UV radiation and water cause different patterns of transformation products.
Source: BAM
Leaching of biocides from facade paints does not only depend on the amount of driving rain, but is also influenced by global radiation, as it has been observed in experiments on facade paints under natural weathering conditions. Here, UV radiation and water contact cause the transformation of active substances.
Less well-known is, how transformation reactions of active substances are reciprocally influenced by water contact and UV radiation. To investigate this, glass plates were coated with biocide-containing facade paints and exposed to controlled UV radiation in a weathering device. Some test specimens were subjected to water contact under laboratory conditions. Transformation products of selected active substances were analyzed in the coatings and in the obtained water samples (eluates) after selected periods of the experiment. Analysis was performed by liquid chromatography coupled to different mass spectrometers, amongst others a high-resolution mass spectrometer.
Lower amounts of the contained active substances were leached from test specimens that were exposed to UV radiation compared to non-exposed test specimens. The obtained transformation products were investigated in more detail for the active substances terbutryn and diuron. Considerably higher amounts of transformation products of terbutryn were observed in the eluates from UV exposed test specimens compared to non-exposed test specimens. Different patterns of transformation products were obtained for a white and a red paint that only differed in the contained pigment. This observation was confirmed by the analysis of the coatings. Certain transformation products were only formed if the test specimens were exposed to UV radiation. Similar observations were made for diuron. However, the transformation of this substance is more complex than initially expected.
The observation that - depending on weather conditions - different emission patterns of active substances and transformation products are to be expected, is also relevant for the assessment of analytical data for surface water samples. It is quite possible, that transformation products indicate sources of biocide emissions, whereas the initially applied active substance is temporarily not detected.
Leaching and transformation of film preservatives in paints induced by combined exposure to ultraviolet radiation and water contact under controlled laboratory conditions
Ute Schoknecht, Helena Mathies, Jan Lisec
published in Water, Vol. 13, issue 17, no. 2390, pages1 - 16, 2021