Identification of microfibers in drinking water with Nile Red. Limitations and strengths

Traditional drinking water treatment plants (DWTP) are not specifically designed for removing microplastics (MPs) from drinking water. Therefore, this emergent contaminant has been identified in water sources and final drinking water. Microfibers from plastic-based materials are a relevant category of MPs that has attracted attention in recent studies due to their significant presence in environmental samples. This study investigated the presence of microfibers (> 10 & mu;m) in the raw water and the final drinking water of a DWTP located in Spain. It was observed that the DWTP studied was capable of removing 86% of microfibers from raw water. Even with this high removal rate, an amount of 613 microfibers/L (including natural, artificial, and synthetic materials) was counted in drinking water after disinfection. The reactive Nile Red was tested to investigate its use for staining microfibers from the mentioned DWTP and also from tap and bottled water samples in order to identify them. It was observed that microfibers from environmental samples can have different manifestations of fluorescence compared to pristine polymers, and it could be related to degrees of degradation and/or adsorption of organic and inorganic material on the microfibers' surfaces. For this reason, the use of Nile Red could help understand the levels of degradation of these materials in the environment, and thus its use could go beyond the identification of MPs, which was initially proposed in previous studies.