Contamination of Pyrenees mountain streams by agricultural synthetic fibre ropes and a first assessment of their potential effect on aquatic and terrestrial gastropods

Despite the ever-growing amount of work devoted to plastic pollution on a global scale, we are still lacking information on the extent and effects of microplastic pollution in mountain terrains and foothills ecosystems worldwide. The present study was specifically triggered by the nearly ubiquitous presence of synthetic fibre ropes in two otherwise pristine valleys of the foothills of the central Pyrenees. In this context, the present work (i) assessed the presence of fibres in the riverbank sediments of two streams of the Pyrenees foothills, and (ii) inferred the potential effects on the local aquatic and terrestrial gastropods fauna on behavioural assays conducted on representative species of Pyrenees springs and streams, i.e. Ancylus fluviatilis and Radix balthica, and two terrestrial gastropods, the endemic snail Obscurella nouleti and the widespread grove snail Cepaea nemoralis. Fibres were present in all samples considered but notably at relatively low concentrations. Other common microplastic items such as fragments, film and foam were remarkably consistently absent from all the samples considered in the present work. These results indicate that the Nistos and Ourse streams are only marginally impacted by plastic pollution in general and by plastic pollution related to agricultural activities in particular. However, the polyethylene fibres studied contained three low molecular weight phthalates which when incorporated into an inert gel, induced systematic behavioural avoidance in all species tested. To avoid underestimating the role of Nistos and Ourse streams as potential microplastic sinks, further work is needed to assess the nature and amount of microplastic items (including fibres) that may have been trapped in foothill soil and in stream sediment surface depending on their shape, density and polymer and/or advected downstream. Similarly, the observed consistent avoidance of rope leachates questions the potential long-term effects of the chemical compounds contained in the synthetic ropes that are extensively used in the agricultural sector and found nearly everywhere in the foothill landscapes.