In my last post I discussed the range of different species that ingest microplastics, and the potential consequences of this ingestion.
Last week (27/7/14), a new study was published in Environmental Science and Technology on the route of microplastics uptake in crabs, which discusses a new mechanisms for uptake. You can find a link to the paper here. (You will need access to ES&T though).
The team of researchers at the University of Exeter (funded through the CleanSea* research project) have been looking at the mechanisms of microplastic uptake and retention in the common shore crab, Carcinus maenas. Their aim was to test the hypothesis that shore crabs can uptake microplastics across the gill surface during inspiration as well as ingestion from pre-exposed food (in this case, the common mussel, Mytilus edulis). They found that polystyrene microspheres (8-10µm) were retained in the body tissues of crabs, both following ingestion and inspiration. Interestingly they observed significantly higher uptake in the posterior gills than the anterior gills, the Watts et al. suggest that:
Crabs appear to uptake microspheres in two ways:
- Ventilation: a masked breathing study found microplastics were uptaken from the water column. All exposed crabs had plastic on their gills.
- Ingestion of prey: dietary exposure also resulted in crabs having microspheres in their stomach. This suggests that trophic transfer of microspheres is possible within the marine food chain, especially at the lower levels.
- They were NOT translocated to the haemolymph system.
- They were excreted in the form of faecel pellets.
- Microspheres take over 6 times longer to leave the body compared to the average excretory phase for food waste.
Now the study of microplastic ingestion by wild and laboratory exposed animals is not uncommon (previous post), what makes this research different is that it looks at the mechanism behind the uptake of microplastics, going beyond the usual ingestion studies.
What are the consequences of this form of microplastic uptake
The mechanism of uptake may play a role in which organisms are more susceptible to microplastic pollution. In the case of the shore crab its ventilation rate is less than that of the common mussel. Watts et al. discuss this in much more detail, but in summary, they suggest that in reference to ventilation rates alone, mussels may be more susceptible to higher levels of pollutants. further research is required on levels of ingestion via feeding and predation
*CleanSea is a multidisciplinary and collaborative research project addressing marine litter from different perspectives. It aims at providing Member States and other stakeholders with improved knowledge, methods and tools to be able to better define, monitor and achieve a marine environment free of harmful litter levels by 2020 (Good Environmental Status -GES- as required by the Marine Strategy Framework Directive -MSFD). In doing so, it will deliver a set of integrated results that will provide transparent and useful guidance to policy makers and stakeholders dealing with marine litter mitigation. http://www.cleansea-project.eu/ ——————————————————————————————————————————————————————————– Paper title: Uptake and retention of microplastics by the shore crab Carcinus maenas Authors: Andrew Watts, Ceri Lewis, Rhys Goodhead, Stephen Beckett, Julian Moger, Charles Tyler, and Tamara Galloway
Abstract: Microplastics, plastics particles <5mm in length, are a widespread pollutant of the marine environment. Oral ingestion of microplastics has been reported for a wide range of marine biota, but uptake into the body by other routes has received less attention. Here, we test the hypothesis that the shore crab (Carcinus maenas) can take up microplastics through inspiration across the gills as well as ingestion of pre-exposed food (common mussel Mytilus edulis). We used fluorescently labelled polystyrene microspheres (8-10 µm) to show that ingested microspheres were retained within the body tissues of the crabs for up to 14 days following ingestion and up to 21 days following inspiration across the gill, with uptake significantly higher into the posterior versus anterior gills. Multi-photon imaging suggested that most microspheres were retained in the foregut after dietary exposure due to adherence to the hair like setae and were found on the external surface of gills following aqueous exposures. Results were used to construct a simple conceptual model of particle flow for the gills and the gut. These results identify ventilation as a route of uptake of microplastics into a common marine non-filter feeding species.
DOI: 10.1021/es501090e Published by Amy Lusher