and perfluorinated chemicals (PFCs),
are of particular importance. PFCs are a group of environmental contaminants of
concern that have received worldwide attention in recent decades. They have been
manufactured and used for more than 60 years, and are continuously released into
the environment during their production, usage and disposal. Because of their
persistence, they are globally distributed in various environmental and human
matrices. Yet, the fate and transportation pathways of this class of contaminants are
still not well understood.
To date, limited information is available on PFC concentrations in wet precipitation
worldwide and their fate in the atmospheric environment. In addition, to address the
issue of long-range atmospheric and oceanic transport of PFCs, there is an urgent
need to examine PFC concentrations in abiotic environmental compartments in the
circumpolar Arctic. The major aims of this PhD research study are to extend our
knowledge on the geographical distribution of PFCs in worldwide atmospheric
precipitates, such as rain, snow and ice cores, to identify their contamination sources,
to examine the effectiveness of wet precipitation as a scavenger of PFCs, and to
study their fate and transport to remote areas (e.g., the Norwegian Arctic). A mass
balance approach involving the determination of total fluorine (TF), inorganic
fluorine (IF) and extractable organic fluorine (EOF) was also adopted for
understanding the fate and distribution of fluorinated compounds in wet precipitation. Furthermore, preliminary measurements of volatile PFC precursors in
ambient air using GC-MS/MS were performed.
The first monitoring study of wet precipitation measured concentrations of 20 PFCs,
including C3-C5 short chain PFCs, using LC/MS/MS in precipitation samples from
Japan (n=31), USA (n=12), China (n=5), India (n=2) and France (n=2). Among the
PFCs measured, perfluoropropanoic acid (PFPrA) was detected in all of the
precipitation samples. Average total PFC concentrations ranged from 1.40-18.1 ng/L
for the seven locations studied. The greatest total PFC concentrations were detected
in Tsukuba, Japan, whereas the lowest concentrations were detected in Patna, India.
PFPrA, perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA) were
found to be the dominant PFCs in Japanese and American precipitation samples. No
observable seasonal trend was found in precipitation samples collected from two
locations in Japan. Annual fluxes of PFCs were estimated for Japan and the USA
and evidence for precipitation as an effective scavenger of PFCs in the atmosphere
was reported.
The second monitoring study focused on quantification of 18 individual PFCs in
snow (n=23), snow core (n=25) and drifting ice core samples (n=20) collected from
five cities in Japan. A few snow samples from downtown Albany (n=6) and
Slingerlands (n=4), New York, USA were also analyzed. For fresh snow samples,
slightly higher concentrations of PFCs were detected in AIST, Tsukuba (urban area)
than Mt. Tsukuba (rural area). When compared to rain samples collected from the
same area (AIST, Tsukuba), similar PFC concentrations and composition profiles
were observed, indicating that fresh snow may also reflect local atmospheric
contamination. All deposited snow samples showed elevated PFC concentrations, with the worst case found in deposited snow collected near a car park and hotel in
Zao, which is a famous ski resort in north-eastern Japan. These results indicated that
deposited snow is not indicative of recent PFC atmospheric pollution and that the
timing of sampling of snow samples should be taken into account when interpreting
PFC concentration patterns. Similar to Japanese precipitation, the dominant
compounds found in Mt. Tateyama snow cores and Shiretoko drifting ice cores were
PFOA and PFNA. N-ethyl perfluorooctanesulfonamidacetate (N-EtFOSAA), which
is commonly used in local industries, was also detected in snow core samples, as Mt.
Tateyama was situated in Toyama, which is an industrial area. Similar PFC
composition patterns were found within layers of the upper drifting ice cores (above
sea level), while each layer showed a unique composition profile, suggesting that the
contamination sources of PFCs differ during the formation of drifting ice. PFC
composition profiles of the bottom of the ice core (the layers below sea level)
strongly reflected PFC contamination during drifting ice formation and its
movement towards the coast.
After investigation of regional atmospheric contamination by PFCs in wet
precipitation, the global transportation and fate of PFCs were studied. The third
monitoring study reported the concentrations of 17 PFCs in two ice cores (n=26),
surface snow (n=9) and surface water samples (n=14) collected along a spatial
gradient in Svalbard, Norway, in the European Arctic. Concentrations of selected
ions (Na+, SO4 2−, etc) were also determined for tracing the origins and sources of
PFCs. Perfluorobutanoic acid (PFBA), PFOA and PFNA were the dominant
compounds found in ice core samples. Higher concentrations of PFOA, PFNA and
perfluorooctane sulfonate (PFOS) were detected in the middle layers of the ice cores
representing the period of 19972000. Lower concentrations of C8-C12 perfluorocarboxylates (PFCAs) were detected in comparison with concentrations
measured previously in an ice core from the Canadian Arctic, indicating less PFC
contamination in the European Arctic. Average PFC concentrations were found to be
lower in surface snow and melted glacier water samples, while increased
concentrations were observed in downstream river water collected near the coast.
Perfluorohexanesulfonate (PFHxS) was detected in the downstream locations, but
not in the glacier, suggesting local sources of this compound. Long-range
atmospheric transport of PFCs was the major deposition pathway for the glaciers,
while local sources (e.g., skiing activities) were identified in the downstream
locations.
In order to assess the risk of fluorinated compounds in wet precipitation, mass
balance analysis were performed using combustion ion chromatography for fluorine
(CIC-F). Concentrations of TF and IF were measured in rain (n=50) and snow
samples (n=14). EOF was extracted from several rain (n=10) and snow samples
(n=6) using specific solid phase extraction (SPE) procedures for removal of
inorganic fluorides. Concentrations of 19 known individual PFCs were also
determined. The geographical distribution of TF and IF in precipitation among
several locations was compared. The highest concentrations of TF (arithmetic mean:
919,000 ng-F/L) and IF (6520 ng-F/L) were found in Kawaguchi (industrial area),
whereas the lowest concentrations (TF: 384,000 ng-F/L; IF: 2530 ng-F/L) were
found in Tsukuba (science city with no industry). These results suggested that
precipitation can reflect primarily local contamination sources of both total and
inorganic fluoride ions. The contributions of EOF and IF to TF for different kinds of
wet precipitation samples were also further investigated. A high percentage of
non-extractable organic fluorine (OF-to-TF ratio: 99%) was found in precipitation samples, in contrast to what was observed in seawater (<20%). This difference may
be due to the forms of fluoride present in the atmosphere and water - fluoride tends
to bind to particulates in the atmosphere and exist as organic fluoride, while it
dissolves in water and ionizes. Known PFCs were found to contribute around
0.0001-0.001% to EOF, suggesting the need to identify the unknown fluorinated
chemicals present in the precipitation samples.
Volatile environmental pollutants undergo long-range transportation through the
atmosphere, and atmospheric processes such as wind and chemical reactions can
determine atmospheric concentrations in particular region. Therefore, in the last part
of my PhD study, preliminary measurements of volatile polyfluorinated precursors
in Japanese ambient air using GC-MS/MS were performed. Concentrations of seven
volatile polyfluorinated precursors, including fluorotelomer alcohols (FTOHs),
sulfonamides (FOSAs), and sulfonamidoethanols (FOSEs), were determined in
ambient air samples collected at both ground level (n=5) and an altitude of 450 m
(n=2) in Japan during August 2009. A helicopter was used to collect air samples
from Tsukuba to Kamakura (inland air), and from Kamakura to Hachijyo Island
(oceanic air) at a height of 450 m. At the same time, ground air samples were also
collected from the heliport and AIST in Tsukuba, as well as Kawaguchi, Kamakura
(urban areas) and Hachijyo Island (rural area) to study the transport of these volatile
precursors. Similar to PFCs, higher concentrations of total FTOHs and were detected
in urban areas (404 μg/m3) than in rural areas (349 μg/m3). Taking 8:2 FTOH and
N-EtFOSA as examples, around 80-90% of the measured concentrations were
detected at a higher level in the atmosphere, while only 10-20% remained near the
ground. These results indicated that FTOH and FOSA/SE contamination is largely
regional, although the potential for long range transportation of the compounds cannot be neglected.
In the present study, wet precipitation was found to reflect local PFC contamination
in the atmospheric environment, and to be an effective scavenger of PFCs. Although
the production and use of PFOS and it derivatives were phased-out starting from
2002 by 3M, this compound can still be found in worldwide atmospheric
precipitates even in the glacial ice cores from the European Arctic. Long-range
atmospheric transport of PFC precursors is the most feasible pathway through which
these compounds reach the remote areas. Therefore, in addition to detection of
PFCAs and PFASs, efforts should be made on developing analytical methods for
several new classes of perfluorinated surfactants (e.g., perfluoroalkylphosphonic
acid (PFPAs), perfluoroalkylphosphinites (PFPiAs), etc.), which are considered to be
PFCA precursors, and volatile precursors of PFCs (i.e., FTOHs and FOSA/SEs), not
only in air samples, but in different kinds of environmental matrices (e.g. water and
sediment). Tracing these chemicals can help to identify the major PFC
contamination sources and to understand the degradation pathways of these
compounds into PFCs in the environment. Regionally, PFC contamination in
Chinese estuaries is a major concern, and the fate, transport and degradation
pathways of PFCs should be examined in both atmospheric and aquatic systems in
China.
| Date of Award | 3 Oct 2012 |
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| Original language | English |
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| Awarding Institution | - City University of Hong Kong
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| Supervisor | Kwan Sing Paul LAM (Supervisor) |
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