Photodegradation of octylisothiazolinone and semi-field emissions from facade coatings

Ulla E. Bollmann,Jes Vollertsen,Michael Schlüsener,Greta Minelgaite,Kai Bester,Thomas A. Ternes

doi:10.1038/srep41501

Ulla E. Bollmann, Jes Vollertsen + Show 4 more

Open Access

https://doi.org/10.1038/srep41501

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Abstract

Amongst others, 2-octyl-isothiazol-3(2 H)-one (OIT) is used as film preservative in water-based polymer resin paints and renders to prevent the growth of moulds and bacteria. It is known that biocides leach from facades with rainwater and end up in the environment via stormwater runoff. In the present study the leaching and fate of OIT used in facade coatings was determined under natural conditions. Potential phototransformation products were initially identified in laboratory experiments using UV-light. Afterwards, the leaching of OIT and seven degradation products were studied on artificial walls equipped with organic top coatings formulated with OIT. A mass balance, including the leached and remaining amounts of OIT and its seven transformation products, can explain up to 40% of the initial amount of OIT. The OIT remaining in the material after 1.5 yr is by far the largest fraction. The study shows that in the assessment of biocides in coating material, transformation products need to be taken into account both in leachate and remaining in the material. Furthermore, in case of volatile degradation products, the emissions to air might be relevant.

Highlights

While the analysis of the fraction remaining in the render after the exposure period revealed significant amounts of OIT remaining in the render materials, it showed gaps of more than 70% in the mass balance[15,20]
Kandavelu et al.[29] tested the photocatalytic degradation of methylisothiazol-3(2 H)-one (MI) and chloro-2-methylisothiazol-3(2 H)-one (CMI) in water in the presence of nanocrystalline titanium dioxide and determined that paint grade titanium dioxide is not having any influence on the photodegradation of isothiazol-3(2 H)-ones
UV-irrigation of OIT led to degradation products with the following signals in electrospray positive ionization (ESI+) scans: 214.1252 Da, 158.1527 Da, 198.1486 Da, 184.1701 Da, 172.1696 Da, 130.1954 Da and 216.1595 Da

Summary

Introduction

While the analysis of the fraction remaining in the render after the exposure period revealed significant amounts of OIT remaining in the render materials, it showed gaps of more than 70% in the mass balance[15,20]. Photodegradation is expected to be the most common dissipation pathway[15,20,21,22], as biocides need to migrate from the solid material to the surface water film to be active and, are susceptible to sunlight when reaching the coating surface. Over 19 months the run-off water was collected event-resolved Both the run-off as well as the remaining fractions of OIT and its transformation products were analysed in the render at the end of the experiment. Such mass balances of OIT have never been published before

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