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Investigating the potential uptake of microplastic-derived carbon into a boreal lake food web using carbon-13 labelled plastic
Summary
In one of the most rigorous field experiments of its kind, scientists added isotopically labelled polystyrene microplastics to an enclosed section of a Canadian lake and tracked whether plastic-derived carbon entered the food web over four months. They found no measurable leaching of carbon from the plastics into the water or into plankton and algae, suggesting that under natural lake conditions, polystyrene microplastics degrade extremely slowly. This is reassuring in one respect — carbon isn't quickly moving from plastics into aquatic food chains — but it also means microplastics persist in the environment for very long periods.
Microplastics degrade slowly over time, leaching carbon (C) that could be subsequently incorporated into aquatic food webs. Current estimates of microplastic degradation vary, and little is known about microplastic-derived C fate under natural environmental conditions. To investigate whether microplastics leach C that is subsequently incorporated into aquatic food webs, we added isotopically enriched microplastics to Lake 378 at the Experimental Lakes Area in Ontario, Canada. In an ∼1100 L limnocorral (in situ open-bottom enclosure), we added 99% 13 C-labelled polystyrene (8–216 µm in longest dimension) at a nominal concentration of 3268 particles/L. A second limnocorral without microplastics served as a negative control. Monthly measurements of δ 13 C-DIC and δ 13 C-DOC in filtered water revealed no detectable leaching of 13 C from the plastic. Compound-specific isotope analysis of δ 13 C in amino acids of bulk plankton and periphyton revealed a slight (0.5‰) enrichment in 13 C, within the range of natural variability for these organisms. Under the natural conditions of temperate oligotrophic lakes, degradation of microplastics is likely a very slow process that was not possible to detect in this 4-month experiment. Future studies should focus on assessing degradation of microplastics under realistic field scenarios to improve estimates of degradation pathways and associated time scales.