– In a study promoted by the IIM in collaboration with the University of Cádiz and published in Journal of Hazardous Materials, researchers have revealed for the first time the translocation of polystyrene nanoplastics into mussel hemocytes, cells that play a decisive role in the immune system, and have described how their effects trigger the loss of functional parameters. It was also observed that most nanoplastic particles are found in the digestive gland, while their number decreases in muscle tissue and gills.
– In another study promoted by ICMAN in collaboration with the IIM and the universities of Cádiz and Huelva, published in Scientific Reports, it was found that mussel immune cells show different response capacities when exposed to nanoplastics.
Santiago de Compostela, 17 June 2020. The Spanish National Research Council (CSIC) is advancing a line of research on the effects of nanoplastics and microplastics. The Immunology and Genomics group at the Institute of Marine Research (IIM, Vigo) had been studying the effect of different pollutants on the immune system of the mussel, a species considered a pollution sensor. With the incorporation of Dr Marta Sendra into the group, work began on the effect of polystyrene nanoplastics on mussels, bringing together research on ecology and pollution previously developed at the Institute of Marine Sciences of Andalusia (ICMAN) with the study of the impact of pollutants and pathogens on the immune response of marine organisms carried out at the IIM.
Nanoplastics are a rapidly growing research topic, but many aspects remain little explored in relation to species such as bivalves. In this context, CSIC researchers have recently reported the results of their studies on different aspects of nanoplastics and mussels through articles published in high-impact scientific journals: Journal of Hazardous Materials and Scientific Reports.
“Millions of tonnes of plastic are produced worldwide every year, with polystyrene, used for example in food packaging, among the most abundant. Its fragmentation and degradation commonly gives rise to microplastics (smaller than 5 mm) and nanoplastics (smaller than 1 μm). This is an environmental concern that also raises questions from the perspective of food safety, because these particles could enter the food web and therefore be present in food intended for human consumption,” explains Dr Antonio Figueras.
“Bivalves, such as mussels, are a model group for investigating incorporation and consequences in marine species because of the volumes of seawater they filter and because they are consumed, and they could play an important role in transferring these particles to the food chain. It is known that plastic particles are rapidly cleared by bivalves. However, there is also evidence that this clearance is not complete and that around 10% passes into the species,” CSIC scientists indicate.
The study in collaboration with the University of Cádiz
The group designed a study to determine the effects of polystyrene nanoplastics of different sizes (50 nm, 100 nm and 1 μm) on the immune system of the Galician mussel (Mytilus galloprovincialis), as well as their distribution in the different parts of the organism.
The scientists carried out an in vitro and in vivo study to answer three main questions: Can the immune function of mussels be affected when these organisms are exposed to nanoplastics? Could nanoplastics disrupt the cellular level of the immune system by affecting the main functions of hemocytes, cells that play a key role in that system? What would be the main mechanism used by the mussel immune system to deal with infection and exposure to these plastics?
First, the distribution of polystyrene nanoplastics in different mussel tissues was described. In general, most particles were found in the digestive gland, while their number decreased in muscle tissue and gills.
“Their presence in muscle tissue appears to be a nanoscale characteristic, so nanoplastics can be interpreted as being able to cross the epithelial membrane, the cell membrane and ultimately translocate into cells. In addition, their translocation into hemocytes could increase resilience times, uptake by vital organs and unwanted effects on the species,” says Dr Marta Sendra.
After showing that nanoplastics are internalized by mussel tissues, translocated into the hemolymph and incorporated by hemocytes, the researchers determined their influence on motility — the ability of hemocytes to move spontaneously and independently. Hemocytes are adherent cells capable of infiltrating tissues and migrating to infected and damaged areas.
Second, faster translocation of polystyrene nanoplastics into the hemolymph was detected after three hours of exposure. The results revealed that hemocyte activity was higher under exposure to 50 nm nanoplastics, while speed and accumulated distance decreased when cells were exposed to 1 μm particles. It was also observed that, because of the resilience of hemocytes under acute exposure to nanoplastics followed by bacterial infection, these cells were able to cope with the infection by recovering their phagocytic capacity.
Sendra, M., Saco, A., MP, Yeste., M. Romero, A., Novoa, B., & Figueras, A. (2019). Nanoplastics: From tissue accumulation to cell translocation into Mytilus galloprovincialis hemocytes. resilience of immune cells exposed to nanoplastics and nanoplastics plus Vibrio splendidus combination. Journal of Hazardous Materials. – https://doi.org/10.1016/j.jhazmat.2019.121788
The study in collaboration with ICMAN and the universities of Cádiz and Huelva
The IIM, ICMAN and the universities of Cádiz and Huelva found that the immune cells of the Mediterranean mussel show different response capacities when exposed to nanoplastics. The mussel immune system is efficient against non-self substances, so the research team worked on the idea that the immune cells or hemocytes of this species could react to the presence of nanoplastics.
The cells of the mussel immune system are classified into three populations: granular, semigranular and hyaline hemocytes. The objective of the study was to determine the effects of environmentally relevant concentrations of polystyrene nanoplastics of different sizes (50 nm, 100 nm and 1 µm) on the immune response of this Mediterranean mussel species, considering the three defined cell populations.
According to Sendra and Blasco, “the results have shown for the first time how different populations of the mussel immune system respond differently to exposure to nanoplastics. The granulocyte population showed the greatest sensitivity to nanoplastic exposure compared with semigranular hemocytes and hyaline cells. The research provides new information at the cellular level on the behaviour of this emerging pollutant and its interaction with its environment.”
Sendra, M., Carrasco-Braganza, M.I., Yeste, P.M. et al. Immunotoxicity of polystyrene nanoplastics in different hemocyte subpopulations of Mytilus galloprovincialis. Sci Rep 10, 8637 (2020). https://doi.org/10.1038/s41598-020-65596-8