It is hypothesized that environmental contamination by
per- and
polyfluoroalkyl substances (PFAS) defines a separate planetary boundary
and that this boundary has been exceeded. This hypothesis is tested
by comparing the levels of four selected perfluoroalkyl acids (PFAAs)
(i.e., perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid
(PFOA), perfluorohexanesulfonic acid (PFHxS), and perfluorononanoic
acid (PFNA)) in various global environmental media (i.e., rainwater,
soils, and surface waters) with recently proposed guideline levels.
On the basis of the four PFAAs considered, it is concluded that (1)
levels of PFOA and PFOS in rainwater often greatly exceed US Environmental
Protection Agency (EPA) Lifetime Drinking Water Health Advisory levels
and the sum of the aforementioned four PFAAs (Σ4 PFAS) in rainwater
is often above Danish drinking water limit values also based on Σ4
PFAS; (2) levels of PFOS in rainwater are often above Environmental
Quality Standard for Inland European Union Surface Water; and (3)
atmospheric deposition also leads to global soils being ubiquitously
contaminated and to be often above proposed Dutch guideline values.
It is, therefore, concluded that the global spread of these four PFAAs
in the atmosphere has led to the planetary boundary for chemical pollution
being exceeded. Levels of PFAAs in atmospheric deposition are especially
poorly reversible because of the high persistence of PFAAs and their
ability to continuously cycle in the hydrosphere, including on sea
spray aerosols emitted from the oceans. Because of the poor reversibility
of environmental exposure to PFAS and their associated effects, it
is vitally important that PFAS uses and emissions are rapidly restricted.
Perfluoroalkyl acids (PFAAs) are
persistent organic substances
that have been widely detected in the global oceans. Previous laboratory
experiments have demonstrated effective enrichment of PFAAs in nascent
sea spray aerosols (SSA), suggesting that SSA are an important source
of PFAAs to the atmosphere. In the present study, the effects of the
water concentration of PFAAs on their size-resolved enrichment in
SSA were examined using a sea spray simulation chamber. Aerosolization
of the target compounds in almost all sizes of SSA revealed a strong
linear relationship with their water concentrations (
p
< 0.05, r
2
> 0.9). The enrichment factors (EF)
of
the target compounds showed no correlation with their concentrations
in the chamber water, despite the concentrations varying by a factor
of 500 (∼0.3 to ∼150 ng L
–1
). The
particle surface-area-to-volume ratio appeared to be a key predictor
of the enrichment of perfluoroalkyl carboxylic acids (PFCAs) with
≥7 perfluorinated carbons and perfluoroalkanesulfonic acids
(PFSAs) with ≥6 perfluorinated carbons in supermicron particles
(
p
< 0.05, r
2
> 0.8), but not in
submicron
particles. The different enrichment behaviors of PFAAs in submicron
and supermicron particles might be a result of the different production
mechanisms of film droplets and jet droplets. The results suggest
that the variability in seawater concentrations of PFAAs has little
influence on EFs and that modeling studies designed to quantify the
source of PFAAs via SSA emissions do not need to consider this factor.
The effective enrichment
of perfluoroalkyl acids (PFAAs) in sea
spray aerosols (SSA) demonstrated in previous laboratory studies suggests
that SSA is a potential source of PFAAs to the atmosphere. In order
to investigate the influence of SSA on atmospheric PFAAs in the field,
48 h aerosol samples were collected regularly between 2018 and 2020
at two Norwegian coastal locations, Andøya and Birkenes. Significant
correlations (
p
< 0.05) between the SSA tracer
ion, Na
+
, and PFAA concentrations were observed in the
samples from both locations, with Pearson’s correlation coefficients
(
r
) between 0.4–0.8. Such significant correlations
indicate SSA to be an important source of atmospheric PFAAs to coastal
areas. The correlations in the samples from Andøya were observed
for more PFAA species and were generally stronger than in the samples
from Birkenes, which is located further away from the coast and closer
to urban areas than Andøya. Factors such as the origin of the
SSA, the distance of the sampling site to open water, and the presence
of other PFAA sources (e.g., volatile precursor compounds) can have
influence on the contribution of SSA to PFAA in air at the sampling
sites and therefore affect the observed correlations between PFAAs
and Na
+
.
Combining expert knowledge, SMARTS-based cheminformatics and the ontology-based ClassyFire, the categorization of PFASs with open cheminformatics approaches is explored with a set of 770 PFASs.
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