Dynamics of microplastic fibres in Blanes Bay (NW Mediterranean) from 2014 to 2021

Abstract

Microplastics (generally defined as plastics < 5 mm) represent a significant fraction of the plastic waste in marine environments worldwide. When ingested, they can be hazardous for many organisms and their contaminants can be transferred to upper levels of the food chain, even becoming a potential risk to human health. The quantification of this fraction in the water column depends largely on the methodology used (different net types and mesh size or different volumes of bulk samples) and most of them do not detect sizes smaller than 100 μm (usually smaller than 300 μm), underestimating the abundances of microplastics in the water. In this study, monthly data (from 2014 to 2021) from the Blanes Bay Observatory (NW Mediterranean) were analyzed with the aim of determining the seasonal and medium-term temporal dynamics of surface microplastic fibres in an oligotrophic zone slightly affected by river discharges and human activity. Fibres were observed and counted using the Utermöhl method (sedimentation of an aliquot of water sample and observation under an inverted microscope) which allows the quantification of smaller sizes (up to 50 μm) than those detected by the usual methods. Microplastic fibres were present in practically all the samples in a range between 10 and 720 fibres per liter, and no clear seasonal or medium-term temporal pattern was observed. The relationship of microplastic fibre abundances with environmental variables such as freshwater inputs (i.e. river discharges, urban runoff, sewage outflow) or those derived from anthropogenic activities (such as fishing or tourism) will be discussed