Biofilms and POPs: the effect of microplastics on oceans

We live in the "plastic age", with an annual production that reaches tens of millions of tons. Most of this waste ends up in landfills or back into the environment. The durability and slow degradation of plastics - which can take centuries to decompose - contribute to the formation and accumulation of microplastics (MPs). In turn, these MPs are dispersed in the environment, both in terrestrial and marine environments (SIDDIQUE, 2025). Microplastics are generally considered so when their particles are smaller than 5 mm. These small particles may be introduced directly into the marine environment, for example in the form of microspheres, present in cosmetics and industrial abrasives, or they may originate through the fragmentation of larger plastic waste, as in the process of degradation of various packaging. Due to the increasing global production of plastic, a considerable fraction of this waste ends up being deposited in the marine environment. This is because large quantities of packaging and other plastic items are often discarded on beaches, where direct exposure to ultraviolet radiation, high temperatures and abrasion favor the formation and propagation of microparticles from the wear of the initial plastic material. 

Different types of plastics, such as low and high density polyethylene, polypropylene, polystyrene and PVC, have distinct physical properties - such as density and resistance - that determine their behavior in the water column, their buoyancy and environmental fate (ANDRADY, 2011; SIDDIQUE, 2025).  The large amount of microplastics in the environment does not only represent a problem of physical pollution, but also represents a problem regarding the accumulation of persistent organic pollutants (POPs) and biofilms (ANDRADY, 2011; VIRSEK, 2017; MATOS, 2023; SIDDIQUE, 2025). 

In addition to microplastics, persistent organic pollutants (POPs) are chemical substances of toxicological concern for human health and the environment. These substances are able to bioaccumulate in tissues of living organisms and still be transported over long distances. It is common that these POPs are found in environments very distant from where they were used (ANDRADY, 2011). Some studies conducted in Brazilian oceanic islands have recorded the presence of these substances in the tissues and blood of seabirds, as a right reflection of changes in the environment (DIAS et al, 2013). Microplastics have a hydrophobic characteristic, which facilitates the concentration of these toxic substances, usually present in low concentrations in the aquatic environment, such as in the sea. These contaminants, such as polychlorinated biphenyls (PCBs), dichlorodifenyltrichloroethanes (DDTs), and polyaromatic hydrocarbons (PAHs), can accumulate at very high levels in microplastics, representing a potential source of toxicity for marine organisms that ingest them, as well as being accumulated through the food chain (ANDRADY, 2011; MATOS, 2023). 

Biofilms are organized communities of microorganisms, such as bacteria, fungi, protozoa and algae, which adhere to surfaces and become involved in an extracellular polymer matrix (VIRSEK, 2017). This matrix, composed mainly of water, polysaccharides, proteins and extracellular DNA, acts as a protective shield, allowing microorganisms to survive in adverse conditions (NASCIMENTO; SENA, 2017). Microplastics also serve as a biofilm-forming surface, creating ecological niches that can favor colonization by microorganisms, including pathogens strongly harmful to aquatic organisms (VIRSEK et al, 2017; SIDDIQUE, 2025). An example is Aeromonas, a genus of bacteria with potential cause of hemorrhagic septicaemia and boils in fish, and easily found in microplastic particles  (VIRSEK, 2017). In addition to the dissemination and concentration of pathogens, the formation of biofilms on microplastic particles is strongly related to the emergence of bacterial resistance to antibiotics. Biofilms favor the horizontal transfer of resistance genes, facilitating the spread of resistant bacteria (SIDDIQUE, 2025). 

Given that the generation of microplastics occurs predominantly at the interface between the terrestrial and marine environment - as in beaches -, cleaning these areas can be an effective strategy to reduce the formation of microplastics  (ANDRADY, 2011). The removal of large plastic debris before it is degraded and fragmented can have a positive impact not only on the aesthetics of beaches, but also on the health of marine ecosystems. Each of these points highlights the complexity of the processes leading to the formation of microplastics and the associated environmental consequences. This understanding is critical to developing more effective mitigation and management strategies for marine plastic pollution. 

Author: Amanda de Castro - Deputy Director of Internal Communications at GEAS Brazil

Revision: Iago Junqueira - Partner of GEAS BRASIL by The Wild Place

Savage Panel July/2025

BIBLIOGRAPHICAL REFERENCES:

ANDRADY, A. L. Microplastics in the marine environment. Marine Pollution Bulletin, v. 62, p. 1596-1605, 2011.

DIAS, P. S. et al. Persistent organic pollutants and stable isotopes in seabirds of the Rocas Atoll, Equatorial Atlantic, Brazil. Marine Ornithology, v. 46, p. 139-148, 2018.

MATOS, A. E. Panorama da contaminação por poluentes orgânicos persistentes em mamíferos marinhos da costa brasileira. Florianópolis: Universidade Federal de Santa Catarina. 2023. Dissertação (Oceanografia). 

NASCIMENTO, I. R.; SENA, T. L. Biofilmes bacterianos: colonização e identificação de micro-organismos causadores de infecção em cateter venoso central. Brasília: Centro Universitário de Brasília. 2017. Relatório final de pesquisa de Iniciação Científica.

SIDDIQUE, A. et al. Microplastics and their role in the emergence of antibiotic resistance in bacteria as a threat for the environment. Environmental Chemistry and Ecotoxicology, v. 7, p.614-622, 2025. 

VIRSEK, M. K. et al. Microplastics as a vector for the transport of the bacterial fish pathogen species Aeromonas salmonicida. Marine Pollution Bulletin, v. 125, p.301-309, 2017.