Kurunthachalam Kannan
Wadsworth
Center, New York State Department of Health
Persistent organic pollutants (POPs) are a group of
organic chemicals exhibiting the combined properties of persistence, bioaccumulation,
toxicity, and long-range environmental transport. Currently, twelve substances or substance
groups are included under the Stockholm Convention on POPs. The United Nations Environmental
Program (UNEP) also suggests the need for identifying additional POPs as candidates
for future international action. While
monitoring studies are being implemented in developing countries to evaluate
sources and effects of the twelve POPs, the samples or sample extracts collected
for current monitoring can be used for the determination of emerging POPs
in environmental and biological matrices. Such planning will provide effective and
efficient use of resources. Several
contaminants such as, polybrominated diphenyl ethers (PBDEs), polychlorinated
naphthalenes (PCNs), and
perfluorooctanesulfonate (PFOS) are reported as
emerging global environmental contaminants. In this presentation, environmental distribution,
sources, dynamics and impacts of a new class of global contaminants, namely
perfluorinated compounds (PFCs), will be discussed.
Perfluorinated compounds are used in a wide variety of consumer
products for more than 50 years. These
compounds are persistent and bioaccumulative in
the food chain. But, until recently,
the environmental distribution of PFCs was unknown.
Recent developments in analytical techniques using high performance liquid
chromatography-negative ion electrospray tandem
mass spectrometry (HPLC-MS/MS) permitted the survey of PFCs in biota and water on a global scale. The HPLC-MS/MS analysis detected PFOS,
perfluorooctanesulfonamide (PFOSA), perfluorooctanoic
acid (PFOA) and perfluorohexane sulfonate
(PFHS) in human blood and wildlife tissues from all over the world. In biological matrices PFOS is the
most abundant compound of all the perfluorinated
acids measured so far. In water,
PFOA is a major perfluorinated contaminant detected
in several locations. In air samples,
particularly in indoor air, fluorotelomer alcohols
and perfluoroalkylsulfonamidoalcohols are the major
perfluorochemicals measured.
High concentration of PFOS in biological samples including
humans and wildlife is due to its great biomagnification
potential. Despite the predominance
of PFOA in water samples, the bioconcentration and
biomagnification potentials of this compound are relatively
low. While PFOS is a metabolic
product of various sulfonated perfluorochemicals,
PFOA is a metabolite of fluorotelomer alcohols and
is also processing aid in the production of various fluoropolymers.
The occurrence of PFCs in
remote marine environment has led to several hypotheses related to long-range
transport of PFCs. PFOS and PFOA, because of their strong
acidity, are expected to be present in ionized form, with little propensity
for volatilization, under normal environmental conditions. Atmospheric transport of relatively more
volatile precursor compounds, such as polyfluoroalkylated
sulfonamides, sulfonamidoalcohols, and fluorotelomer alcohols, to remote marine locations, where
the precursors break down, by biological or non-biological degradation processes,
to PFOS and PFOA, has been a plausible explanation for the occurrence of these
compounds in biota from remote areas. However, studies on the measurement
of precursor compounds in water or air from remote areas are not available.
Precursor compounds are also expected to be present in biota which
has less metabolic capacity. Monitoring of precursor compounds in biotic
and abiotic matrices is a subject of further investigation.
The complex chemistry of PFCs
also poses problems in their risk assessment. Toxicological studies have focused primarily
on PFOA and PFOS, but not on intermediates of PFC metabolism and precursor
compounds. PFOS has been
shown to affect genes involved in hormone regulation and fatty acid metabolism.
Further studies are needed to understand the toxic effects of precursors
of PFCs including telomer
alcohols. Studies are also needed to understand the
critical endpoint (most sensitive biomarker of exposure) of toxicity, which
can be used in the assessment of risks from exposure to PFCs.
Overall, perfluorinated
acids are global environmental pollutants.
Several of the PFCs are persistent and bioaccumulative in the food chain. These compounds can reach remote
marine environment. The mechanisms of transport and toxic effects
of these compounds are the subjects of further investigations.