Abstract
As a rapidly accelerating expression of global change, plastics now occur extensively in freshwater ecosystems, yet there is barely any evidence of their transfer through food webs. Following previous observations that plastics occur widely in their prey, we used a field study of free-living Eurasian dippers (Cinclus cinclus), to test the hypotheses that (1) plastics are transferred from prey to predators in rivers, (2) plastics contained in prey are transferred by adults to altricial offspring during provisioning and (3) plastic concentrations in faecal and regurgitated pellets from dippers increase with urbanization. Plastic occurred in 50% of regurgitates (n=74) and 45% of faecal samples (n=92) collected non-invasively from adult and nestling dippers at 15 sites across South Wales (UK). Over 95% of particles were fibres, and concentrations in samples increased with urban land cover. Fourier transform infrared spectroscopy identified multiple polymers, including polyester, polypropylene, polyvinyl chloride and vinyl chloride copolymers. Although characterized by uncertainty, steady-state models using energetic data along with plastic concentration in prey and excreta suggest that around 200 plastic particles are ingested daily by dippers, but also excreted at rates that suggest transitory throughput. As some of the first evidence revealing that plastic is now being transferred through freshwater food webs, and between adult passerines and their offspring, these data emphasize the need to appraise the potential ecotoxicological consequences of increasing plastic pollution.
Highlights
With annual global production approaching 350 million tonnes (MT) and another 33 billion tonnes expected by 2050 (Rochman et al, 2013), ecosystem contamination by plastic is a rapidly growing component of global change
This is one of the world's first studies to illustrate how plastic is being transferred through food webs in natural freshwater environments
We designed the work to test three hypotheses predicting that plastics might be transferred from invertebrate consumers to dippers as riverine predators, between adults and their altricial offspring, and that effects would be most pronounced in more urban landscapes
Summary
With annual global production approaching 350 million tonnes (MT) and another 33 billion tonnes expected by 2050 (Rochman et al, 2013), ecosystem contamination by plastic is a rapidly growing component of global change. In some contrast to marine systems (Provencher et al, 2019), much of this freshwater ecological work has represented primary consumers, while most investigations of the transfer of plastics through aquatic food webs in general have been in artificial (Farrell & Nelson, 2013; Setälä, Fleming-Lehtinen, & Lehtiniemi, 2014) or seminatural systems (Nelms, Galloway, Godley, Jarvis, & Lindeque, 2018) This is despite food web transfers being key to understanding the ecotoxicology and exposure of organisms to environmental pollutants (Kelly, Ikonomou, Blair, Morin, & Gobas, 2007; Windsor, Ormerod, & Tyler, 2018). We base the third of these hypotheses on observations that plastic in dipper prey reaches higher concentrations where wastewater makes up a greater proportion of river discharge, and on the fact that the largest concentrations of benthic microplastic in the United Kingdom appear to be linked to urban sources (Horton, Svendsen, et al, 2017; Hurley et al, 2018; Windsor, Tilley, et al, 2019)
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