Environmental Engineering Reference
In-Depth Information
1
Introduction
As a result of the restriction imposed by the European Union, regulations
on antifouling paints containing organotin biocides have been proposed due
to their negative impact on marine environment [1, 2]. New alternative for-
mulations have been developed based mainly on the metal copper or its
oxide. However, these formulations are less efficient at inhibiting fouling
by algae. To remedy this deficiency, booster biocides [3] (chlorothalonil,
dichlofluanid, diuron, irgarol 1051, Sea-Nine 211, TCMS pyridine, TCMTB,
zinc pyrithione, and zineb) have been added to some products in order to
prevent the growth of bacteria, macroalgae, mussels, and other invertebrates.
Due to their widespread use considerable coastal concentrations of these
biocides have been found in areas of high yachting activity, particularly in
marinas and sportive harbors [4-7].
In order to understand and predict their fate in the natural environ-
ment and to assess their risk, it is necessary to improve our knowledge of
their chemical reactions and degradation rates under environmental con-
ditions. Photochemical transformation is one of the main abiotic degrada-
tion pathways occurring in natural waters and has received increasing in-
terest in recent years [8]. The photochemical fate of the above-mentioned
booster biocides is reviewed herein. Phototransformation of antifouling bio-
cides under natural conditions may be a complex process. In order to un-
derstand the mechanisms involved it is necessary to investigate both dir-
ect photolysis and indirect (photosensitized) transformations under relevant
experimental conditions. Direct photolysis occurs when a given pollutant
absorbs UV-visible light energy and undergoes transformation. Indirect or
sensitized photolysis occurs either by direct energy transfer from the ex-
cited species [9] to the pollutant or by leading to the formation of reactive
species such as singlet oxygen or hydroxy radical, which enter into a series
of reactions [10-12]. Since the steady-state concentrations of the above-
mentioned reactants are predominantly a reflection of the concentrations of
nitrate, cDOM, and bicarbonate levels, the rate of photodecomposition and
fate of an organic pollutant could vary as a function of the composition of
water.
Photodegradation is also affected by factors controlling the spectral dis-
tribution, intensity, and duration of sunlight. Such factors include latitude,
cloud cover, date etc. and UV-B radiation absorption by atmospheric ozone.
Moreover the penetration of near UV radiation in natural waters is influenced
by factors such as depth of mixing, turbidity, presence of dissolved material
absorbing in near UV, etc. In moderately turbid coastal waters, incident light
with wavelengths of 380 nm or less is almost completely attenuated at depths
of 1-2 m but, in very clear parts of the ocean, 20 mmayberequiredtoremove
90% of the radiation entering the surface.
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