Environmental Engineering Reference
In-Depth Information
aqueous environment and the pathways of transformation) and (ii) toxicity
assessment.
Analytical results confirmed the occurrence of both direct and photosensi-
tized mechanisms for the photodegradation of organic booster biocides in the
aquatic environment. Kinetics for both mechanisms followed a pseudo-first-
order law. All the compounds considered in the present review underwent
direct photolysis in solar light. However, in most cases the reactions were
slow because either the pollutants absorbed light poorly or they were poorly
photoreactive. The only exceptions were zinc and copper pyrithiones, which
were susceptible to direct photolysis and degraded in a few minutes. Re-
garding indirect processes, the rates of phototransformation for most of the
biocides were higher in natural water samples than in pure water, indicating
that photosensitized processes took place in natural water samples, thereby
limiting the long-persistence of these chemicals in the aqueous environment.
In contrast (e.g., for dichlofluanid), the photodegradation in natural waters
was partially hampered by the presence of DOM. Thus, DOM could have
both a photosensitizing or an optical filter effect. The identified photoprod-
ucts were of diverse structural nature, showing that phototransformation of
antifouling biocides under natural conditions may be a complex process.
Finally, in most cases reduced toxicity was found after the photoinduced
transformations, a fact very important for the risk assessment of biocides.
The only exception was diuron, which was quite persistent under the ir-
radiated conditions studied (both under natural and simulated solar light)
demonstrating quite long half-lives; on the other hand more toxic byproducts
appeared, possibly showing synergistic effects.
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