Photolytic degradation of N,N-diethyl-m-toluamide in ice and water: Implications in its environmental fate

Article abstract of DOI:10.1016/j.jphotochem.2013.08.001

The photochemical transformation of N,N-diethyl-m-toluamide (DEET), one of the most widespread and efficient mosquito repellents, has been investigated. Initially, photoinduced DEET degradation was investigated in liquid samples, at 20 C and 0 C, and in ice (-15 C), aimed to simulate all possible photoinduced processes occurring in water and in cold environments. Under UV-illumination, DEET degradation was more efficient in ice than in water. The evaluation of transformation products (TPs) formed during the photolysis in solution and in ice evidences mostly the same degradation products, but with different concentration ratio and some peculiar differences. An hypothesis about what kind of processes may play a role is reported. In solution, the oxidative process mostly involved were (poly)hydroxylation or oxidation of the hydroxyl groups, while in ice N-dealkylation and monohydroxylation prevail. Finally, DEET and its TPs were searched out in snow and river water in wintertime.

Full text of DOI:10.1016/j.jphotochem.2013.08.001

Journal of Photochemistry and Photobiology A: Chemistry 271 (2013) 99–104
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photolytic degradation of N,N-diethyl-m-toluamide in ice and water:
Implications in its environmental fate
P. Calzaa,∗, C. Medanab, M. Sarroa, C. Baiocchib, C. Mineroa
a Dipartimento di Chimica, Università di Torino, via P. Giuria 5, 10125 Torino, Italy
b Dipartimento di Biotecnologie Molecolari e Scienze della Salute, Università di Torino, Via P. Giuria 5, 10125 Torino, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2013
Received in revised form 26 July 2013
Accepted 2 August 2013
Available online 12 August 2013
The photochemical transformation of N,N-diethyl-m-toluamide (DEET), one of the most widespread and
efficient mosquito repellents, has been investigated. Initially, photoinduced DEET degradation was inves-
tigated in liquid samples, at 20 ◦C and 0 ◦C, and in ice (−15 ◦C), aimed to simulate all possible photoinduced
processes occurring in water and in cold environments. Under UV-illumination, DEET degradation was
more efficient in ice than in water. The evaluation of transformation products (TPs) formed during the
photolysis in solution and in ice evidences mostly the same degradation products, but with different con-
centration ratio and some peculiar differences. An hypothesis about what kind of processes may play a
role is reported. In solution, the oxidative process mostly involved were (poly)hydroxylation or oxidation
of the hydroxyl groups, while in ice N-dealkylation and monohydroxylation prevail. Finally, DEET and its
TPs were searched out in snow and river water in wintertime.
Keywords:
DEET
Ice
Photolysis
HRMS
© 2013 Elsevier B.V. All rights reserved.
Transformation products
1. Introduction
transformation products (TPs) were searched in natural samples.
Fifteen TPs were identified in Po river waters and four different
N,N-diethyl-m-toluamide (DEET) is one of the most widespread
and efficient mosquito repellents diffused worldwide, included in
Pharmaceuticals and Personal Care Products (PPCPs) list and in
some emerging contaminant list [1]. This mosquito repellent is
widely used in Europe and in America, where a consumption of
1800 tonnes per year is estimated. It can be considered as an
emerging contaminant of environmental concern because of its
continuous release into the aquatic environment, its persistence
and evidences of ecotoxicological effects [2].
Only 20% of DEET is absorbed by skin, metabolized and excreted;
mostly will then be washed away entering in the aquatic sys-
tem [3]. Its wide use and high stability have led it to become a
ubiquitous pollutant; it was found worldwide in aquatic environ-
ment (i.e. Australia, Germany, Holland, Norway, Italy, USA) [4] to a
level ranging from 0.1 ng L−1 to up 1.1 ␮g L−1 [5] in surface waters,
groundwater and waters for human consumption [4,6–11].
Earlier studies were concerned with simulation by TiO2-
mediated photolysis of N,N-diethyl-m-toluamide [12], where
a total of 51 unknown DEET degradation products (TPs) were
identified and characterized by multiple stage mass spectrometry,
and focused on their identification in Po River water (North Italy
[13]). In the latter case, all the possible main and secondary
transformation routes were proposed; within this framework, the
fate of DEET in the river water was clarified.
The identification of N,N-diethyl-m-toluamide, in aerosols was
recently documented [14] and this prompt us to extend the inves-
tigation on the fate of this pollutant to other environmental
comparts, e.g. snow, with particular focus on cold environments.
The role of snow in the distribution and the fate of organic con-
taminants [15,16] as well as in hosting possible (photo)chemical
transformations in regions of high altitude and latitude [17–19]
has received growing attention. While photochemical processes
in aqueous media have been extensively investigated, significantly
fewer published studies regarded photochemical transformations
of anthropogenic organic contaminants in ice. Most of the avail-
able studies investigated direct photochemical processes under
controlled laboratory conditions [20–25] and indicated efficient
photochemical reaction for several species. In cold environments,
snow and ice exhibit a marked influence on the photochemi-
cal transformation of semi-volatile organic contaminants [17,18].
Hydrophobic or hydrophilic solute molecules are known to become
spontaneously segregated at grain boundaries of ice during the
freezing process. As ice forms from freezing water, pure water
crystallizes first, and solutes are excluded from the bulk and con-
centrated at the surface [26]. This results in a chemically enriched
liquid-like layers at the surface, grain boundaries and interstitial
pores of snow and ice, which can affect the type and rates of chem-
istry that may occur. Such a solute-concentration enhancing effect
∗
Corresponding author. Tel.: +39 0116705268; fax: +39 0116705242.
E-mail address: paola.calza@unito.it (P. Calza).
1010-6030/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jphotochem.2013.08.001

100
P. Calza et al. / Journal of Photochemistry and Photobiology A: Chemistry 271 (2013) 99–104
may cause the solute organic molecules to self-organize and their
chemical reactivity is significantly altered [27,28].
The formation of photoproducts may be of toxicological rel-
evance if they are formed in ice and subsequently released
with spring melt [25]. As an example, the photodegradation of
chlorobenzenes or chlorophenols in ice can give rise to more persis-
tent polychlorinated biphenyls or chlorohydroxybiphenyls [22,29].
Pollutants could be incorporated to snow by wet or dry deposition
processes [30]. If they do not absorb solar radiation, they may still
react with other reactive photochemically produced species, such
as hydroxyl radicals [31,32]. The reaction with hydroxyl radicals is
often the dominant removal pathway for organic pollutants in natu-
ral waters [33]. However, when aromatics are present at the surface
of frozen water (ice), this reaction pathway may not occur: recent
studies have shown that at air–ice interfaces hydroxyl radicals
do not react to an appreciable extent with aromatic compounds,
including benzene, whereas in aqueous solution these reactions
occur at near diffusion-limited rates [34–36].
Fig. 1. DEET (40 mg L−1) degradation in ice (−15 ◦C), m.p. water (0 ◦C) and water
(20 ◦C) under UV-illumination.
2 with HCl 37%, concentrated on SPE cartridge and analyzed by
HPLC/HRMS.
Strata X solid phase extraction (SPE) cartridges (Phenomenex,
Bologna, Italy) were used for extracting snow and river water
In an attempt to clarify the fate of DEET in cold environments,
we have performed a laboratory investigation on DEET photolysis
in both water and ice; the degradation photokinetics was evaluated
and main TPs were identified in water and ice phases. The same TPs
were then searched out in river water and snow.
samples. Samples were spiked with 10 ␮L isoxsuprine (1 mg L−1
,
3.3 ␮M) used as recovery standard. Elution was performed with
2 mL CH3OH and 2 mL of 2% ammonia in CH3OH. Eluted solutions
were dried under nitrogen flux and then reconstituted with 200 ␮L
0.05% (10 mM) formic acid and directly injected into HPLC/MS.
Quantitative data were obtained through an external calibration
after normalization on isoxsuprine signal. Limit of detection (LOD)
for DEET after concentration on SPE cartridges was 0.5 ng L−1
(2.6 pM). With this method, DEET and all formed TPs showed a
recovery percentage > 90%.
2. Experimental
2.1. Materials and reagents
N,N-diethyl-meta-toluamide (DEET) (purity 97%), isoxsuprine
hydrochloride were from Sigma Aldrich. Formic acid (99%) was
from Merck (Milan, Italy). HPLC grade water was obtained from
MilliQ System (Millipore, Milan, Italy). HPLC grade acetonitrile
(BDH) was filtered through a 0.45 ␮m filter before use.
2.5. Analytical techniques
2.5.1. HPLC-HRMS
The chromatographic separations followed by a MS detector
were run on a C18 column Phenomenex Luna, 150 mm × 2.0 mm,
thermostated at 30 ◦C using an Ultimate 3000 HPLC instrument
(Dionex). Injection volume was 20 ␮L and flow rate 200 ␮L/min.
Gradient mobile phase composition was adopted: 5/100 formic
acid 0.05%/acetonitrile in 0/35 min. A LTQ Orbitrap mass spec-
trometer (Thermo Scientific, Bremen, Germany) equipped with an
atmospheric pressure interface and an ESI ion source was used as
detector. The LC column effluent was delivered into the ion source
using nitrogen as sheath and auxiliary gas. The source voltage was
set at 4.5 kV. The heated capillary was maintained at 265 ◦C. The
acquisition method used was previously optimized in the tuning
sections for the parent compound (capillary, magnetic lenses and
collimating octapoles voltages) in order to achieve the maximum
of sensitivity. The tuning parameters adopted for ESI source have
been the following: capillary voltage 7.00 V, tube lens 55 V. Mass
accuracy of recorded ions (vs calculated) was 5 millimass units
(mmu) (without internal calibration).
2.2. Procedures for irradiation
Photolysis experiments were carried out in quartz cells con-
taining DEET at 10, 20 or 40 mg L−1 (52, 104 or 208 ␮M) and
illumination was provided by a Philips Ultraviolet Light Bulb 15
Watt TUV G15 T8 lamp with emission maximum at 254 nm. Tem-
perature within the cell was controlled by a thermostatic bath and
fixed at +20 ◦C, 0 ◦C or −15 ◦C. In the case of photolysis in ice, DEET
solutions were frozen overnight at −15 ◦C before illumination.
2.3. Sampling procedure
Snow samples were collected in Coazze, a town located at 750 m
above sea level, 40 km west of Turin, Italy, in a huge area far from
streets. It can be considered countryside, with a limited contribu-
tion of anthropic contamination. Snow sampling was performed at
three different points, all located in Coazze. At each point 10 L of
melted water was sampled.
River water samples were collected in a sampling campaign per-
formed in Turin at three sampling points, all located close to the
city centre and before the town wastewater treatment plant. Late
winter samples were collected from February 1, 2009 to March 8,
2009 and repeated in March 2010. Summer samples were sampled
from 1 to 4 July 2008 and repeated on July 2009 with the procedure
described elsewhere [13]. Samples were collected 2 m far from the
river border using brown glass bottles; samples are then kept in the
dark and promptly analyzed.
3. Results and discussion
3.1. UV-photolysis in water and ice
3.1.1. DEET degradation
DEETdegradationunderUVlightas a functionof irradiationtime
in water, melted water and ice is plotted in Fig. 1. While DEET disap-
pearance rate at 20 and 0 ◦C are very similar, its photodegradation
takes place faster in ice than in the solution. Quicker photoly-
sis on ice could be attributed to different reasons. Although light
scattering and reflection lower the quantum yields of the photo-
processes occurring in ice or snow [37], the increased rate could
be attributed to an enhanced local concentration of the pollutant
2.4. Extraction procedures
River water and snow samples were extracted by adopting
the more appropriate procedure. All samples were acidified at pH

P. Calza et al. / Journal of Photochemistry and Photobiology A: Chemistry 271 (2013) 99–104
101
Fig. 3. TPs formed under DEET (40 mg L−1) irradiation at 0 ◦C: (top) main TPs; (bot-
tom) secondary TPs.
Fig. 2. TPs formed under DEET (40 mg L−1) irradiation at 20 ◦C in water: (top) main
TPs; (bottom) secondary TPs.
resistance to de-ethylation was observed, because only the
demethyled/hydroxylated TP (namely 194) and monohydrox-
yled compounds (208) formation was detected. Then, after 2 h
of irradiation, hydroxylated/demethylated product (180) and
poly-hydroxylated TPs (240 and 222) were formed.
at the grain boundaries of the ice crystals; the specific concentra-
tion effect [37,38] then increases the probability of intermolecular
reactions. DEET absorption spectrum is shown in Fig. S1 as sup-
plementary material. Even if DEET spectrum does not overlap that
of the solar radiation, recent studies point out that the absorption
spectra of aromatic compounds, e.g. phenol derivatives, exhibit sig-
nificant batochromic shifts to wavelengths overlapping those of
solar radiation at an air–ice interface [24,34,36], so suggesting that
direct photolysis could be an important removal pathway in cold
regions [39].
Photolysis at 0 ◦C (see Fig. 3) evidences the formation of
almost the same TPs already discussed at 20 ◦C, formed at sim-
ilar relative ratio, even if at lower amount. The only difference
3.1.2. DEET transformation products
Along with DEET degradation, several TPs were formed and
detected by LC-HRMS. Their evolution profiles as a function of irra-
diation time are plotted in Figs. 2–4. All these TPs are well-matched
with DEET TPs formed in laboratory simulations and were previ-
ously characterized [13]; the proposed structures are collected in
Table S1 as supplementary material.
Fig. 2 reports the temporal profiles of TPs produced dur-
ing photolysis experiments in water (20 ◦C) and include three
compounds with m/z 208 (attributed to N,N-diethyl-4-hydroxy-3-
methylphenylamide, N,N-diethyl-2-hydroxy-3-methylphenylam-
ide (208-B and C) or N,N-diethyl-3-hydroxymethylphenylamide
(208-A)), a compound labelled 164 and attributed to N-ethyl-
3-methylphenylamide, N-ethyl-4-hydroxy-3-methylphenylamide
(180), N,N-diethyl-3-hydroxymethylphenylamide (namely 194)
N,N-diethyl-oxo-3-methylphenylamide (206), N,N-diethyl-trihy-
droxy-3-methylphenylamide (240), N,N-diethyl-oxo-dihydroxy-3-
methylphenylamide (222). It comes up that main TPs formed
through photolysis in aqueous phase are monohydroxy deriva-
tives (208), while dealkylation product (164 and 180) are formed
in minor amount. The formation of hydroxy- or peroxosubstituted
photoproduct should be attributed to the presence of oxygen in
liquid water as a biradical species [40].
Fig. 4. TPs formed under DEET (40 mg L−1) irradiation at −15 ◦C in ice: (top) main
Different kinetics of TPs formation lead us to assume
different attack of hydroxyl radical. Indeed, an initial
a
TPs; (bottom) secondary TPs.

102
P. Calza et al. / Journal of Photochemistry and Photobiology A: Chemistry 271 (2013) 99–104
Scheme 1. Proposed DEET’s transformation pathways under UV irradiation.
with different DEET concentrations (10 or 20 mg L−1) and the
intermediates profiles are plotted in Figs. S2–S7 as supplementary
material. By changing the initial DEET concentration, remarkably
changes in the 164 concentrations are observed, so that it could be
proposed the 164 formation in ice through an intermolecular elec-
tron transfer from N-atom of DEET to the phenylcarbonyl group of
DEET, via a common photoinduced process [41], and subsequent
dark transformations. It is a concentration dependent process and
should be more pronounced in ice, due to the concentration effect,
so accounting for the increased concentration of 164.
All TPs recognized during photolysis experiments may be linked
through the transformation pathways summarized in Scheme 1.
A comparison of TPs formed during the photolysis in solution
(Fig. 2) and in ice (Fig. 4) evidence the occurrence of two main
pathways, namely hydroxylation (to form 208) and dealkylation
(to obtain 164) occurring in the two phases, while the formation
of TP 222, 240 and 244 takes only place in solution or in melted
water. Key differences between the two system clearly arise when
comparing the main TPs relative ratios detected in ice or water,
stands on the lack of polyhydroxylated compounds, e.g. 222
and 240 and the formation of TPs N,N-diethyl-oxo-trihydroxy-
3-methylphenylamide (238) and N,N-diethyl-tetrahydroxy-3-
methylphenylamide (244).
Looking closer to ice photolysis TPs (Fig. 4), a monotonic increase
of products is obtained like that found in water solution with almost
the same time window, although with some peculiarities. In ice
phase dealkylation, and particularly N-dealkylation, is the favoured
reaction. Formation of TP 164 (N-dealkylated DEET) is strongly
favoured and it becomes the main TP. Additionally, compared to
the other conditions, formation of TP 180 becomes favoured too.
TPs temporal profiles evidence a fast production of compound 164,
formed through N-dealkylation, followed later by hydroxylation
with subsequent formation of TP 180. Dealkylation occurring in
frozen aqueous solutions, could involve oxygen; singlet oxygen
formed by sensitization of 3O2 by triplet excited species may be
a reactant [22]. Besides, the formation of dihydroxy derivatives is
prevented in ice.
In attempt to clarify the mechanism involved in the 164 and
180 species, experiments were repeated in ice and water (20 ◦C)

P. Calza et al. / Journal of Photochemistry and Photobiology A: Chemistry 271 (2013) 99–104
103
analytical standard were not available and a quantitative analy-
sis cannot be performed. TPs 222-B and 222-C (hydroxylation and
oxidation) were formed as main products, while several other TPs
(208-A and B, 164, 180, 210-A, 210-B and 210-C) were detected at
lower amount [13]. This is well matched with data obtained under
UV irradiation at 20 ◦C, where the key pathway passes through the
polyhydroxylation/oxidation processes; the predominance of path-
way 3 (see Scheme 1) in summertime underlines the importance
of photolysis processes.
4. Conclusions
Through the different photolysis tests and the use of a high-
resolution MS technology, the different paths of transformation
occurring in aqueous and solid phase have been clarified.
This study evidences the potential for abiotic processes to dif-
ferently contribute to DEET transformation in temperate or cold
environments. Identification of degradation products can provide
information about which type of process took place for DEET
transformation. N-dealkylated TPs could be used as a marker of
a photolysis process occurring in frozen phase. This raises the
issue that these compounds are likely to be formed in sunlit snow
and ice, complimenting other formation routes in the environ-
ment, such as photo-oxidation in the atmosphere and surface
waters. The combined effects of prolonged sunlight exposure dur-
ing spring/summer and the potential for enhanced reactivity on
snow and ice could make photochemical degradation of DEET in
snow-covered environments an important transformation route.
Conversely, in aqueous phase hydroxylation and oxidation pro-
cesses prevail and became the main transformation route occurring
in summertime in temperate climate.
Fig. 5. Relative ratio among key TPs formed through photolysis in solution and ice.
Table 1
DEET concentration in the different environmental samples.
Sample
DEET (ng L−1
)
Snow
42
21
97.6
12
4
4
4
2
Snow after sunny day
River water (summer)
River water (winter)
as shown in Fig. 5. From the graph it can be clearly seen that the
formation of compound 164 and, at longer irradiation time, 180
mostly occurs by photolysis in ice phase. TP 208 is similarly formed
in both matrices, with 208-D only exception. However, the relative
TPs ratio 164/208 overtakes from 0.25 (in solution) to 0.35 (melted
water) and 13 (in ice), while 180/208 increases from 2.5 × 10−3
(ice) to 2.8 × 10−3 (melted water) and 0.27 (water), so providing a
discriminating item helpful in the attribution of the DEET sources.
The overall presented data permits to identify path 2 (see
Scheme 1) as a peculiar transformation route occurring in ice, while
paths 1, 3 and 4 should be ascribed to photolysis in solution. TPs
164 and 180-B could be therefore utilized as a marker of cold envi-
ronment photolysis. By evaluating the relative ratio among this
compound and other TPs formed in river water through abiotic
degradation (paths 2 and 3), discrimination on the DEET sources
could be conceivable.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.
jphotochem.2013.08.001.
References
[1] M. Stuart, D. Lapworth, E. Crane, A. Hart, Science of the Total Environment 416
(2012) 1–21.
[2] J.A. Weeks, P.D. Guiney, A.I. Nikiforov, Integrated Environmental Assessment
and Management 8 (2012) 120–134.
[3] D.L. Sudakin, W.R. Trevathan, Journal of Toxicology – Clinical Toxicology 41 (6)
(2003) 831–839.
[4] S.D. Costanzo, A.J. Watkinson, E.J. Murby, D.W. Kolpin, M.W. Sandstrom, Science
of the Total Environment 384 (2007) 214–220.
3.2. In field analysis
[5] D.W. Kolpin, M. Skopec, M.T. Meyer, E.T. Furlong, S.D. Zaugg, Science of the Total
Environment 318 (2004) 119–130.
[6] K.H. Langford, K.V. Thomas, Journal of Environmental Monitoring 10 (2008)
894–898.
[7] K. Quednow, W. Püttmann, Environmental Science and Pollution Research 16
(2009) 630–640.
[8] M.W. Sandstrom, D.W. Kolpin, E.M. Thurman, S.D. Zaugg, Environmental Toxi-
cology and Chemistry 24 (5) (2005) 1029–1034.
[9] J. Schwarzbauer, S. Heim, Water Research 39 (2005) 4735–4748.
[10] S. Weigel, J. Kuhlmann, H. Huehnerfuss, Science of the Total Environment 295
(2002) 131–141.
[11] S. Weigel, U. Berger, E. Jensen, R. Kallenborn, H. Thoresen, H. Huehnerfuss,
Chemosphere 56 (2004) 583–592.
[12] C. Medana, P. Calza, F. Dal Bello, E. Raso, C. Minero, C. Baiocchi, Journal of Mass
Spectrometry 46 (2010) 24–40.
[13] P. Calza, C. Medana, E. Raso, V. Giancotti, C. Minero, Science of the Total Envi-
ronment 409 (2011) 3894–3901.
In field analysis were performed in snow and river samples. A
broad-spectrum of qualitative analysis was executed on all sam-
ples, aimed to be aware of the overall organic matter and pollutants
content (data not shown). Quantification of DEET was carried out on
all samples and data are collected in Table 1; snow and river water
samples highlighted the presence of DEET, whose concentrations
depend on diverse seasons and matrices. As expected, in river water
DEET concentration is maxima in summertime (average concentra-
tion 97 ppt), but its presence is evidenced also in winter samples
(12 ppt). Interestingly, DEET was also detected in snow samples, at
a concentration level higher in fresh snow (42 ppt) rather than in
snow subjected to solar light exposure (21 ppt).
[14] C. Balducci, M. Perilli, P. Romagnoli, A. Cecinato, Environmental Science and
Pollution Research 19 (2012) 1875–1884.
[15] B.M.J. Herbert, S. Villa, C. Halsall, Ecotoxicology and Environment Safety 63
(2006) 3–16.
[16] O. Gustafsson, P. Andersson, J. Axelman, T.D. Bucheli, P. Komp, M.S. McLachlan,
A. Sobek, J.O. Thorngren, Science of the Total Environment 342 (2005) 261–279.
[17] A.M. Grannas, A.E. Jones, J. Dibb, M. Ammann, C. Anastasio, H.J. Beine, M. Bergin,
J. Bottenheim, C.S. Boxe, G. Carver, G. Chen, J.H. Crawford, F. Domine, M.M. Frey,
M.I. Guzman, D.E. Heard, D. Helmig, M.R. Hoffmann, R.E. Honrath, L.G. Huey, M.
DEET’s TPs were also searched for in all samples. In wintertime,
no TPs were recognized neither in snow nor in river water, rea-
sonably due to the lower DEET concentration and to the scarce
occurrence of photolysis process.
In summertime key TPs were identified in river water, i.e. the
hydroxyl-derivative and oxo-derivatives, whose formation was
mainly attributed to indirect photolysis processes [13]; for TPs

104
P. Calza et al. / Journal of Photochemistry and Photobiology A: Chemistry 271 (2013) 99–104
Hutterli, H.W. Jacobi, P. Klan, B. Lefer, J. McConnell, J. Plane, R. Sander, J. Savarino,
[30] F. Wania, R. Semkin, J.T. Hoff, D. Mackay, Hydrological Processes 13 (1999)
P.B. Shepson, W.R. Simpson, J.R. Sodeau, R. von Glasow, R. Weller, E.W. Wolff,
T. Zhu, Atmospheric Chemistry and Physics 7 (2007) 4329–4373.
[18] P. Klan, I. Holoubek, Chemosphere 46 (2002) 1201–1210.
[19] E. De Laurentiis, M. Minella, V. Maurino, C. Minero, M. Brigante, G. Mailhot, D.
Vione, Chemosphere 88 (10) (2012) 1208–1213.
[20] Y. Dubowski, M.R. Hoffmann, Geophysical Research Letters 27 (2000)
3321–3324.
[21] N. Matykiewiczova, J. Klánová, P. Klán, Environmental Science and Technology
41 (2007) 8308–8314.
[22] J. Klanova, P. Klan, D. Heger, I. Holoubek, Photochemical & Photobiological
Sciences 2 (2003) 1023–1031.
[23] J. Weber, R. Kurková, J. Klánová, P. Klán, Environmental Pollution 157 (2009)
3308–3313.
[24] T.F. Kahan, D.J. Donaldson, Environmental Science and Technology 44 (2010)
3819–3824.
[25] L. Bláha, J. Klánová, P. Klán, J. Janosek, M. Skarek, R. Ruzicka, Environmental
Science and Technology 38 (2004) 2873–2878.
[26] R. Kurkov, D. Ray, D. Nachtigallov, P. Klan, Environmental Science and Technol-
ogy 45 (2011) 3430–3436.
[27] D. Heger, P. Klan, Journal of Photochemistry and Photobiology A: Chemistry
187 (2007) 275–284.
[28] P. Klan, J. Janosek, Z. Kriz, J. Photochem, Journal of Photochemistry and Photo-
biology A: Chemistry 134 (2000) 37–44.
[29] P. Klan, D. Del Favero, A. Ansorgova, J. Klanova, I. Holoubek, Environmental
Science and Pollution Research 8 (3) (2001) 195–200.
2245–2256.
[31] J. Dolinova, R. Ruzicka, R. Kurkova, J. Klanova, P. Klan, Environmental Science
and Technology 40 (2006) 7668–7674.
[32] C. Anastasio, A.L. Jordan, Atmospheric Environment 38 (2004) 1153–1166.
[33] E.L. Viskari, R. Rekila, S. Roy, O. Lehto, J. Ruuskanen, L. Karenlampi, Environ-
mental Pollution 97 (1997) 153–160.
[34] T.F. Kahan, D.J. Donaldson, Photolysis of polycyclic aromatic hydrocarbons on
water and ice surfaces, Journal of Physical Chemistry A 111 (2007) 1277–1285.
[35] V.F. McNeill, A.M. Grannas, J.P.D. Abbatt, M. Ammann, P. Ariya, T. Bartels-
Rausch, F. Domine, D.J. Donaldson, M.I. Guzman, D. Heger, T.F. Kahan, P. Klán,
S. Masclin, C. Toubin, D. Voisin, Atmospheric Chemistry and Physics 12 (2012)
9653–9678.
[36] D. Ardura, T.F. Kahan, D.J. Donaldson, Journal of Physical Chemistry A 113 (2009)
7353–7359.
[37] D. Heger, J. Jirkovsky, Y. Dubowski, M.R. Hoffmann, Geophysical Research Let-
ters 27 (2000) 3321–3324.
[38] V.F. Petrenko, R.W. Whitworth, Physics of Ice, Oxford University Press, Oxford,
1999.
[39] G.A. Rowland, A.R. Bausch, A.M. Grannas, Environmental Pollution 159 (2011)
1076–1084.
[40] D. Dulin, H. Drossman, T. Mill, Environmental Science and Technology 20 (1986)
72–77.
[41] D.E. Falvey, C. Sundarajan, Photochemical & Photobiological Sciences 3 (2004)
831–838.