Leaching and Transformation of Film Preservatives in Paints Induced by Combined Exposure to Ultraviolet Radiation and Water Contact under Controlled Laboratory Conditions

Abstract

Stormwater from urban areas can transport biocidally active substances and related transformation products from buildings into the environment. The occurrence of these substances in urban runoff depends on the availability of water, and on ultraviolet radiation exposure that causes photolytic reactions. In a systematic laboratory study, painted test specimens were exposed to either ultraviolet radiation, water contact, or a combination of both. Leaching of the biocidally active substances carbendazim, diuron, octylisothiazolinone, terbutryn, and selected transformation products of terbutryn and diuron were observed under various exposure conditions. Remaining concentrations of these substances in the paint were quantified. It was demonstrated that the distribution of active substances and transformation products in eluates and in the coatings themselves differs with exposure conditions. Strategies for environmental monitoring of biocide emissions need to consider the most relevant transformation products. However, environmental concentrations of biocidally active substances and transformation products depend on earlier exposure conditions. As a consequence, monitoring data cannot describe emission processes and predict expected leaching of biocidally active substances from buildings if the data are collected only occasionally.

The Impact of Weather Conditions on Biocides in Paints

“…Higher relative humidity delays drying, i.e., higher amounts of water are available in the paint film for transport processes, and higher driving rain induces transfer into runoff. A similar course of the leaching process was observed under laboratory conditions, where test specimens were exposed to the combined influence of UV radiation and water contact [ 8 ], i.e., the amount of terbutryn in the eluates decreased rapidly, and TBSO and TB-DesE were the main transformation products at the beginning of the experiment. During later phases, higher amounts of TBOH and TBOH-DesE were observed.…”

“…The diuron transformation products, monuron and dichloroaniline, were determined in the extracts from the test specimens and in a few runoff samples at the end of the experiment. The inclusion of transformation products into the test program was motivated by literature data [ 2 , 5 , 7 ] and our own studies [ 8 ]. See Supplementary Information SI S3 for details on the LC-MS analysis of runoff samples and extracts from test specimens.…”

“…Biocidal active substances (hereafter referred to as active substances) are often added to coatings to protect them from algal and fungal growth. When exposed to weathering, these substances in the rather thin coating layers can be transformed by photolysis and hydrolysis, and the active substances, as well as transformation products, may leach into runoff water [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. This means that not only the original active substances, but also transformation products, can contribute to the environmental impact of biocidal products.…”

“…It was demonstrated that pigments have an effect on the photolysis of terbutryn, diuron, and OIT in paint films, whereas carbendazim is less affected by exposure to UV radiation under laboratory conditions [ 7 ]. In an extended laboratory experiment that included periods of water contact in combination with exposure to UV radiation, it was demonstrated that water contact and UV radiation mutually influence transformation processes and leaching of substances [ 8 ]. Transformation of terbutryn due to photolytic and hydrolytic reactions and biodegradation was investigated in laboratory studies [ 16 ].…”

“…The investigated paint formulations were identical to those used in laboratory studies [ 7 , 8 ]. A white paint contained titanium dioxide and a red paint contained hematite.…”