Up and away: ontogenic transference as a pathway for aerial dispersal of microplastics

Abstract

Microplastics (MPs) are ubiquitous pollutants found in marine, freshwater and terrestrial ecosystems. With so many MPs in aquatic systems, it is inevitable that they will be ingested by aquatic organisms and be transferred up through the food chain. However, to date, no study has considered whether MPs can be transmitted by means of ontogenic transference, i.e. between life stages that use different habitats. Here, we determine whether fluorescent polystyrene beads could transfer between Culex mosquito life stages and, particularly, could move into the flying adult stage. We show for the first time that MPs can be transferred ontogenically from a feeding (larva) into a non-feeding (pupa) life stage and subsequently into the adult terrestrial life stage. However, transference is dependent on particle size, with smaller 2 µm MPs transferring readily into pupae and adult stages, while 15 µm MPs transferred at a significantly reduced rate. MPs appear to accumulate in the Malpighian tubule renal excretion system. The transfer of MPs to the adults represents a potential aerial pathway to contamination of new environments. Thus, any organism that feeds on terrestrial life phases of freshwater insects could be impacted by MPs found in aquatic ecosystems.

Keywords: Culex pipiens; Malpighian tubules; food chain; life stage; microplastics; ontogeny.

Figure 1.

Uptake counts of MPs across larval (a,b), pupal (c,d) and adult (e,f) Culex mosquito stages following single (a,c,e) and mixed (b,d,f) exposures to 2 and 15 µm beads. Means are ±s.e. (n = 5 per experimental group).

Figure 2.

Epi-fluorescent microscope images showing fluorescent MP particles within (a) the abdomen of an adult mosquito before dissection and (b) the abdominal Malpighian tubules following dissection.