Rapp. Comm. int. Mer Médit., 37,2004
235
DETERMINATION OF ZN- PYRITHIONE IN ADRIATIC COASTAL SEAWATER SAMPLES
BY CATHODIC STRIPPING VOLTAMMETRY
Marta Plavšic
1*
and Constant M.G. van den Berg
2
1
Rudjer Boskovic Institute, Center for Marine and Environmental Research, POBox 180, 10002 Zagreb,
Croatia - * plavsic@rudjer.irb.hr
2
Oceanography Laboratories, Earth Sciences Department, Liverpool L69 7ZL, UK - Vandenberg@liverpool.ac.uk
Abstract
A method was adapted here to determine the anti-foulant pyrithione in natural waters. The method is based on cathodic stripping
voltammetry (CSV) in the presence of Triton-X-100 to separate the pyrithione peak from interfering thiol compounds. The detection limit
in UV-digested seawater was 1.5 nM for a deposition time of 60s. The method is applied for the determination of Zn- pyrithione in coastal
samples of the Adriatic sea.
Key words: Zn-pyrithione, electrochemistry, Adriatic sea, anti-foulant
Introduction
Zinc pyrithione, ZPT, ( zinc-2-pyridinethiol-N-oxide (IUPAC),
CAS [13463-41-7]), belongs to a group of antifouling paint booster
biocides which are added to antifouling paints to improve their
efficacy. These biocides have become prevalent , followed a ban on
the use of triorganotin biocides in antifouling paints for small boats in
the late 1980’s[1]. ZPT is used extensively also an antiseborrehic
agent in hair care [2]. Both of these commercial applications made
ZPT an analyte of interest . Several studies of the fate of pyrithione in
the environment and its toxicity to aquatic life have been made [2,3].
Goka [2] showed on Zebrafish and Japanese Medaka that ZPT induces
significant teretogenic effects on larvae of both species. Kobayashi
and Okamura [3] found ZPT much more toxic to sea urchins than
tributyltin oxide (TBTO). Assessment of the impact of pyrithiones
(PT) has been complicated by lack of a sensitive and reproducible
method of analysis. Methods developed for detection of ZPT in hair
care and cosmetic products ( HPLC and polarography) [4,5] could in
principle be used for natural waters but they require a very large
preconcentration step suffering from poor recovery and
reproducibility. The method developed recently [6], for analytical
determination of ZPT in natural waters in the presence of Triton-X-
100, has good reproducibility, sensitivity and can alleviate the
in?uence of other S - containing compounds which are present in
natural waters. This newly developed method is applied here for the
determination of ZPT in samples from the coastal area of the Adriatic
sea, Mersey river estuary and marinas.
Experimental
Instrumentation and reagents
The voltammetric system comprised a
µ
Autolab voltammeter
(Ecochemie) and a static mercury drop electrode (Metrohm 663VA),
PC-controlled using GPES 4.8 Windows software (Ecochemie). The
reference electrode was double junction Ag/saturated AgCl with a salt
bridge filled with 3M KCl. The counter electrode was a glassy carbon
rod, and the voltammetric cell was glass. A 1 mM stock solution of
zinc pyrithione (SIGMA) was prepared weekly. A potential of -0.1 V
was applied to adsorb the pyrithione using an adsorption time of
typically 60 s. Then an equilibration time of 10 s was allowed, and the
potential was scanned in the differential-pulse mode from -0.05 to -
1.2 V. (modulation time 0.01 s, interval 0.1 s, step height 0.010 V and
pulse amplitude 0.050 V).
Results and discussion
Pyrithione gives a peak at -0.3 V in the presence of Triton-X-100
(2-4ppm ), when added to pH 9 ( ammonia buffer) seawater sample.
Cyclic voltammetry (CV) across a long potential range (-0.05V to
-1.2V) showed that the voltammetric peaks for ZPT and glutathione
are well separated , even in the presence of 1000nM of glutathione.
The first peak appears at a potential E = -0.3 V and is due to the
reduction of mercury in an adsorbed complex with pyrithione, while
the second peak appears at E = -0.5 V and is due to the presence of
glutathione in the sample .
The height and potential of the ZPT peak are affected by variations
in the pH and electrochemical parameters (adsorption time, potential,
etc), and by the concentration of Triton-X-100 which is used for much
improved sensitivity.
It has been reported that low water solubility and rapid
photodegradation are probably significant factors in the removal of
ZPT from surface waters, with a half-life of 4 hours under ambient
room light [7]. The pyrithione is indeed readily broken down by
ambient UV light, but it is likely that such UV is much reduced in
estuarine waters , marinas and in waste water outfalls, so it is not
known whether the photolytic process is important in nature. Samples
stored under ambient conditions appeared stable. After 8 hours
standing under ambient conditions in a translucent polyethylene bottle
on the lab bench, the remains of the bulk solution containing 200 nM
of ZPT were analysed and produced peaks of equal height to the
original measurements made with fresh sample[6]. Localized high
concentrations of pyrithione could be expected due to the reduced UV
light , embayment of high concentration waters in marinas or at waste
water outfalls.
The marina sample (within a docks complex off the River Mersey ;
UK) was determined to contain 105
±
5 nM pyrithione [6]. A sample
from the marine Rogoznica lake (Croatia, in the vicinity of marina
Frapa ) was found to contain 120 ±5 nM pyrithione. Seawater
samples from other coastal areas of the north Adriatic sea were
analysed as well. The concentrations in these samples were 24-44 nM
of pyrithione.
Conclusion
These preliminary measurements indicate that pyrithione may well
occur widespread in the environment, and it will be interesting to
investigate its source and fate (anti-fouling agent, shampoos, or other)
in different coastal waters.
Acknowledgements
Marta Plavšic gratefully acknowledges the financial support of the
Croatian Ministry of Science and Technology .
References
1-Thomas K.V., 2001. The environmental fate and behaviour of
antifouling paintbooster biocides: a review. Biofouling,17 : 73-86 .
2-Goka K., 1999. Embryotoxicity of Zn- pyrithione, an antidandruff
chemical, in fish, Environ.Res., 81 : 81- 83.
3-Kobayashi N., Okamura H., 2002. Effect of new antifouling
compounds on the development of sea urchins. Mar. Pollut. Bull.,44 : 748
-751.
4-Voulvoulis N., Scrimshaw M.D., Lester J.N.,1999. Analytical methods
for the determination of 9 antifouling paint booster biocides in estuarine
water samples. Chemosphere, 38: 3503-3516.
5-Wang L.H., 2000. Determination of zinc pyrithione in hair care
products on metal oxides modified carbon paste electrode.
Electroanalysis, 12 : 227- 232.
6-Mackie D.S., van den Berg C.M.G., Readman J., 2003 .Determination
of pyrithione in natural waters by cathodic stripping voltammetry. Anal.
Chim Acta., submitted.
7-Thomas K.V., 1999.Determination of the antifouling agent zinc
pyrithione in water samples by copper chelate formation and high –
performance liquid chromatography atmospheric pressure chemical
ionisation mass spectrometry. J. Chromatogr. A.,833(1):105-109.
