The following story could be told by a small piece of plastic: once upon a time, bacteria were part of a large group called Firmicutes. Usually, they were found in sewers and sewage, but on one particular winter day, they were discovered in the estuary waters of the Mondego River in microplastics. Scientists were the ones who revealed it after collecting it plastic items in these waters and having them analyzed in the laboratory.
The story just told is part of a work carried out by Portuguese scientists who used small fragments of plastic and microplastics as environmental storytellers. Overall, the great moral of the story was the realization that the communities of bacteria associated with plastics collected in the Mondego estuary and nearby beaches were different from those that naturally existed there.
Through replies sent by e-mail, José Marques tells PÚBLICO that the main objective of the work was to analyze communities of bacteria living in small fragments of plastic (less than 20 millimeters) and microplastics (less than five millimeters) in transitional aquatic environments such as estuaries and coastal areas. That is, the so-called “plastisphere” – the bacterial community associated with plastics. José Marques did a master’s degree in ecology at the University of Coimbra and completed it with this work.
During the winter of 2020, water samples were collected at the mouth of the Mondego River and in the area of beaches adjacent to the mouth of this river. Plastic and microplastic fragments found in the samples were then isolated in the laboratory. Genetic material related to plastics and bacteria was extracted into this environment. Genomes of bacterial communities were then analyzed and spectroscopy techniques were used to better understand the synthetic nature of the plastics to know whether they were, for example, polyester or polyethylene.
This is how the results are now published in the scientific journal Science of the Total Environmentarticle edited by Filipa Bessa, researcher at the Center for Marine and Environmental Sciences (Mare) of the Faculty of Science and Technology of the University of Coimbra and one of the supervisors of José Marques’ master’s thesis.
Overall, the bacterial communities associated with plastics from Mondego and nearby beaches were found to be different from those found naturally in aquatic environments. Mainly pathogenic bacterial strains were identified, such as e.g LactococcusTHE Staphylococcus and Streptococcusas well as groups commonly identified in sewers and wastewater as members of gender Firmicutes. Others found exclusively in marine environments were also identified. “[O estudo] it may indicate that these particles ‘came from somewhere else’ or that they arrived at the water or sand collection sites a while ago,” says José Marques.
There are reasons to say that plastics do not tell their own stories. As they are very small in size, it is often difficult to follow their course. Therefore, bacteria are an essential aid. “Bacteria that colonize the surface of small plastic fragments can give us clues about their routes and even their origin,” emphasizes José Marques.
The origin and journey of plastics
Through his study, there are two big stories that can be told. First, the presence – exclusively or in high abundance – of bacteria commonly found in sewage and sewage in estuarine microplastics, which may indicate that at least part of the release to the environment could have been through these pathways. course of the river.
The other story tells us that the unique presence in estuarine microplastics of bacteria commonly found in marine environments such as seawater may have been caused by the transport of these particles from the sea to the estuary. This may have contributed more substantially to the overall levels of microplastic contamination in estuaries. “The plastic sphere could be useful in revealing the origin and journey of plastics in aquatic environments. They can be environmental storytellers, like ‘Tell me what bacteria I’m carrying and I’ll tell you where I’m from,'” compares the first author of the study.
And how does this study tell us if the waters in Portugal are more or less polluted? Filipa Bessa points out that the study focuses on transition zones – land-sea and river-sea – and that these are considered transport pathways for many pollutants to the ocean. There have been several studies showing the presence of plastics on beaches and rivers in Portugal, but the question of the possible effects associated with these particles remains, says the researcher. For this purpose, analyzes should be made on these plastics and their colonizers. “This was the first step in this area in Portugal, which allowed us to confirm the idea of the ubiquity of microplastics in the environment, but also to conclude that the bacterial communities that colonize plastics that reach rivers and beaches can be very persistent and travel long distances”, explains the scientist. In this way, the dynamics of these particles in the environment can be better understood.
For now, the results of this work confirm that estuaries can be sites of plastic accumulation, through different fronts: upstream (from the river), from the sea (with the tides) and laterally (banks with high population density and accumulated garbage ). In the future, it is intended to know the residence time of bacteria and plastics in order to be able to assess their possible effects on animals.