Photobleaching of Microplastics from Recyclable Plastics

When improperly disposed recyclable plastics break down, microscopic pieces of the material become environmental pollutants. The physical properties of microplastics can be determined using fluorescence microscopy. However, persistent illumination of microplastics at the fluorescence excitation wavelength results in photobleaching, which reduces the fluorescence intensity of the sample, often irreversibly. The effects of photobleaching are analyzed by exposing microplastic samples to 405 nm laser light at two different intensities for an experimentally relevant time of 30 minutes while taking a video recording of the resulting fluorescence decay. This is followed by taking periodic single images to examine possible fluorescence recovery. Our results set experimental constraints on the imaging intensity and imaging time for fluorescence microscopy studies of microplastics. Implications for further analysis of microplastics using secondary fluorescence techniques are also evident. Investigators can use our results to create more effective experimental designs, which will allow for more accurate investigations into the environmental consequences of microplastics.