Researchers have found a previously unknown way for plastic to contaminate the food chain. They show for the first time that insect larvae consume microplastics from freshwater environments, which they retain through to their adult stage where they became prey for a range of animals.
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Amanda Callaghan’s team at the University of Reading, UK, investigated whether mosquitoes retained the plastics in their body through their development (Biol. Lett., doi: 10.1098/rsbl.2018.0479). They tested this by feeding two sizes of fluorescent polystyrene particles - two and 15 microns - to mosquito larvae in their third larvae stage. Then they took samples when the larvae shed their skin; when they transformed into a non-feeding stage called a pupa; and when they emerged from the water as a flying adult.
The team found the beads in all the life stages. On average, a larva contained over 3000 beads and an adult 40 beads. The team found beads in the gut and in the mosquito version of the kidney, which survives the development process intact.
The results have important implications, says Callaghan, as any aquatic insect that can eat microplastics in the water could carry them in their body to their flying stage when they are eaten in their thousands by dragonflies, birds and bats. ‘This is eye-opening research, which has shown us for the first time that microplastics are able to navigate several life stages in flying insects, allowing them to contaminate all kinds of living creatures not normally exposed to them.’
Martin Wagner, a biologist at Norwegian University of Science and Technology, says this is the first research published on the retention of microplastics during insect metamorphosis. However, he points out that the authors used a very high concentration of microplastics – 800m particles per litre. His own team has conducted an unpublished but similar experiment at lower concentrations and did not observe a transfer.
The most important question, he says, is whether the phenomenon is specific to microplastics. ‘Insects live in an environment full of natural particles and it remains to be seen whether it happens for those particles, too. If so, the animals certainly evolved features to deal with a transfer of particles throughout their development.’