Solar UV radiation exacerbates photoinhibition of a diatom by antifouling agents Irgarol 1051 and diuron

Marine diatoms are ubiquitously distributed in both coastal and open oceans, playing an important role in global primary productivity. In coastal waters, they are exposed to various pollutants in addition to multiple environmental stressors. Here, we show the pennate diatom Nitzschia sp. isolated from the East China Sea decreased its photosynthetic performance under the combined influences of two typical marine organic pollutants (Irgarol 1051 and diuron), that are frequently used as biocides to prevent biofouling, and solar UV radiation (UVR). Nitzschia sp. was sensitive to both pollutants under visible light (PAR) without UVR, even at the lowest concentration (0.5 mu g L-1) tested; higher levels led to greater reductions in its photochemical yield. When additionally exposed to UVR (280-400 nm), the inhibition of the quantum yields by the antifouling pollutants was exacerbated, reflecting a synergistic impact of the pollutants and UVR. Exposure to UVR brought about 5-20% reduction at different levels of Irgarol 1051, diuron, and their mixture, with a higher reduction percentage due to UVR observed at lower concentrations of the pollutants. Our results indicate that even low levels of antifouling agents can result in significant impacts on diatoms in the presence of solar UVR, implying that combinations of UVR and organic pollutants could be a potential method to control-target algal biofouling.