Investigating microplastic trophic transfer in marine top predators

Abstract

Microplastics are highly bioavailable to marine organisms, either through direct ingestion, or indirectly by trophic transfer from contaminated prey. The latter has been observed for low-trophic level organisms in laboratory conditions, yet empirical evidence in high trophic-level taxa is lacking. In natura studies face difficulties when dealing with contamination and differentiating between directly and indirectly ingested microplastics. The ethical constraints of subjecting large organisms, such as marine mammals, to laboratory investigations hinder the resolution of these limitations. Here, these issues were resolved by analysing sub-samples of scat from captive grey seals (Halichoerus grypus) and whole digestive tracts of the wild-caught Atlantic mackerel (Scomber scombrus) they are fed upon. An enzymatic digestion protocol was employed to remove excess organic material and facilitate visual detection of synthetic particles without damaging them. Polymer type was confirmed using Fourier-Transform Infrared (FTIR) spectroscopy. Extensive contamination control measures were implemented throughout. Approximately half of scat subsamples (48%; n = 15) and a third of fish (32%; n = 10) contained 1-4 microplastics. Particles were mainly black, clear, red and blue in colour. Mean lengths were 1.5 mm and 2 mm in scats and fish respectively. Ethylene propylene was the most frequently detected polymer type in both. Our findings suggest trophic transfer represents an indirect, yet potentially major, pathway of microplastic ingestion for any species whose feeding ecology involves the consumption of whole prey, including humans.

Microplastic ingestion ubiquitous in marine turtles

“…The polymer make‐up of marine plastic debris may aid in identifying possible sources, degradation, fate and reasons for ingestion (Jung et al, ; Nelms et al, ). The polymers identified through FT‐IR analysis reflect the recently reported polymer diversity globally described for microplastics (Gago et al, ).…”

“…Laboratory studies have shown trophic transfer of microplastics between invertebrates and within planktonic food webs (Dawson et al, ; Farrell & Nelson, ; Macali et al, ; Setälä et al, ). In addition, a recent study by Nelms et al () on grey seals ( Halichoerus grypus ) and wild‐caught Atlantic mackerel ( Scomber scombrus ) suggested that trophic transfer represents an indirect but potentially major pathway for any species whose feeding ecology involves the consumption of whole prey.…”

A catchment‐scale perspective of plastic pollution

“…Once in food webs, plastic particles may be retained through transfers through multiple pathways (Windsor, Tilley, Tyler, & Ormerod, ) and cycling between trophic levels, moving upwards through the food web as a consequence of predation (e.g. Nelms, Galloway, Godley, Jarvis, & Lindeque, ) and re‐entering the basal resources through egestion. The residence time of plastic particles within the biological component of food webs is unknown.…”

Towards an ecology of soil microplastics

“…However, experiments showing significant harm sometimes do so only with microplastic concentrations beyond what is common in the current environment (Cunningham & Sigwart, ; Lenz, Enders, & Gissel, ; Phuong et al, ). Trophic transfer of microplastics to higher levels of the food web, commonplace in marine systems (Carbery, Connor, & Thavamani, ; Nelms, Galloway, Godley, Jarvis, & Lindeque, ; Setälä, Fleming‐Lehtinen, & Lehtiniemi, ), has so far been only indirectly shown in terrestrial environments (Huerta Lwanga, Mendoza Vega, et al, ). If microplastics can be transferred from prey to predators in soil, it could result in microplastics escaping the confines of soil and spreading throughout the above‐ground food web, via the many terrestrial animals (including vertebrates) that consume soil invertebrates, but requires further investigation.…”

“…Trophic transfer of microplastics to higher levels of the food web, commonplace in marine systems (Carbery, Connor, & Thavamani, 2018;Nelms, Galloway, Godley, Jarvis, & Lindeque, 2018;Setälä, Fleming-Lehtinen, & Lehtiniemi, 2014), has so far been only indirectly shown in terrestrial environments (Huerta Lwanga, Mendoza F I G U R E 1 Diagram showing common microplastic shapes, six of the most common plastic polymers (Geyer, Jambeck, & Law, 2017), and sources and observed concentrations of microplastics in urban (1: Fuller and Gautam (2016)), riparian (2: Scheurer and Bigalke (2018)) and agricultural soils (3: Zhang and Liu (2018), 4: Piehl et al (2018), 5: Corradini et al (2019). Note that microplastic concentration in (5) Vega , et al, 2017).…”